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 mostrncritical problems in geomechanics. Because of scale effects, there is no simple method for the determination ofrnin situ shear strength parameters from the results of the laboratory tests conducted on small rock joint specimens;rnfor this reason in situ tests on large rock joints have been developed and are sometimes conducted. However theserntests are expensive and time consuming; consequently there is a great interest for simulating in situ shear tests inrnlaboratory by developing high capacity apparatus and testing large rock joint samples. For this purpose, a newrndirect shear test apparatus has been developed in the Laboratoire de mécanique des roches et de caractérisationrnnon destructive at the Université de Sherbrooke, Québec, Canada. This new system offers high shear load (uprnto 1000 kN) and normal load (up to 250 kN) for testing different samples with surface sizes ranging fromrn30×30 cm to 100×100 cm. The servo-controlled loading system allows testing of the joints by controlling thernforce or the displacement under cyclic loading (up to 300 cycles) and dynamic loading (with frequency 3–4 Hz)rnboth in horizontal and vertical directions. This paper presents the characteristic of the apparatus, experimentalrnmethodology and some results of the tested joints. A procedure for the preparation of replicas from in situ rockrnsurfaces with a Room Temperature Vulcanizing silicone (RTV) is described. These replicas are used as samplesrnto be tested with the new shear apparatus.