For over a century, researchers in geotechnical engineering and related fields have been puzzled about the behaviour of large rock avalanches. In particular, they wanted to know why these landslides travel much further than predicted and so cause major disasters and hazards around the world.
Professor Tim Davies of Lincoln University's Natural Resources Engineering Group, in the Environment, Society and Design Division, has a led a team from the University and the Institute of Geological and Nuclear Sciences (GNS) Lower Hutt that has developed the world's first "fragmenting rock rheometer".
A rheometer is a machine that is able measure the flow properties of materials by shearing them under pressure. In this particular rheometer, pieces of rock are not only made to flow past each other but they are subjected to such extreme stresses that they shatter in the process and generate additional stresses. This has never been accomplished before and it has led to verification of a detailed theory that explains the long runout of large rock avalanches.
The new machine uses the principle of a cylindrical cone and plate rheometer - kitchen juice extractors work the same way. The rheometer tests the flow properties of rock fragments as they are crushed and sheared. Sensors linked to data loggers record the internal stresses in the fragmenting rock material.
"It is important to be able to predict the behaviour of rocks under stresses that are sufficiently strong enough to break them," says Professor Davies, "because that ultimately allows us to predict the extent of the hazard from the collapse of mountainsides."
"Such events - like the Poerua Valley landslide in Westland in 1999 and the Mount Cook collapse of 1991- threaten infrastructure and land use in mountain valleys.
"We are delighted to have been able to produce this machine. It has been a real team effort involving a large number of people over several years," says Professor Davies.
He praised in particular the meticulous design and construction talents of Rick Diehl, Senior Technical Officer in Natural Resources Engineering at Lincoln University.
"Without Rick's attention to detail and his ingenuity this project could never have got off the ground.
"One of the challenges we faced was building the rheometer so that it was robust enough to allow our tests and measurements at the high stresses needed to cause rock fragmentation. We also had to solve the problem of rock dust produced when the rocks broke, which could cause the machine to jam."
The team has undertaken preliminary tests with a number of different rock materials such as coal, and is now testing other rocks such as greywacke and limestone. Completion of the testing programme is expected to take a further two years.
Professor Davies and colleague Dr Mauri McSaveney of GNS have published their theory for rock avalanche runout in the international scientific literature. They have also presented keynote papers on the subject at specialist technical workshops in Europe and, last month (May), at an international conference in Italy.
The research programme is funded by the Public Good Science Fund through the Institute of Geological and Nuclear Sciences Ltd.
For further information contact
Ian Collins, Journalist, Lincoln University, Canterbury
Tel: (03) 3252811 ext 8549.
Email: Ian Collins