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In this study, the joint shear strength of low-strength Hungarian sandstones of different grain size and surface roughness was investigated. The direct shear tests along discontinuities were performed under constant normal load. Previously, the direct shear test basic rock mechanic parameters of the investigated intact rocks were determined, such as the UCS value. The goal of the investigation is to determine the effect of the surface properties, such as surface roughness, grain size, and surface quality, on the joint shear strength of Hungarian sandstones. The failure curves derived from the experimental results of direct shear tests under laboratory conditions, and the empirical results according to Barton and Choubey (1977) were compared.

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Abstract

This paper provides test results and interpretation of the shear strength of granitic rocks. The samples were obtained from Bátaapáti (South Hungary), where the low and medium-activity nuclear waste storage facility of Hungary is under construction. The experiments were carried out under laboratory conditions by using direct shear strength tests of samples drilled and cut from larger granitic blocks. The friction angles of both the maximal and residual shear stress, as well as the cohesion, were detected for various joint systems and also for the cut surface of the granitic rock. The interpretation of test results includes the evaluation of normal stress versus shear strength for cut, moderately rough, rough and calcite-filled joints. The tests have demonstrated that the average internal angle of friction for granitic rocks exceeds 20°, with a maximum of 39° for rough surfaces. Calcite-filled joints have lower friction angles, in the range of 16–23°. The peak shear strength of granitic test specimens was between 0.8 and 4.1 MPa, depending on the surface and joint fill.

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Pollack Periodica
Authors: Ildikó Buocz, Nikoletta Rozgonyi-Boissinot, Ákos Török, and Péter Görög

This paper presents a brief summary of the main existing shear strength test methods on both intact and fractured rocks, such as the triaxial, half-half notched specimen and direct shear strength tests. A detailed description of how to carry out a direct shear strength test on rocks along discontinuities are provided, supported by test results. The analyses include the interpretation of the tests and the calculation of the maximal and residual shear strength, as well as their angle of friction and apparent cohesion. These parameters depend on the properties of the rock and the discontinuity, such as the joint surface roughness, the rock texture orientation, the filling material, the thickness of the discontinuities, the scale effect and the magnitude of the applied normal force during the test. Their effect is discussed.

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The paper summarizes the results of direct shear strength tests carried out on Opalinus Claystone deriving from a fault zone, at the site of Mont Terri (North-Western Switzerland). In Mont Terri an Underground Rock Mechanical Laboratory is conducting studies aimed at specifying the rock mechanical parameters of the rock surrounding, which is at the same time the potential host rock of a highly active radioactive waste disposal facility. The samples for the tests were derived from blocks and cores collected from the main fault zone, during the excavation of a tunnel, named: Full scale Emplacement demonstration experiment Gallery (FE Gallery). Direct shear strength tests were carried out on 50x50 mm samples undergoing a 1 MPa constant normal load, where the natural shear plane was parallel to the direction of the shear. The orientation of the bedding planes in the samples was recorded and the maximal shear strength and residual shear stress were determined. The maximal shear strength values obtained from the tests fell in the interval 0.34-0.78 MPa, while the residual values fell between 0.31 and 0.72 MPa. The effect on the shear strength of different angles defined by the bedding and the shear plane of the samples was also examined. The bedding of the samples enclosed different angles with the shear plane, ranging from 0 to 49 degrees.

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