Investigation on failure characteristic and instability mechanism of red sandstone including serrated joints under variable angle shear

Abstract

Numerous landslide disasters indicate that, when the developing direction of rock joint with different undulating angle is in line with the slope inclination, which will trigger or accelerate the slope instability. Hence, it is necessary to reveal the failure mechanisms of rock mass under the coupling action of the different undulating angle of rock joint and the slope inclination. In this study, a series of variable angle shear tests were carried out on red sandstone including serrated joint planes with different undulating angles. The mechanical responses and the variations of shear strength of joint samples under variable angle shear were analyzed in detail. Subsequently, by performing comparisons among macro-failure characteristics of samples, AF and RA obtained from acoustic emission test, and the principal strain field achieved from DIC tests; the main failure mode of joint rock under variable angle shear is regarded as shear fracture. Last but not least, based on the mechanics analysis and macro-failure modes of samples, we proposed a novel criterion factor of instability ${\eta }_{d}$ and the instability mechanism of variable angle shear test is identified as the slipping instability and fracture instability, which provides further reference in the following study of mechanical property of rock materials under variable angle shear.