Publications

The highway embankments and railway tracks constructed on soft soils are particularly vulnerable to increased cyclic stress, which can cause uncontrolled deformation, undrained failure, migration of fines and associated mud pumping. This paper presents a significant contribution to the field by reporting the effectiveness of geosynthetics in mitigating fluidization potential of soft soil. Laboratory experiments were undertaken using a dynamic filtration apparatus (DFA) and a cyclic triaxial apparatus (CTA) to analyse the cyclic response of soft subgrade under impeded drainage conditions.

Show more…  This study critically evaluates the role of geosynthetics in controlling the occurrence of soil fluidization by assessing the build-up of excess pore water pressure (EPWP), the variation in particle size distribution (PSD) and the moisture content (MC). The outcomes of this study reveal that prefabricated vertical drains (PVDs) are effective in alleviating the EPWP developed in middle or deeper soil layers, whereas geocomposites can facilitate surficial drainage. This paper emphasizes the practical implications and the significance of improved drainage and swift dissipation of EPWP on low-lying saturated soils for enhanced track design. Show less…

15YGPC 15th ANZ Young Geotechnical Professionals Conference Adelaide 2024

Peat/organic soils are characterised by low undrained shear strength, high compressibility and are susceptible to significant ground settlements, creating challenges for engineers and developers. Since construction in 2015, a housing subdivision in Auckland, has been impacted by ground settlement and distortions to foundations and superstructures. The pattern of distortions are indicative of differential settlements resulting from mixed foundation types, being part-piled and part-ground bearing over soft compressible peat.

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Mixed foundations are sometimes used where dwellings are built adjacent to or over services, with piles being used to transfer loads to below the level of the services. A number of dwellings within the subdivision, which were constructed with mixed foundation types, have required regular intervention works to maintain dwelling serviceability. Foundation distortion correction works were trialled on one damaged property with the purpose of proving the adopted remedial methodology and substantiating future foundation performance.

The remedial works involved disconnecting piles and implementing staged and cycled surcharge loading with water tanks on the foundation slab. This method was used to verify the performance of the slab and to measure the dwelling response to the change of support. Water tanks were positioned near the locations of the most significant distortions and subjected to loading cycles over several weeks while monitoring changes in floor distortion. The trial results successfully demonstrated compliance of the corrective works with the performance expectations of the New Zealand Building Code.

This paper presents the challenges and solutions implemented on the trial property during the foundation distortion correction works.

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15YGPC 15th ANZ Young Geotechnical Professionals Conference Adelaide 2024

As our understanding of natural hazards and climate risk improves, how do we enable individual decision makers to be best informed? Our paper will focus on the communication of risk information, and how the psychology of individuals controls the success. Through looking at existing research to understand the differing ways we perceive and communicate risk, our paper highlights the requirement to ensure more effective public risk information and enable effective decision making within our communities. We focus on two key aspects that inform an individual’s response to risk, the cognitive and emotional dimensions, which refer to how much people know and understand about risk, and how someone feels about risk. Our paper will capture the psychological responses when informed about risk and look to establish principles for risk communication for differing individuals and communities. Concepts such as ‘probability neglect’ further impact risk information and decision making of the public, demonstrating the need for our industry to better communicate risk to enable effective decision making.

NZSEE 2025 Annual Conference

Many state-of-practice methods for predicting liquefaction manifestation, such as the Liquefaction Severity Number (LSN), are known to suffer from significant overprediction in regions characterised by complex soil profiles comprising interbedded sands, silts, and clays. These methods typically analyse discrete soil layers, and sum results layer-by-layer, which does not properly account for system effectsa. Show more…We demonstrate that machine learning techniques can be used to identify cases where simplified layer-bylayer liquefaction vulnerability indices give overestimated surficial liquefaction manifestation. Specifically, we have developed a convolutional neural network model. With the aim of better accounting for system effects, the model considers the full length of a CPT profile simultaneously to capture system effects of soil profiles such as interbedding, rather than processing and then aggregating information in discrete layers.
A database of over 47,000 case histories was used for training and model evaluation, spanning ten New Zealand earthquakes. Special techniques were used to address sampling bias and class imbalance. Finally, an adjustment procedure is proposed, which uses the machine learning model to improve the accuracy of LSN for specific site categories, resulting in significant accuracy improvements.
This research has been funded by Toka Tū Ake EQC to advance liquefaction science, and support a range of applications in New Zealand, including local government planning, public engagement and education, and loss modelling. Show less…

NZSEE 2025 Annual Conference

The Manukau Harbour is located on the West Coast of New Zealand’s North Island in the Auckland Region. It has been identified as a potential greenfield port location to replace the cargo operation of the Ports of Auckland, which is located on the East Coast within the Waitematā Harbour. Exposure to large and persistent swell from the Southern Ocean and Tasman Sea, high tidal range, fast tidal currents, and a very large and shallow ebb tide delta at the Manukau Harbour entrance present several challenges to opening and maintaining a navigation channel in this location. Show more…To test the feasibility of the proposal, an in-depth understanding of the ebb tide delta dynamics and sediment transport mechanisms was needed. Using data collected from the field, satellite imagery, and a combined analytical and numerical modelling approach we have estimated capital dredge volumes and importantly rates of sediment infill to the channel at differing temporal scales from individual storms to annual rates and decadal evolution. It has been shown that the ebb tide delta has a rotational morphology over an approximate 20 to 25-year cycle which can affect the capital dredge volumes by up to 10M m3 depending on the position of the channel and banks within the cycle. A net movement of sediment from the south to the north through longshore processes have been shown to contribute 1.5M m3 / year to the system, however, it is the sediment recycled around the ebb tide delta through wave and tidal flows that look to govern the maintenance dredge requirement and therefore the viability of the harbour serving as a port location. Work is still progressing to finalise the technical feasibility of this. Show less…

35th Pianc World Congress, Cape Town, 2024

Liquefaction is a major concern regarding earthquake damage to infrastructure. Recent earthquakes in New Zealand and resulting liquefaction caused significant damage to buried pipeline systems. Following the 4 September 2010 Mw=7.1 Darfield earthquake, five earthquakes (22 February 2011, Mw=6.2, 13 June 2011, Mw=5.3 at 1 p.m. and Mw=6.0 at 2:20 p.m. and 23 December 2011, Mw=5.8 at 1:58 p.m. and Mw=5.9 at 3:18 p.m.) and thousands of aftershocks have been recorded in the area of Christchurch, NZ. Show more…These earthquakes termed the Canterbury Earthquake Sequence (CES) are unprecedented in terms of repeated earthquake shocks with substantial levels of ground motion affecting a major city with modern infrastructure. This study focuses on the effects of 22 February 2011 Christchurch earthquake induced liquefaction on buried pipelines. Correlations were developed between pipe damage, expressed as repairs/km, and a recently developed parameter called liquefaction severity number (LSN). Cone Penetration Test (CPT) based liquefaction triggering procedures were used to calculate LSN values. Studies by Tonkin and Taylor [1,2] and van Ballegooy et al. [3, 4, 5, 6] have shown that LSN provides a good correlation with land and esidential house foundation damage observations recorded in Canterbury. According to results obtained in this study for buried pipelines, LSN has reasonably good correlation with asbestos cement (AC), cast iron (CI) and polyvinyl chloride (PVC) pipeline damage. Show less…

16th World Conference on Earthquake Engineering, Santiago, 2017

In many countries, levees and flood defences raise (or have raised until recently) different issues associated to their ageing and often too to a lack of proper management during long periods of time. Show more…This leads to uncertain safety and performance, and sometimes catastrophic consequences. In this paper, based on an international confrontation of experience and lessons learned, we present the most important of these issues and a framework to better organize the management of these structures: identification of existing portfolios of structures, organizing them into consistent systems, the need for a high-level policy, for a proper local management and for technical guidance. Show less…

Role of dams and reservoirs in a successful energy transition : proceedings of the 12th ICOLD European Club Symposium 2023 (ECS 2023, Interlaken, Switzerland, 5-8 September 2023) p. 972-978. (EurCOLD)

The Seismic Assessment of Existing Buildings Guideline, Section C4: Geotechnical Considerations, was first published in July 2017. That first issue included several aspects of assessment which had not been previously applied, including allowance for the non-linear behaviour of soils (geotechnical step change). Show more…The subsequent 6 years have provided the opportunity to apply the geotechnical step change methodology to various building assessments and to obtain feedback. This has highlighted the need to clarify and further develop the geotechnical step change methodology. A project is now in progress to update C4. This paper reports on the likely conclusions of the update project. Those conclusions are yet to be recorded in an update of C4. The update to C4 is to clarify the purpose of the step change factor of 2. The purpose of that factor is to provide an assessed %NBS which represents a buffer from loss of gravity support of the structure. A method has been developed to vary the step change factor between 1 and 2 depending on the ability of the structure to maintain gravity support and the life safety consequences of loss thereof. The step change methodology has been extended to cover earthquake induced ground displacements which are not covered by the current C4. Guidance is to be provided on the level of conservatism to be applied in evaluating geotechnical parameters and allowance for uncertainty. It is also proposed to enhance the guidance on desk top studies and other aspects of geotechnical assessment. Show less…

NZSEE Conference 2024 Wellington

Many state-of-practice methods for predicting liquefaction manifestation, such as the Liquefaction Severity Number (LSN), are known to suffer from significant overprediction in regions characterised by complex soil profiles comprising interbedded sands, silts, and clays. These methods typically analyse discrete soil layers, and sum results layer-by-layer, which does not properly account for system effectsa. Show more…We demonstrate that machine learning techniques can be used to identify cases where simplified layer-bylayer liquefaction vulnerability indices give overestimated surficial liquefaction manifestation. Specifically, we have developed a convolutional neural network model. With the aim of better accounting for system effects, the model considers the full length of a CPT profile simultaneously to capture system effects of soil profiles such as interbedding, rather than processing and then aggregating information in discrete layers.
A database of over 47,000 case histories was used for training and model evaluation, spanning ten New Zealand earthquakes. Special techniques were used to address sampling bias and class imbalance. Finally, an adjustment procedure is proposed, which uses the machine learning model to improve the accuracy of LSN for specific site categories, resulting in significant accuracy improvements.
This research has been funded by Toka Tū Ake EQC to advance liquefaction science, and support a range of applications in New Zealand, including local government planning, public engagement and education, and loss modelling. Show less…

NZSEE Conference 2024 Wellington

Geopier Rammed Aggregate Piers® (RAPs) are a ground improvement technology that creates a densified column of aggregate surrounded by a stiffened matrix soil. This paper describes the design and construction of RAPs at Te Kaha, a $683-million Multi-Use Arena under construction in Christchurch, New Zealand. CLL Projects are constructing 8331 RAPs including 1092 tension RAPs to depths between 5.5 to 12m to provide a ground improvement system supporting the arena. Show more…Design considerations include estimation of soil densification in a wide range of soil conditions (sand, silty sand, silt and gravel), analysis of liquefaction triggering before and after ground improvement, numerical analysis to predict the bearing capacity and settlement of the foundations, and prediction of uplift capacity for tension RAPs. The design predictions and the actual results from verification testing are compared, including pre- and post- improvement CPTs and tension load tests. At Te Kaha the RAP installation resulted in a significant increase in penetration resistance of sandy soils between the RAP elements. The CPT results consistently underestimated the fines content of the soil. The tension load test results showed that the uplift capacity is dependent on the soil conditions at the tip of the tension RAP. If adequate confinement cannot be achieved at the base the tension RAP ‘unravels’ and the capacity is much lower than typical design methods would predict. Show less…

8th International Conference on Earthquake Geotechnical Engineering (ICEGE), 2024, Osaka

Variable or unknown ground conditions are a major contributor to uncertainty in a geotechnical project and arise as a result of the geomorphological processes that shaped the land. The planning of a ground investigation programme can be thought of as a sampling optimisation problem, seeking to balance precision, accuracy, and costs through selection of an investigation density that achieves a degree of residual uncertainty that is sufficient for the intended purpose. Show more…This study draws on detailed observations of the patterns of liquefaction-induced land damage mapped across Christchurch City during the 2010 – 2011 Canterbury Earthquakes, and uses the variability in the observed damage as a proxy for variability in the underlying shallow ground conditions. The correlation between investigation density and residual uncertainty in ground conditions is examined using a Monte Carlo approach, varying size of the study area and the investigation spacing. The hypothesis is that as the total area investigated increases, the spacing between investigations can be increased while still achieving the same degree of residual uncertainty in the ground conditions. The results of this study were used to set the minimum investigation density recommendations for land use planning and subdivision in the New Zealand guidance on geotechnical investigations for earthquake engineering. Show less…

8th International Conference on Earthquake Geotechnical Engineering (ICEGE), 2024, Osaka

Following the September 4th 2010 Mw7.1 and February 22nd 2011 Mw6.2 Earthquakes in Canterbury, New Zealand, liquefaction-induced lateral spreading was observed along the Avon and Heathcote rivers. Detailed field measurements following the events provide a benchmark to evaluate the efficacy of lateral spreading prediction models under real world conditions. Show more…This paper presents the development of 2D effective stress finite difference models in FLAC2D of two transects along the rivers, and compares numerical results to observed displacements for the two major seismic events. The liquefiable soil was modelled with the PM4Sand model, and an automated calibration procedure was developed to determine the model inputs based on CPT results. The displacements during the earthquake excitation and post-shaking during pore pressure dissipation were quantified. Overall the simulations show reasonably consistent ground displacements at the channel free-face for both events and both transects, though recognising significant uncertainties in the simulations and field measurements. The results of the numerical simulations highlight the importance of both geometric (notably the channel width) and soil properties as key factors that influence lateral spreading displacements. The simulation results provide some confidence that detailed finite difference models can reasonably capture the expected level of ground movement during a lateral spreading event. Show less…

8th International Conference on Earthquake Geotechnical Engineering (ICEGE), 2024, Osaka

The Resource Management Act 1991 (RMA) protects wetland and river features through section 13. How these features are defined depends on which piece of legislation is relied upon, with slightly different definitions included in the RMA, the National Policy Statement for Freshwater Management 2020 (NPS FM) and Regional Plans. While many of these definitions are similar, small nuances can wreak havoc – both in what to call something and subsequently what the consenting implications are. Show more…Since the introduction of the NPS FM, defining these features has become a hot topic, mostly, in our opinion, because of the prohibited activity status applied to many activities affecting natural inland wetlands in the original version of the National Environmental Standards for Freshwater (NES F) (September 2020).
Consequently (and despite having been subject to protection in some form since 1991), delineation of wetlands and whether something was a stock-pugged river or a degraded wetland became a point of contention. ‘Is it a wetland’ has become as triggering to some as the concept of nuclear power (of note as it is one of the widely recognised prohibited activities in Aotearoa New Zealand).
One theme all these definitions have in common is an implied state of mutual exclusivity and stationarity – that if something is a river, it can’t be a wetland (and vice-versa) and that they will remain static through time. What these definitions, policies and rules fail to appreciate is that, in reality, rivers and wetlands are aquatic ecosystems that exist on a continuum of form and function.
From a scientific point of view, aquatic systems have significantly more nuanced characters, behaviours and values (e.g. types such as intermittent, perennial, wandering, braided, valley fill, marsh, swamp…). How these systems behave is driven not by a definition in a piece of legislation, but rather by the prevailing landscape and ecological controls. River and wetland systems may fluctuate between different forms and states depending on numerous climatic, hydraulic and landscape factors.
Policy aside, it is the science, form, and function of these aquatic systems that tells us what we need to do to maintain their ecological and morphological integrity, not the definition introduced by the government of the day. Understanding the character and behavior of these systems in their landscape context is essential to inform decision making, ensuring that water sensitive urban design and nature-based solutions are implemented in a way that respects the processes and functions of these systems, and ensures a measure of success.
Within this paper we describe the science behind the characterisation of these aquatic systems, reflecting on their ecological and morphological function, and what this means for designing nature-based stormwater and flood management solutions that work with the landscape and ecological processes and controls. We explore the implications of the statutory framework and what this means in practice in respect of stormwater management. Lastly, we highlight how wetlands and streams provide an opportunity to integrate ecological, amenity, stormwater and flood management outcomes, while enabling future development. Show less…

NZ Stormwater Conference 2024

In this second article of a two-part series, Brad discusses market-based mechanisms such as incentives and disincentives, innovative impact finance and delivery models that could improve our infrastructure efficiency based on success abroad.

