UC engineering expert helping directly in Christchurch’s rebuild

December 4, 2012

University of Canterbury’s civil and natural resources engineer Professor, Misko Cubrinovski, is helping in the Christchurch rebuild by working with the Stronger Christchurch Infrastructure Rebuild Team (SCIRT) on repairing 2000 km of water mains and 2000 km of sub-mains.

His preliminary geo-spatial analysis of the damage data indicated that, on average, there was one break/fault per kilometre of damaged pipelines. Eighty percent of the damaged pipe networks were in soils that suffered liquefaction.

In addition, there are about 2000 km of wastewater pipes, of which nearly 700 km were either out of service or with limited service one month after the earthquake.

``We are continuing our collaboration and support of Christchurch City Council (CCC) and SCIRT engineers, designers and managers,’’ Professor Cubrinovski said.

`` We will pass our research outcomes to CCC and SCIRT in the course of the study and will continue to provide technical advice on a regular basis.

``Both the detail and the big picture are very important. Use of flexible pipe materials and joints that can accommodate large ground movements, trench and manhole details protecting the pipelines and minimising relative movements between the pipes and surrounding soils and many other engineering solutions that reduce damage and improve overall performance of the networks are required.

``However, this has to be achieved in a cost effective way and therefore we have to accept some damage, or even design the system to fail at a particular location where quick repair and reinstatement will be easily achievable.

``Large areas of Christchurch are susceptible to liquefaction of moderate to severe intensity. Since these networks are distributed across the city, their exposure to liquefaction hazards is very high.A robust and balanced approach is needed to provide an affordable system that will ensure good performance during earthquakes.

``This is well understood in CCC and SCIRT and there are many dedicated people who work very hard in achieving these goals. I have seen many excellent contributions and good stories of this nature, and UC is certainly making a very strong contribution in these efforts.’’

One of the projects Professor Cubrinovski led after the February 22 earthquake last year focused on the impacts of liquefaction on the potable water and wastewater systems of Christchurch. The project started in April last year and worked closely with a group of about 10 people from the CCC. The team started work on the rebuild even before SCIRT was established.

Before the earthquakes, very few people had any deep understanding of liquefaction and its impacts on infrastructure. The CCC and SCIRT engineers and Professor Cubrinovski had lengthy discussion about liquefaction, how it evolves during earthquakes, the resulting ground deformation and how it affects engineering structures and buried pipes in particular.

They discussed many details about the potable and wastewater pipe networks of Christchurch, for example, grading and density of backfills in trenches, characteristics of different pipe materials and connections.

There was an immediate need for CCC, and then SCIRT, to quickly start the reinstatement/recovery work on these lifelines and for that purpose they needed area-specific design criteria addressing liquefaction hazards. This, in turn, required zoning of Christchurch with respect to ground conditions and liquefaction susceptibility/severity.

``We quickly produced a so-called Liquefaction Resistance Index Map for Christchurch which identifies five different zones and for each zone specifies parameters (such as ground strains and displacements) that are used in the design of the networks. This map has been used as a principal tool by SCIRT engineers for preliminary screening in the design process.

``The map is unique because it provides back-calculated liquefaction resistance purely based on observations of manifested liquefaction and recorded ground motions. This is invaluable information because it synthesises all the complexities and specific characteristics of our soils and their response during actual earthquakes,’’ he said.

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