The rocks encountered in civil and mining engineering applications are invariably jointed. The presence of joints in rock makes them anisotropic and weak in strength behaviour. One of the techniques for enhancing the rock mass strength is to provide rock bolts. Assessment of strength of reinforced jointed rock is a challenging task before the geotechnical engineers. The strength of reinforced jointed rock depends on characteristics of intact rock, joint and rock bolt. An experimental study has been conducted to assess the mechanism of strength enhancement in jointed rocks due to provision of rock bolts. NX size cylindrical specimens of natural rocks having natural joints at variable orientation have been tested under uniaxial loading condition. Tests were also conducted on the bolted specimens. The results have been used to come out with an expression, which correlates the strength and deformation of intact rock to that of jointed rock without, and with reinforcement.

1 Introduction

Rock bolts are used as a primary support in many rock structures. Bolts increase the stiffness of the rock mass against external tensile or shear forces. In past, several studies have been conducted by researchers to evaluate the strength of jointed rock reinforced with rock bolts. The strength of reinforced rock has been reported to be dependent on various factors like strength of the parent rock (Egger & Zabuski 1991, Pellet & Egger 1996, and Sakurai 2010), joint orientation, angle of inclination between joint and bolt, and diameter of bolt (Bjurström 1974, Ludvig 1983, Pellet & Egger 1996, Grasselli et al. 1999, and Grasselli 2005). Effect of failure mode on engineering response of jointed rock has been emphasized by Singh (1997) and Singh et al. (2002) which is also an important factor in the case of jointed rocks. In present work, the effect of joint orientation on the strength and deformation behaviour of unreinforced and reinforced natural joint rock has been investigated.

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