Water New Zealand Journal Issue 235 July/August 2024 p. 38-42

Cycline Gabrielle severly damaged a large portion of the Palmerston North to Gisborne line (PNGL). The damage included large embankment washout failures, blocked/damaged culverts, underslips/overslips, scour damage to tracks, loss/reduction of drainage, silt inundation and structural damage to bridges/tunnels. Show more…Tonkin & Taylor Ltd were engaged by KiwiRail to provide specific geotechnical field support during the initial ‘Make Safe’ works on the Napier to Wairoa section of the PNGL.
The premise of the ‘Make Safe’ works is to undertake works that reduce the likelihood of further damage and deterioration of the line under normal annual rainfall conditions and across the next two winters. This was considered to be a suitable timeframe to allow the ‘Make Safe’ requirements to still be satisfied based on the level of engineering being undertaken across the line. Importantly, the focus was not necessarily to reinstate the track for train movements but rather to allow , where possible, rail enabled plant to access sections of the line safely. Show less…

NZ Geomechanics News Issue 107 June 2024 p. 82-91

Finding the right funding to fix our massive infrastructure gap will be key to ensuring a sustainable water future. Show more…In the first of this two-part series, Brad explores alternative funding sources that could be used to help bridge the water infrastructure gap. Examples inlude our sovereign wealth funds such as our NZ Super Fund, ACC and KiwiSaver, which collectively represent $200 billion. Show less…

Water : official journal of Water New Zealand Issue 234 May/June 2024 p. 26-32

Source water risk management plans (SWRMPs) are comprehensive plans designed to help manage and protect the quality and quantity of drinking water at its source. The Water Services Act 2021 mandates the development and implementation of SWRMPs for all registered water suppliers in New Zealand. Show more…While limited guidance exists for SWRMP development, Tonkin & Taylor Ltd has worked with clients to provide a robust and scalable methodology across varied water supplies and multiple regions, including Auckland, Canterbury, Wellington, and the Hawkes Bay. This paper outlines our process and methodology, which includes identification of potential contaminant sources (hazards), catchment risk assessments (CRA) and the development of source-specific SWRMPs. An overview of several case studies is also presented to illustrate the process and outcomes. Show less…

Water New Zealand Annual Conference, 2023, Wellington

In the realm of flood management, the pursuit of resilience remains elusive, hindered by a fundamental challenge: the absence of a shared understanding of what resilience entails and the benchmarks we aspire to achieve. Past flooding incidents in New Zealand and overseas serve as stark reminders of the repercussions of navigating preparedness, response, and recovery without a clear definition of resilience. Our cautionary tale is beginning to write itself. Show more…This paper will explore differing definitions to seek alignment, including Treasury’s discussion that “the concept of resilience is wider than natural disasters and covers the capacity of public, private and civic sectors to withstand disruption, absorb disturbance, act effectively in a crisis, adapt to changing conditions, including climate change, and grow over time”.
Judith Rodin’s influential work focuses on the triple nature of resilience—asset management with its associated risk frameworks, psychological resilience, and systems thinking—each integral to comprehending the multifaceted landscape of resilience within the flood context.
At its core, resilience transcends mere asset protection; it embodies a symbiotic relationship between infrastructure resilience and human adaptability. Rodin’s framework underscores the imperative of integrating asset management principles, risk management frameworks such as ISO 31000, with a profound understanding of human resilience—the ability to cope and recover from stressors inherent in natural hazard events. Lessons from the Christchurch earthquakes showed the importance of building social capital from grassroots, a fundamental factor for resilience.
Moreover, in a world governed by complex systems and associated interdependencies, the significance of systems thinking cannot be overstated. Flood management operates within a dynamic ecosystem of interconnected variables, necessitating a paradigm shift towards holistic, systems-based approaches to resilience-building. This paper explores how our definition of resilience must be flexible enough to stay relevant in an increasingly complex world, whilst staying pragmatic to be effectively applied in everyday use.
Indicators and metrics are paramount for understanding the efficacy of our strategies. However can resilience be measured, and how do we differentiate risk from resilience? Following defining resilience, these will be the focal questions for this paper.
Simply put, high resilience communities can be described as those where impacts are not felt as deeply, and recover rapidly to be stronger post-event, providing metrics such as depth of impact (absorption) and speed of recovery (adaptability). Beyond these, infrastructure metrics include robustness and redundancy. Exploring how these can be measured is critical to helping monitor and tailor resilience interventions accordingly.
As we navigate the complexities of defining resilience within the stormwater and flood sector, it becomes evident that resilience is not a static endpoint but a perpetual journey—a moving goalpost that adapts to evolving challenges and aspirations.
Ultimately, this paper advocates for a collective re-evaluation of our approach to resilience within flood management, emphasizing the need for a shared vocabulary and framework. By embracing a nuanced understanding of resilience—one rooted in systems thinking and human adaptability—we can embark on a transformative journey towards a more resilient future, where storms will continue to disrupt, yet communities recover stronger. Show less…

Water NZ Stormwater Conference, 2024, Wellington.

Rocking foundations can offer significant benefits in terms of seismic performance, environmental outcomes and constructability. This paper explores the use of a simplified design procedure for rocking foundations and compares the design estimates to both displacement-based assessment and nonlinear time history analysis. Several simplifying assumptions were applied to the building design and modelling in this paper to isolate the role of rocking foundations. Show more…These assumptions are explicitly stated and would need to be addressed for the application on real buildings. However, this paper presents a pathway for adoption of rocking foundations in design. The simplified procedure that has been proposed for adoption in TS1170.5 is for low- to mid- rise buildings (less than 15 m to the uppermost floor or heavy roof), as well as other specific building criteria. However, by assessing both a 3-storey and 6-storey buildings, this paper shows how the procedure could be utilised for other structures provided appropriate validation is performed and constraints are assessed. The use of rocking foundations for multi-storey apartment buildings can enable more sustainable, cheaper, and easier to construct buildings and this paper provides support that the potentially higher initial design (and review) costs associated with this can be managed and justified. Show less…

NZSEE Conference 2024 Wellington

Whanganui Prison occupies a highly constrained site from which stormwater is discharged directly to the sensitive receiving environments of Lake Pauri, Lake Wiritoa, and surrounding wetlands. An application by Ara Poutama Aotearoa / Department of Corrections to renew the existing discharge consent was lodged in 2013. This provided an opportunity for Corrections to think differently about the way it manages stormwater, and about its own role as an environmental steward. The consent was granted in 2020 following extensive information gathering, concept development, consultation, and collaboration, in which cultural aspirations and the unique operational requirements of a prison came to shape the design process. Show more…SThis paper describes the evolution of stormwater treatment design at Whanganui Prison over the last ten years. It illustrates how the way in which the problem is defined, and the perspectives behind this, drives the design response and, ultimately, the nature of the outcomes.
Central to this journey was Corrections’ partnership with the Whanganui Prison Tangata Whenua Engagement Group (WPTWEG). This vital collaboration shifted the focus of stormwater treatment from simply meeting minimum regulatory requirements to ensuring that the health of the lakes was at the centre of all decisions. This saw the early treatment concept mature into a comprehensive water management philosophy that accounts for cultural values as well as regulatory targets and practical engineering considerations.
The initial treatment concept focussed on proprietary devices retrofitted into a severely hydraulically-constrained stormwater network that discharges to a sensitive but degraded coastal lake environment. The concept was developed without a thorough understanding of the environmental setting, the nature of the discharge quality, or an explicit statement of what the devices were expected to achieve. However, when elements of importance to local iwi were captured alongside the operational and security requirements of the prison, and site investigations improved understanding of contaminant sources, the design criteria widened to include cultural and environmental objectives.
Under the guidance of the WPTWEG, a hybrid design – currently under construction – was developed in which nature-based elements were adopted to reinstate some aspects of the natural water cycle that had been lost. Rainwater harvesting and a naturalised outfall are proposed to further contribute to this outcome.
Corrections’ journey has demonstrated that contemporary stormwater management is not a purely technical or engineering endeavour. When the principles of Te Mana o te Wai are allowed to inform stormwater management decisions, a range of positive outcomes beyond just regulatory compliance can accrue.
The Whanganui experience has led Ara Poutama Aotearoa / The Department of Corrections to change the way in which it implements water quality improvement at its facilities. Cultural input to design is now sought as a matter of course, including at facilities that do not face the same pressures on freshwater protection as Whanganui. Show less…

Water NZ Stormwater Conference, 2024, Wellington

Hutt City Council (HCC) was granted $99 M of funding through the Infrastructure Acceleration Fund (IAF) to deliver stormwater and wastewater infrastructure improvements to enable growth, a project now known as Water Infrastructure for Growth (WIG). The stormwater infrastructure improvements are aimed at removing impediments to housing for predicted population growth in Lower Hutt in the late 2020s and 2030s. This intensification will be entirely brownfield redevelopment. The WIG project is critical to enabling the local stormwater network to keep pace. Its growth-and future-oriented objectives (rather than seeking to solve a present-day flooding problem), and immediate infrastructural focus, are challenging the project team to ensure the project benefits can be realised over time. Show more…Stopbanks provide the wider area with fluvial flood protection from Te Awa Kairangi – the Hutt River, but the low-lying area behind the stopbanks is prone to stormwater flooding. Moreover, the existing stormwater infrastructure in the Opahu Stream catchment, behind the stopbanks, is already at capacity. Even accounting for the on-site storage required under HCC’s District Plan, the frequency and intensity of stormwater flooding is projected to worsen with future growth, and particularly as the effects of climate change and sea level rise continue to be realised. HCC has identified various preferred intensification areas and types of development within the catchment. The scale of predicted future flooding is too great a problem to overcome through reliance on hydraulic neutrality and minor network upgrades alone.
This project is currently at feasibility and optioneering stage, with potential solutions being assessed against: (i) the additional capacity they provide in the primary network; (ii) the level of reduction to flood hazard in the preferred growth areas; and (iii) affordability. Given the significant existing constraints, the upgrades will require pumped solutions to convey stormwater from the Opahu Stream to Te Awa Kairangi. However, early in the optioneering stage the project team explored options that sought to maximise the use of Water Sensitive Urban Design concepts such as: (i) utilising and enhancing existing overland flow paths, (ii) improving stream conveyance/daylighting, and (iii) detention storage on areas of existing green space.
In addition to the infrastructure improvements which are the focus of the WIG project, the work has brought into sharp focus a need for a broader approach to maximise project benefits in the face of uncertainty. Some lessons learnt and recommendations for wider implementation include identifying and preserving overland flow paths in the course of development; masterplanning and steering development into areas better able to be serviced by stormwater infrastructure, while implementing stricter hydraulic neutrality requirements outside of these areas; and identifying large publicly owned sites for on-site stormwater management.
This paper will provide a summary of the infrastructural solutions being considered for this brownfield urban intensification, and the wider actions that are likely to be required in order for predicted growth to be enabled without increasing flood risk to current and future residents. Show less…

Water NZ Stormwater Conference, 2024, Wellington

Stormwater management is a critical aspect of creating sustainable and resilient cities in the face of pressures such as ongoing urbanisation, ageing infrastructure, climate change, loss of productive soils and infrastructure affordability. However, the continued degradation of our waterways is evidence that the prevailing notion of ‘sustainable’ stormwater management isn’t working and a paradigm shift is required. This paper explores the application of systems thinking to the domain of stormwater management, emphasising the importance of adopting a holistic perspective and using non-structural solutions to enhance system resilience and regenerative outcomes (i.e. outcomes that achieve restoration across multiple domains rather than simply the reduction of harm. Show more…Systems thinking is a holistic approach to understanding and solving problems by examining the interconnected relationships and dynamics within systems. Unlike linear thinking (which focuses on isolated cause-and-effect relationships) or reductionist approaches, systems thinking recognises the interdependence of various elements to better understand system behaviour. In this sense, systems thinking is a perspective that can be applied to any technical field and is needed more than ever to develop robust and enduring responses to society’s many complex challenges.
Stormwater management in New Zealand in recent decades has typically focused on managing three primary objectives: (1) flooding, (2) stream erosion and (3) water quality. These have typically been managed with the adoption of structural solutions such as pipes and devices such as ponds, while the implementation of approaches such as Water-Sensitive Urban Design (WSUD) has been limited. This approach of focusing on managing the symptoms of changes to the water cycle (runoff quality and quantity) rather than root causes (e.g. increases in impervious area) has contributed to an urban environment characterised by high imperviousness that results in poor stormwater outcomes as well as a host of non-stormwater related city planning issues.
However, as urbanisation continues at a historic pace and local government faces increasing financial pressure, can we really continue to rely on (attempting to) engineering our way out of the problem? The conventional approach to stormwater management, with a heavy reliance on engineered devices and infrastructure, has led to residual environmental effects (as demonstrated by the continued degradation of our waterways), low levels of resilience, and high embodied carbon emissions. Is this approach really sustainable?
Approaches such as WSUD and sponge cities are discussed as examples of a systems thinking approach that can provide more robust and resilient solutions than conventional stormwater management (when applied well). However, incorrect implementation and limited uptake of these approaches shows that these frameworks are not enough on their own without further system interventions.
This paper seeks to use a systems thinking lens to examine the current approach to stormwater management in New Zealand, why it is falling short, and examples of systemic solutions that could lead to better outcomes. The aim of this paper is to equip stormwater practitioners with some of the language, tools and principles of systems thinking in the context of stormwater management to aid with a shift toward regenerative solutions. Show less…

Water NZ Stormwater Conference, 2024, Wellington

Design or assessment of structures founded on ground with a potential for seismic induced ground displacements requires careful consideration of the associated soil structure interaction (SSI). These seismic ground displacements could be due to liquefaction and cyclic displacement or lateral spread, or due to slope instability. Potential ground movement and SSI includes considerable uncertainty. Show more…Three case studies describe application of these principles. These principles include developing possible scenarios of ground movement, ground and structure shaking and SSI, and testing the design relative to these scenarios. Relative stiffness of ground and structural elements needs to be considered in developing these scenarios. Is the structure pushing the ground or is the ground pushing the structure? The impact of SSI on the magnitude of ground displacement needs to be considered. Will the SSI arrest the ground movement or will the ground movement potentially pull the structure apart? The presented principles and case studies focus on qualitative and simplified numerical assessments. Where considered appropriate and necessary, higher level analyses including dynamic finite element modelling could be undertaken. These higher level analyses should be to supplement rather than replace the simplified methods described in this paper. Higher level analyses could be particularly useful in understanding possible mechanisms of SSI. Assessment would require engineering judgement considering all available information. Show less…

