To investigate the effect of sandy fillings on the shear strength of rock joints

direct shear tests were conducted on single-joint fine-grained marble specimens infilled with four types of sands with different frictional coefficients. The results show that the peak shear stress of unfilled marble joints was greater than those of infilled marble joints under a same normal stress. It is indicated that the existence of sandy fillings reduced the shear strength of rock joints. A new empirical formula for the shear strength of the unfilled joints was proposed

expressed by the three-dimensional roughness parameter of maximum valley depth of the joint surfaces

and its calculated shear strength of the unfilled joints roughly coincided with their test values. An empirical formula of peak shear strength for infilled fine-grained marble joints was also obtained

expressed by the friction coefficients of infilled sands. the predicted shear strength of infilled rock joints was in accordance with the test values. Above conclusions have some helps to evaluate the stability of infilled jointed rock mass in rock engineering.