STRENGTHS OF ROCK MASS MODELS WITH ROUGH FRACTURES UNDER LARGE CONFINEMENTS

Abstract

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.