NZSEE Conference 2024 Wellington

The Peka Peka to Ōtaki Expressway (PP2Ō) is a 13 km long, 4-lane expressway located on the Kāpiti Coast north of Wellington, New Zealand, serving as a replacement for the existing State Highway 1 (SH1). To the south, it connects with the MacKays to Peka Peka Expressway, and its northern extension reaches beyond the Taylors Road intersection on the current SH1. Show more…At both the southern and northern sections of the alignment, soft and highly compressible peat and organic silt up to about 7 m depth were encountered. The presence of soft soils is a consequence of topographical and geological factors which has resulted in poorly drained conditions.
This paper provides an overview of the ground improvement techniques implemented to address geotechnical challenges associated with these soft soils, and the observational approach adopted during the construction phase. Show less…

New Zealand Geomechanics News Issue 106 December 2023 p. 50-60

Delivery of major transport infrastructure projects at the coast requires a careful balance between numerous project drivers, including cost, program, environmental, regulatory and stakeholder considerations. These often-conflicting drivers have the potential to disrupt a project, if not managed carefully, leading to delays, cost over-run, conflict and sub-optimal outcomes. Show more…The Ngā Ūranga ki Pito-One Project comprises a 4.5 km shared pathway between Ngā Ūranga and Pito-One in Te Whanganui-a-Tara, Wellington. The Project will be located on the seaward side of the state highway and the rail corridor and will provide safe walking and cycling infrastructure and enhance the transport corridor’s resilience. The Project includes all of the above-mentioned drivers including partner and stakeholder expectations, very tight environmental and ecological constraints, budget expectations, a difficult design environment adjacent to a major fault-line and exposed to southerly wind and wave climates, limited local rock supply and construction workspace.
Delivery of the Project from concept design through to construction is being delivered by the Te Ara Tupua Alliance, comprised of owners Waka Kotahi NZ Transport Agency, working in partnership with mana whenua (Indigenous partners), contractors HEB and Downer and designers Tonkin + Taylor. To address the many project challenges, an innovative approach to design was implemented during initial concept phases. This included an agile design philosophy with sprint design and review cycles enabling fast paced integration of design, construction, environmental and cultural objectives. This approach included several innovations in the final design, most notably the adoption of modified XblocPlus® concrete armour units for primary armouring. These single-layer, pattern-placed units are to be used for the first time in Australasia and have resulted in significant cost and programme savings to the Project, but have also included bespoke modifications to achieve improved aesthetic, ecological and cultural outcomes. Show less…

Australasian Coasts & Ports Conference, 2023, Sunshine Coast, Queensland

The Te Ara Tupua Ngā Ūranga ki Pito-One (Ngauranga to Petone) Project comprises a 4.5 km shared (pedestrian/cycling) pathway between Ngā Ūranga (Ngauranga) and Pito-One (Petone) in Te Whanganui-a-Tara, Wellington. The Project will be located on the seaward side of the State Highway 2 and the rail corridor and will provide safe walking and cycling infrastructure as well as enhancing the resilience of the transport corridor. The Project involves temporary and permanent works in and adjacent to the coastal marine area, including multiple rock and concrete armour revetments, ūranga (landings), seawalls, offshore habitats and culvert extensions, and will result in over 5 Ha of permanent marine habitat loss. Show more…To avoid, minimise and compensate for the impact on the marine environment, a number of innovative ecological enhancements have been incorporated into the Project design. Two rock armour offshore habitats will provide undisturbed roosting habitat for coastal avifauna. 235 little blue penguin nesting boxes will be incorporated within the revetment and Ūranga. Gravel beaches will be nourished to provide 10-25 years of resilience to future sea level rise. Over 240 ECOncrete® tide pools will be integrated in clusters within the intertidal bench of the rock revetments and offshore habitats, providing habitat and water retaining features for marine life as well as foraging habitat for coastal birds. Finally, some 1850 XblocPlus® units, that form part of the revetment, will be ecologically enhanced using increased surface complexity. The integration of these ecological enhancements within the design was developed in collaboration between ecologists, landscape architects, engineers and mana whenua and drew inspiration from the existing ecology, coupled with cultural narrative.
This project will be the first application of many of these ecological enhancement features in New Zealand. The features will improve the ecological value of the coastal pathway and provide a more resilient marine ecosystem within Te Whanganui-a-Tara (Wellington Harbour). The project provides a case study for how ecological features can be successfully implemented into coastal infrastructure and an opportunity to measure the ecological performance of these features in a New Zealand context, so that future installations can more accurately predict the ecological gains likely to be achieved when balancing against unavoidable biodiversity losses. Show less…

Australasian Coasts & Ports Conference, 2023, Sunshine Coast, Queensland

Modern-day coastal engineering faces two key challenges: firstly, providing adequate protection under anthropogenic increases in sea level, and secondly, reducing environmentally detrimental engineering practices that are further driving changes to the climate. With this, nature-based solutions that minimise detrimental environmental effects whilst providing sufficient protection are increasing in their uptake. At present, the application of these nature-based engineering strategies is restricted to low-energy wave environments with minimal spatial constraints. Hybridisation (combined use of nature-based and traditional hard engineering strategies) enables the use of these nature-based principles in higher-energy and urban environments. This paper explores the use of hybridisation with coastal vegetation, by exploring the ability of vegetation to attenuate wave overtopping flow on the crest of coastal defence structures. Show more…Physical modelling experiments were conducted in the University of Auckland’s wave flume with a small-scale sloped seawall retrofitted with model vegetation on the crest of the seawall. This preliminary testing found that the model vegetation reduced mean overtopping discharges by 60-80% when evaluated against their nonvegetated counterpart. Numerical model testing was conducted by calibrating to and expanding on the physical model analysis. This was achieved by implementing a one-dimensional non-hydrostatic XBeach model. Numerical model testing used a multiple linear regression analysis to test the sensitivity of the wave overtopping response to various vegetation parameters. From this, the reduction in mean overtopping flow due to the incorporation of vegetation was found to be most strongly correlated to vegetation width, stem density and stem diameter, with increases in any of these parameters leading to substantial decreases in mean overtopping flow.
Both the physical and numerical model testing were limited by their use of idealised structure and vegetation parameters. However, despite these limitations, this study provides a framework for future testing that should seek to further solidify the wave overtopping performance of this hybrid strategy. Show less…

Australasian Coasts & Ports Conference, 2023, Sunshine Coast, Queensland

The Te Ara Tupua Ngā Ūranga ki Pito-One Project comprises a 4.5 km shared (pedestrian/cycling) pathway between Ngā Ūranga and Pito-One in Te Whanganui-a-Tara, Wellington with dual outcomes of rail/road corridor resilience improvement and mode shift. The project presented the challenging design requirements of managing the safety of shared path users through a coastal edge design that is controlled by tight geometric (elevation and toe position) constraints, a range of unique edge protection structures, and a bimodal wave climate. This challenge was addressed through site and design specific physical and numerical modelling, data driven overtopping analysis and a forecast model development for safety management during operation. Show more…The range of edge protection structures proposed include XblocPlus armour unit revetments, rock armour revetments with mid-tide berms of varying width, and vertical concrete seawalls with return crest walls. The present empirical guidance on overtopping performance of these structure configurations is not widely developed in literature, at least with sufficient reliability to inform design on this project. An additional complicating factor was a bimodal wave climate, the swell component of which was discovered to have a significant effect on anticipated overtopping flows.
As such, structure- and site-specific physical modelling was undertaken to inform the overtopping analysis at the UNSW Water Research Laboratory. The results of the physical model tests were used to develop site-specific, data-driven formula based on relationships between relative overtopping and relative freeboard, as presented in the EurOtop manual. These relationships were used to understand overtopping potential along the project site both now and in the future through development of a 30-year overtopping timeseries. In parallel, a two-layer phase resolving, non-hydrostatic XBeach solver was calibrated to match the wave transformation of the bi-modal wave climate and physical model overtopping results allowing wave conditions and resultant overtopping flows to be extracted anywhere along the project site.
This was used to inform design crest levels future adaptation timeframes and options, and to develop an overtopping forecast model to inform path warnings and closure during operation. The results of this analysis highlighted the importance of understanding site-specific influences on overtopping flows, not all of which are able to be fully understood through adoption of standard empirical overtopping formula. Show less…

Australasian Coasts & Ports Conference, 2023, Sunshine Coast, Queensland

Urban beaches in semi-sheltered harbor environments are highly valued public spaces that require detailed understanding of coastal dynamics for appropriate management. Understanding the dynamics these environments is challenging due historic management interventions such as renourishment and hard infrastructure. As a result, commonly applied modelling and hazard assessment methods are not necessarily appropriate for semi-sheltered often fetch-limited urban beaches, without site-specific calibration. Show more…This paper focuses on the calibration and potential applications of three different numerical models to better understand coastal processes on the Sandringham Beach in Port Phillip Bay, Victoria. First, the shoreline position model ShorelineS was applied to understand beach rotation, seasonal trends in shoreline movement and long-term rates of shoreline change. Model calibration was informed by monthly monitoring data, including drone-based topographic surveys and wave buoy data. Next, the storm response model XBeach was calibrated using observed wave events and measured changes in the coastal profile. The models were collectively used to give new insight on the beach dynamics at short, medium, and long timescales.
Outputs of the XBeach and ShorelineS modelling were then used to inform variables for projecting shoreface translation to sea level rise using the ShoreTrans model, where the sensitivity to different trajectories of barrier rollover and translation were assessed. Isolating the cross-shore adjustment in ShoreTrans allowed the idealised beach topography to be reconstructed for a sea level rise scenario representing the year 2100. Balance of alongshore sediment flux was achieved by passing volume from profile to profile according to the net sediment balance in the system, informed by long-term rates.
The paper introduces a conceptual a multi-model workflow that is proposed for exploring present day and future scenarios, with application for hazard management and adaptation design. Show less…

Australasian Coasts & Ports Conference, 2023, Sunshine Coast, Queensland

This paper presents a review of the Golden Cross Landslide near Waihi 17 years after its successful stabilisation by use of major drainage and earthworks. The landslide is interesting because of its size,
2100 m long, 500 m to 1000 m wide and up to 145 m deep, and supports a large tailings dam retaining approximately 1.7 million cubic metres of tailings from the previous gold mining operation. Show more…The paper includes a review of historic and current landslide movement rates (from inclinometer and GPS data), piezometric data and presents an assessment of the ongoing effect of the stabilisation measures. Comment is also made on the long term relative effectiveness of the various stabilisation
measures from the nearly 20 years of data available. Show less…

12th Australia – New Zealand Geomechanics Conference, Wellington, 2015

The 10 km stretch of foreshore between two of New Zealand’s largest cities Wellington and Hutt City is a crucial infrastructure corridor combining cycleway, road and rail, as well as sub-surface utilities. Recent storm events have caused significant damage to, and overtopping of, the current rock revetment structure resulting in the rail line being undermined and closed for extended periods. Future proofing the foreshore is integral for the longevity and function of this corridor and the Te Ara Tupua Alliance have been tasked with redeveloping it. Show more…UNSW Water Research Laboratory (WRL) undertook a large physical modelling program (over a 100 individual tests) to assist optioneering for a range of coastal protection designs. 2D flume testing was conducted to assess both the stability and overtopping performance of rock and concrete armoured (modified XblocPlus) revetments and vertical walls equipped with sloped crown walls.
All tests were conducted using irregular wave time series derived from several spectral conditions. Analysis of wave buoy records showed that both wind waves and swell entering the harbour could be expected to impact the project area. As such, sensitivity testing for overtopping was conducted using custom-generated bimodal conditions with different wind/swell ratios. Physical model testing results showed that overtopping volumes were highly sensitive to the long period wave component within the bimodal spectrum.
The findings of this extensive physical modelling program highlight the limitations of standard empirical methods for assessing overtopping under bimodal wave climates, the importance of extending beyond conventional unimodal wave climates when designing coastal structures, and the importance of using on-site wave data to best model potential overtopping volumes and safely optimize designs. Show less…

Australasian Coasts & Ports Conference, 2023, Sunshine Coast, Queensland

The Ōpōtiki Harbour Development involves stabilising the entrance of the Waioeka River to allow reliable and safe access for maritime activity. Te Ara Moana a Toi (“A path to the sea”) is the first major river training works to be constructed in Aotearoa, New Zealand in over 100 years. The project involves constructing twin 400m long training wall breakwaters, dredging a 120m wide navigable channel into the Harbour, closing the natural river mouth, and forming a new dune habitat. Show more…Construction of the Ōpōtiki Harbour Development Project commenced in late 2020 by HEB Construction. The opening of the new harbour entrance is expected to be completed in late 2023/early 2024.
Construction at the end of a dynamic sand spit within the coastal zone is inherently uncertain with dynamic morphological processes and testing environmental conditions. As expected with a project of this scale, the coastal environment has provided many challenges and opportunities for designers and constructors alike during the construction stage. This paper covers significant construction milestones, environmental monitoring data, challenges, and innovations undertaken during construction. These include construction observation techniques, environmental monitoring data, and innovations developed to successfully undertake construction of the new harbour opening while being 300m offshore within the surf zone. These challenges and innovations include the ground improvement methods undertaken, withstanding and adapting to extreme wave conditions during construction, dredging techniques, and the philosophy behind the new channel opening and subsequent existing river mouth closure expected to occur in mid-2023. Show less…

Australasian Coasts & Ports Conference, 2023, Sunshine Coast, Queensland

The Ōpōtiki Harbour Development (“OHD”) is the first river port to be constructed in over 100 years in New Zealand. Te Whakatōhea have developed an offshore mussel farm and onshore processing factory and need a navigable harbour entrance to connect these resources. Show more…The OHD scheme comprises twin 400 m long training walls to fix a dynamic river mouth, around 700,000 m3 of dredging in intertidal and subtidal areas and approximately 20 hectares of constructed fore and mid dune to close the existing river mouth. The OHD is located in a sensitive estuary environment fed by two major rivers. The estuary contains numerous threatened fauna, is subject to constant morphological change and provides an important recreational resource for the Community.
To ensure opportunities for innovation in design and construction were optimised, the resource consents granted for the OHD deferred most environmental impact avoidance, remediation, or mitigation to a suite of Environmental Management Plans (“EMP”) to be prepared in parallel with the Detailed Design of the project. These EMP manage a range of impacts, such as sediment contamination, saline wedge connection to inanga spawning habitat, disturbance to dotterel breeding areas, water quality (TSS and clarity), native fish migration, training wall related downdrift erosion, and sediment deposition within riverine riparian vegetation and seagrass assemblages.
Timeframes to design and construct the OHD were very tight with many inter-dependencies in the project plan. The Technical Liaison Group (“TLG”) comprising representatives of tangata whenua and a range of regulatory agencies were required to contribute to the development of the EMP.
To ensure the OHD project was delivered within a compressed programme, meticulous planning and execution of the environmental management regime was required. To this end, partnership was key. The OHD design and construction project team worked with the ocean, rivers, nature, tangata whenua, regulators, the Community, and other professionals. Show less…

