Investigation of new land strengthening methods.
As part of its research function, EQC is investigating the viability of new land strengthening methods for properties such as those in TC3 that are prone to liquefaction. If successful, the research would provide a range of techniques for anyone contemplating building, and possibly provide more economic methods for strengthening land under existing properties.
One of these research methods is the use of an earthquake simulator. The photo above shows a specially designed truck known as T-Rex, that has been brought over from the United States to assist in the investigations of new land strengthening methods. The T-Rex truck creates intense, but highly localised, shaking that diminishes rapidly the further one is from the truck. This shaking is applied to areas of test site land to assist in the evaluation of the strengthening methods being trialled.
Some of the techniques being trialled can potentially repair land without the need to shift or demolish the existing house. If successful, this would be a real breakthrough because, currently, there are no or few effective land repair solutions where the house is largely undamaged. In many cases fixing the land typically requires shifting or demolishing the house.
There is a great deal of interest in the work being undertaken with input from HNZC, MBIE, CERA, local authorities and international specialists. Even if the outcomes of the research are promising, we can’t confirm at this stage that they would be sufficiently advanced to form part of EQC’s land settlement process.
Tonkin and Taylor is guiding the trials, supported by reviewers from the University of Canterbury, Cornell University, UC Berkeley, University of Texas and leading engineering consultancy firms.
The methods being trialled include:
- Rapid Impact Compaction: This involves compacting the ground by a hydraulic ram attached to a digger
- Rammed Aggregate Piers: This involves drilling into the ground, filling the holes with gravel, and then compacting the gravel with a hydraulic ram
- Low Mobility Grout: This involves injecting a cement-based solution into the ground under pressure to form a series of underground pillars. The cement-based product is quite thick and has a concrete-like consistency
- Horizontal Soil Mixing: This involves horizontal directional drilling beneath a site with cement mixed into the soil to create horizontal columns. The objective is to stiffen the crust and suppress liquefaction.
The trials were conducted on unoccupied cleared land in parts of the residential red zone, at two sites in Avonside Drive in Avondale and in Wairoa Street in Bexley.
The trials began on Monday 13 May and were completed in December 2013.
The trials involve improving the land and then subjecting each test site to a short period of shaking to observe how it performs. To create the shaking, this specially designed truck known as T-Rex, supplied by the University of Texas, has been brought over from the United States. The vibration is not expected to last for much more than a few minutes and should not be noticeable beyond 100 metres or so from the test site.
The test sites are contained within a fenced off safety area.