Study on the effect of unloading rate on the rockburst failure and energy characteristics with FDEM
A 2D numerical model considering the mineral heterogeneity for simulating rockburst experi-ment was established using image processing method and finite-discrete element method(FDEM).The granite rockburst experiments under different unloading rates were simulated according to experimental loading/unloading paths and boundary conditions.The failure process,crack development and energy transformation characteristics were analyzed,and the influence mechanism of unloading rate on the rock-burst of the heterogeneous granite was investigated.The research results show that reducing the unloading rate leads to lower damage to both the model and specimen,resulting in less prominent dynamic failure.With the unloading rate decreasing,the cracks tend to develop along the oblique direction in the range of 30° to 50° during the unloading process,with an increase in shear crack proportion but a decrease in ten-sile crack and tensile-shear mixed crack proportion.During failure,a large amount of the external work is input by upper loading platen,releasing all elastic strain energy and leading to sudden increases in dis-sipation energy and kinetic energy.With decreasing the unloading rate lower than threshold(1 MPa/time step),both the external work and kinetic energy decrease,while the dissipation energy shows a slight increase.The change rates of the different energy also decrease,respectively.Reducing the unloading rate effectively suppresses the suddenness of the rockburst.
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