FRACTURE BEHAVIOR AND SIZE EFFECT IN FISSURE EXTENSION DIRECTION OF ROCK MASS CONTAINING TWO INTERMITTENT FISSURES WITH THEIR STRIKES IN DIFFERENT SURFACES

The occurrences of discontinuities in natural rock masses are generally different, which leads to the failure of ligaments between two intermittent joints in rock masses becoming a complex 3D rock mechanics problem. This paper aims to investigate the fracture behavior and size effect in fissure extension direction of this type of rock mass. It carries out the uniaxial compression tests of rock-like specimens with different geometries and sizes containing two intermittent fissures with their strikes in different surfaces. And combined with the CT scanning technology, it analyzes the influences of size and strike difference angle on mechanical responses, failure patterns and 3D ligament connection mechanisms of rock masses. The results show the follows. The failure of two ends out of the ligaments is mainly caused by the propagation of wing cracks or anti-wing cracks along the direction of loads. The fracture patterns of ligaments are influenced by both the size of specimen and the strike difference angle. The increase of fissure extension size can lead to the tension factors of ligament increasing. Strike difference angle greatly reduces the probability of ligament connection and mainly controls the twisted degree of the ligament fracture surface. The peak strength and elastic modulus decrease and then tend to be flat with the increase of the size. However, the variation of peak strength and elastic modulus becomes more complicated with the increase of the strike difference angle. The trend difference angle and size change together cause the overall three-dimensional asymmetry of the sample, and further affect the peak strength dimensional modulus and plasticity. The research results can provide theoretical support for the failure mechanism and stability evaluation of complex fractured rock mass engineering controlled by ligament.