Prestons News

Nov 2012 - A whole lot of shaking at Prestons

Dr. Jan Kupec and David Schwartfeger with the impact rollerEarth tremors currently being felt around the203 hectare Prestons subdivision in north-east Christchurch are of the good variety - they are mechanically made and are helping densify the land, as opposed to the natural ones that have occurred over the last two years.

Ngāi Tahu Property, which is undertaking the first stage of development on the northern side of Prestons, is using a giant land stabilisation machine on parts of the development to pack the soil particles more closely together to prevent liquefaction and bring all the land at Prestons to TC1 standard.

David Schwartfeger, Development Manager for Ngāi Tahu Property, said that the majority of the development is already classified as TC1 and this remediation was to bring localised areas of TC2 land up to the higher standard.

"We commenced work on site at the beginning of November to remediate 25 hectares which should take contractors approximately 20 weeks."

The three-sided elliptical roller, which weighs approximately 40 tonnes, will go back and forth across the treatment site between 20 and 40 times to pack the soil particles to their densest configuration, which will prevent settlement and any liquefaction from happening.

"It certainly does shake the earth, but the benefits of improving the ground from TC2 to TC1 are far-reaching meaning that standard foundations for concrete slabs or timber floors can be used, thus saving money on foundations, and negating the need for further geotechnical reports," he said.

Dr. Jan Kupec, Technical Director, Ground Engineering, with Aurecon Group, who is overseeing the ground desification, said that the liquefaction susceptibility on the site was marginal anyway.

"Prestons suffered no liquefaction or lateral spreading or any other seismically associated hazards during the entire earthquake series.  The reason for this low susceptibility to earthquake damage is because of dense dune deposits (formed by the wind) in contrast to fluvial deposits around rivers and streams, which are more prone to liquefaction and lateral spread.

"This low susceptibility means we only have to treat selected areas to bring them up to TC1 standard rather than the entire development.  Densification such as this works well on sandy soils such as we have at Prestons and once treated the soil will not settle or spread.

"The machine is used frequently overseas on large infrastructure and mining projects and after an initial trial earlier this year we found it ideal for treating the site.  The earthworks are subject to stringent quality assurance and control testing to confirm that the desired ground improvements have been achieved.  The result of the testing will be provided as part of the subdivision certification submitted for approval to the Christchurch City Council," he said.

The first 200 sections within the Korowai nieghbourhood are selling extremely well.  Available sections range in size from 450m2 to 650m2 with prices starting at $198,000.  It is hoped that a further 200 sections will be released early in 2013.

Prestons is designed to be a sustainable urban village that will ultimately contain 2,500 houses and be home to 8,000 residents.  It is bounded by Mairehau Road to the south and Lower Styx Road to the north and is bisected by Prestons Road.

For more information on purchasing sections call our sales manager, John Almao on 0508 773 786 or 021 677 077.  Alternatively you can visit our sales office at 441 Prestons Road, open Wed-Sun 12-4pm.