Study On Stress Wave Propagation And Crack Extension Law Of Rock Blasting Under High In-Situ Stress

In recent years,with the gradual depletion of shallow resources,the demand for deep resource development has been growing.During the blasting process of deep rock masses,which are subjected to the influence of high in-situ stress,and the damage evolution mechanism of the rock mass under blasting loads exhibits significant differences compared to when there is no stress constraint.A thorough investigation of the propagation of blasting stress waves and the laws of crack extension under high in-situ stress will help to reveal the failure mechanisms of rock masses in high-stress environments,thereby enhancing the economic efficiency and safety of deep resource development.In this study,based on rock blasting theory and using independently calibrated granite RHT constitutive model parameters,the finite element software ANSYS/LS-DYNA was employed to conduct numerical simulations on single-hole rock mass blasting,jointed rock mass blasting,and cut blasting under different in-situ stress conditions.The propagation of blasting stress waves and crack extension patterns under various stress conditions were analyzed and summarized.The primary research tasks were as follows:(1)By conducting Split Hopkinson Pressure Bar(SHPB)cyclic impact tests on granite specimens under different confining pressures,it was found that the confining pressure effect has a significant impact on the mechanical properties and failure mechanisms of rocks.Through a combination of theoretical,experimental,and simulation approaches,along with SHPB impact tests and SHPB numerical simulations,a complete set of granite RHT constitutive model parameters were calibrated.The rationality and accuracy of the RHT constitutive model parameter calibration were also verified.(2)Numerical simulations of single-hole blasting under different in-situ stress conditions were carried out,revealing that the blasting crack extension under the influence of ground stress exhibits a distinct directional characteristic.A fitting function relationship between the crack extension length and the in-situ stress was established for each condition.The simulation results were used to investigate the impact of ground stress on stress wave propagation in different blasting areas,as well as the variation of peak stress in monitoring units with respect to ground stress.The relationships between rock mass damage degree D,particle peak velocity(PPV),and scaled distance l under different in-situ stress conditions were explored,and the PPV threshold for rock mass vibration safety criteria under various stress conditions was determined.This threshold value is subject to the inhibitory effect of in-situ stress and increases with the rising level of ground stress.(3)Two types of jointed rock mass blasting numerical models were established,and it was found that the presence of joints enhances the damage concentration in the rock mass on the blast-near side of the joints,but also restricts the crack extension on the blast-far side of the joints.Under the influence of biaxial unequal in-situ stress,blasting cracks extend in the direction of the maximum principal stress,and as the lateral stress coefficient increases,the crack propagation direction becomes more concentrated.The constraint effect of in-situ stress on jointed rock mass impacts the peak stress,vibration velocity,and transmission coefficient of monitoring points on both sides of the joints.(4)Analyzing the damage evolution process of cut blasting,it was found that the resistance generated by in-situ stress and the damage anisotropy caused by the lateral stress coefficient are the primary reasons for the difficulties in deep rock mass cut blasting.When the lateral stress coefficient is greater than 2,it is difficult for the damage cracks between excavation holes to connect.Reducing the spacing between excavation holes and increasing the diameter of the hollow holes can optimize the fragmentation effect of deep rock mass excavation blasting.