In this paper, we can clarify the relationship between the shear behavior of natural rock joint and three parameters (joint surface roughness, material strength and effective normal stress) through the direct shear test in laboratory. Based on the results of the shear test, we can understand that the shear behavior strongly affects joint surface roughness, material strength and effective normal stress. We can establish the relationship between peak shear strength, dilatancy curve and the parameter which is estimated by joint surface roughness in consideration of material strength and effective normal stress.
Generally speaking, the mechanical behavior of a jointed rock mass is strongly controlled by rock joints and/or discontinuities. The mechanical behavior of rock joints is represented by normal and shear behavior. The shear behavior of rock joints is affected by several parameters: namely, joint surface roughness, material properties of the intact rock, normal confining conditions, weathering of the joint surface, infilling material, etc.. Due to the combined effect of these parameters, it is not easy to estimate precisely the shear behavior of rock joint. Barton (1977) presented his empirical relationship between peak shear strength and joint surface roughness, material property of intact rock, and the normal confining stress. In Equ. (1), JRC is estimated by back analyzing the shear tests that have been performed. By performing shear tests, peak shear strength and effective normal stress can be known from the tests results. JCS is decided by a schmidt hammer test. Then, applying these parameters to Equ. (1), JRC is calculated. On the other hand, Thapa et al. (1995) described how to estimate joint surface roughness from the borehole survey by using Borehole Scanner System (Tanimoto et al, 1992) and image processing techniques. Then, based on the results, they simulated the shear behavior through both kinematic displacement dilation analysis and Discontinuous Deformation Analysis. Using this method, if we establish a relationship between the shear behavior of rock joints and several joint properties ( joint surface roughness, material properties of intact rock, normal confining condition, etc.), we can determine the shear behavior of a rock joint from the borehole survey. We carry out the direct shear tests of rock joints under various confining conditions. For the shear tests, we use reproduced specimens as well as natural rock joints. We, then, consider the influence of joint surface roughness on shear behavior. In addition, when we make reproduced specimens, we change the combination ratio of water, cement and sand. Then we discuss the influence of material strength. Through these laboratory shear tests, we can estimate the peak shear strength and displacement dilation in consideration of joint surface roughness, material strength of intact rock and effective normal stress.
Specimens, which we employ in the laboratory direct shear test, include natural joints taken from core samples (60 mm in dia.). After choosing 8 kinds of natural joint surface roughness, we make impressions of them, respectively. Then, by using the impressions, we make reproduced plaster specimens.