Australasian Coasts & Ports Conference, 2023, Sunshine Coast, Queensland

The use of single layer, concrete armour units for coastal edge protection in place of rock is becoming increasingly common. Revetments constructed from these units can provide benefits of a reduced footprint, reduced material usage and transport costs as suitable rock becomes increasingly difficult to source, and reduced construction timeframes. Show more…XblocPlus® units have been adopted as the primary armouring for a major shared-path infrastructure project within Te Whanganui-a-Tara, Wellington Harbour. The Ngā Ūranga ki Pito-One Project comprises a 4.5 km shared (pedestrian/cycling) pathway between Ngā Ūranga and Pito-One. The XblocPlus® units are patternplaced interlocking armour concrete units that remain stable at steep slope angles while providing high coastal performance. However, these units have had limited application in seismically active regions. Therefore, the behaviour of the individual armour units and overall revetment during, and following seismic activity was assessed in detail to assess performance and enable development of a post-seismic inspection and repair strategy.
The response of a revetment to seismic shaking, particularly the interlocking of the individual XblocPlus® units and interaction with the ground profile below is complex and could not be determined using a single method or model. Therefore, a suite of complementary models was used to assess the behaviour of individual components and combined performance of the revetment asset under the design earthquake events. This paper describes the various physical and numerical models used to determine performance and to inform the design and repair strategy of XblocPlus® revetment.
The physics-based model Unreal Engine was calibrated against uni-directional testing on a physical shake table and run for 3D design earthquake timeseries to assess how the individual XblocPlus® units reacted to shaking. Limit equilibrium and time history finite element modelling were carried out to understand how the ground profile supporting the revetment might perform. These results were then used in the 3D physics-based model in Blender to determine the unit response to slope deformation. The XblocPlus® response to shaking and slope deformation was combined to create a post-seismic revetment condition, which in turn was tested by physical modelling in a wave flume against to assess hydraulic stability performance under moderate storm events (i.e., before a repair could be enacted). Following this, an inspection and repair strategy was developed. Show less…

Australasian Coasts & Ports Conference, 2023, Sunshine Coast, Queensland

Wave overtopping occurs as waves pass over the coastal edge and flow onto the land behind. This can result in a hazard to vehicles and pedestrians and flooding or damage to the built environment. To date, predictive formulae for overtopping have been primarily developed in a laboratory setting. Comparatively few studies involve the field measurement of overtopping because environmental conditions such as wind and water levels have a large influence on the overtopping rate (amongst many other factors), and the measurement of overtopping discharge is practically difficult due to enormous spatial and temporal variation in overtopping volumes. Show more…This paper discusses key challenges for local government coastal managers in New Zealand relating to overtopping hazard, highlighting a need for pragmatic guidance on monitoring, application within an adaptive management, and assessment of Relative Sea Level Rise (RSLR) effects on future hazard.
Two methods to measure wave overtopping in the field were investigated in this study; using either catch devices that measure volume, or camera monitoring. This paper shows, by considering a site along Tamaki Drive in Auckland, how monitoring and measurements of overtopping is important as part of the Ministry for the Environment (MfE) recommended Dynamic Adaptive Policy Pathway (DAPP) approach to managing associated hazards.
Finally, this study shows how future overtopping hazards associated with RSLR can be assessed by remodelling incremental rises applied to historic water level records. It is found that even small amounts of RSLR can dramatically increase the exposure of coastal communities to overtopping hazards. Show less…

Australasian Coasts and Ports Conference, 2013, Sydney

Over the past 40 years, the advantages of utilising geosynthetic barriers versus traditional earthen barrier materials have been well documented: greater project economy, extended service lives, enhanced environmental protection, greater site safety, etc. Show more…Achievements such as conserving water resources and enabling beneficial site reuse have even given geosynthetic engineering a level of social importance. As such, the use of geosynthetic barriers has increasingly been required by government regulators around the world. This is true in modern waste management landfill design. However, there are still regions and applications in which the use of these barrier technologies should be more widely adopted. This paper highlights an overview of applications where geosynthetic barriers are used, and where regulation or recommendations are available, and it describes other emerging applications where geosynthetic barriers are starting to be used. Show less…

12th International Conference on Geosynthetics, 2023, Roma, Italy (12ICG)

Auckland Council owns and operates approximately 600 stormwater ponds and wetlands, most of which involve dams. This valuable infrastructure supports the financial, social, cultural, and environmental wellbeing of communities, present and future, by providing flood mitigation, water quality treatment, amenity, ecological value, and cultural heritage value, as well as mitigating the impacts of land development and climate change. Show more… In the first few months of 2023, the Auckland region was subject to two catastrophic storm events in quick succession, including Auckland’s largest ever rainfall event. This paper shares the experience from the emergency response for a large portfolio of stormwater dams in a regionwide, multi-month series of record floods, to share learnings with others that may face similar situations. Several factors were identified as beneficial for emergency response. These included having a mature dam safety management system, a practiced response team, and pre-established relationships with dam safety advisors and contractors. In a series of large-scale storm events, other hazards will likely need to be considered alongside the dam safety threat, the health, safety, and wellbeing of the response team requires extra consideration, and there is especial value in simple systems and concise communication. Show less…

ANCOLD 2023 Conference on Dams

Geopier Rammed Aggregate Piers® (RAPs) are a ground improvement technology that creates a densified column of aggregate surrounded by a stiffened matrix soil. This paper describes the design and construction of RAPs at Te Kaha, a $683- million Multi-Use Arena under construction in Christchurch, New Zealand. Show more…CLL Projects are constructing 8331 RAPs including 1092 tension RAPs to depths between 5.5 to 12m to provide a ground improvement system supporting the arena. Design considerations include estimation of soil densification in a wide range of soil conditions (sand, silty sand, silt and gravel), analysis of liquefaction triggering before and after ground improvement, numerical analysis to predict the bearing capacity and settlement of the foundations, and prediction of uplift capacity for tension RAPs. The design predictions and the actual results from verification testing are compared, including pre- and post- improvement CPTs and tension load tests. At Te Kaha the RAP installation resulted in a significant increase in sandy soils between the RAP elements. The CPT results consistently underestimated the fines content of the soil. The tension load test results showed that the uplift capacity is dependent on the soil conditions at the tip of the tension RAP. If adequate confinement cannot be achieved at the base the tension RAP ‘unravels’ and the capacity is much lower than typical design methods would predict. Show less…

14th Australia New Zealand Conference on Geomechanics, Cairns, 2023

The New Zealand Building Code (like many others) is a performance-based standard; however, the application of performance-based design is rare in practice. Typical design practice considers the capacity of individual elements in the building and does not allow for the full load-displacement response of the building system. This paper presents a case study where a performance-based design approach was used for the design of a new building on an existing foundation system and how it was able to illustrate compliance with the New Zealand Building code. Show more…The case study found that a capacity-based design approach was likely an impractical way to illustrate compliance with the Building Code. Given the significant negative project impacts including programme delays, environmental impacts and cost increases associated with adopting a new foundation system, a performance-based assessment was completed. With strong interaction between the geotechnical and structural engineers, a non-linear vertical pile spring analysis was undertaken, allowing the design team to demonstrate that the existing foundation system complied with the building code, avoiding the significant negative project impacts. Show less…

14th Australia New Zealand Conference on Geomechanics, Cairns, 2023

Claystone deposits are commonly intercepted in road slope cuttings, for example in Southern Queensland and thus the understanding of the shear behaviour of these deposits is important for geotechnical engineers for design, construction, and maintenance works. These sedimentary deposits are often weakly bonded, and the engineering behaviour is akin to heavilyoverconsolidated plastic clays. Show more…Apart from difficulties in sampling these deposits, interpretation of shear behaviour in triaxial tests is often challenging. The paper presents the results of a triaxial investigation and discusses some of the challenges involved in the conduct and interpretation of the results. Further, the pitfalls of directly using the laboratory shear results at the field scale are highlighted, drawing attention to the potential for progressive and delayed failures that are observed in the field. Some requirements for constitutive modelling for numerical analysis are also emphasized. Show less…

14th Australia New Zealand Conference on Geomechanics, Cairns, 2023

COP27 (United Nations Framework Convention on Climate Change Conference of the Parties) demonstrated the critical role of governments and non-state actors (communities, cities, businesses, etc) in driving momentum for climate action. Aotearoa New Zealand (NZ) made commitments at COP27 as part of the global effort to tackle climate change. To deliver these pledges, alignment in infrastructure policy and action is required. Show more…The infrastructure industry must proactively make bold, disruptive changes to set international best practice. This paper assesses current policy direction and sets out how NZ asset management practices can contribute to retaining the 1.5°C limit through:
– Including marginalised communities in policy-making
– Co-design with iwi/Māori
– Integrated and systems thinking approach to renewals planning
– Asset valuations using asset lives which consider climate hazard exposure
NZ industry-wide collaboration and paradigm shift must underpin the practical and radical changes required in this international climate crisis. Show less…

IPWEA 2023 Conference, Rotorua

The Seismic Assessment of Existing Buildings, Technical Guidelines for Engineering Assessments (“the Guidelines”) provides engineers with a consistent means to assess the seismic behaviour of existing buildings with respect to life safety. The expectation for a new building designed in accordance with current good practice is that it should be able to sustain in excess of 1.5-2 times the ULS displacement while still achieving its life-safety objectives. Show more…This same expectation is transferred to the assessment of existing buildings with ULS scaled to reflect the %NBS rating attained. To achieve this expectation in the evaluation of the effects of geotechnical aspects on existing building behaviour the Guidelines require that the behaviour of the soils under ever increasing levels of seismic shaking be considered. However, when this behaviour is expected to lead to a rapid deterioration in the soil resistance available (referred to as a step change), the capacity of the soil is required to be limited to half of either the deformation or the level of shaking at which the deterioration is estimated to occur. Within the Guidelines, geotechnical Severe Structural Weakness provisions have prescriptive requirements for certain types of buildings, but the geotechnical step change provisions are open to interpretation, particularly when considering the impact on the supported structures. This paper will provide commentary on the intent and application of the geotechnical step change provisions and will present practical examples taken from real-world projects. Show less…

NZ Society for Earthquake Engineering (NZSEE) Conference 2021 Christchurch

Liquefaction during the Canterbury Earthquakes caused significant damage to the built environment of Christchurch and provided a significant challenge to the rebuild effort. This paper describes the process that the geotechnical engineering community went through to overcome this challenge, and how the lessons learned and the new knowledge acquired has been used to design and construct new buildings in Christchurch. Show more…The first part of this paper describes key lessons learnt from the earthquakes, summarising information from land damage mapping throughout Christchurch from four major earthquakes. The second part of this paper summarises research projects carried out by MBIE in 2011 to assess foundation performance using blast induced liquefaction techniques. One key finding from both the damage observation and the research projects was that the thickness and strength of the non-liquefiable crust layer has an enormous impact on the occurrence and severity of land damage in the earthquakes. The final part of this paper describes how this lesson has influenced the foundation design for new ‘anchor projects’ in the Christchurch CDB, including the Justice and Emergency Services Precinct, the Christchurch Hospital Acute Services Building, Canterbury Multi Use Arena, Te Pae Christchurch Convention Centre, the Tūranga Central Library and the repair of the Christchurch Town Hall. Show less…

NZ Society for Earthquake Engineering (NZSEE) Conference 2021 Christchurch

A new wharf structure was proposed for Te Wānanga in central Auckland. Due to the complex geometry of the proposed wharf, which included plan irregularity, open apertures, deck-suspended planter boxes, suspended nets and a step down in level, a 3D finite element model was developed for the structure to undertake design. Push-over analysis that incorporated both modelling of non-linear hinges and the effect of non-linear soil-structure interaction was undertaken. Show more…This paper highlights the collaborative approach undertaken between the geotechnical and structural designers to achieve a practical and efficient design solution by detailing the design methodology and the technical challenges in the modelling approach. The proposed Te Wānanga structure consists of bored reinforced concrete filled steel tube piles of varying founding depths supporting a reinforced concrete deck slab. The spatially varying founding depths result in significant variation in pile stiffness. To capture the non-linearity of the stress-strain relation of the soil as well as the effect of the spatially varying pile stiffness, a series of non-linear load-deformation (p-y) curves were developed for each soil unit along the depth of the piles. These p-y curves were then converted into uncoupled lateral non-linear springs to be input into the 3D structural model using multi-linear elastic link elements. By modelling the p-y curves in the 3D model, programme efficiencies were gained by reducing the number of design iterations of soil spring stiffnesses required between the structural and geotechnical engineers. Show less…

NZ Society for Earthquake Engineering (NZSEE) Conference 2021 Christchurch

Earthquake shaking can cause liquefaction in certain types of soil. The associated loss of soil strength and stiffness coupled with any lateral ground movement can impart large lateral loads (kinematic loads) to buildings and their foundations, which can be very damaging. In addition to the kinematic loads, the foundations are also subjected to lateral inertia loading (base shear) from the building. Show more…Inadequate consideration of these loads can result in unacceptable performance of the foundation and structure. Various methods to assess the components of kinematic load for pseudo-static analyses are available. This paper presents a literature review of these methods. It was found that calculated kinematic loads on a pile can vary significantly depending on the method chosen, and soil profile present. Comparisons are made for an example soil profile, and suggestions provided for design. This paper also presents a literature review of recommended combinations of concurrent base shear and kinematic loads. It was found that there is significant variability between guidelines, and the majority of the guidelines are typically for low period structures (bridges, wharves etc). Suggestions are provided on percentages of peak base shear to consider in combination with kinematic loads, and factors to consider when making this selection. Show less…

NZ Society for Earthquake Engineering (NZSEE) Conference 2023 Auckland

Liquefaction-induced lateral ground displacements (lateral spread) can be damaging to buildings and their foundations. Buildings can either be designed/strengthened to tolerate such displacements, or ground improvement (e.g. compaction, grouting etc.) may be implemented to mitigate these displacements to a tolerable magnitude. For existing buildings that cannot tolerate such displacements, foundation strengthening is not always a feasible option and site constraints limit ground improvement options. Show more…Therefore non-routine engineering solutions will be required. This paper presents the development of such a solution (an in-ground pile wall to mitigate lateral spread) for a site occupied by existing buildings located on a reclaimed waterfront in Wellington. Lateral spread ground displacements cannot be reliably predicted and there is uncertainty in prediction of the loads imposed on the in-ground pile wall by lateral spreading ground. Appreciating these uncertainties, the design included both displacement-based and force-based approaches along with sensitivity analyses. The sensitivity analyses considered the uncertainty in the input parameters and in the analysis methods. Resilience in the event of earthquake shaking or ground displacements beyond the design allowances was provided. Show less…

NZ Society for Earthquake Engineering (NZSEE) Conference 2023 Auckland

When designing and constructing revetments, there is often a drive to reduce the footprint due to space constraints and a limited supply of suitable rock armour materials. Concrete armour units present a potentially more sustainable solution to revetment construction than traditional rock armour. Show more…These units are constructed from concrete in a specifically designed configuration to interlock and remain stable at steep slope angles while providing enhanced coastal performance. However, these units have had limited application in seismically active areas. The seismic behaviour of the revetment and the concrete armour units has been assessed to understand the performance during and following earthquake shaking. XblocPlus® units have been adopted as the armouring for a major shared path project along the shores of Te Whanganui-a-Tara (Wellington Harbour). Understanding the various mechanisms of displacement and the performance of the revetment during and after a seismic event was crucial in determining whether the units would be a viable alternative. This paper discusses the different models used to understand seismic performance and inform the design. Show less…

NZ Society for Earthquake Engineering (NZSEE) Conference 2023 Auckland

Liquefaction-induced lateral ground displacements (lateral spread) are typically assessed using empirical methods where a continuous weak (liquefied) layer is expected. These methods may not be appropriate for variable ground conditions where continuous weak (liquefied) layers are not expected. Show more…End-tipped reclamation fill materials on the Wellington Waterfront are highly variable, and the materials tend to vary by zones rather than continuous sub-horizontal layers. Numerical methods in conjunction with a ‘smeared’ soil strength offered a possible means of evaluating lateral spread potential in this situation. This paper presents the process adopted to estimate lateral spread potential using smeared strengths of liquefied soils for a site on the Wellington Waterfront. The determination of smeared strengths was based on a weighted average strength of soils divided up by soil behaviour type (Ic) from CPT testing and depth. The smeared strength approach was considered appropriate for predicting lateral spread displacements at locations relatively distant from the reclamation edge (i.e. A distance of > 2 times the depth to the base of the liquefiable materials). At locations within proximity of the reclamation edge there is a risk of a local zone of weaker fill materials dominating the overall strength, so the smeared strength may not be representative. Sensitivity analyses and engineering judgement were applied to the results of the lateral spread predictions when considering the potential range of ground displacements for the site. Show less…

