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 mécanique des roches et de caractérisation non destructive at the Université de Sherbrooke, Québec, 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.

1 Introduction

The province of Quebec (Canada) is one of the world largest producers of hydroelectricity. During last decades, more than 6000 dams have been constructed and are distributed all over the province territory. However, some dams are old as they were built in the 1920–1930 and they are still in service. As a consequence, older concrete gravity dams (those over fifty years) are systematically studied by Hydro-Quebec, as a part of the dam safety program in place. However, in some cases, special attention may be paid to the foundation and the rock-concrete interface. For safety evaluation, all the causes are considered and among them are those related to the foundations mainly the shear strength along discontinuities or damrock interfaces. This requires taking into account the most accurate quantification available of the shear strength parameters of these discontinuities. If possible, the shear strength of discontinuities should be measured using the results of in situ tests, as they essentially take into account the scale effect. However, in situ tests are always time consuming in terms of preparation of the specimens and transportation of the equipment and hence, quite expensive. As a result, only a small number of in situ tests can be performed for a given project. To investigate larger samples under stress environments, higher forces are necessary and high capacity loading systems have to be developed (Bidaut et al. 2006, Konietzky et al. 2012). The aim of this project is to bring the concept of in situ direct shear tests performed on dam sites into the laboratories by replicating the real surface roughness of a discontinuity. The paper describes the components, set-up and technical data of an in-house developed system which is capable of testing large samples up to 100 cm×100 cm under different monotonic and dynamic loading conditions.

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