Experimental study on shear strength of rough rock joints under various saturations

Abstract

In order to investigate the change of the shear strength of rock joints with saturation, artificial rock joints with various roughness were reproduced by mixing cement, sand, fly ash and water at a mass ratio of 1:3:0.4:0.55 based on 3D-laser scanning and 3D-printing technologies, and the saturation of the joints was controlled according to the calculated joint void volume. Subsequently, a series of direct shear tests were carried out on the reproduced joints with various roughness and saturations under a constant normal stress of 0.2 MPa. Experimental results indicate that the average peak shear strength of rock joints decreases by 28.4% when the saturation increases from 0 % to 100 %, and the peak shear strength of the rock joints with a JCR of 12.9, 10.1 and 7.3 respectively decreases by 35.7%, 28.5% and 16.1%. Besides, the residual shear strength also reduces with increasing the saturation, and the reductions dependent on the joint roughness range from 7%-12%. Further analysis shows that the weakening of the shear strength of rock joints arises from the mechanical effect and lubricating effect of water exerted on the rough joint surface, and that, as the joints get rougher, the water-rock interaction area becomes greater, inducing a higher deterioration in mechanical properties. According to the findings from this study, it is emphasized thatthe effect of the water saturation on the degradation of the shear strength should be analyzed when designing rock mass projects.