The Ministry of Business, Innovation and Employment (MBIE) has released updated technical guidance for repairs and rebuilds relating to the Canterbury earthquakes.
There are now more ground improvement and foundation options for repairing and rebuilding structures on some TC3 land. This is the land classified as having a moderate to high risk of liquefaction in an earthquake, where geotechnical investigation and engineering foundation design are required before new foundations can be built.
MBIE has said that the update is based on research data collected from recent extensive ground improvement trials and follows thorough peer review by international experts. The ground improvement trials tested how well various solutions performed under simulated earthquake conditions.
The new options are intended to provide more choice so that a simpler and more affordable option can be constructed, while still providing an appropriate level of protection for houses and compliance with the Building Code.
The following methods of types of ground improvement systems are included in the guidance:
- Shallow densified crust (excavated and recompacted soil or replacement fill, dynamic compaction or rapid impact compaction);
- Shallow cement stabilised crust (cement-mixed soils, either by excavating and recompacting or in situ mixing);
- Deep soil mixing (soil mixed or jet-grouted columns);
- Deep stone columns; or
- Crust reinforced with inclusions (intermediate depth highly compacted aggregate columns, stone columns or driven timber piles).
The guidance includes the advantages and disadvantages of each of the methods, and the criteria that makes options suitable for various types of property.
Under the previous guidance, low mobility grout (LMG) had been included as an option for deep soil mixing. There has been considerable discussion among experts as to whether LMG would actually perform suitably. In this update, it has been omitted as an option so is therefore no longer recommended as a repair methodology.
The updated information can be found in:
- section 15.3; and
- appendix C4.
The full technical guidance is available here, although this does not yet include the newly released updates.
This information will be of interest to insurers and homeowners whose homes are on TC3 land.
The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.
