Environment Canterbury today released a review of liquefaction information for Christchurch and neighbouring districts outside the green and red zones.
The review report maps areas where building projects will no longer need expensive 15-metre deep ground tests and other areas where these tests will still be required.
The report covers 20 years of liquefaction studies and draws on the experience of the 2010 and 2011 Canterbury earthquakes.
Environment Canterbury Commissioner Donald Couch says the report 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,” Mr Couch said.
The main purpose of the report is to 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,” Mr Couch said.
“A map in the report shows areas of solid ground where damaging liquefaction is unlikely and areas of more variable ground quality where liquefaction assessment is needed during site investigations.”
This means that for many areas of Canterbury, fewer deep geotechnical investigations will be required than at present, while those that are carried out will be better targeted.
“You might still need a shallower geotechnical investigation for other hazards though – for example, for susceptibility to flooding or land subsidence,” Mr Couch said.
Kelvin Berryman of GNS Science says 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.
Environment Canterbury has been liaising closely with territorial authorities, CERA and the Ministry of Business, Innovation and Employment to help inform their natural hazards and building consenting activities.
“It is pleasing that this collaborative work is resulting in the development of consistent processes through MBIE’s Building & Housing Guidelines, which now include a section on liquefaction testing specifically taking account of this report,” Donald 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.”
The occurrence of liquefaction depends on whether underlying soils include liquefiable sediments, which have very distinctive characteristics, and whether these sediments are saturated by water.
The area where future “design-level”earthquakes are unlikely to cause land damage from liquefaction includes the western part of the project area and most of Banks Peninsula.
The area where future design-levelearthquakes may cause ground damage from liquefaction (and the effects may be complex and damaging to ground, buildings and infrastructure) includes the eastern part of the project area and some low-lying areas of Banks Peninsula.
The Natural Hazards Research Platform is the funding body that co-ordinates central government natural hazards research funding. It includes GNS Science, NIWA and tertiary sector organisations.