Comprehensive knowledge of the shear mechanism of both joints and rock bridges is required to assess the shear strength of a weakness plane. In this study, the shear behavior of specimens containing a single non-persistent rough joint is investigated. A novel procedure was used to prepare casted specimens embedding a non-persistent (disc-shaped) rough joint using 3D printing and casting technology, and the shear strength of the specimens was examined through a direct shear testing program under constant normal load (CNL) condition. Three levels for three different variables of the joint roughness, rock bridge ratio, and normal stress were considered, and the effects of these factors on the shear behavior of prepared samples were tested. The experimental results show a clear influence of the three variables on the shear strength of the specimens. It is proved that the shear strength cannot be traditionally evaluated by simply adding the shear strength of the jointed zone to that of the bridged zone as if the zones are under identical normal stress. The results also show that normal stress applied to the embedded jointed zone of weakness planes is smaller than that to the bridged zone but still considerable and should thus be considered during shear strength evaluation.

1. Introduction

When the engineering dimensions of an investigated site exceed the average joint size in the domain, the joints should be considered non-persistent and thus surrounded by intact rock (rock bridge). The continuity of a joint is generally limited by a closed convex curve or other pre-existing geological structures (Zhang and Einstein, 2010). Considering non-persistent joints, an enforced failure plane is formed by the interaction between non-persistent joints and intact rock that surrounds the joints. Although not only the joints but also the rock bridges between them have a significant effect on the shear behavior (Gehle and Kutter, 2003), most of experimental and numerical research have been focused on the shear behavior of persistent rock joints (Asadi et al., 2012; Bahaaddini et al., 2013; Barton, 1976, 1971, 1972; Barton and Choubey, 1977; Ladanyi and Archambault, 1969; Lee et al., 2014). Relatively few studies have investigated the shear behavior of rock masses containing nonpersistent joints surrounded by intact rock. The spatial properties of joints in a rock mass as well as normal load and mechanical characteristics of the intact rock and joint surface were investigated (Asadizadeh et al., 2018; Gehle and Kutter, 2003; Ghazvinian et al., 2007; Savilahti et al., 1990).

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