The shear strength of discontinuities has an important influence on the stability of rock slopes. The presence of reliable direct shear laboratory testing data is critical to characterize the discontinuity strength, however, it is often lacking. This is typically due to the limited number of available direct shear tests and samples per geotechnical unit, usually leading to a high variability in results and a limited understanding of the factors controlling the defect shear strength. Moreover, geoscientists usually deal with laboratories utilizing variable methodologies or apparatuses, and no corrections applied for changing area and dilation to the test results.
Provided with more than 200 direct shear tests from several different mine sites, this paper discusses the validation and interpretation of shear strength of rock defects using open joint and saw cut direct shear samples. Special interest is dedicated to the use of saw cut samples, highlighting the value that this type of samples may represent for different scenarios, its validation will be evaluated by comparing results against natural samples to evaluate correlation to joint shear strength and intact rock strength.
This paper includes a review and analysis of data from different laboratory facilities and rock types as well as the influence of joint condition parameters on the overall defect shear strength. The use and estimation of peak and basic friction angles are also discussed, including corrections for area and dilation, typically used in the industry. A comprehensive statistical analysis is conducted to analyze direct shear test results, correlating to the influence of joint condition such as roughness, infill, aperture, and other parameters controlling the strength of geotechnical units. The importance of sampling, drilling conditions and laboratory considerations are also discussed.
