An Investigation into Factors Contributing to Movement of a Slow-Moving Rockslide at the Revelstoke Dam, British Columbia

摘要

The Marble Shear Block is a rockslide located between the spillway and tailrace on the right bank of the Revelstoke Dam, British Columbia. The Marble Shear is a thin graphitic foliation shear that forms the base of the Marble Shear Block. Failure of the Marble Shear Block could result in damage to the spillway and the tailrace area. The stability of the Block was reassessed for higher piezometric pressures and the design seismic event. The geological model was updated using additional geological and piezometric information from recent site investigations. An extensive instrumentation data review found that piezometric pressures close to the head of the slide had increased; however, this did not result in corresponding increases in slope movement. Instrumentation data showed that the 175 m high concrete dam moved downstream during reservoir filling and annually rocks back-and-forth due to thermal loading. The initial movement of the dam and this cyclic rocking motion was found to correlate with the movements observed in the Marble Shear Block. A finite element analysis showed that the movements of the concrete dam causes displacements along the centimetre-thick Marble Shear (which forms a continuous feature from underneath the concrete dam to the Marble Shear Block) and likely contributes to the downslope movement of the Marble Shear Block. Updated stability analyses also showed that the Marble Shear Block is currently stable and is more sensitive to piezometric pressures at the toe of the slope than the head of the slope.