Researchers from The University of Texas at Austin are conducting a study that will help a city rebuild after a string of earthquakes, thanks to a boost from the U.S. National Science Foundation and the government of New Zealand. The knowledge gained could one day help set building codes in earthquake-prone areas in the United States and abroad.
This summer, two faculty members and two graduate students from the Cockrell School of Engineering conducted field research in Christchurch, the second largest city in New Zealand, where six powerful earthquakes hit in 2011.
Since then, as many as 7,500 homes have been abandoned because of earthquake damage, and approximately 2,400 out of 3,000 structures in the central business district have been demolished. During the earthquakes, different parts of Christchurch were affected by liquefaction the process by which water-saturated sediments, or soil, temporarily become liquid-like.
The government of New Zealand supported the earthquake-related research with $2.2 million to fund the construction of 16 ground improvement sites in different soils around Christchurch. The government provided UT Austin researchers free access to the testing sites. In addition to New Zealand's support, the U.S. National Science Foundation (NSF) is funding the project through a grant worth approximately $200,000.
The research will help address a critical problem facing Christchurch and the Canterbury region: rebuilding on land that remains at risk of liquefaction in future earthquakes. The research team, which arrived in New Zealand in mid-June, completed the field project in mid-July.
"This liquefaction field work has never been done before and represents critical, basic research as well as important practical knowledge for Christchurch to move forward in its developments," said Kenneth Stokoe, principal investigator on the project and professor in the Department of Civil, Architectural and Environmental Engineering. "The study will impact the future Christchurch society through the development of more robust seismic designs of residential structures for more than 15,000 homes."
Currently, little information exists on the types of ground improvement methods that can be used to improve the resiliency of residential structures and low-rise buildings in future earthquakes. Researchers conducted full-scale field tests of shallow ground improvement methods, evaluating which soil improvements will perform best in future earthquakes.
The grant, which is part of NSF's Rapid Response Research (RAPID) program, will be used to fund expenses and salaries associated with the project, which is called "RAPID: Field Investigation of Shallow Ground Improvement Methods for Inhibiting Liquefaction Triggering." The project's goal is to determine whether various ground improvement methods help inhibit liquefaction, and which of the methods tested would be most cost-effective. Civil engineering assistant professor Brady Cox is also a lead on the project.
The liquefaction testing was conducted using a large mobile shaker truck, called T-Rex, that is operated by NEES@UTexas at UT Austin, which is part of The George E. Brown Jr. Network for Earthquake Engineering Simulation (NEES). The 64,000-pound T-Rex is used to simulate a wide range of earthquake shaking levels. The shaker truck was transported to New Zealand earlier this year for use in another NSF-funded (NEES) project involving deep seismic profiling.
Stokoe and his team have worked closely with their colleagues from the University of Canterbury and geotechnical engineer Sjoerd van Ballegooy of Tonkin and Taylor Ltd. who have been working hard to help Christchurch recover from the aftermath of the earthquakes.
This research will have applications for earthquake-prone cities in the United States, as well as numerous other parts of the world. The first phase of testing should be complete by August.
"We will work for another year to dig deeper into the basic research findings," Stokoe said. "This stage mainly determines which ground improvement methods are best suited for Christchurch and will allow them to move forward in rebuilding a resilient city."