MICROSTRUCTURE FRACTURE CHARACTERISTICS AND DILATANCY EFFECT OF ROCK BRIDGE UNDER DIRECT SHEAR TESTS

The jointed rock masses with incomplete end joints and coalescence mechanisms of rock slopes are often encountered in engineering construction. They are complex. In order to reveal the relationship between the failure characteristics and dilatancy effect of end rock bridge under different joint connectivity rates and normal stresses, we carry out the direct shear test of the rock bridge to explore the failure process of the front locked section slope. The whole process of shear stress change is analyzed by high-speed photography and AE characteristic parameters. After test, we find that the shear failure process of the end direct shear specimens can be divided into five stages: crack compaction, stable crack propagation, progressive propagation, strain softening and residual strength stage. The decrease of joint connectivity rate and the increase of normal stress lead to the increase of peak shear displacement and peak shear stress. The joint connectivity rate and normal stress have significant influence on the failure characteristics of rock mass. When the joint connectivity rate is high and the normal stress is small, the cracks propagate in a straight line. With the decrease of the length of joint connectivity rate, the phenomenon of shear dilatancy occurs, and the cracks become irregular curves. Meanwhile, the increase of normal stress causes the dilatancy phenomenon to fluctuate. The AE characteristics are consistent with the rock bridge crossing process. The peak number of AE events increases with the decrease of the joint connectivity rate and the increase of normal stress. The tests demonstrate that the microscopic failure characteristics and dilatancy effect of rock bridge are extremely significant for studying the failure mechanism of the locked section slope as a guide.