Importance of Tensile Strength on the Shear Behavior of Discontinuities

Abstract

In this study, the shear behavior of discontinuities possessing two different rock wall types with distinct separate compressive strengths was investigated. The designed profiles consisted of regular artificial joints molded by five types of plaster mortars, each representing a distinct uniaxial compressive strength. The compressive strengths of plaster specimens ranged from 5.9 to 19.5 MPa. These specimens were molded considering a regular triangular asperity profile and were designed so as to achieve joint walls with different strength material combinations. The results showed that the shear behavior of discontinuities possessing different joint wall compressive strengths (DDJCS) tested under constant normal load (CNL) conditions is the same as those possessing identical joint wall strengths, but the shear strength of DDJCS is governed by minor joint wall compressive strength. In addition, it was measured that the predicted values obtained by Barton's empirical criterion are greater than the experimental results. The finding indicates that there is a correlation between the joint roughness coefficient (JRC), normal stress, and mechanical strength. It was observed that the mode of failure of asperities is either pure tensile, pure shear, or a combination of both. Therefore, Barton's strength criterion, which considers the compressive strength of joint walls, was modified by substituting the compressive strength with the tensile strength. The validity of the modified criterion was examined by the comparison of the predicted shear values with the laboratory shear test results reported by Grasselli (Ph.D. thesis n.2404, Civil Engineering Department, EPFL, Lausanne, Switzerland, 2001. These comparisons infer that the modified criterion can predict the shear strength of joints more precisely.

Influence of Discontinuity Inclination on the Shear Strength of Mont Terri Opalinus Claystones

“…Discontinuities happen to be often the weak points of rock materials, since, if movements in the rock mass occur, it tends to happen along these surfaces. The point where the initiation of the movement along the surfaces takes place, depends on the shear strength along the discontinuities, and therefore their investigation is one of the most important topics in rock mechanics [1,2,3]. The shear strength of rocks along discontinuities is influenced by several factors, for example, surface roughness of the joint, joint infill material, elevation of the plane of the sample surface in respect to the shear plane in the direction of shear, rock strength, normal stress acting on the sample surface, humidity, bedding, and in situ stress conditions...etc [4,5,6,7,8,9].…”

Shear strength testing of consolidated claystones: breakpoint detection of shear stress versus shear displacement curves, a statistical approach

“…Moayedi et al 2019. In the case of the Mont Terri Claystone, low shear stresses are recorded. Therefore it is a more significant challenge to detect breakpoints compared to high shear stresses of gneiss, migmatites (Renaud et al 2019), sandstone Basu 2018, Casagrande 2018), granite/diorite (Kim and Jeon 2019;Lee et al 2005;Singh and Basu 2016), limestone (Cai et al 2018;Morad et al 2019;Renaud et al 2019), quartzite (Singh and Basu 2018) or even to mortar (Ghazvinian et al 2012). This is linked to the fact that the shear surfaces of claystones are much smoother, therefore it is more difficult to observe surface changes related to shearing.…”

“…Previous analyses mainly dealt with the analysis of rock-rock (Grasseli and Egger 2003;Casagrande et al 2018;Kim and Jeon 2019;Morad et al 2019) and concrete-rock interfaces (Ghazvinian et al 2012;Renaud et al 2019). Approaches focusing on analyzing surface roughness (Muralha et al 2014;Özvan et al 2014), using photogrammetry (Casagrande et al 2018;Kim and Jeon 2019;Morad et al 2019) and statistical analyses of surfaces (Cai et al 2018;Renaud et al 2019) are also common.…”

Numerical Analysis of the Anisotropy and Scale Effects on the Strength Characteristics of Defected Rockmass

“…e UCS/TS ratio plays a vital role in the fracturing process and mechanical behavior of rocks [24]. Ghazvinian conducted a series of direct shear tests of the rock joint, which indicated that the tensile strength of the rock matrix had a significant effect on the shear strength behavior of the jointed rockmass [38]. Hence, the tensile strength affects the tension and compression behaviors of real rocks.…”