NZ Society for Earthquake Engineering (NZSEE) Conference 2023 Auckland

The New Zealand Building Code is performance based. However, the most commonly adopted design methods utilise capacity-based Verification Methods such as B1/VM1. Although considerable time and cost is typically associated with design approaches which deviate from the Verification Methods, such as an Alternative Solution, it does present designers with the opportunity to assess the response of buildings with greater certainty. Show more…This allows for more explicit consideration of the stress and strain response in individual elements and in the founding soils, and as such an Alternative Solution approach can be particularly advantageous for the design of atypical buildings, buildings where foundation response is of particular interest, or buildings that integrate existing elements. A case study is presented in this paper where nonlinear time history analysis was implemented within an Alternative Solution approach to validate reinstatement of a building that suffered earthquake damage by reusing the existing foundation system. The uncertainty in ground conditions and foundation response was able to be incorporated into the design through detailed ground modelling including the effects of liquefaction, allowing nonlinear pile springs to be developed and conservatism reduced through the assessment of individual pile performance. The performance of individual elements of the lateral load resisting system was also assessed, allowing for an efficient superstructure design. The paper will discuss the modelling and analysis techniques adopted in application of the Alternative Solutions approach, including amalgamation of international best practice with NZ standards and modelling of and performance criteria adopted for piles and critical superstructure elements. The paper will also comment on the advantages of this approach in relation to conventional design approaches. Show less…

NZ Society for Earthquake Engineering (NZSEE) Conference 2023 Auckland

The site of the New Dunedin Hospital straddles the location of the original shorelione prior to extensive reclamation works in the late nineteenth century. As a result, ground conditions vary. During the concept design phase, the design team arrived at piles as the logical foundation choice due to the high load and performance demands of the buildings as well as site constraints such as boundaries. To assess the risks and realise the benefits for the project, Tonkin & Taylor Ltd recommended a full scale trial of driven piles. Show more…Screwsol piles were installed and tested adjacent to bottom driven steel tube (BDST) displacement piles, providing a useful comparison with an alternative low noise and vibration option. Screwsol piles are constructed using an auger to displace soil and place concrete via the auger stem. This method is similar to CFA piles, except soil is displaced laterally by the auger rather than removed. Screwsol piles also incorporate a threaded shaft to furhter enhance shaft friction capacity. Pile driving analyser (PDA) testing was used to assess the as-built capacity of both pile types, and extensive monitoring was undertaken to measure noise andvibration levels, including attenuation with distance from the works.
The BDST pile capacities exceeded expectations by a significant margin. Screwsol piles may still be used for associated structure foundations, especially in sensitive areas where noise and vibration limits are critical.
Clearly a full scale pile trial test is not feasible for most projects. The NDH project provided a unique opportunity providing sufficient time for a piling trial in parallel with demolition of the previous building. Show less…

NZ Geomechanics News Issue 104 December 2022 p. 78-82

The Shrink Swell Test is used ubiquitously in New Zealand for expansive soil testing. However, emerging research continues to cast serious doubts on its soundness and suitability for this purpose. Show more…The evidence suggests that the test has an initial moisture contents bias: the Shrink Swell index value mostly depends on the moisture content of the soil when it was sampled. This paper revisits the findings published in NZ Geomechanics News (Rogers et al. 2020), and presents three further developments since the publication of the original paper. Show less…

NZ Geomchanics News Iss. 104 December 2022 p. 62-68

The ground improvement applications and examples in this paper are planned to augment MBIE Module 5. This paper presents some ground improvement applications and their design and specification for earthquake hazard mitigation. Ground improvement methods by densification using vibro compaction and stone columns and solidification methods such as soil mixing and jet grouting are discussed. Show more…Design approaches are demonstrated through key considerations (applicability, construction methodology and quality control), and the applications of each selected method are discussed. Show less…

NZ Society for Earthquake Engineering (NZSEE) Conference 2023 Auckland

Seawalls were constructed in sections between 1879 and 1925 to form Quay Street on the waterfront of downtown Auckland. These seawalls have essentially remained structurally unchanged since they were first constructed and now support the transport hub for Auckland, including ferry terminals, bus services, Britomart and the current CRL development, as well as supporting Auckland’s prime waterfront buildings. Show more…Seismic assessments of the seawalls showed that Quay Street was vulnerable to liquefaction/cyclic softening induced lateral spread. Seismic strengthening was proposed to provide seismic resilience to Quay Street for the next 100 years, providing post-disaster functionality for transportation services and protecting essential utilities located landward of the proposed strengthening alignment. Four sections of the 600 m total length of seawalls were established and design options considered to respond to the desired outcomes in each section as well as the different seawall types in these sections, the changing ground conditions, and construction considerations including a tight construction timeframe with concurrent activities, and a wide range of stakeholder interactions. The three seismic strengthening solutions that were designed and constructed are a jet grout column shear wall, anchoring the existing seawall, and a palisade wall. This paper presents the development of the final design solutions and the technical challenges and lessons learned from the concurrent design of the four sections of the seawall. These challenges and lessons learned included understanding the liquefaction/cyclic softening and lateral spreading hazard, developing a design methodology for jet grout column shear walls, validating pseudo-static design procedures with time history finite element analysis, dealing with constructability challenges, and undertaking staged geotechnical investigations to deliver optimised design solutions. Show less…

NZ Society for Earthquake Engineering (NZSEE) Conference 2021 Christchurch

New Zealand coastal infrastructure is currently at the onset of deteriorating performance associated with ageing of coastal protection infrastructure, ongoing sea-level rise, and potentially outdated design methodologies. The near-term decrease in performance can be attributed to two key components: an increase in structural damage, and an increase in wave overtopping frequencies (a precursor to more sustained coastal inundation).

This article provides an overview of a research project currently underway at the University of Auckland.

New Zealand Coastal Society special publication 5, November 2022 p. 79-86

Expansive soils are present across the wider Auckland region and in many other parts of New Zealand, where residential buildings are increasingly supported on shallow slabs and footings in clay-rich soils subject to shrinking and swelling behaviour. Currently NZS3604 provides first-line guidance on the identification of these so-called expansive soils, based on the use of Atterberg Limits and Linear Shrinkage. Since 1999, NZS3604 has codified the use of Australian Standard AS2870 to guide residential foundation design which requires the classification of a site based on the expected ground surface movement. Show more…There are several limitations in the application of AS2870 to New Zealand conditions, which have been known about for some time, yet still remain unresolved today. Of even greater concern, however, is the unreliability of the shrink swell test for New Zealand soils. If the test results are unreliable, then so too must be the site soil classification from which it is derived. Apart from New Zealand, no other country (besides Australia) has adopted the shrink swell test to classify expansive soils.
Internationally there are alternative methods available to systematically identify and classify expansive soils for the purposes of foundation design, including the Volume Change Potential approach used in Britain. Without the shrink swell test, AS2870 cannot be practically applied in New Zealand. This paper reviews the known problems associated with NZ’s current approach to identifying and classifying expansive soil, comparing it with some international alternatives and poses the question: Is it time to ditch AS2870 from the New Zealand Building code. Show less…

New Zealand Geotechnical Society (NZGS) Symposium 2021

Tremie concrete enables the construction of deep foundations such as piles and diaphragm walls as it is self-compacting, can be placed under a support fluid and is resistant to segregation. As the urban landscape within New Zealand increases in density, deeper and more complex foundations are required. Show more…These deep foundations generate higher structural demands and often require much longer concrete pour times. Consequently, tremie concrete is increasingly becoming a highly engineered material with concrete additions and admixtures used to adapt the concrete to a specific application. These challenges have contributed to major construction issues overseas and the formation of an industry led consortium to develop guidance. This paper summarises tremie concrete guidance and discusses key considerations for tremie concrete in a project life cycle for a New Zealand context. A case study of concrete testing carried out on a recent project in Auckland is presented. Show less…

New Zealand Geotechnical Society (NZGS) Symposium 2021

The Wynyard Edge Alliance (Auckland Council, the Crown represented by Ministry of Business, Innovation and Employment, Downer, McConnell Dowell, Beca, Tonkin & Taylor Ltd) was formed to design and construct the infrastructure to support the 36th America’s Cup event in Auckland. In addition to the core infrastructure required for the event, a wider programme of works is underway on the waterfront. Show more…One of these projects is the extension of the Daldy Street stormwater pipeline – the Daldy Street Outfall Extension (DSOE) which is a Healthy Waters project (a department of Auckland Council). The DSOE scope of works was included as part of the WEA scope of works in 2019. The DSOE works involves the extension of the pipeline from its current outfall position underneath North Wharf, to a new outflow position at the end of Wynyard Point. To complete this, 510m of High-Density Polyethylene (HDPE) pipe is to be placed beneath Brigham Street.
Cutter Soil Mixing (CSM) was adopted as the preferred ground improvement methodology to stabilise the site to enable the trench excavation. This paper intends to report the quality and performance of the panels produced by the Cutter Soil Mix method, as well as to compare different sampling methods, including Wet Sampling, Double Tube Sampling and core sampling from boreholes. It will also discuss the interlocking observed between two adjacent panels and discussions around the practicality of the CSM method in similar site conditions. Show less…

New Zealand Geotechnical Society (NZGS) Symposium 2021

The load transfer between liquefaction induced lateral spreading ground and jet grout shear walls is a complex mechanism. The shear walls comprise rows of jet grout columns, constructed in a primary-secondary sequence to ensure the minimum required overlap, and are aligned parallel to the direction of the lateral movement. Show more…The displacements experienced by the shear walls generate shear, compressive and tensile stresses that need to be accommodated by the treated soil block without exceeding its capacity. This is particularly relevant in the overlapping sections of the shear walls, to ensure that all columns act as a single block, as well as the inward and outward columns of the block, where the maximum compressive and tensile forces are generated.
To ensure an appropriate load transfer throughout the height of the shear wall, standard design methods rely on empirical column overlap versus diameter ratios to establish the minimum geometry requirements of the shear walls. However, these methods need to be adapted to suit a seismic design scenario as the available guidance for the design of in situ soil treatment shear walls appears to be limited to static load cases.
To validate previous adaptations to the available design guidance for static load cases, time-history analyses have been undertaken on a range of selected earthquakes. This paper discusses the assumptions and outcomes of the finite element modelling (FE) and presents a comparison between the FE and the modified pseudo-static design approaches. Show less…

New Zealand Geotechnical Society (NZGS) Symposium 2021

Wastewater systems provide a critical service to society, and their vulnerability to the impacts of climate change. places the health and sanitation of many communities at risk. The impacts of climate change on wastewater systems are numerous and can lead to wide ranging implications over changing timescales. This paper considers the significance of the impacts and implications, how they will be distributed across different groups, how they will manifest in different contexts and locations, and conclude by proposing a range of guiding principles for local government decision makers. Show more…The research firstly considered direct climate-related impacts on a range of wastewater system elements (including reticulated wastewater systems, on-site wastewater systems and treatment plants), in both urban and peri-urban settings in New Zealand. The impacts identified for each aspect of the wastewater network were found to fit within three broad impact themes; nuisance flooding spills and odour, water quality deterioration due to increased uncontrolled discharges and damage to infrastructure.
The research shows that the immediate and long-term implications resulting from these impacts are likely to be experienced widely across the social, cultural, environmental and economic domains. Examples include loss and damage to assets – leading to disruption to communities, water quality deterioration with consequential social, environmental, economic and cultural effects, public health risks, and economic costs related to damages, foregone production and insurance. Cultural implications are of particular importance in a New Zealand context, given the strong connection of Māori to the environment and water. Show less…

Climate Risk Management 31 (2021) Paper 100262

Historical records indicate that consequential liquefaction has occurred during upwards of 11 earthquakes in New Zealand since European settlement and prior to 2010. Post-event observations of land damage have been collated into an online geospatial database that is now publicly available. The dataset outlines areas that have historically liquefied, and thus are susceptible to liquefaction during future events, and may be used to supplement Level A (Desktop) and Level B (Calibrated Desktop) liquefaction hazard assessments as per the MBIE (2017) guidelines. Show more…Interrogation of the dataset indicates that liquefaction has primarily occurred in low elevation areas proximal to waterways with 80 percent of the collated reports within 500 m of a river or stream. Comparison of CPT traces in areas where liquefaction was and was not reported following the 2016 Kaikoura earthquake show that liquefaction predominantly manifested in areas containing comparatively thick layers of low relative density silty sands under PGA in excess of ~0.1g. The collated dataset enables calibration of liquefaction triggering assessments against actual observations when combined with estimated ground shaking intensities of the causative earthquake. Comparison of the predicted liquefaction hazard in Whakatane with that observed following the 1987 Edgecumbe earthquake outlines areas of inconsistent prediction. Potential reasons for the over-predictions include interlayering of soil types within distal floodplains and/or back swamp environments, and/or the presence of pumice. It is anticipated that this work will help to characterize settings, and/or geomorphic conditions where liquefaction typically manifests. The collated dataset provides a valuable tool for desktop hazard studies and in the verification of liquefaction hazards as interpreted from simplified analyses. Show less…

New Zealand Geotechnical Society (NZGS) Symposium 2021

System response using dynamic effective stress modelling can capture the holistic behaviour of a potentially liquefiable soil deposit, including interaction between different soil layers. Compared to a conventional liquefaction triggering analysis, a system response assessment can either predict more or less damage depending on the characteristics of the soil profile. This paper describes a case study where considering the system response resulted in a more realistic prediction of liquefaction effects than a simplified CPT based triggering assessment. Show more…The soil profile at the site comprises upper loose to medium dense sand (from 0-9 m depth), overlying silt (9- 12.5 m), and overlying a lower loose sand layer (12.5-19.5 m). A simplified liquefaction triggering analysis predicted liquefaction occurring from 2 to 6 m depth and 12.5 m to 19.5 m in an Ultimate Limit State (ULS) earthquake event.
Several large diameter tanks are to be constructed at the site. Using a simplified liquefaction analysis, ground improvement was required to 8 m depth to improve bearing capacity and mitigate differential settlements.
A liquefaction system response analysis was carried out using an effective stress time history analysis of a 1D soil column. The model was created in FLAC with a PM4Sand constitutive model for the liquefiable sand layers. The results showed that liquefaction would first occur in the very loose sand layer from 12 to 19.5 m depth, reducing accelerations in the soil column above by approximately 50%. Because of this “base isolation” effect, liquefaction was not triggered in the loose to medium dense sand above 9 m depth in the ULS event. From this result it was concluded that ground improvement is not required to support the tank
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New Zealand Geotechnical Society (NZGS) Symposium 2021

