Rock Crack Propagation Experiment And Numerical Simulation Research

The strength of rock decreases because of the structural surfaces.The structural surfaces will initiate,propagate and coalesce due to external loads,which is a key factor controlling the stability of fissured rock slopes and dangerous rocks.At present,most studies focus on the stability analysis at the crack tip.However,studying on crack propagation related to engineering is seldom found.Analytical method can predict the initiation angle,but the crack propagation tests of rocks are difficult to perform due to technology difficulties.Therefore it is necessary to examine crack propagation using numerical methods.Based on fracture mechanics,the experiments and numerical simulation are carried out and the rock crack propagation with the engineering examples is researched,the main tasks and related conclusions are as follows:(1)Tensile-shear fracture testing of cracked sandsonte is carried out,the displacement-load curve is obtained,and crack initiation,propagation under loading is examined.The effects of the crack length,angle,and load position on peak strength and opening displacement at the crack tip are discussed.The results indicate that the peak load position has the largest impact on peak strength and opening displacement at the crack tip,the second is crack length,and the angle is minimal.(2)The stress at the crack tip of the test model under loading is examined using ANSYS.The effects of initial crack length,angle and load position on the stress intensity factor are analyzed.The results show that tensile-shear stress concentration first emerges in the crack tip.At the same time,the compression-shear stress concentration occurs at the bottom of the model.The crack initiates and propagates along the stress concentration area.(3)Based on the extended finite element method,the static crack propagation program is written using FORTRAN.The grid boundaries are independent of the crack surface when crack propagation is simulated.And the enforcement nodes have been set at the crack tip to ensure the accuracy.The quasi-static crack propagation process of the model is examined,which shows that crack propagation path agrees well with the experimental results,and verifies the the program.The stress state at the crack tip and dynamic stress intensity factor are computed during the crack propagation.(4)Based on rock dynamic fracture,the dynamic crack propagation program is written using FORTRAN,and examined it by a case study.The crack propagation of cracked rock slopes or dangerous rocks are analyzed under different conditions.The results indicate crack propagation under dynamic load can be considered as the new crack is repeatedly subjected to stress concentration and relaxation,and there are two types of fracture modes including tensile-shear and compression-shear.The initiation angle is most important among the factors that cause rock crack propagation under external loading.