New Zealand’s Earthquake Commission (EQC) has released a report on making residential land less vulnerable to liquefaction, following two years of research involving local and US experts.

EQC GM Research and Education Hugh Cowan says before the Canterbury earthquakes in 2010/11 strengthening residential land in areas prone to liquefaction was rarely carried out.

“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,” Dr Cowan said.

The EQC has identified four methods for strengthening cleared residential land, and the type of land on which each method will be most effective.

The methods involve stone columns, timber poles, reinforced soil-cement rafts or reinforced gravel rafts

The Ministry of Business, Innovation and Employment has incorporated the methods into its guidelines for repairing and rebuilding in Canterbury on land designated Technical Category 3, where “moderate to significant” land damage from liquefaction is possible in large quakes.

The research has also identified a method known as horizontal soil mixed beams, which can be used to strengthen land where homes are still in place. However, this can be used in limited circumstances only, and is significantly more expensive than methods for cleared land.

The research program was led by the EQC’s geotechnical engineers Tonkin + Taylor and included contributions from the University of Canterbury, Housing New Zealand and the New Zealand Transport Agency.

Contributions were also made by liquefaction experts from various US universities, the US National Science Foundation and the US Network for Earthquake Engineering Simulation.

Dr Cowan says the research will be useful to property owners, engineers, builders and property developers, private insurers, local authorities and central government agencies.

The summary report and fact sheets are available here.