The City Rail Link project connects the existing Britomart rail terminus in Auckland’s CBD with the Mt Eden Station on the North Auckland Line. The c.3km-long route traverses a wide range of geology and ground conditions. Most of the tunnelling will be within Waitemata Group rocks (East Coast Bays Formation, ECBF) that underlie much of the wider Auckland region, while shallower structures at the north and south of the project will also encounter younger sediments (Tauranga Group); volcanic materials (Auckland Volcanic Field, AVF); made ground (including reclamation). . Show more…Desk studies and early site investigations established a broad model of ground and groundwater conditions, while later investigations focused on specific design requirements, material characterisation and/or ground risks (and opportunities). Targets included a 10m-thick mega-bed (in ECBF) at Karangahape Rd Station; anomalous ECBF weathering profiles; complex AVF materials and geometry at the south end of the project; a pre-Holocene paleo-channel under Britomart; post-volcanic spring/pond deposits in the valley between two volcanoes in the south; and undocumented structures in the built environment. Various works packages were procured using a variety of contract styles. However, procurement documentation has generally included a geotechnical baseline report (GBR), supported by ground data in geotechnical data reports. An observational approach was specified for parts of the works, particularly where opportunities for ground investigation during the design phase were limited. Innovation during procurement includes the use of 3D ground models in two of the contracts. A static 3D model was included (for information) for the Mt Eden enabling works area, to illustrate the complex relationships between proposed structures and varied ground units. In a world-first, for Seequent’s Leapfrog/Central the main works tender included a cloud-based 3D geology model and geotechnical database for each tenderer, readily allowing development of their own geology model and facilitating alignment on geotechnical risk during the Alliance GBR process. Show less…

New Zealand Geotechnical Society (NZGS) Symposium 2021

The existing literature contains no shortage of attempts at defining ‘collapsible soils’, all largely focussed on outlining the often unique properties and conditions required for collapse settlement to take place. First recognised and studied by Jennings and Knight (1957), collapse settlement can, in its simplest form, be considered as the radical rearrangement of soil particles upon wetting to result in a significant reduction in the total volume of the soil mass. Show more…It is this behaviour, and subsequent impact on structures founded within such materials, that make the timely identification and accurate characterisation of collapsible soils significant to the geotechnical professional.
This paper provides a brief overview of the collapse settlement phenomenon as documented in the existing literature. It includes a discussion of published findings regarding the potential for collapse settlement to occur in New Zealand soils, and some of the more widely recognised methods used to:
1. Identify the potential for collapse settlement to occur on site (i.e. recognising materials which may have a ‘collapsible’ fabric and which, under particular conditions, may undergo collapse settlement),
2. Assess the potential severity of collapse settlement (qualitative evaluation), and
3. Assess the potential magnitude of collapse settlement (quantitative evaluation).
The paper concludes with a brief discussion of collapse behaviour from an effective stress perspective and why this should be considered when assessing collapse settlement
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New Zealand Geotechnical Society (NZGS) Symposium 2021

Landslides are widespread natural hazards that are responsible for substantial economic and societal damage globally each year. In NZ, landslides frequently occur on soil and rock, triggered by high rainfall, seismic activity, and land-use change and/or disturbance. Show more…This study fcouses on Gisborne district, an area particularly susceptible to landslide hazards because of the area’s steep slopes, relatively young, soft geology, land-use change, extreme rainfall events and extgra-tropical cyclones. However the extent and rate on going slope deformation in Gisborne is poorly known. Indeed, detecting ground deformation related to landslides is vital for identifying and managing areas at risk.Interferometricsynthetic aperture radar (InSAR) is an active remote sensing imaging tool used tro map and monitor surface deformation, with a cm to mm-scale of accuracy. Show less…

NZ Geotechnical Society (NZGS) Symposium 2021 Dunedin

Resilience to natural hazards requires integrated risk management – from hazard identification and risk register, hazard warnings and risk communication, to preparation for and response when an event occurs. Medium-range hazard warnings play a vital role in strategic and tactical planning for resilience to natural hazards. Research advancements have rapidly improved observation, modelling and analysis of natural hazard forecasting for disaster risk reduction. Show more…However, many of these advances have not been tailored to benefit communities at risk as geophysical and hydrometeorological hazards continue to claim thousands of lives and cause irreparable damage to homes, businesses and critical infrastructure. This paper discusses the opportunities to use medium-range ensemble forecasting to support decision making to increase the resilience of communities and the ways to embed holistic early warning systems in risk-informed sustainable development. It provides a set of recommendations for medium range forecasting applications for people-centred early warnings and disaster preparedness. Show less…

Progress in Disaster Science Volume 12, December 2021, Article 100203

New Zealand’s Natural Disaster Insurance Scheme, administered by the Earthquake Commission, is world leading. The scheme is designed to complement private insurance cover (increasingly sum insured rather than replacement) to wherever possible to put the customer back to a similar position that existed prior to the natural disaster. Show more…After natural disasters occur, it has been normal political practice to reasure the affected community that life will get back to ‘normal’ as soon as possible.
The thinking changed after the second Christchurch earthquake in February 2011. The question then became: ‘should rebuilding occur in the same locations?’. Why rebuild in areas of multiple natural hazard risk, particularly if the vulnerability to those hazards was increasing?
In the midst of yet another natural disaster, the floods in Wesport, natural hazards scientist Nick Rogers ponders the role of insurance in rerecovery, adaptation and resilience. Show less…

National Business Review 23 July 2021

It can be challenging for designers and constructors to integrate fish passage at culverts whilst simultaneously satisfying hydraulic, project, and construction requirements. The inclusion of fish passage into the hydraulic design of culverts is complex but can provide ecological benefits that are essential to the lifecycles of numerous aquatic species and the respective ecosystems that they live in. The Peka Peka to Ōtaki Expressway will replace a 13km stretch of existing State Highway 1 (SH1) and traverses several catchments of varying magnitude and associated watercourses. Show more…The project’s culvert and fish passage detailed design package was completed in 2017, pre-dating the NZFPG, the New Zealand Fish Passage Guidelines (NIWA, 2018). Fish passage measures were proposed for each structure based on a combination of resource consent conditions, project requirements, and available design references at the time. The design approach balanced hydraulic design, project, and construction requirements whilst relying on informed judgement in the absence of comprehensive New Zealand-based fish passage guidance. Examples of the fish passage measures implemented include culvert embedment below the natural stream bed level, natural and artificial substrates placed in the culvert barrels, grouted rock, rock climbing holds, and sloped cross-section inverts for both culverts and newly constructed channels.
This design-build project is approaching completion of construction, with many of the fish passage measures now installed. Construction monitoring has highlighted successes and challenges of implementing fish passage in complex and variable natural systems as part of a major civil engineering project. This paper presents as-built examples and shares key learnings regarding factors for success. The value of a clear design philosophy and integrated approach to fish passage is highlighted. Other important factors for success include understanding geomorphological, fluvial and sediment transportation processes, rigorous construction monitoring, and establishing a unified understanding between the designer and contractor. Show less…

Water New Zealand Stormwater Conference, 2021, Tauranga

The adage, “A picture is worth a thousand words” conveys the general concept that complex and multifaceted ideas can be captured in a single image. Photographs (and video) are widely accepted as a media format that can communicate flood information better than verbal or written descriptions. Local Government New Zealand’s 2014 think piece “Managing natural hazard risk in New Zealand – towards more resilient communities” identified a single natural hazards information portal was critical to improve natural hazards management. Show more…As such, a central New Zealand flood photograph repository could greatly support our efforts to enhance flood risk reduction while improving readiness, response, and recovery for flood episodes. With those aims in mind, The NZFloodpics (www.nzfloodpics.co.nz) initiative was launched in 2017 to develop a crowd-sourced and georeferenced national flood photograph database for the benefit of all New Zealanders. NZFloodpics provides a conduit that links people nationwide who experience floods with a database that stores searchable flood photographs with spatiotemporal metadata. The value of a national flood photograph archive is well established; however, the value of the crowd-sourced, citizen science platform and GUI (graphical user interface) used to document contemporary floods is equally (and possibly more) valuable. The NZFloodpics GUI/website has an easy to share URL, which also facilitates rapid sharing over social media, mainstream media and across professional networks.
The NZFloodpics initiative is a non-commercial venture, providing a free flood information resource for flood hazard and flood risk management. It has been used so far by multiple agencies to support flood response work and for the collection of data that underpins flood reduction and readiness programs. NZFloodpics has also helped facilitate the exchange of flood information between communities, organisations, agencies and interested parties. 2021 Stormwater Conference & Expo Our paper will cover the origins and motivations for NZFloodpics, highlighting the value of a crowd-sourced, community-centric contribution toward a national flood photograph portal. Examples of community and industry knowledge capture will be demonstrated for the Bay of Plenty, Northland, Auckland, and Nelson regions. A wider context for how NZFloodpics will be expanded and institutionalized within the NIWA-led “Flood Resilient Aotearoa” MBIE Endeavour research program will be provided. Our presentation will also cover some details about how NZFloodpics will be harnessed in parallel with historical and satellite-based imagery to create nationally consistent flood maps. NZFloodpics photographs are (and will continue to be) freely downloadable, so we will offer initial ideas about future database and GUI applications as public and industry participation increases
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Water New Zealand Stormwater Conference, 2021, Tauranga

Liquefaction ejecta were a key mechanism of liquefaction-induced land damage and residential house damage during the 2010–2011 Canterbury earthquake sequence. To gain insight, 244 well-documented liquefaction ejecta case histories of ejecta occurrence, its quantity, and its effects on infrastructure were developed. Show more…The authors take advantage of a comprehensive dataset of thousands of CPTs and boreholes, LiDAR surveys, aerial photographs, ground surveys, and liquefaction land damage documentation from insurance claims. The ejecta database includes 61 sites that underwent four major earthquakes that produced varying degrees of liquefaction-induced land damage ranging from no ejecta to extreme ejecta. Liquefaction ejecta coverage and amounts for each of the four primary earthquakes of the Canterbury sequence were extracted using both LiDAR-based and photographs-based approaches because direct measurements of the ejecta-induced settlement were not available. The ground conditions and seismic demand leading to the differing quantities of ejecta-induced settlement during the Canterbury earthquakes were characterized. The database will hopefully lead to the development of methods that estimate the likelihood of liquefaction ejecta and the amount of ejecta-induced ground settlement at a site. Show less…

Geo-Congress 2022 : geophysical and earthquake engineering and soil dynamics : selected papers from Geo-Congress 2022, Charlotte, North Carolina, March 20-23, 2022 (GSP 334) p. 520-530

Pyes Pa West (commonly referred to as “The Lakes”) has been one of the fastest growing and most popular residential subdivisions in the Tauranga area. Its location close to the city centre, Tauriko Business Estate for employment opportunities, Tauranga Crossing shopping precinct, easy access to SH36 (to Rotorua) and SH29 (to Hamilton/Auckland), as well as the diversity of housing choice and affordability has proved to be exceptionally popular and an attractive place to live and work. Show more…The development area is located on the lower Nanako Stream catchment, which feeds into the Kopurererua Stream which then discharges into the Tauranga Harbour near Judea. Managing stormwater and flooding within this catchment has been very complicated due to several factors that have made reaching a suitable and appropriate solution difficult to achieve, these include:
• Several historical inappropriate development areas along and adjacent to the floodplain, including residential developments along Pengary Lane along the Nanako Stream and Judea Industrial area at the confluence of the Kopurererua Stream and Tauranga Harbour estuary;
• Historical and ongoing infilling of floodplain areas, both consented and non-consented, which has reduced the capacity of the floodplain to accept flood events;
• Steep escarpments either side of the stream with roading and residential developments either side subject to geotechnical risk and potential failure during flood events; and
• Several flood management and flow control devices (dams, ponds, culverts, treatment devices, etc) throughout the catchment creating flooding risks (e.g. due to dam break scenarios).
Tauranga City Council (TCC) has been developing a comprehensive stormwater solution, to effectively and sustainably manage stormwater and flooding in the catchment of the Nanako Stream.
In order to understand the flood attenuation and stormwater treatment needs of the catchment, hydraulic modelling has been undertaken to determine the volume of water that needs to be attenuated so as to protect downstream properties from flooding effects, as well as the ecological values of the stream.
Through the evolution of this work, a proposed solution has been developed. With these works in place, there is predicted to be no increase in peak flood levels or an increase in maximum flow rates.
Additionally, the works will improve the stability and resilience of existing embankments, increasing safety for downstream properties and the public. All existing and new dams will be designed and constructed in accordance with the New Zealand Dam Safety Guidelines. Show less…

Water New Zealand Conference 2021 (Rescheduled to February 2022)

The threat of sea-level rise to New Zealand’s existing three waters infrastructure is becoming increasingly evident, from recent research, the predicted effects of climate change, and from observations. The economic and environmental impacts of sea-level rise are predicted to be significant, given the majority of New Zealanders live and work in coastal towns and cities, and our ageing infrastructure was not designed for rising seas. Show more…In parallel, the cumulative effect of urban development on water quality is becoming of greater public interest, with a desire for social responsibility and kaitiakitanga (guardianship) of our waterways. This is also being regulated through stricter legislation, such as the 2020 National Policy Statement for Freshwater Management.
Engineers typically design stormwater infrastructure for a 50 to 100-year design life. Therefore, best-practice design must now consider how to achieve required water quality outcomes while recognising the effects of expected sea-level rise over the design life.
For constrained, low-lying brownfield sites in coastal areas, this presents challenges—both physically and economically.
In this paper, we present a case study of the stormwater infrastructure design for the 36thAmericas Cup (AC36) project. The project, located in Wynyard Quarter, Auckland, involved the development of multiple wharves and yard areas—historically, the sites of various industrial and trade activities—as well as the development of upper Brigham Street and public amenity areas (Silo Park Extension).
Physical constraints on the AC36 project were significant, including limited space, ground contamination and settlement, large impervious areas, low available hydraulic head, and co-ordination with other services.
We present and discuss the technical design and water quality requirements, the analytical tools applied to overcome the constraints, and the novel design solutions. We identify the design limitations and key design inputs which the prudent designer must consider to deliver stormwater treatment infrastructure future-proofed against the effects of sea-level rise.
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Water New Zealand Stormwater Conference, 2021, Tauranga

Karangahape Road Station will be a new underground station on the Contract C3 of City Rail Link project in Auckland. The C3 comprises of 3.5 km twin-tunnel underground rail underneath Auckland’s city centre, two new underground stations at Aotea and Karangahape and expanded station at Mount Eden. The Karangahape Road Station is a 30 M-deep mined binocular underground station, with two shafts, platforms, lifts, escalators, rooms housing station and tunnel services equipmewnt, and an entrance at Merciry Lane and Beresford Square. Show more…This paper presents the story of the future proofing through project development of the station design, starting as a six-car station with a single entrance in reference design. The station will be built to accommodate nine-car trains. One of the key decisive facors being unprecendented increase in rail patronage in Auckland. Longer platform tunnels extended the tunnel mining to zones of shallow overburden and demands for tunnel ventilation brought challenges for ground support of large span platform tunnels at junctions with ventilation adits. Show less…

17th Australasian Tunnelling Conference, 2021, Melbourne

Sea-level rise will cause erosion of land, deeper and increasingly frequent flooding and will eventually permanently inundate low-elevation land, forcing the adaptation of seaside communities to avoid or reduce risk. To inform adaptation planning, we quantified the effects of incremental relative sea-level rise (RSLR) on exposed land area, number and replacement value of buildings within Tauranga Harbour, New Zealand. The assessment compared three coastal hazards: flooding, permanent inundation and erosion. Show more…Increasingly frequent coastal flooding will be the dominant trigger for adaptation in Tauranga. In the absence of adaptation, coastal flooding, recurring at least once every 5 years on average, will overtake erosion as the dominant coastal hazard after about 0.15–0.2 m RSLR, which is likely to occur between the years 2038–2062 in New Zealand and will rapidly escalate in frequency and consequence thereafter. Coastal erosion will remain the dominant hazard for the relatively-few properties on high-elevation coastal cliffs. It will take 0.8 m more RSLR for permanent inundation to reach similar impact thresholds to coastal flooding, in terms of the number and value of buildings exposed. For buildings currently within the mapped 1% annual exceedance probability (AEP) zone, the flooding frequency will transition to 20% AEP within 2–3 decades depending on the RSLR rate, requiring prior adaptive action. We also compared the performance of simple static-planar versus complex dynamic models for assessing coastal flooding exposure. Use of the static-planar model could result in sea level thresholds being reached 15–45 years earlier than planned for in this case. This is compelling evidence to use dynamic models to support adaptation planning.Show less…

Journal of Waterway, Port, Coastal and Ocean Engineering (ASCE) 147(3) May 2021

In this study, the entrainment mechanisms of unconfined turbidity currents that interact with a linear rectangular obstacle will be investigated and compared with confined studies. Laboratory experiments will be performed in a lock exchange basin, where the width allows unconfined and partially unconfined flows, with varying initial current densities. Show more…Ambient fluid entrainment, based on the Morton-Taylor-Turner (MTT) hypothesis, was found to be comparable to previous confined studies; however, in situ current density decreased at a greater rate than the latter. It was shown that this was probably caused by the unconfined lateral spreading of the current before the obstacle. The entrainment parameter had a weak relationship with Froude, Reynolds, and Richardson numbers for nonobstructed tests, which was similar to previous studies. However, this was not the case for obstacle tests, which experienced a greater variance in entrainment velocity and head height. Of note, head height was less than that for equivalent confined tests, which suggested that in a practical setting, confined studies might overestimate the obstacle height needed to block current propagation.Show less…

Journal of Waterway, Port, Coastal and Ocean Engineering (ASCE) 147(3) May 2021

A quarry in the Melbourne suburb of Lilydale reached the end of its productive life and was sold together with surrounding land for residential and commercial development. The quarry is up to 140m deep and as part of the planned development the client wished to backfill the quarry with approximately 9 million cubic metres of stockpiled overburden accumulated from the quarrying operation. Show more…An assessment of the potential settlement of the fill was made using oedometer tests to simulate the initial compression, with samples then saturated to simulate the potential for groundwater recovery to cause aditional settlement., The quarry filling has reached approximately 50% of its planned height and settlement monitoring has been undertaken. The paper details the innovative earth filling strategy, the site work undertaken and assesses the measured behaviour of the unsaturated compression that has taken place to date from a theoretical and practical perspective. The findings of this paper will provide meaningful technical guidance and reference for future large-scale earthworks projects.Show less…

Proceedings of the 20th International Conference on Soil Mechanics and Geotechnical Engineering, 2022, Sydney.

