Designing for Resilience where the only Constant is Change
Annual Conference
❄
The Canterbury earthquakes damaged the wastewater pipes in Christchurch, reducing the security and resilience of the remaining network. An alliance between Canterbury Earthquake Recovery Authority, Christchurch City Council and New Zealand Transport Agency, and five non-owner participants created the Stronger Christchurch Infrastructure Rebuild Team (SCIRT). Working with many other companies they are all combining together for the vision of creating resilient infrastructure for Christchurch.
The liquefaction effects and damage of large flexible pipelines has not been well documented around the world, and initial investigations found very few examples. With multiple large diameter flexible pipelines being installed after the earthquakes, which included Pressure Main 11 (PM11), the design of these carried a large number of uncertainties. In particular, the soil strengths were thought to potentially change during a liquefaction event to a very low value, and then return to lower than the existing soil strength.
Designing Pressure Main 11 on its current soil strength no longer ensured a resilient design. To ensure redundancy against seismic effects for the installed pipeline, measures to mitigate the potential loss of side support were trialled. A geogrid / geotextile wrap around the embedment material was shown to provide additional support to the pipe after the side support was removed. This trial verified the structural design of the pipeline and removed the need for the additional mitigation measures.