Triaxial and direct shear tests to estimate the parameters of rock-joints and rock-shotcrete interface

Design analysis of support system for underground tunnels is largely influenced by the joint properties and interfacial properties of Rock-Shotcrete. This paper discusses a method to determine the joint properties of rock, including shear and normal stiffness of Rock-Shotcrete (reinforced with fibers), and rock-rock using Triaxial test setup. The results from direct shear test for clay filled and unfilled joints are compared with triaxial tests results on joints. The comparison showed triaxial tests are consistent with direct shear tests results. Hence, triaxial tests based experimental plan was made which involves testing of rock-shotcrete interface at various orientations to obtain the interface behavior. Special moulds were casted to prepare rock-shotcrete specimens in the laboratory. Two different strain gauge arrangements were made to check for variations in deformations on rock and shotcrete as compared to the interface. The confining stresses considered for the triaxial testing were in range of actual stress conditions at the location of tunnel. The results of few direct shear tests on clay filled rock joint samples are presented. The aim of this paper is to discuss an experimental plan which has been useful for obtaining shear strength and stiffness parameters for rock joint and rock shotcrete interface.