Study On The Law Of High Geostress Hard Rocks Fracture With The Method Combining Borehole-Induced Unloading And Multi-Picks Cooperative Cutting

The failure of non-blasting tunneling in high geostress hard rock is a difficult problem in deep mining engineering.A new method to study on the theory and experiments of hard rock induced unloading and multi-picks cooperative rock fracture is a fundamental work that is urgently demanded in deep mine excavation.In this paper,a combination of numerical simulation and experimental analysis is adopted to demonstrate the strength degradation and stress transfer during hard rock borehole unloading,the relationship between unloading borehole formation and rock strength index is established,the quantitative relationship between rock strength parameters and cutting force is analyzed,the influence law of cutting distance and cutting angle on the cutting force under unloading of hard rock is studied,the hybrid system model of drilling and cutting is set up,the cooperative rock breaking law of borehole-induced unloading and multi-picks is demonstrated.The research results have the important theoretical significance and widely application perspective in high geostress hard rock tunneling technology and rock burst hazard prevention.The ABAQUS finite element method was applied to establish a numerical model for induced unloading of bored rocks,and the unloading law of high geostress stress rocks under different drilling conditions was simulated.The results show that:when the depth remains in the same level,the depth of the slice decreases from the shallow to the deep while the stress concentration initially decreases and then increases continuously;when the depth remains different,the stress concentration area increases in the beginning and then decreases as the depth increases;If the diameter remains the same,the depth of the slice decreases from shallow to deep while the range of stress concentration initially decreases and then increases continuously.If the diameter changes,the stress concentration area increases as the diameter of the borehole increases;In different geostress stress conditions,the optimal drilling parameters fluctuate with the change in geostress stress and finally remain in a stable state.When the borehole spacing increases,the minimum unloading residual stress of the rock mass after unloading under all arrangements initially increases and then decreases continuously,and the decreasing rate is less than the increasing rate,and the results are similar when the hole spacing are 0.2m and 0.25m respectively.Therefore,if the hole spacing exceeds a certain value,the unloading ability of the borehole to the rock mass decreases.According to the induced unloading law of high geostress stress rock under different drilling parameters,the finite element analysis method was applied to compare and study on the pick cutting characteristics of unloaded rock.The results show that:when the cutting angle is 30°,the whole process is under high stress,and it is not suitable for excavation of granite after unloading with holes.The cutting efficiency is better when the cutting angle is 45° and 60°.The force of the pick is the smallest at 60°,which is the best cutting angle for unloading rock with holes;at 0.08m and 0.085m pick pitches,the three-dimensional stress on the picks is relatively large,so it is not suitable to choose.When the pick pitch is 0.075m,the efficiency of cutting granite is the best;The maximum eigenvalues of the X and Z stresses on teeth and No.2 picks are smaller than those of No.1 and No.2 asynchronous cuts,so synchronous cutting is better than asynchronous cutting.By decomposing the unloading field into the initial stress,the train field,the unloading stress and the unloading strain field,the equivalent model of unloading analysis is established,and the variation of Poisson's ratio,elastic modulus,internal friction angle and cohesion with unloading time is analyzed respectively.The error of the function fitted by MATLAB is small and the function can be directly applied to engineering calculation;The physical model of rock and percussion bit is established by using ABAQUS finite element analysis software,and the energy consumption of rock breaking per unit depth is obtained by numerical simulation of rock breaking by percussion bit,which provides a theoretical and practical value for the evaluation model of rock impact performance.Based on the theory of the hybrid system,the structural analysis,model building and solution of induced unloading and continuous cutting system are carried out.The results show that the cooperative rock breaking process of the drilling and cutting includes a large number of continuous variables(displacement,speed,pressure,etc.)and discrete driving events(motor,valve,etc.),and has obvious hybrid characteristics,thus it can be defined as a typical hybrid system.Therefore,an HPN model corresponding to the rock breaking process is established based on the hybrid Petri net modeling method.The improved hybrid particle swarm optimization algorithm(MPSO)is applied to solve the above-mentioned hybrid system model,which provided theoretical support for field test analysis.Cutting experiments are carried out at the working face.The actual cutting performance of the induced unloading and continuous cutting systems under different geostress conditions is tested.The results prove that in the conditions of 40MPa and 50MPa ground stress,when the borehole unloading scheme is adopted in the working face,the tunneling performance and efficiency are greatly improved.The peak current of the tunneling motor is correspondingly reduced to realize the purpose of energy saving and consumption reduction.The rectangular unloading scheme is the best scheme,and its corresponding peak cutting current is the smallest.The hexagonal unloading scheme is slightly worse than the rectangular unloading scheme,but its unloading efficiency is better than the triangular unloading scheme.There are 79 figures,40 tables,124 references in the paper.