Capital’s slopes put to the quake test
Six locations across Wellington are being drilled to find out how they would hold up in a major earthquake.
GNS Science is undertaking a slopes stability study – a project that started in 2017 with three boreholes drilled at a site near St Gerard’s Monastery in the suburb of Mt Victoria.
It is a big deal forWellington, which has close to 1000 slips each year. Project leader Chris Massey, of GNS Science, said slopes in the suburbs of Mt Victoria, Island Bay, Kingston, Ngauranga and those overlooking State Highway 2 had already been drilled. Drilling in Newlands was also under way.
The chosen areas were characteristic of Wellington’s topography, Massey said.
‘‘Most slopes in Wellington – to create homes and roads they’ve had to be cut and filled.’’
Drilling at the monastery site produced a ‘‘surprising’’ amount of useful information. It was one of hundreds in Wellington that had been modified through urbanisation, Massey said.
GNS drilled 50 metres, to the level of Oriental Parade, he said. Seismometers were then placed in one of the holes near the monastery to measure the strength of shaking during earthquakes.
The findings will be used to reduce cases of slips and failures.
Massey said the Kaiko¯ura earthquake had exposed the vulnerability of some Wellington areas. The risks to critical and nationally significant infrastructure were not well known. But the scientists were not suggesting that the chosen areas were unsafe, he said.
In 2015, the three-year project was contracted to GNS Science for $1.5 million by the Ministry of Business, Innovation and Employment (MBIE). Wellington City Council, the New Zealand Transport Agency and Wellington Water had input into its planning. City council engineer Derek Baxter said Wellingtonians lived with many natural hazard risks.
‘‘In recent years, we’ve had close to 1000 slips per annum. Understanding the triggers, be they earthquakes or raininduced, helps us plan better.’’
MBIE contestable investments manager Max Kennedy said there was a wide range of uses for the research. ‘‘We expect the research will provide benefits not only to Wellington, but provide direction for future cut-and-fill earthworks operations for the rest of New Zealand.’’