Numerical simulation of the effect of internal hole defect size on the mechanical properties of limestone

To better understand the effect of the size of hole defects on the mechanical properties of a rock mass, the two-dimensional particle flow discrete element code (PFC2D) is used to establish rock mass models with single circular hole defects of different diameters. Taking the defect size (area) as the only variable, uniaxial compressive strength (UCS) tests are carried out on each model. The stress-strain, contact force chain, crack evolution, meso-damage and failure, and mechanical properties of each model are compared and analyzed. The results show that with the size enlargement of the circular hole defects, the UCS and elastic modulus of each model decrease gradually, and the defect size is negatively correlated with the mechanical strength of the rock samples. The size of the hole defects affects the entire process of contact force chain and crack evolution. The larger the aperture dimension of the circular hole defects in each model, the greater the concentration degree of the contact force chain, the earlier the crack initiation, and the higher the degree of crack penetration in post-peak stage. The number of cracks has a decreasing trend as the hole size increases, and the model is more prone to failure. Under the condition of the same defect area, the strength and failure characteristics of rock models with different numbers and arrangements of hole defects are compared and discussed.