Ensuring new buildings can withstand liquefaction effects
In November 2019 a change was made to Acceptable Solution B1/AS1 preventing it from being used on liquefaction-prone ground. This change came into effect on 29th November 2021. The change was made as a result of the experience of the Canterbury earthquakes, and subsequent recommendations made by the Royal Commission of Inquiry.
Foundation performance is critical to satisfactory performance of buildings during earthquakes, especially the control of settlement and distortion of the building structure and fabric in relation to the importance level of the building.
The classification of a building’s Importance Level (1 to 5) is set out in Table 3.2 of the AS/NZS1170.0:2002 and is determined by the risk to human life, the environment, economic cost, and other risk factors in relation to its use.
Designers must specify foundations with a resilience that reflects the importance level of the structure and the liquefaction hazard if present.
Explore our map viewer which illustrates seismic liquefaction vulnerability in our District.
Buildings categorised Importance Level 1 (IL1 under AS/NZS1170:2002) are minor structures as failure is not likely to endanger human life such, structures are typically:
IL1 buildings have no performance requirements under SLS seismic load conditions, and therefore have no amenity requirements relating to liquefaction induced ground deformation in response to an SLS design earthquake event (level of shaking).
However, IL1 structures do have performance requirements under ULS seismic load conditions. It is likely that a ‘life safety’ design requirement at Ultimate Limit State (ULS) for a 1/100-year event, should be able to be provided, in most cases on a TC2 site, by a suitably detailed structure on a TC1 type foundation system.
Understanding Technical Categories (TC1, TC2, TC3) : Technical categories
Buildings categorised Importance Level 2(IL2) and above will require a higher level of assessment and are typically:
Informative only, regarding Building Importance Levels and the associated structures can be found here: A3 Building importance levels
Each site will be considered on its own merits, the designer is responsible for ensuring the building consent application contains enough geotechnical information to allow the Building Consent Authority (BCA) to establish compliance with the NZBC.
Note: The use of NZS 3604 for the design of the superstructure (i.e. everything from the ground floor plate up) is acceptable for the construction of any house within the scope of NZS 3604 (i.e. the dimensional limitations are adhered to, and the use is limited to Importance Level 2 (AS/NZS 1170.0))
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