EXPERIMENTAL STUDY ON DAMAGE AND FAILURE ENERGY EVOLUTION OF BRITTLE ROCKS UNDER UNIAXIAL COMPRESSION

Brittleness plays an important role in rock fracture mode and damage evolution. In this paper,uniaxial compression tests were carried out on 6 kinds of brittle rocks with different lithology from a railway tunnels. Based on the analysis of stress-strain process,failure mode and energy evolution characteristics,a calculation method of brittleness index was established by comprehensively considering the pre-peak elastic energy accumulation rate,post-peak energy dissipation degree and dissipation rate. Furthermore,the damage variable was characterized by energy dissipation,and the feasibility and rationality of establishing brittleness evaluation index from the perspective of damage evolution were discussed. The results show that: (1)The stress-strain curves of different rocks show different degrees of brittle drop after the peak. (2)Based on the brittleness index established in this paper,the brittleness degree is in the order of gabbro,metasandstone,quartz schist,coarse-grained granite,slate and marble. (3)The damage evolution process of brittle rock based on energy dissipation presents an "S" shaped development trend,which can be divided into five stages: initial damage,damage maintenance,damage stable development,damage accelerated development and damage mitigation to termination,which can well reflect the whole process of micro-crack pressure sealing,initiation and development,expansion and penetration until macroscopic failure in rock.