Machine parameter evaluation of a direct shear testing machine for rocks

Shear strength is an important parameter for the economical and safe design of mining and civil structures in rock or bearing on rock. A number of test configurations have been used for the determination of shear strength of rock in the laboratory but results from triaxial compression tests are considered to be the most accurate for use in the design of structures in rock. Direct shear test on rock, because of its simplicity, is becoming more popular for shear strength analysis of rock in mining and civil structures. In this method, shear strength of intact material as well as along specific planes of weakness can be easily determined. The problem, however, is that widely accepted test equipment and procedures have not been developed, and therefore the agencies using these test results are unsure how confidently these results can be applied to the design of their structures. The machine design itself needs further investigations. A research project has been initiated in the Department of Mining Engineering of the University of Missouri-Rolla, where machine and test parameters would be investigated. These include stiffness and strength of potting compound, separation between the shear boxes as a function of shear surface profile, application ofmore » normal and shear loads, the rate of displacement and tipping of the upper shear box. The experimental results will be verified with triaxial compression tests. A finite element analysis of test configuration will be performed to determine the difference between average and maximum shear stress along the shear plane.« less