Increased Liquefaction
Vulnerability
Fact sheet August 2014
Settling Land Claims for Increased Liquefaction Vulnerability
One of the features of the Canterbury Earthquakes was the significant damage caused by land that liquefied
as a result of the earthquakes. Liquefaction occurs when soil below the groundwater level temporarily loses
strength and stiffness when shaken. Liquefaction can have several effects – including the ejection of sand and
silt, often in significant amounts.
About Increased Liquefaction Vulnerability
or inundation of sand and silt – because it is the result
of ground surface subsidence which is not always obvious.
Increased Liquefaction Vulnerability (or ILV) is a form of land damage
recognised by EQC. In some parts of Christchurch the earthquakes
caused changes to residential land that mean some properties are
now more vulnerable to liquefaction damage in future earthquake
events, and are now more likely to experience more severe
liquefaction damage in future earthquake events.
It is also a form of land damage that had not previously been
identified by EQC before the Canterbury earthquakes.
These things make ILV a complex form of land damage. A detailed
engineering assessment is needed to determine whether a
property has experienced ILV as a result of the earthquakes.
In summary, EQC’s geotechnical criteria for ILV will be met if:
1. A property is vulnerable to damaging liquefaction in a future
1 in 100 year earthquake
The main factors contributing to liquefaction vulnerability are:
• The strength, intensity and duration of shaking likely to be
experienced in the future
2. AND if the land has become materially more vulnerable
(i.e. damaged) as a result of the subsidence caused by
the earthquakes.
• How far below the surface the ground water is
How does EQC know if a property has ILV?
• The nature and thickness of the upper soil layers
ILV is different to some other forms of damage such as land-cracking
• Soil type and layering below the groundwater table.
ENGINEERING ASSESSMENT
Is the property vulnerable to damaging
liquefaction in a 1 in 100 year earthquake?
NO
✘
ILV has not
occurred
YES
Has the property become more vulnerable (i.e. damaged)
as a result of the subsidence caused by the earthquakes.
NO
✘
ILV has not
occurred
YES
Properties that have not qualified
for ILV are still potentially entitled
to compensation from other forms
of land damage.
✔
ILV has occurred
Note: Once ILV is confirmed, under engineering assessments, EQC still has to assess whether ILV has had an impact on the value of the
property before a settlement occurs.
0800 DAMAGE (0800 326 243)
or visit us at www.eqc.govt.nz
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Increased Liquefaction Vulnerability Fact Sheet August 2014
Where did the data come from?
The data used to assess liquefaction vulnerability comes from a variety of sources:
DATA COLLECTION
Shaking
intensity
Geotechnical
Drilling
Groundwater
Monitoring
Ground Surface
Elevations
SEISMOLOGY REPORTS
AT MORE THAN 12,000 SITES
AT MORE THAN 900 LOCATIONS
HEIGHT ABOVE SEA LEVEL
To understand soil
characteristics.
Monitor the depth to the
groundwater over 3 years
to determine the range in
groundwater levels.
Measurement of ground surface
elevation to see how much the
land has subsided.
Provide expected future levels
and duration of shaking for
different “return period”
earthquakes (e.g. 1 in 100 or
1 in 250 year earthquake).
Qualifying for an ILV settlement
One aim of this work has been to allow EQC to determine
the cost of repairs, so that settlement offers can be made
for ILV properties.
In order to qualify for a settlement, EQC also needs to assess
whether ILV has had an impact on the value of your property. It
is important that you appreciate there is the possibility that you
may not be entitled to any settlement from EQC. We will provide
further information about these matters as they affect individual
properties in the coming months.
More information on this programme can be found at
http://bit.ly/1mGhxuH
EQC is yet to complete the Ground Improvement Pilot. To
complete the settlement process we need to work through
the potential repair strategies to ensure that they comply
with regulatory guidelines and are fit for purpose.
How does EQC calculate settlement values for ILV?
As with most land claims, settlement for ILV will be by cash
rather than reinstatement or repair.
There are four methods being trialled. Some of them are
intended to strengthen soil on bare land prior to a rebuild.
In other situations, land that is materially vulnerable to
liquefaction lies beneath a lightly damaged house. In these
cases a land improvement technique that avoids the need
to move or demolish the house is needed and we are trialling
a method for this.
EQC’s preference is to settle land claims by providing a cash
payment based on the amount it would cost to repair or reinstate
the land. However, it may not be possible in some cases to
identify a repair method to the land which is feasible and
consentable. Where there is no feasible repair method EQC
is exploring alternative settlement options.
For more information on the methods visit http://bit.ly/VGEoLm
When will cash settlement offers be made by EQC?
EQC and private insurers have been undertaking a Ground
Improvement Pilot, where we are physically repairing ground
on around 50 properties that have experienced ILV.
Find out more
To get more information on EQC cover for land damage visit www.eqc.govt.nz/land or call 0800 DAMAGE (0800 32 62 43). You can
also find detailed provisions on EQC cover in the Earthquake Commission Act 1993 at www.legislation.govt.nz. The provisions of
that Act will be applied by EQC at all times. This guide is a summary only.
0800 DAMAGE (0800 326 243)
or visit us at www.eqc.govt.nz
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