Liquefaction occurs when soil
below the groundwater level
temporarily loses strength and
stiffness when shaken. This can
cause the soil to temporarily
“liquefy” and large quantities of
water, fine sand and silt can be
ejected to the surface, causing
the ground surface to deform,
placing huge stress on buildings
on top of liquefied ground.
In parts of Canterbury, rebuilding will occur on land that
is vulnerable to liquefaction in future major earthquakes.
There are two options
for managing this risk.
EQC is funding research into new ground improvement methods that can
be used with foundation design to get the best outcome for homeowners.
Four ground improvement methods used in large scale civil construction
Projects ARE BEING TRIALlED to see if they can be successfully down-
scaled for residential use in Canterbury - both on bare land and beneath
existing houses.
Geotechnical engineers Tonkin & Taylor are guiding the trials, supported by
reviewers from the University of Canterbury, Cornell University, UC Berkeley,
University of Texas and other leading engineering consultancy firms.
Once initial testing has been completed, and data is analysed, eqc will
co-ordinate a pilot programme where these techniques can be fully costed
and deployed in a residential setting as a final proof of concept. eqc are
expecting final results to be available in late 2013.
To assist in the trials, we have helped bring a specialised geophysical test
“truck” called T-Rex from the University of Texas.
Once the ground has been IMPROVED by
one of the methods, the effectiveness of
the ground improvement is tested using
a T-Rex machine. the T-rex creates intense,
but highly localised, shaking to simulate
an earthquake allowing the effects of the
IMPROVEMENTS to be tested and measured.
Data from the testing will be analysed
to determine the effectiveness of each
strengthening method.
IMPROVING
Liquefaction Vulnerable Land
1 2
large improvement
in soil strength
target improvement
in soil strength
moderate improvement
in soil strength down to
several metres in depth
liquefiable SOIL
liquefiable SOIL
non-liquefiable crust
non-liquefiable crust
liquefiable SOIL
liquefiable SOIL
non-liquefiable crust
non-liquefiable crust
TRENCH
liquefiable SOIL
liquefiable SOIL
non-liquefiable
crust
non-liquefiable
crust
liquefiable SOIL
liquefiable SOIL
Gravel
gravel
non-liquefiable
crust
non-liquefiable
crust
Four ground improvement methods
This method involves compacting the ground using a falling weight
attached to the arm of a digger. It works best in sandy soils.
Vibrations need to be managed to limit disturbance to neighbours.
This method involves pushing
gravel into the ground using
a large hydraulic ram attached
to a digger. as this occurs, the
soil between the gravel columns
is compacted.
This involves injecting concrete
into the ground, under pressure,
to form a series of underground
pillars of concrete bulbs. this
compacts the ground between
the compact pillars.
This involves horizontal directional
drilling under an existing building
to a trench. A tool is attached
to the drill and as it is drawn
back, cement is mixed into the soil
to create horizontal columns of
cemented soil.
liquefiable SOIL
liquefiable SOIL
non-liquefiable crust
non-liquefiable crust
TRENCH
1
2
T-REX
For more information go to: www.eqc.govt.nz
or freephone 0800 DAMAGE (0800 326 243)
COMPACTION
RAPID
IMPACT
RAMMED
PIERS
AGGREGATE
MOBILITY
GROUT
LOW
HORIZONTAL
MIXING
SOIL
vulnerable
GROUND improvement
heavy duty
FOUNDATION DESIGN
Pilot
This research programme is supported by:
