Avalanche release is a brittle process meaning that fracture toughness rather than shear strength may be the fundamental parameter controlling slope stability. The results of a series of experiments to measure the fracture toughness of soft slab are reported. Snow was found to be toughest in mode I. The mode II and mode III values are approximately equal, and about 70% of the mode I. The mode II and mode III values are approximately equal, and about 70% of the mode I value. The fracture toughness of a weak layer was found to be about 1 kPa m<sup>1/2</sup>. In addition to shear strength and/or fracture toughness, the coefficient of basal friction between the slab and the substrate is of obvious importance to slab avalanche release. Various sources suggest that the coefficient of friction for dry slab is quite variable, but a value of about 0.6 seems quite typical. Incorporating this and other typical snow parameters into shear band models gives a critical crack size of the order of ten metres. This is much too large to be produced by a skier. We discuss two alternative release mechanisms for skier triggered avalanches. The first of these is the interaction between local skier damage and the complex pattern of internal shear cracks assumed to lead to natural failure. The other mechanism is the whumpf of flexural wave, which is caused by compressive collapse and subsequent loss of shear strength of the weak layer. The relative importance of these two processes combined with highly variable basal friction can explain the wide variety of different behaviour associated with skier triggered avalanches. Examples of such behaviour are: a skier triggering a well tracked slope, slopes that whumpf (and sometimes can be felt to move and crack) but do not avalanche, and remotely triggered avalanches.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:651172 |
| Date | January 2006 |
| Creators | Fyffe, Blair |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/13864 |
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