Shear strength testing of rock discontinuity surfaces has been undertaken at a considerable number of open pit gold mining operations in Western Australia, as part of geotechnical studies of pit wall stability. These mining operations are located in geological settings that are typified by highly weathered and/or chemically altered rocks that contain significant structural fabric in which accurate and representative measurement of shear strength is essential.
Little of the published rock discontinuity shear test work and back-analysis of failures has been conducted on weathered discontinuity surfaces, at low normal stress levels which are comparable to Western Australian conditions. Available shear strength data are reviewed and the following aspects of shear strength testing are considered:
the need for shear strength test work and the amount of testing required;
review of laboratory testing methods and the quality of the results;
presentation of the test results;
discussion of the shear strength failure criteria;
interpretation of the test results;
summary of test results for a variety of rock types, degree of weathering and discontinuity surface conditions;
a review of laboratory and field shear strength data to illustrate the amount of variability that can occur;
and a monitoring strategy is proposed to manage the uncertainty associated with discontinuity shear strength.