Verification of Some Rock Mass Strength Criteria Using Laboratory Test Models

The objective of this study is to determine rock mass strength and deformability in the laboratory by simulating joints in sandstone specimens. The results are used to assess the predictive capability of rock mass strength criteria developed by Hoek-Brown, Ramamurthy-Arora, Yudhbir and Sheorey. Empirical criteria developed by Goodman, Yoshinaka and Yamabe and Ramamurthy criteria are used to predict the deformation modulus of rock mass. Triaxial compressive strength tests have been performed on cubical sandstone specimens with nominal dimensions of 60×60×60 mm³ and 80×80×80 mm³.A true triaxial load frame is used to apply confining pressures up to 12 MPa. The joints are simulated by saw-cut surface. The compressive strengths and deformation modulus of rock specimens decrease exponentially with increasing joint frequency. Under the same joint frequency the deformation modulus tends to increase with confining pressure. When the major principal stress is normal to the joint planes the specimen strength is greatest and the deformation modulus is lowest. Hoek-Brown strength criterion can effectively describe the specimen strengths under all configurations. The m and s parameters decrease rapidly with increasing joint frequency and joint set number. Ramamurthy criterion can best describe the deformation modulus of rock specimens under all configurations.