Kurt Douglas

Towards field bounds on rock mass failure criteria

Abstract Various rock mass failure criteria are being validated against field performance as part of a large research program into the geotechnical risk of concrete gravity dams. The project has sought rock structures which may contribute to providing either upper or lower bounds to various failure criteria and therefore the emphais has been on finding sites with high quality field and laboratory data. The first two sites investigated have been Chichester Dam foundation and Nattai North escarpment failure both in New South Wales, Australia. The paper summarises the existing information for both cases. Each case has been analysed using the distinct element method. The results of these analyses allow the field occurrence to be compared with the commonly used Hoek-Brown empirical rock mass failure criterion. As expected the bounds on the various failure criteria are very broad and care must be taken when placing any reliance on any particular criterion.

Rock Mass Erodibility

AbstractErosion of rock masses by water typically involves unraveling of blocks of rock along existing defects in a manner that is not represented by analytical solutions for sediment transport or ...

The influence of geological conditions on erosion of unlined spillways in rock

Erosion in 33 unlined spillways in rock has been studied for dams in Australia, South Africa and the USA. Geological factors which influence the amount of erosion have been identified using published and project data and spillway site inspections by the authors. These are the orientation, persistence, spacing and nature of rock defects including bedding partings, joints, foliation and shears. The presence of kinematically viable blocks which can be detached and the persistence of the basal defect for these blocks are the most important factors. Where spillways discharge on to a natural slope the presence of valley stress relief features, such as sheet joints parallel to the slope, or kinematically viable blocks, often with open sub-vertical defects, can lead to significant erosion even with small spillway discharges. The mechanism can be one of slope instability rather than erosion as water pressure destabilizes the slope. A rock mass characterization index, the ‘Rock Mass Erodibility Index’ (RMEI), which considers spillway flow conditions and erosion mechanisms, has been developed. It can be used as a guide to spillway erosion and, when coupled with stream power for spillway flows, provides a method for preliminary assessments of likely amounts of spillway erosion.