2009-01-07_REPORT - M1977211 - Laserfiche WebLink

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Risk of Future Rock Movement The existing rockslide material has reached a level of equilibrium and we would expect only minor adjustments of the rubble in its current condition, provided no other activity occurs that would disturb it. That is not the case with the quarry wall above the scarp. The upper blocks of the quarry walls, defined by the area between the main headscarp of the December 2nd rockslide and the incipient scarp above it, are in a pre-failure condition. In addition to the incipient scarp there is also evidence of fresh dilation cracks in the weathered granite within this upper block along the cut slope of the quarry road (Figure 5). The steep eastward-dipping sedimentary strata and weakened nature of the granite, coupled with the pre-existing adverse structure of the fault zone and the lack of lateral support at the current headscarp of the rockslide, would place this remnant of upper quarry wall in a very high risk category of future failure. Such a failure would result in additional landslide and rockfall hazards to the slope below. In addition, failure of rock material above the current headscarp would subsequently load the rockslide material below, adversely affecting its current equilibrium state. Conclusions and Recommended Future Actions Based on the site observations and the material reviewed, it is the opinion of the CGS that, even though the adverse geologic and structural conditions were well known, or should have been well known, they were not given the consideration they required during mining activities, even though past failures had occurred. Other mine activities further drove potential 9 Figure 5. One of many dilation cracks observed in the grussy granite along the upper quarry road where it lies between the major incipient scarp and the December 2 landslide headscarp