Shear behaviour of a cement grout tested in the direct shear test

Portland cement grouts are widely used in the mining industry to bond cable bolts with the surrounding rockmass. Numerous laboratory and field tests showed that bond failure of the cable/grout interface is the dominant failure mode. Previous research has found that shear behaviour of the grout along a pre-defined plane plays a significant role in determining the nature of the bond failure in a cable bolt reinforcement system. In this study, the shear behaviour of a Portland cement grout was investigated based on a direct shear test. Two different boundary conditions were considered being a constant normal load (CNL) and constant normal stiffness (CNS). Under CNL condition, five different normal pressures between 0.1 MPa and 6.0 MPa were examined. While under CNS condition, the initial normal pressure was set to value within the same range. Also, a CNS of 10 kN/m was added. The cohesion, internal friction angle and shear strength of the grout were acquired. The results showed that there is a linear relationship between the shear strength of the grout and resultant normal pressure. However, under the CNS condition, the shear strength of the grout was found to be generally higher comparing to the CNL condition, most likely because sample dilation resulted in an increase in the normal pressure. Consequently, shear strength of the grout also increased.