Alternative Methodology for Interpreting Discontinuity Direct Shear Data

CIM Vancouver 2016
Mr Matthew King (Geotechnical Engineer - Piteau Associates Engineering Ltd.), Ms Sheila Ballantyne (PhD Candidate - University of British Columbia, Department of Mining Engineering), Prof Davide Elmo (Assistant Professor, Rock Mechanics - University of British Columbia, Department of Mining Engineering)
Direct shear testing is a standard laboratory technique used to determine the shear strength properties of discontinuities. The results are useful for rock mass characterization and are a key input in a wide range of rock slope stability analysis methods. Several approaches to interpreting direct shear data as described in various rock mechanics textbooks and industry standards and guidelines are discussed. An alternative interpretation methodology supported by extensive rock discontinuity shear strength data from both direct shear testing and field mapping from various projects throughout North and South America is presented. This methodology shows that reliable peak strength properties are often difficult to obtain from small scale direct shear testing of rock discontinuities. A more reliable approach is to interpret lower and upper bound values of shear strength based on the testing data. The proposed approach enables the characterization of discontinuity shear strengths by defining the range of expected values from testing results where peak behavior is not observed.
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