Rock-blasting Crack Propagation Under Different Biaxial Lateral Pressures

Research on rock-blasting fractures is not only conducive to the improvement of rock mass dynamics theory but is also closely related to the national mineral energy strategy.With the increasing demand for mineral energy,mining engineering of mineral resources and related scientific research are gradually expanding to underground deep rock masses.The initial stress state of a deep rock mass has a significant impact on the rock-blasting effects.The initial stress state in a rock mass and the explosion together determine the rock-blasting crack propagation law and the final distribution of the fracture zone.Therefore,with the help of theoretical analyses,model experiments and numerical simulations,the blasting dynamic response of a deep rock mass can be explored.The main research content and results of our study are as follows.Combined with the detonation theory and rock fracture characteristics,a blasting numerical calculation method(MPM-CDEM)that couples the material point method and the continuum discontinuum element method was proposed.The feasibility and accuracy of the proposed blasting numerical calculation method were verified using existing experimental results.The numerical results show that the blasting numerical calculation method coupling the material point method and the continuum discontinuum element method can not only correctly simulate the propagation process of the detonation wave but can also successfully calculate the interaction between the explosive products and the rock.In particular,it can successfully simulate the process of explosive gas wedging into the crack surface in the rock-blasting process.The numerical simulation results of a rockexplosion fracture show that the crack propagation law and fracture zone distribution in the rock blasting were accurately simulated.The theoretical analysis shows that a high-strength stress concentration appears around the blast hole under lateral pressure.Model experiments of the rock-blasting crack propagation law of a concentric charge structure under different lateral pressures were performed using an experimental platform with bilateral pressure loading.The experimental results show that the rock-blasting crack propagation law is affected by the initial stress state.The magnitude of the lateral pressure loading affects the length and number of rock-blasting cracks,while the different lateral pressure conditions change the direction of the propagating crack.Under the condition of biaxial lateral pressure loading,when the lateral pressure is loaded to a large value,the blasting crack expands in the direction not constrained by the lateral pressure.The numerical simulation results show that the change in the lateral pressure ratio has little effect on the shear failure in the rock mass near the blast hole but has a greater effect on the tensile failure of the rock.The model experiments of the crack propagation law of eccentric charge rock blasting under different lateral pressure conditions were performed on cubic granite specimens.The experimental results show that the number of cracks distributed on the wall of an eccentric side blast hole is relatively large.The change in the lateral pressure ratio makes the propagation of the rock-blasting crack deflect toward the direction of the larger lateral pressure.In particular,compared with the rock-blasting crack on the eccentric side,the rock-blasting crack on the non-eccentric side deflects at a larger angle with the change in the side pressure ratio.The numerical simulation results show that the blasting energy distributed in the rock mass near the blast hole wall on the eccentric side is relatively large compared with that on the non-eccentric side.Therefore,the number of blasting cracks is also relatively large.The theoretical analysis shows that the initial guided crack of slotted cartridge blasting is determined by the strength of the rock material,the initial stress state in the rock and the blasting pressure formed at the slit after the initiation of the explosion.With the aid of the bilateral pressure model experimental system,a rock slit blasting experiment was performed on a cubic granite specimen.The experimental results show that,compared with the experimental results of rock blasting with an ordinary charge structure,slotted charge blasting has an obvious energy accumulation effect and a directional effect.The experimental results of rock slit blasting under different lateral pressures show that the crack propagation direction of the slit blasting changes with the lateral pressure ratio.In addition,the structural parameters of the slotted pipe have an obvious influence on the slotting effect.The numerical simulation results show that,with changing side pressure ratio,the blasting crack in the cutting direction deflects to the larger side pressure direction.When the lateral pressure perpendicular to the slit direction is relatively large,a long blasting crack will occur in the non-slit direction.Combined with the caustics method,a dynamic crack propagation law experiment for a layered rock was performed on a drop hammer impact experimental platform.The experimental results show that different interface dip angles affect the crack propagation morphology.A larger interface dip angle results in a longer crack propagation distance in the interface.As the crack propagates to the interface,the propagation speed and stress intensity factor at the crack tip decrease accordingly.The numerical simulation results show that an increase in the interface strength makes it easier for the dynamically propagating crack to penetrate the interface.Combined with the dynamic photoelastic experimental system,model experiments of the blasting crack propagation law of a lower rock under lateral pressure were performed.The experimental results show that the lateral pressure perpendicular to the interface increases the velocity and stress intensity factor of the blasting crack tip near the interface.Therefore,the lateral pressure perpendicular to the interface makes it easier for the blasting crack to penetrate the interface and expand.