The effects of grain size and different multi-stage shearing techniques on shear strength along rock discontinuities
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(2020) 11:27
ORIGINAL PAPER
The effects of grain size and different multi-stage shearing techniques on shear strength along rock discontinuities Alina Vattai1 · Nikoletta Rozgonyi-Boissinot1 Received: 24 October 2019 / Accepted: 3 September 2020 © The Author(s) 2020
Abstract The effects of grain size and different multi-stage shearing techniques on shear strength along discontinuities were analyzed in this study. Laboratory direct shear tests were carried out on plaster mortar with maximum grain sizes of 0.5 mm and 1.0 mm. All specimen surfaces were essentially similar, copied from the same natural, Hungarian coarse-grained sandstone joint with a low joint roughness coefficient (JRC 8). Tests within two different normal stress ranges (σn 0.25–0.5 and 0.5–1.5 MPa) were performed simultaneously. Specimens tested using the technique involving modified shearing with repositioning were sheared three times while being subjected to the same degree of normal stress (shearing sequence n 1, 2, 3) and those with multi-stage technique without repositioning were subjected to shearing once at three different degrees of normal stress. The changing values of the peak friction angle calculated from the resulting peak shear strength-normal stress data pairs (τp − σn ) were examined. Failure curves were estimated using linear regression, according to the Mohr–Coulomb failure criterion. The differences between the various peak friction angles obtained from experiments in which different multi-stage shearing techniques were used tend to increase in significance with the increasing number of shearing sequences. Peak friction angle values vary according to grain size of the material, though further investigations using more grain sizes are required to establish the extent of the effect on shear strength along discontinuities. Keywords Shear strength of rock joints · Multi-stage direct shearing · Plaster mortar · Grain size Mathematics Subject Classification 70-05 · 82-05 · 86A99
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Alina Vattai [email protected] Department of Engineering Geology and Geotechnics, Budapest University of Technology and Economics, M˝uegyetem rkp. 3, 1111 Budapest, Hungary 0123456789().: V,-vol
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GEM - International Journal on Geomathematics
(2020) 11:27
Abbreviations JCS Joint wall compressive strength JMC Joint matching coefficient JRC Joint roughness coefficient
List of symbols A A0 aj c C i ij β φ φb φr σc σn σnj σt τ τp τr ӨA Өmax Ө*max
Total joint contact area Maximum possible contact area Contact area of individual asperities Cohesion, apparent cohesion 3D roughness parameter Inclination angle of teeth Variable angle of asperities Angle between foliation plane and shearing direction Friction angle Basic friction angle Residual friction angle Uniaxial compressive strength of intact rock Normal stress Normal stresses acting on the individual asperities Brazilian tensile strength of intact rock Shear strength along discontinuity Peak shear strength a.d Residual shear strength a.d Average angle of asperities faci
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