Lowes Pit in Hastings was originally a quarry for rock/gravel extraction and dates back to the 1940s. The pit, which sits within the municipal drinking water source protection zone (SPZ) intercepts the shallow groundwater table and currently also receives stormwater runoff from a highly industrialised catchment. The water quality of discharges to the pit are typical of an industrialised catchment and ongoing concerns about the interaction between the pit water quality and the unconfined groundwater aquifer have been raised. In response to the perceived threat to its drinking water supply, Hastings District Council (HDC) undertook an assessment of the potential risks and have now completed detailed studies of the Lowes Pit stormwater catchment and groundwater systems. Show more…The Council has also approved a suite of solutions to minimise the identified risks and deliver targeted community outcomes. The main objectives of the project were to assess 1.) the risk of stormwater pollutants in Lowes Pit to drinking water supplies and 2.) the general risk of pollution effects in line with urban stormwater management guidance and requirements such as the Hawke’s Bay Regional Council Waterway Guidelines for Stormwater Management. An initial evaluation of risk by assessing in-pit water quality data relative to the drinking water and ANZECC guidelines indicated that dissolved metals, E.coli, turbidity and phosphorus were possible water quality parameters of concern. This desktop assessment was then followed up by detailed site investigations and monitoring in which dry and wet weather sampling of the stormwater network, in-pit stratigraphic water quality sampling and a drone-based bathymetric survey were undertaken. Confirmation of overland drainage pathways and visual inspection of the stormwater network at strategic locations were also undertaken as part of the site investigation.
Since E.coli contamination was of particular concern in terms of water supply risk, qPCR testing for a subset of wet and dry weather samples was included. Laboratory testing revealed that there was no evidence of human sewage present in the stormwater network during the dry weather and small wet weather sampling events. It also confirmed that ruminant animals were the most likely source of E.coli in the network. Detectable levels of nutrients, heavy metals and Polycyclic Aromatic Hydrocarbons (PAHs) were also confirmed in the stormwater network while laboratory testing of the pit sediment indicated significant metal accumulation in the vicinity of the stormwater outlets. General urban stormwater pollution risk from heavy metals, sediments and PAHs were classified as medium to high risk. Assessment of the water quality data combined with groundwater modelling indicated a very low risk of pollution to water supplies from Lowes Pit. Based on the abovementioned a risk mitigation plan consisting of source control measures as well as multi-barrier pollution reduction systems was recommended for implementation. The multi-barrier system consists of low-cost IoT real time monitoring sensors, automated deflection of first flush runoff to the foul sewer system, treatment of post-first flush runoff, and conversion of Lowes Pit to an engineered natural filtration system
.Show less…

Water New Zealand Stormwater Conference, 2021, Tauranga

Considering damage and loss of lives, cyclones are the most severe natural disaster in Bangladesh. One of the most important cyclone mitigation measures is to temporarily evacuate the vulnerable population on receipt of warning and look after them by arranging shelters with adequate facilities. To ensure effective and efficient evacuation, it is important to better understand people’s protective actions and hazard decision making. This paper provides an assessment of the factors associated with evacuation to cyclone shelters in coastal areas in Bangladesh over the past 30 years.Show more…
It is based on the comparative study of Cyclone Amphan (2020) and three major historical cyclones: Gorky (1991), Sidr (2007) and Aila (2009). Primary data sources included surveys, focus group discussions, key informant interviews and formal and informal conversations; and secondary data sources included reports, policies and design documents. 210 participants from seven coastal districts severely affected by Cyclone Amphan are selected for the study. While substantial improvements in the disaster response infrastructure were made in the last three decades, shelter evacuation rates are still low. It was found that the majority of people are still taking a ‘wait-and-see’ approach mainly due to the fear of losing property. It was found that partial evacuation, observing environmental cues prior to evacuation and seeking refuge in neighbours’ houses, is indirectly associated with the fear of losing property. There is also inadequate spatial distribution of cyclone shelters with minimal facilities. This study provides recommendations to intensify risk-based planning for cyclone shelters and gender-responsive efforts to ensure a safe environment for the community to seek refuge at shelters with proper planning at the community level.Show less…

Progress In Disaster Science Volume 11, October 2021, Article 100179

The Rawene Reserve landslips occurred in 2017 and resulted in the partial loss of a sealed carpark behind the Mokoia Road shops in Birkenhead, Auckland. The landslips are inferred to have occurred within uncontrolled fill materials placed in a gully during the 1960s and 1970s, and along softened and pre-sheared zones within residually weathered soils of the East Coast Bays Formation. Show more…The main landslip formed a debris flow of material which travelled up to 300 m downslope damaging local infrastructure, and inundating properties and local streams. Emergency action and stabilisation measures were undertaken by Auckland Council to prevent further movement, to make the surrounding area safe and allow for longer term repair works. Stabilisation measures included temporary sheet piles, cantilevered timber pole walls, an anchored concrete piled palisade wall, earthworks, and subsoil drainage. Engineered fill was placed to buttress the slope and form a new carpark. Construction was completed and the carpark reopened in October 2019, two years after the initial landslip event. Monitoring of strain in the piles using rebar strainmeters confirmed pile performance. The project was challenging given its urban location, multiple affected stakeholders and the emergency response required.Show less…

Proceedings of the 7th International Young Geotechnical Engineers Conference, 2022, Sydney

Wave overtopping of coastal infrastructure such as rail, road and shared pathways can be hazardous to users and potentially threaten structural integrity and reliability. A Trigger Action Response Plan (TARP) provides a robust framework for mitigating risk by defining response actions based on escalating trigger levels. Show more…These actions, and their expected frequency of occurrence can be implemented into construction or operational programs and adjusted as new data becomes available or engineering modifications are made.
This paper presents an overview of this framework applied to a case study at Ōhau Point, north of Kaikoūra, New Zealand. This site was significantly impacted during the November 2016 magnitude 7.8 earthquake with a large landslip inundating both the State Highway 1 road and Main North Line rail corridors. Recovery works undertaken by the North Canterbury Transport Infrastructure Recovery (NCTIR) Alliance reinstated the roadway further seaward and at a lower level than previous due to residual landslide and rockfall risk. A unique combination of steep offshore bathymetry and rock outcrops resulted in focusing of wave energy and overtopping to occur at a higher frequency and magnitude than expected. This overtopping posed risks to the recovery team and the public and potentially to the structure itself during extreme events.
A work programme was initiated to investigate and mitigate this risk. This comprised field data collection including detailed bathymetric and topographic surveys, an offshore wave buoy and camera system, numerical wave hindcast, development of image processing techniques to automatically detect overtopping events and physical modelling of the 3D environment to quantify overtopping flows during typical and extreme events. The programme resulted in the development of a Trigger Action Response Plan (TARP) defining threshold wave and water level conditions for a range of actions including traffic management, road closure and post-event structural inspection. This TARP was successfully used to manage risk while longer term mitigation measures were tested and implemented. The TARP was then modified to incorporate the reduced overtopping magnitude and frequency resulting from the engineering worksShow less…

Australasian Coasts & Ports 2021 Conference, Christchurch

Te Wānanga, Auckland’s new waterfront public space, is part of the Downtown Infrastructure Development Programme, which aimed to revitalise the waterfront of downtown Auckland through a series of interconnected projects. The public space comprises an approximately 1,600 m2 suspended reinforced concrete wharf, featuring both an irregular seaward edge and numerous irregularly shaped apertures for architectural features. Show more…These include deck-mounted suspended steel planters which hold large Pōhutukawa trees, woven suspended nets, open apertures with sculpted steel balustrades and suspended mussel floats and ropes, as well as a series of safety piles along the seaward edge. Te Wānanga aims to blend the boundary between the city and the harbour with its architectural design inspired by New Zealand’s coast and culture. The unique architectural form, the low-lying deck level, proximity to Quay Street seawall, interface with simultaneous projects, and time pressure all added technical complexity. Overcoming this required in-depth analysis of wave-structure-soil interaction and close collaboration with the project partners. Development of a comprehensive structural model allowed for geometrical complexity to be accurately considered for rapid assessment of alternative construction staging options and for sensitivity analyses to varying ground conditions to be carried out. This allowed risks associated with unforeseen ground conditions during the construction phase to be managed. An adaptive design approach allowed for the architectural form of the low-lying deck to be retained whilst managing the future risk of wave overtopping through the later raising of the deck level. Wave uplift proved to be a significant load, especially for future sea level scenarios over the design life. However, seismic loading and durability considerations provided the critical design case scenarios..Show less…

Australasian Coasts & Ports 2021 Conference, Christchurch

Cobham Drive, Wellington, is the site of a newly constructed footpath and cycleway with 430 m of associated erosion protection in the form of rock revetment. Habitat enhancement over and above rock placement was required to provide habitat complexity and enhanced ecological function post-construction.Show more…
Marine flora and fauna that reside in coastal areas are impacted by anthropogenic changes to coastlines, leading to loss of coastal habitat and their associated ecosystem services. Ecological enhancements or interventions are becoming increasingly common to address human induced changes to coastlines. Drawing on local and international examples, we identified ecological enhancement features to re-instate ecological values in a hard-engineered environment.
The first feature was pre-cast enhancement tiles that were designed to incorporate ecological specifications in tandem with cultural aspects. The tiles were designed at 400 mm x 400 mm (width and height) and 100 mm deep, using concrete with an ‘acid finish’ that provided additional texture and roughness.
Secondly, we recommended retrospective amendments to the rock revetment material in the form of drill-cored rock pools of varying diameter and depth to mimic natural rock pools in the intertidal zone.
The proposed enhancements were designed within site constraints, such as the small tidal range, local site conditions, rock type and size that was used for erosion protection and known fauna (little penguins / kororā) in the immediate vicinity.
Further, to protect kororā using the site for nesting and moulting, T+T ecologists developed a fauna management plan to protect kororā during construction, and to identify appropriate mitigation in the form of Department of Conservation standard nesting boxes that were installed by contractors above high tide and landward of the revetment.Show less…

Australasian Coasts & Ports 2021 Conference, Christchurch

Areas susceptible to coastal erosion have traditionally been mapped as lines on a map. This was based on single values that were derived using a ‘building block’ approach. More recently, coastal erosion extents have been assessed probabilistically to account for environmental and data uncertainty. Nonetheless, single lines are still typically mapped for selected probabilities of exceedance. Show more…Often, many lines are mapped because of specific sea level rise scenarios, timeframes and selected probabilities of exceedance that are typically considered and this can be confusing for stakeholders. Furthermore, coastal erosion extents can also be useful when undertaking risk assessments for coastal adaptation planning, but single lines are of limited value.
Instead of mapping multiple lines for selected probabilities of exceedance, a raster-based mapping approach can be used for both hazard and susceptibility assessments. This allows the full range of probabilities of exceedance being mapped in a combined manner. Raster maps can be shown in the form of a graduated shading, which can be used to find a probability of exceedance for a selected scenario for a location of interest (e.g. road or house). Separate shadings can be created for each timeframe and sea level rise scenario, which could be integrated in a web-based tool using a slider to select the scenario of interest. This would enable probabilistic risk assessments to be undertaken, as well as providing useful information for landowners and infrastructure managers.
This paper outlines how probabilistic methods and improved mapping can enhance the overall effectiveness and engagement from a coastal erosion susceptibility assessment. This includes full probabilistic assessments and raster-based mapping for beach shorelines. For cliff shorelines, a quasi-probabilistic approach is typically adopted, with the cliff toe retreat assessed probabilistically with single stable angles projected landward from a selected probability of exceedance up to where it intersects with ground levels. Raster based mapping for cliff shorelines using a fully probabilistic approach is introduced to allow raster maps being created for cliff shorelines.
The motivation for these improvements is to assist with effective and strategic management at the coast and to assist with communicating uncertainty to communities and stakeholders.Show less…

Australasian Coasts & Ports 2021 Conference, Christchurch

Tsunami pose a significant risk to many urban centres in New Zealand. Having methods to assess the extent and flow regimes of tsunami allow the development of appropriate mitigation measures. Simulation of tsunami inundation using numerical methods has typically been undertaken assuming a bare-surface terrain with roughness coefficients applied based on land cover, rather than incorporating buildings and vegetation into the elevation model. Show more…This is often a consequence of computational limitations restricting the spatial resolution able to be modelled during large-scale tsunami inundation assessments. These coarse resolutions mean that buildings and infrastructure are unable to be realistically modelled. This is of particular concern in dense, urban environments where tsunami flow characteristics are likely to be strongly influenced by built infrastructure.
This research investigated the effect that spatial resolution, roughness coefficient parameterisation and buildings/topographic representation had on the expected flow characteristics during a hypothetical modelled tsunami inundation event. A high-resolution study area at Mount Maunganui, New Zealand was selected due to its characteristics as a densely built-up, low-lying area, with a known existing tsunami hazard. Non-linear shallow water wave equation (NLSW) based models were employed during this study.
The study showed that results were most substantially influenced by different building representations in the simulations. Results showed that buildings had the ability to block and channelize flow, resulting in differences in maximum flow depths, peak flow velocities and hazard classification between the bare-surface terrain and higher-resolution building-resolving models. The addition of buildings led to higher peak depths and velocities in certain locations thereby increasing or decreasing the expected hazard potential during the modelled event. The high-resolution model outputs are also able to be more effectively used to promote community engagement with respect to tsunami hazard and encourage improved public understanding of the threat. Building-resolving simulations can be presented visually in a high-resolution, three-dimensional (3D) animation, thereby allowing the public to appreciate the potential devastation of a tsunami event in a real-time video format.Show less…

