Following the Canterbury earthquakes, affected land was zoned to indicate the potential of future land damage due to liquefaction or lateral spreading under earthquake loading. In order to apply a corresponding zoning for unaffected land, as well as land in other provinces, a zoning system has been adopted for mapping purposes. In this way a guide to the appropriate level of site investigations that would be warranted for any particular development could be indicated on hazard maps for any district. In view of the implications of the events in Canterbury, Queenstown Lakes District Council commissioned a revision of liquefaction hazard maps covering their urban regions. This article addresses the developed zoning system, as well as its application within council. The zoning system is pragmatic and allows owners and developers to tailor investigations to the level of hazard presented. It could be readily applied to other areas of New Zealand, particularly those situated on recent normally consolidated sediments where subsurface information from liquefaction investigations is sparse. To facilitate liquefaction assessment in such cases, a heavy duty dynamic probe (in common use in the UK) has been adopted that allows testing in remote areas or where access is poor, to depths of up to 25m, at somewhat lower mobilisation cost than the more traditional testing rigs (CPT or SPT).
A practical seismic liquefaction zoning system for risk management of urban development