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
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
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
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.
Rigorous analysis of pre-sales risks is vital as residential property developments grow in cost, size and complexity.
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