EXPERIMENT RESEARCH ON FRACTURE OF MIXED GNEISS WITH A CIRCULAR CAVITY UNDER UNIAXIAL COMPRESSION

On account of the complexity of fracture mechanism of hard rock surrounding the underground tunnel， uniaxial compressive experiment of the mixed gneiss specimen with a circular cavity at center was carried out，and the whole process of fracture initiation and propagation was observed carefully． The different uniaxial stresses of primary crack，slabbing crack and remote crack around the cavity of mixed gneiss were obtained． The stress averaging method was adopted for the analysis of primary crack initiation and slabbing crack initiation based on the mechanical properties of mixed gneiss． The results of stress averaging method were basically agreed with the experiment results and the disadvantages of theoretic analysis were discussed． At last，the scale effects of cavity dimension were also studied．