Australasian Coasts & Ports 2021 Conference, Christchurch

A magnitude 7.8 earthquake struck the Kaikōura coastline in November 2016 causing widespread uplift and landslides closing State Highway 1 and Main North Rail Line. Ōhau Point was the location one of the largest and most challenging landslides, with more than 160,000 cubic meters of rock falling from the surrounding cliffs and inundating the road and rail corridors. Show more…Recovery works by the North Canterbury Transport Infrastructure Recovery (NCTIR) Alliance reinstated the roadway further seaward and at a lower level than previous due to residual landslide and rockfall risk. A unique combination of steep offshore bathymetry and rock outcrops resulted in focusing of wave energy and overtopping to occur at a higher frequency and magnitude than was initially expected. This overtopping presented a potential hazard to road users and to the road infrastructure itself during extreme events. This paper presents the results of extensive physical modelling undertaken at the Water Research Laboratory at UNSW Sydney to investigate the overtopping processes and to assist NCTIR in evaluating options for mitigating hazard at the site. The section of road and seawall at the site is fronted by a nearshore zone with highly complex bathymetric features, and as such, a quasi-threedimensional model was required to simulate the complex 3D effects of the nearshore wave field and overtopping process.Show less…

Australasian Coasts & Ports 2021 Conference, Christchurch

In June 2017 Emirates Team New Zealand defeated Oracle Team USA, seizing the opportunity to host the 36th America’s Cup on the Waitematā Harbour in Tāmaki Makaurau Auckland. Auckland last hosted this international sporting event in 2003. Continued urban regeneration along Auckland’s waterfront meant that the previous event infrastructure had since been redeveloped for other uses.Show more…
The lack of space to host the event was a serious test for the City. Together with central Government, Auckland Council recognized the significant potential economic, social and reputational benefits of the Cup to Auckland and New Zealand – the opportunity to adapt a waterfront brownfield site at pace, helping a flagship event and the City to thrive. Delivery of the complex, highly visible project with an immovable deadline, called for a proactive and collaborative approach. The Wynyard Edge Alliance was formed by Auckland Council and central Government in July 2018 to design and construct the infrastructure.
This case study examines how, by coming together around a collective goal of “creating a stage for the America’s Cup and a waterfront destination that Kiwis and visitors love”, the Wynyard Edge Alliance, and its participants, overcame challenges relating to land availability, water space and funding constraints to deliver the infrastructure required to host the event in time for the syndicates arrival. It particularly focuses on:
• how the split between temporary and permanent infrastructure was used to maximise legacy value within funding constraints.
• the design issues faced in terms of design life, durability and contamination.
• accommodating the wide-ranging needs of superyachts, international race syndicates and vibrant public
spaces.
• the solutions found to accommodate sea level rise for new infrastructure and address resilience challenges
for 100-year-old wharves and reclamation
• repairs to repurpose and extend the useful life of the 100-year-old Wynyard Wharf
Keywords: America’s Cup, temporary infrastructure, marine structures, repurposing and reuse, brownfield.Show less…

Australasian Coasts & Ports 2021 Conference, Christchurch

Ground improvement by means of Controlled Modulus Columns (CMCs) usually involves the construction of a Load Transfer Platform (LTP) over the CMCs, especially for construction of low embankments over soft soil, to carry the overburden load and transfer to the CMCs, thereby not loading the surrounding soft soils, and avoiding excessive total and differential settlement. Show more…This paper provides a case study of a design undertaken for CMCs without an LTP, taking advantage of a relatively high embankment (4.5 m). Compacted fill and gravel working platform layers have been considered to be sufficient to dissipate any differential settlement at the surface of the embankment, without a need for an LTP. Available settlement monitoring data has confirmed the settlement to be within tolerable limits. Advantages of this method include time and cost savings, as well as environmental benefits.Show less…

14th Australia & New Zealand Young Geotechnical Professionals Conference, Rotorua, 2022

A public open space on the Tāmaki Makaurau waterfront known as ‘Te Wānanga’ has been constructed as part of a wider transformation of the Tāmaki Makaurau downtown area. The project constitutes a tidal shelf of interconnected spaces, a coastal forest, and apertures to the sea below. Green-lipped mussel (kūtai) restoration is incorporated into the design, with the aim of re-establishing ‘living’ systems in the Tāmaki Makaurau urban marine environment. Show more…Māori knowledge and philosophy have strongly influenced the co-design process. Green-lipped mussels were once abundant in the Hauraki Gulf, before overfishing and pollution caused stocks to collapse in the mid-1900s. Successful translocations of mussels have been undertaken as part of the ‘Revive our Gulf’ project, but have not previously been attempted in the Tāmaki Makaurau city centre. Trials of pile wraps and a novel floating buoy system seeded with mussels were deployed in June 2020, to inform the final deployment in May 2021. Success criteria include survival and growth rates of mussels, and establishment of other native and non- native species, with the aim of providing targeted substrate and systems to enhance native biodiversity. So far, the mussels are holding their own, and attracting other native species even in this heavily impacted environment. However, as seen in other urban marine environments, there is competition from invasive species such as Undaria and the Mediterranean fanworm. Given its location in the heart of the city the project provides an excellent opportunity to educate the general public about pollution and invasive species, and to showcase the cultural and ecological benefits of shellfish restoration through a co-design process.Show less…

Australasian Coasts & Ports 2021 Conference, Christchurch

River mouths are often highly dynamic environments, fluctuating in location and depth with riverine and coastal processes. Where river training structures restrict the river to a fixed location, these structures must be protected against the effects of scour occurring within the main channel. Show more…One possible toe protection method is to construct a “falling toe” (or “falling apron”) to launch material onto the developing slope formed by the scour. Data from physical model studies and field installations are limited, making it difficult to assess the general behaviour of the falling toe during the scour process and therefore the optimal placement volume and geometry.
This paper describes a physical model study undertaken at the University of Auckland Fluid Mechanics Laboratory to investigate the performance of the toe armour during scour, and to document the scour development (and the response of the falling toe) during several experiments. The physical model study was undertaken at a geometric scale of 1:30 within a recirculating hydraulic flume. Time-dependent scour depth measurements obtained using an array of acoustic sensors and time-lapse photograph observations are combined with photogrammetry and post-test excavations to gain a complete understanding of the behaviour of the falling toe in response to scour of the channel test section.
As the scour developed within the channel, the falling toe was launched to create a 1:2 slope protected by a single layer of armour material, irrespective of the presence of an underlayer. The toe of the armoured slope was periodically buried and uncovered by bedforms under live-bed conditions. The amount of crest retreat was governed by the scour depth and the number of armour layers providing material to the protected slope. Scale and model effects are discussed along with general principles for design.Show less…

Australasian Coasts & Ports 2021 Conference, Christchurch

Communication and interaction between the project structural and geotechnical engineers are critical to obtain an efficient building solution for the site, building owner and occupants. This is particularly important at concept development phase when building form and type is being assessed. This paper provides a case study of soil-structure interaction and the holistic concept development of a four-storey apartment type building and concrete raft foundation overlying potentially liquefiable soil. Show more…It examines how a lightweight structure can have benefits from a sustainability, seismic performance, and overall cost perspective. The site comprised liquefiable soils approximately 3 m below foundation level. The Structural Engineer and Geotechnical Engineer worked together to examine the seismic and sustainability performance of a robust reinforced concrete raft foundation for three potential superstructure types: timber, reinforced concrete and steel. For simplicity, this paper presents the two maximum and minimum structural types for seismic performance and sustainability, being reinforced concrete and timber. It was established that the seismic performance of a lightweight timber structure was significantly improved compared to a conventional concrete structure. As a result, the timber structure option only required a 400 mm thick concrete raft. Whereas the conventional concrete structure option required a 900 mm thick concrete raft with poor seismic performance, and potential for additional ground improvements. It was also assessed that the timber structure option had significantly less embodied carbon compared to a conventional concrete structure. A major contribution to this was the differences in the concrete raft thickness. The improvement in foundation design, improvement in seismic performance, and reduction in embodied carbon contributed to the building owner’s selection of the timber structure concept and avoided the need for expensive ground improvement.Show less…

14th Australia & New Zealand Young Geotechnical Professionals Conference, Rotorua, 2022

The Ōpōtiki Harbour Development Project involves stabilising the entrance of the Waioeka River to allow reliable and safe access for maritime activity. This project is the first major river training works to be designed in New Zealand in over 100 years and includes twin 400 m long training wall breakwaters, dredging of a navigable channel into the harbour, and closing the natural river mouth. Show more…Accurate definition of wave height reaching the structure is a key design parameter for armour sizing, setting crest elevation and determining wave penetration into the harbour. To model wave processes for the design, a high-resolution numerical wave model was required to resolve nearshore transformation, refraction, diffraction, and reflection off the structure. The fully non-linear Boussinesq model Funwave-TVD was used to for this work, in conjunction with physical modelling in the wave basin with WRL. This paper discusses how numerical and physical modelling methods were used in a complementary and iterative manner to inform and test the design. Reflection was a key consideration during the modelling work. Reflection and any resulting convergence needed to be accounted for within the breakwater channel, however, amplification from reflection radiating out to the open sea needed removing to optimise the unit sizing. Wave reflection in the numerical model was assessed using a range of linear and directional spectral methods, with limited success. Improved handling of reflection for the design objective was achieved by repeating simulations with and without the breakwater structures. Reflection off the structures was controlled in the numerical model using a local friction on the breakwater face that achieved a reflection coefficient of 0.3-0.4 to match physical modelling observations. Physical modelling results were also used to validate and calibrate the numerical model. A scaled version of the final design was tested in a 3D physical model for confirmation of stability.Show less…

Australasian Coasts & Ports 2021 Conference, Christchurch

The Ōpōtiki Harbour Development Project involves stabilising the entrance of the Waioeka River to allow reliable and safe access for maritime activity. This project is the first major river training works to be designed in New Zealand in over 100 years and involves construction of twin 400 m long training wall breakwaters, dredging a navigable channel into the Harbour, and closing the natural river mouth. Show more…The design solution chosen involves conventional rubble mound breakwaters armoured with Hanbar concrete armour units and includes a wide rock armoured toe apron. Design of the Harbour entrance breakwaters has involved a complex process of defining both coastal and river design parameters that input into the detailed design of the structures. Key aspects of both coastal and river processes were modelled numerically and physically with the results of the modelling feeding into the detailed design of the structures. Data obtained from site investigations was used to inform and calibrate the modelling and design decisions alongside predicted climatic changes to the coastal and river hydrology over the design life of the structures. Compared to the engineers of 100 years ago we have a greater understanding of the construction environment and more design tools, however this creates additional challenges. This paper discusses how the respective models were used to calibrate and evaluate the design parameters from both coastal and river processes. It also discusses some of the design philosophy and decisions made during detailed design particularly in relation to design wave height and the effects of waves against currents, the choice of KD value for stability design of the armour units, calibration of the calculated and modelled wave overtopping flows, requirements and feasibility for ground improvements, and the design philosophy behind the choice of toe apron design..Show less…

Australasian Coasts & Ports 2021 Conference, Christchurch

On 1 January 2020, the allowable sulfur content of marine fuels, as capped under Annex VI of the International Convention for the Prevention of Pollution from Ships (MARPOL), fell from 3.5 percent by weight to 0.5 percent by weight. Although, at the time of writing, New Zealand had not yet acceded to Annex VI, all ocean-going ships entering New Zealand ports are flagged to states that are party to Annex VI. Show more…Therefore, the effects of the Annex VI ‘Sulfur 2020’ Regulations are expected to largely have been realised. Monitoring for sulfur dioxide and PM10 is undertaken by the Bay of Plenty Regional Council at a number of sites in the Mt Maunganui area close to the Port of Tauranga, which is the largest port in New Zealand in terms of total cargo volume. The monitoring data has been investigated to evaluate the impacts of the Sulfur 2020 Regulations on sulfur dioxide and particulate matter air quality in the Mt Maunganui area. The paper also considers what further air quality improvements might be observed once New Zealand accedes to Annex VI.Show less…

26th CASANZ (Clean Air Society of Australia & NZ) Conference 2022, Adelaide

When installing anchors in weak argillaceous rocks selecting appropriate ultimate grout to ground bond strength parameters can be challenging, yet critical to ensure safe and rational anchor design. Literature notes groundwater and/or drill flush type can influence the ultimate bond strength due to water softening effects. Show more…One tool which can be deployed to increase the capacity of an anchor in weak rock is underreaming, locally increasing the diameter of the anchor fixed length. This paper summarises anchor investigation tests undertaken in the Mount Messenger Formation in North Taranaki. It compares the ultimate capacities of straight shafted anchors drilled with air and water flush, in addition to an underream anchor. The data presented may support anchor practitioners working in similar ‘papa’ lithologies, or equivalent Late-Miocene soft rocks in New Zealand and internationally.Show less…

14th Australia & New Zealand Young Geotechnical Professionals Conference, Rotorua, 2022

Assessment of offensive odour risk in accordance with Environment Protection Authority of Victoria (EPA) Publication 1883 Guidance for assessing odour, June 2022 (EPA Publication 1883) is based on the downwind odour frequency (as measured in a field odour survey) multiplied by the annual wind frequency of that particular downwind direction (which can be sourced from wind measurements or from meteorological modelling). Show more…When odour presence is observed during calm conditions, the frequency of calm conditions replaces the wind frequency in assessing odour risk. By convention, a ‘calm’ is said to occur when wind speeds are less than 0.5 m/s, as this is a typical stall speed for older ‘cup and vane’ type wind instrumentation used in weather stations. However, if newer and more sensitive technologies such as ultrasonic wind sensors are used in the field, wind measurement can be more refined. Accuracy of measurement can be achieved to the level of 0.1 m/s and measurement starting threshold as low as 0.01 m/s. Hence, for assessing odour risk, the definition of ‘calm’ may need to change from convention as field experience corroborates that wind movement can still be physically detected below 0.5 m/s. This case study seeks to explore whether changing the definition of calm winds would affect the categorisation of offensive odour risk under EPA Publication 1883, and how this s may affect the type of wind data to be used for an odour risk assessment.Show less…

26th CASANZ (Clean Air Society of Australia & NZ) Conference 2022, Adelaide

Provision of accurate meteorology both at the surface and upper air levels is a key input for atmospheric dispersion models. At locations which are distant from observation stations in Australia and New Zealand, meteorological datasets have historically been produced using the prognostic model section of The Air Pollution Model (TAPM). Show more…More recently, and since TAPM has ceased to be updated by CSIRO, dispersion modelling has been based on prognostic data that has been downscaled using the Weather Research Forecasting (WRF) model. Due to the computational power required to run the WRF model many practitioners opt to purchase the data from third party suppliers. Modelling from the currently available third party suppliers is based on land use information which is nearly 20 years out of date. This paper presents an approach to incorporate the most accurate available data for terrain (ALOS Global Digital Surface Model (AW3D30)) alongside land use information derived from a blend of the National Vegetation Information System (NVIS) and Catchment scale land use (CLUM) for Australia and the Land Use and Carbon Analysis System (LUCAS) data for New Zealand. This paper uses this information to compare the model predictions for TAPM, WRF using default data and WRF using modified terrain and land use in comparison to observed data in Canterbury, New Zealand to a resolution of 1 km.Show less…

26th CASANZ (Clean Air Society of Australia & NZ) Conference 2022, Adelaide