Effect of microscopic crystal grains on strength and fracture behavior of marble in compressive-tensile stress state

Engineering excavation often causes the compressive-tensile stress state in surrounding rock of underground engineering or rock mass in slops, which usually leads to the tensile or tensile-shear fracture of rock mass in disturbed zone. Based on the numerical simulation method of particle flow, a numerical model of micro-grains in marble was set up considering the grain size and heterogeneity. Based on the test results of classic dog bone-shaped specimens published by Ramsey et al. in Nature, the effectiveness of crystal grain model to simulate the compressive-tensile strength and fracture behavior of rock was verified. The impacts of grain size and heterogeneity on strength and fracture behavior was further studied in the microscopic viewpoint. The results show that the tensile strength of rock increases gradually and the microcrack distribution is more dispersed as the grain size increases. Thus it is less likely to form the connected fractures and it is easy to form the echelon shaped failure zone. As the grain-size increases unevenly, the tensile strength of rock decreases (except for completely uniform model whose tensile strength is always the lowest), the distribution of microcracks is from dispersed to concentrated and it is easily to form the connected fracture surface; with the increase of lateral stress, the impacts of grain size and heterogeneity on the strength and fracture pattern of rocks are obvious. © 2020, Science Press. All right reserved.