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Abbotsford Landslide, Dunedin 1979

The Abbotsford landslide is known as one of New Zealand's worst landslides, not only because of its ...

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Abbotsford Landslide, Dunedin 1979

  1. 1. Abbotsford Landslide, Dunedin 1979 The Abbotsford landslide is known as one of New Zealand's worst landslides, not only because of its size, but becasue it might have been prevented with a little more geological knowledge and foresight. Abbotsford, Dunedin, New Zealand, is situated in Dunedin's Southwest, and is a small quiet city with many historical buildings built by early Scottish settlers. Dunedin is the gateway to the Milford Sound, Queenstown, Invercargill and bluff, some of New Zealand's most pristine and picturesque tourist destinations. Abbotsford landslide occurred on the 8th of August 1979 and caused between NZ$10-15 million worth of damage. Nine houses (but no lives), were lost. In a country as small as New Zealand this was considered catastrophic. Previous History of Landslides The landslide occurred after several telltale signs went unheeded: the area was underlain by thin weak clay material at a 7 degree slope angle, and there was a water main leak at the top of the slide area above an old quarry, plus heavy rain over a short period of time (Hancox 2007). There had also been previous known slips in the area: the sun club slide, motorway landslide and others in the same vicinity. These were all contributing factors to ground failure, and a catastrophe waiting to happen. Investigation work had been initiated in June 1979 because of cracks in the ground which had been noticed by some of the residents, but by then it was too little, too late. Less than two months later the area gave way completely and the massive slide ensued. Investigation and Outcomes of the Investigation Hancox's 2007 retrospective article about the Abbotsford Landslide is flood gate pumps an in-depth study from a geologist's point of view from start to finish. The before and after photos show the detail of previous failure areas such as the sun club and motorway slides which occurred during the
  2. 2. 1960's. They also show the aftermath of the Abbotsford Landslide taken in August 1979. The outcome of the initial investigation by the DSIR (Department of Scientific and Industrial Research) concluded that the Abbotsford landslide could be considered an enlargement of previous landslides (sun club and motorway landslides). It was a typical low angle, translational block slide relating to the thin clay layers and low angle hill sides. Previous excavation at the base of the quarry in the late 1960's lowered stability, plus, the water main leak (which had been leaking for at least three years), compounded by heavy rain, all contributed to the failure. During the 1960/70's slope stability was not something residential developers considered; however, as a consequence of incidents such as this, Geotechnical Engineering of residential developments has become a geological occupation and necessity when building. Geotechnical investigations should not only incorporate soil testing but also local and regional geology, to get an overview of surrounding areas and any previous process pumps landslide history. Be aware of a few straightforward changes which should be added to a standard centrifugal or positive displacement pump. For pumps containing overhung impellers, replacing the shaft with a solid shaft is a easy refinement instead of the common sleeved shafts. Mechanical seals ought to be upgraded by using silicon carbide faces, and elastomers should be replaced with EPDM. Finally, magnetic bearing protectors will prove to be a vast improvement compared to the lip seals which nearly all chemical pumps use to keep bearing sump oil free from contaminants. Past and current photo's of an area show the surface differences over time and give an indication of what ground stability in a particular area could be like in future. Abbotsford Landslide, Dunedin is a classic example of build first, ask questions later - when it's too late! References: Hancox, G.T., (2007). The 1979 Abbotsford Landslide, Dunedin, New Zealand: a retrospective look at its nature and causes. Landslides.