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Ground Improvement Programme

The 2010/2011 Canterbury earthquake sequence included four significant earthquakes. These triggered widespread liquefaction and land damage throughout the region that varied in severity.

Liquefaction occurs when soil below groundwater level temporarily loses strength when shaken. This can cause the soil to liquefy, resulting in water, fine sand and silt ejecting to the surface. This places huge stress on buildings sitting on liquefied ground.

The Ground Improvement Programme was an EQC-led research programme that informed more affordable and practical ways of making residential land less vulnerable to liquefaction.

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Collaborative research

The world-leading collaborative research was undertaken as part of EQC’s role in facilitating research and education that increases New Zealand’s natural disaster resilience.

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Co-ordinated by Tonkin + Taylor for EQC, the programme had contributions from many organisations and leading experts in liquefaction from New Zealand and overseas including:

  • University of Canterbury
  • Ministry of Business, Innovation and Employment
  • Housing New Zealand
  • New Zealand Transport Agency
  • University of Texas at Austin (USA)
  • Oregon State University (Corvallis, Oregon, USA)
  • Brigham Young University (Provo, Utah, USA)
  • US National Science Foundation
  • US Network for Earthquake Engineering Simulation.

The Ground Improvement Programme identified, developed and trialed affordable and practical shallow-ground improvement methods that can be used to strengthen residential land. This research is useful to property owners and developers, engineers and builders, private insurers, local authorities and central government agencies. The findings of the research can be applied throughout New Zealand and globally.

 

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Ground Improvement Trials

The first workstream included a range of ground improvement methods tested in Canterbury to see if they could successfully be applied to residential ground improvement.

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The effectiveness of the methods was tested in two ways:

  • the earthquake simulator or T-Rex
  • ground blasting

Geotechnical engineers Tonkin + Taylor guided these trials with support from a global team,including experts from the University of Canterbury, Cornell University, University of California Berkley, University of Texas, and other New Zealand engineering consultancies.

The trials component of the programme finished in December 2013.

You can find out more in our Residential Ground Improvement: Findings from trials to manage liquefaction vulnerability PDF (6.5 MB)

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Ground Improvement Pilot

In the second workstream EQC worked with several insurance companies including Tower, IAG, Lumley, Vero, Southern Response and AA to investigate how practical it was to use the trialed methods that were identified as promising in real-life situations.

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The aim of the pilot was to understand the practicalities of implementing the methods by coordinating the various parties involved, such as property owners, EQC, insurance companies and local authorities. This work was tendered out on a competitive basis to determine the affordability of the methods and assess local contractor capability.

In total, six ground improvement solutions were constructed on 31 residential green zone properties and two residential red zone properties in Canterbury. Watch the videos below:

Horizontal Soil Mixing - Ground Improvement Trial:

  • the only method that can be installed directly underneath an existing home (i.e. the site isn’t cleared)
  • takes a minimum of two weeks
  • requires specialist equipment and contractor knowledge.

Ground Improvement: stone columns (cleared section only):

  • takes approximately one week
  • requires stockpile area and good front road access
  • requires specialist equipment.

Ground Improvement: driven timber poles (cleared section only):

  • takes less than one week
  • does not require specialist equipment
  • requires stockpile area.

Ground Improvement: deep gravel raft (cleared section only):

  • takes less than one week
  • does not require specialist equipment
  • can be delayed by inclement weather.

Ground Improvement: cement soil mixing (cleared section only):

  • takes approximately one week
  • requires specialist equipment
  • does not require stockpile.

Ground Improvement: rotovated soil mixing (cleared section only):

  • takes approximately one week
  • does not require specialist equipment
  • requires stockpile area.
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Related documents

A list of factsheets and findings from the programme of work.

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