“To the public the focus after an earthquake is on the damage to a structure that the eye can see, but it is the geological nature of the site and the ground conditions that to a large extent influence the severity of damage.
“The events in New Zealand have provided tremendous amounts of new data which we are determined to learn from. The 4 September 2010 Canterbury Earthquake was essentially within the realm of seismic hazard accounted for in the hazard modelling for Canterbury, and while damage was widespread, it was to a degree expected.
“Conversely, the 22 February 2011 earthquake in Christchurch had a greater severity of damage and involved not only lateral shaking but a significant component of vertical motion. The ground motions experienced in some areas were well in excess of the peak acceleration that would be cater for in the design of modern buildings,” said Professor Poulos.
Recommendations included making ground assessments a requirement for properties in high-risk areas, and creating a revised building code with more stringent foundation design standards.
Consideration should also be given to ground treatments that improve the resistance of the ground to liquefaction. There are new technologies that include infusion of silica grout to strengthen the ground and the creation of 'smart soils' which are involve the injection of bacteria and microbes into the earth to strengthen the soil and resist liquefaction. Such technologies have the potential to be particularly useful when treating existing building sites.
Professor Harry Poulos says the latter technology is attractive because it's a natural process in which the bacteria secrete calcium carbonate which cements soil particles and makes the earth more resistant to liquefaction.
"The research out of the Netherlands suggests it is highly promising, although it has not yet been used on a major scale and may take a few years to become a mainstream solution," he said.
The liquefaction susceptibility of Christchurch has been well-known and documented for over two decades, with public information maps and documents having been produced on the earthquake hazard there in the 1990s. Despite this information, thousands of homes have been bought and sold over the years with the liquefaction hazard stated in the land information provided by the council.
Professor Poulos explained; “It would be beneficial for each property to be assessed to understand the ground conditions, so that we can apply new technologies and redesign buildings where necessary to reduce the risk of liquefaction and seismic damage. There may be a push from insurance companies for mandatory assessment which will help the entire community. A ground assessment can identify areas of greater risk, and we can better manage those risks through design and/or technology.
“The international geotechnical community will be able to use our foundation design expertise to develop more robust foundation systems that will withstand future similar events in Christchurch and in other earthquake-prone areas.
“Our job as geotechnical experts is not only to bring the world’s best earthquake research and thinking to New Zealand but also to educate the public about the risks involved and how to minimise these risks.”
Last week marked the anniversary of the 4 September 2010 earthquake in Canterbury – the first in a series of earthquakes that caused widespread devastation and is estimated to have cost as much as NZ$25 billion.
Media contact
Angela James, Manager, Corporate Communications, Coffey International Limited
P: (+61) (2) 8404 4415; M: (+61) 42 8 905 573; E: angela_james@coffey.com
About Coffey Geotechnics & Earthquake Assessment
Coffey Geotechnics is a specialist geotechnical engineering consultancy renowned for solving complex technical challenges applied across a diverse range of ground conditions. We pride ourselves in our ability to provide high-end geotechnical design as well as conducting site investigations, geotechnical interpretation and analysis, and construction advice.
Coffey Geotechnics investigates and analyses the ground’s susceptibility to earthquake-induced deformation. We carry out assessments of land damage throughout the region through inspections, site investigations, soil testing, and detailed liquefaction and lateral spreading hazard analyses. We advise clients on the causes of damage, remediation options and costs.
Specialists in Coffey International Limited, and its subsidiaries including Coffey Geotechnics and Coffey Projects, are trusted advisors to a number of New Zealand’s major businesses, banks and insurers. For example, since the 4 September 2010 Canterbury (Darfield) Earthquake, Coffey has provided specialist advice to various insurers, land developers, domestic clients, the ANZ Bank and the Earthquake Commission (EQC). Our experts have chaired several multi-disciplinary technical meetings on the earthquakes and earthquake response, with leading engineering societies (including the New Zealand Geotechnical Society, the New Zealand Society for Earthquake Engineering and the Canterbury Structures Group), Earthquake Commission, local authorities, insurers and research groups (e.g. GNS Science, University of Canterbury and overseas academics).
