A two-storey house in Christchurch suffered structural damage caused by soil liquefaction following earthquake events in 2011. Large displacements due to lateral spreading were observed at the property, both under the home and across much of the garden towards an adjacent wetland.
As a result, the premium property, a lightweight clad timber frame with polystyrene insulation, built on a concrete ground slab, experienced differential settlements after the recent Canterbury Earthquake Sequence and had a factor of safety against liquefaction of less than 1. Mainmark injected Teretek® resin through numerous injection points under parts of the home and garden along the area near the crest of the slope to the wetland, and used Cone Penetration Test (CPT) monitoring before and after the treatment to measure the degree of ground improvement. The results showed significant improvement was achieved, with predicted liquefaction induced settlement reduced by more than 50%, raising the factor of safety against liquefaction above 1.5.
The objective of this project was to deliver ground improvement to mitigate or reduce lateral spreading of the site under a future serviceability limit state (SLS) level seismic event and improve the foundation performance under an ultimate limit state (ULS) level seismic event
Mainmark used its Teretek resin injection solution to provide ground improvement and mitigate liquefactioninduced lateral spreading effects at the property. The Teretek resin was injected into a strip of ground approximately 4m wide, and between 1m to 5m deep, to create an improved soil block that is able to contain the soil behind it and minimise the lateral spreading potential. This ground improvement technique reduced the predicted liquefaction settlement under an SLS seismic event by more than half.
These results were measured in the garden of the property where there is no overburden soil confinement. The results under the building are predicted to be better because of confinement provided by the added weight of the property. However, a CPT under the home was not possible due to site access restrictions.
The success of this remediation project further validates the positive results previously achieved in the Christchurch ‘Red Zone’ Trials. A full report is now available for review on the New Zealand Geotechnical Society website2 and information is also included in the MBIE Module 5: Ground Improvement of Soils Prone to Liquefaction.
Teretek is a unique two-in-one solution that is a proven method for increasing soil density, foundation bearing capacity and mitigating liquefaction.
The solution addresses underlying ground vulnerability and can be applied under existing structures, or directly into vacant ground in preparation for new construction. When applied beneath existing structures, Teretek resin can assist in strengthening the ground, reduce the need for above-ground improvements and help increase the structure’s asset rating (including the New Zealand New Building Standard percentage rating), at a fraction of the cost of other ground improvement methods, and with no detrimental effects on the environment.
In a process likened to keyhole surgery, Mainmark technicians select a number of injection points specific to the site. The Teretek resin mix is then injected through very small tubes into the ground. The components mix together and expand by chemical reaction, which strengthens the ground and re-levels buildings quickly and with minimal disruption.
The work was completed in 2 weeks in May and June 2017, on time and on budget, and left the landscaping and garden intact, to the satisfaction of both the residents and the supervising engineer.
The project’s engineers, KGA Geotechnical, commented, “We were impressed with the professionalism of the Mainmark team. The results exceeded our expectations in terms of the predicted achieved ground improvement. The Mainmark solution is particularly suited for sites with an existing dwelling where minimal disturbance to the structures is a requirement.”
Project Resources & Downloads
Teretek® Provides Ground Improvement and Reduces Lateral Spreading at Christchurch Residence
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Teretek® Re-levels Busy Transport Yard
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Mainmark Ground Engineering Pty Ltd
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