Triaxial compressive strength tests are performed to determine strength of small-scale rock mass models with different joint sets and frequencies under confining pressure up to 12 MPa. Sandstone specimens (55×55×55 mm3) with joint sets simulated by tension-induced fractures are loaded to failure using a polyaxial load frame. The specimens have joint frequencies ranging from 36 to 54 joints per meter. Hoek-Brown criterion with two material parameters (m and s) can describe the rock mass strengths as well as the criteria of Sheorey, Yudhbir and Ramamurthy-Arora which have three material parameters. The parameter s decreases with increasing joint frequency, while parameter m is less sensitive to the joint frequency. The effects of joint frequencies on the rock mass compressive strengths tend to increase with confining pressure.
Keywords
Triaxial compressive, Joint frequency, Strength criterion, Rock mass