Developing a high capacity direct shear apparatus for the large scale laboratory testing of rock joints

摘要

The reliable determination of the shear strength parameters of rock joints is one of the most critical problems in geomechanics. Because of scale effects, there is no simple method for the determination of in situ shear strength parameters from the results of the laboratory tests conducted on small rock joint specimens; for this reason in situ tests on large rock joints have been developed and are sometimes conducted. However these tests are expensive and time consuming; consequently there is a great interest for simulating in situ shear tests in laboratory by developing high capacity apparatus and testing large rock joint samples. For this purpose, a new direct shear test apparatus has been developed in the Laboratoire de mecanique des roches et de caracterisation non destructive at the Universite de Sherbrooke, Quebec, Canada. This new system offers high shear load (up to 1000 kN) and normal load (up to 250 kN) for testing different samples with surface sizes ranging from 30 × 30 cm to 100 × 100 cm. The servo-controlled loading system allows testing of the joints by controlling the force or the displacement under cyclic loading (up to 300 cycles) and dynamic loading (with frequency 3-4 Hz) both in horizontal and vertical directions. This paper presents the characteristic of the apparatus, experimental methodology and some results of the tested joints. A procedure for the preparation of replicas from in situ rock surfaces with a Room Temperature Vulcanizing silicone (RTV) is described. These replicas are used as samples to be tested with the new shear apparatus.