Experimental Study on the Shear Strength of Sandy Clay Infilled Regular Rough Rock Joints

Infill materials in rock joints usually cause a reduction in the joint shear strength. The shear behavior of rock discontinuities depends upon whether they are clean and unfilled or filled, so this concern invites accurate understanding of the shear behavior and strength of infilled joints. A series of constant normal load direct shear tests was performed to investigate the shear strength of artificial samples with infilled rough joint surfaces having different asperity and infill characteristics. The current study focuses on the effects of factors that influence the shear strength of infilled rock joints samples, with emphasis on forward and reverse shearing. In the forward cycle, the front joint wall is compressed and possibly sheared, and the back side fill is unbonded from the joint surface and slightly disturbed. In the reverse cycle, the disturbed and weakened back side fill is under shearing. The effect of the normal stress on the joint is studied, as this factor plays an important role on the shear behavior of infilled rock joint samples. The results show that joints with low asperity angle exhibit higher shear strength during the forward shearing cycle than the reverse cycle, but in joints with steeper asperity angle, the reverse cycle exhibits greater shear strength. In the reverse cycle, the joint infill has less influence compared to the effect of the rougher surface and higher asperity inclination, even in higher normal stress.