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EQC releases results of world-leading land strengthening research

The Earthquake Commission has today released a report on more practical and affordable ways of making residential land less vulnerable to liquefaction.

The report summarises two years of world-leading research involving New Zealand and international experts, EQC General Manager Reinsurance, Research and Education Dr Hugh Cowan says.

“Prior to the Canterbury earthquakes, strengthening residential land in areas prone to liquefaction was rarely carried out,” Dr Cowan says.

“The research has identified methods previously only viable for commercial-scale projects that can now be used to strengthen residential land, making the homes built on the land more resilient in future earthquakes.”

EQC coordinated the work as part of its role to facilitate research and education that increases New Zealand’s resilience to natural hazards.

“As a result of the research, we have identified four methods of strengthening cleared residential land. We’ve also identified the types of land on which each of the methods will be most effective,” Dr Cowan says.

The methods identified to strengthen the land include:

  • stone columns
  • timber poles
  • a reinforced soil-cement raft
  • a reinforced gravel raft.

These methods have been incorporated into the Ministry of Business, Innovation and Employment’s April 2015 update of its guidelines for repairing and rebuilding structures on some TC3 land in Canterbury.

The research has also identified a method that can be used in some cases to strengthen land where a home is still in place, Dr Cowan says.

“This method, known as a Horizontal Soil Mixed Beams, will provide an option for some home owners, though it can only be used in limited circumstances and is significantly more expensive than the methods that work on cleared land.”

The research programme was led by EQC’s geotechnical engineers Tonkin + Taylor. Input and reviews were provided by experts from the University of Texas at Austin; Brigham Young University, Utah; Oregon State University; University of Canterbury; Cornell University, New York; the University of California, Berkeley; and the University of California, Davis.

“The research will be useful to property owners, engineers, builders and property developers, private insurers, local authorities and central Government agencies,” Dr Cowan says.

The summary report and fact sheets about the various methods are available on www.eqc.govt.nz/GIP.

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