T+T continues to help Canterbury recover

T+T continues to help Canterbury recover

During 2010 and 2011 a sequence of four major earthquakes, and many significant aftershocks, struck the Canterbury region in New Zealand. The magnitude 6.3 earthquake that struck on Tuesday 22 February 2011 caused the terrible loss of 185 lives and thousands of injuries. The sequence of earthquakes also caused severe widespread damage to land and buildings in Christchurch and the surrounding suburbs. The Canterbury rebuild is still continuing as of 2015.

 

The engineering work required after a significant disaster is wide ranging and so our service to the local communities during this time has been multi-faceted with many people involved. The Canterbury Earthquake Recovery Project (CERP) to get the Canterbury community back to a fully functioning region, is one of the largest and longest running infrastructure projects ever undertaken in New Zealand. Our involvement in the CERP has included the full range of geotechnical engineering and environmental services.

 

Our involvement in this project started with the collection of a very large amount of land damage information and geotechnical data. We helped to coordinate large engineering teams consisting of local and international experts to collect and analyse this data. The project has also required significant amounts of IT work to manage this data to enable analysis. For example, IT infrastructure services have been created for CERP such as the Canterbury Geotechnical Database (CGD). The CGD is for the use of professional geotechnical and structural engineers to access geotechnical data and other technical information shared by researchers and other engineers and their clients. The high quality of this technical data has been crucial for the ongoing recovery efforts.

 

The ground type, the low elevation relative to sea level, and the proximity of the land to the tidal zone all combined to cause a large proportion of the land to subside in response to the earthquakes. The subsidence per se is not damage, but it has also caused further types of natural disaster damage to occur that are invisible to the naked eye, that are related to adverse effects on the use and amenity of the land.

 

The fact that the ground surface is lower than it was prior to the earthquakes, has caused the depth to the ground water level to rise, thereby reducing the thickness of the non-liquefying crust. This has, in places, increased the vulnerability to liquefaction (ILV) of the ground that supports buildings. Additionally, the fact that the ground surface is lower, has also, in places, increased the vulnerability of the land to flooding (IFV) during heavy rainfall.

 

Both ILV and IFV have caused significant ongoing hardship in the region in response to further shaking and flooding events. Consequently, the ILV and IFV forms of damage needed to be identified in the first instance to enable communities to be appropriately compensated for the loss of use and amenity. Analysing where ILV and IFV have been incurred has been a challenging engineering exercise. We have been instrumental in both identifying appropriate characterisations of the damage, and carrying out the analysis of the data to establish which land is damaged and to what extent.

 

We have been conducting an innovative and demanding programme of engineering work to carry out this analysis. This is the first time IFV has been recognised as damage anywhere in the world. We have provided the technical leadership in geotechnical and water resources engineering to analyse the available data.

 

In addition to characterising the types of damage, and analysing the extent to which individual properties have suffered ILV and/or IFV damage, we have also been instrumental in identifying and evaluating appropriate forms of land repair methods that could potentially be used to return the damaged land to its pre-earthquake use and amenity. A significant body of work was carried out where ground improvement methods were trialled to ascertain their levels of performance.

 

Many of those who have worked on this project were themselves local to the Canterbury region, or from our offices in other New Zealand centres, or international experts. Four of our engineers have been recognised with Queen’s honours for their service and commitment to communities following the Canterbury Earthquakes. They include Dr Sjoerd van Ballegooy QSO, Nick Rogers QSO, Kate Williams QSM and Mike Jacka QSM. All four continue to work on the CERP project.