Most buildings ‘could take liquefaction’

Press, 14 September 1988, Page 50

Most buildings ‘could take liquefaction’

Most Christchurch buildings could withstand liquefaction in’ an earthquake, says a City Council building engineer. Liquefaction could cause buildings to sink a metre or more into the ground or tilt in an earthquake, but most local buildings could withstand it because of precautions most local designers took to avoid damage from a fall in the city’s watertable, said Mr Bryan Bluck. Between 30 and 40 per cent of Christchurch was built on soil that was vulnerable to liquefaction, which American research had shown was one of the

leading causes of property damage in earthquakes, said Dr Don Elder, a Christchurch geological engineer.

Most Christchurch buildings of three storeys or higher were built on piles that ran deep into the ground in order to prevent them sinking if the water-table fell. Those same piles would support the buildings and prevent serious structural damage to them from liquefaction, which would render the soil temporarily unable to support heavy objects after an earthquake, said Mr Bluck. Because concrete was relatively cheap in the

South Island, most houses were built on a continuous concrete foundation, which would limit the damage they suffered from liquefaction, Mr Bluck said. Such foundations would prevent the tilting that caused the most serious damage from liquefaction and limit the amount they would sink, Mr Bluck said. He estimated most houses in Christchurch would sink only “an eighth of an inch” if the soil under them was subject to liquefaction. “You would have cosmetic damage — things like veneer cracks,” Mr Bluck said.