Land surrounding Christchurch safe from liquefaction - report

Liquefaction was a major problem for Christchurch residents after the major quakes in the area. File photo / Simon Baker

Large swathes of land surrounding Christchurch are unlikely to be affected in the future by the damaging earthquake side-effect of liquefaction, according to a new report.

Released today by Environment Canterbury, it maps areas where building projects outside of already quake-zoned land will no longer need expensive 15 metre-deep ground tests.

The report, which covers 20 years of liquefaction studies and draws on the experience of the 2010 and 2011 Canterbury earthquakes, also shows where testing is still required.

Environment Canterbury Commissioner Donald Couch says it provides an up-to-date assessment of the need for geotechnical investigation of liquefaction-susceptible ground in eastern Canterbury.

"This comprehensive piece of work gives our communities better information for those considering building outside areas already zoned by the Canterbury Earthquake Recovery Authority (Cera)," Mr Couch said.

"The practical effect of this is that costly investigations will no longer be done in areas where they are not needed and will be focused on areas where they can ensure appropriate building solutions.

"This is the way it should be in helping make sure our buildings are as safe as possible for the future of Canterbury."

Liquefaction is the phenomenon where sandy soil turns to liquid during ground shaking and pushes up through the ground.

It has been responsible for extensive damage to buildings and land in Canterbury during the earthquake sequence which started in September 2010.

The report will provide territorial authorities and communities with general guidance on where geotechnical investigation and engineering assessment of liquefaction potential may or may not be required for plan changes, and for subdivision and building consents.

It may also be useful for lifeline utility and emergency management planning.

The report covers the Christchurch City Council area, including Banks Peninsula, and eastern parts of the Waimakariri, Selwyn and Hurunui districts, but does not include other parts of Canterbury or land that has already been zoned by Cera.

Kelvin Berryman of GNS Science said his organisation, and the Natural Hazards Research Platform he chairs, were pleased to be involved in co-ordinating and funding the report.

"I am sure the results of this collaborative effort will be very helpful for the Christchurch rebuild and appropriate building work throughout Canterbury," Dr Berryman said.