Study On The Influence Mechanism And Prevention Measures Of Stress Concentration On Surrounding Rock Stability In Block Caving Undercutting

Block caving is a large-scale,low-cost and high-efficiency mining method,and its economic efficiency is comparable to that of open pit mining,which is the preferred method for low-grade and large-scale mineral resources development.The formation mechanism and transfer law of the stress concentration in the surrounding rock in front of the undercut advance line are the core points of the study of block caving,which is the key factor to determine the service life of the extraction structure.In this paper,we analyze the formation mechanism,influencing factors and distribution law of high stress in front of the undercut advance line,and combine mine pressure theory,elastic-plasticity theory and rock bearing theory to reveal the transfer of high stress in front of the undercut advance line to the extraction structure on its stability.(1)Systematically reveal the formation mechanism,calculation formula,influencing factors(rock capacity,unedercut level depth,undercut advance distance)and distribution characteristics of high stress concentration in front of the undercut advance line,and apply elastic thin plate theory to reveal the relationship between the position of adjacent undercut advance lines(spacing,row distance)on the influence law of stress concentration in front of the undercut advance line,and theoretically analyze the impact law of undercut advance line.Theoretically analyze the deformation and damage mechanism of the surrounding rock of the roadway in front of the undercut advance line and its influencing factors.(2)Applying the theory of elastic mechanics half-plane body,we analyzed the distribution law of high stress transfer to the extraction structure(in the state of unexcavated poly mine trough)in front of the bottom pulling line,applied Mathematic software to visualize the stress law of the extraction structure,analyzed the influence law of stress concentration coefficient and horizontal depth of undercut level on the stress distribution of the extraction structure,and theoretically provided theoretical guidance for the selection of undercut strategy,excavation timing and location of poly mine trough.Theoretically,it provides theoretical guidance for the selection of the undercut strategy and the excavation timing and location of the polygon.(3)Based on the theory of plastic slip line field,the influence range of the deformation damage of the extraction structure is analyzed,and the MohrCoulomb strength criterion is combined to analyze the influence mechanism of the compressive strength of the rock mass,the undercut advance distance and the horizontal depth of the undercut on the plastic slip damage of the extraction structure,and the excitation conditions of the slip damage of the bottom structure are analyzed,and the principles of the extraction structure arrangement are determined theoretically.(4)Based on the theory of ultimate equilibrium,and the theory of rock base bearing capacity,combined with the Mohr-Coulomb strength criterion,the mechanism of influence of rock mechanical parameters(internal friction angle isφ,cohesion c)and the height of mine release on the plastic slip damage of the extraction structure is analyzed;based on the theory of rock unloading,the mechanism of damage to the extraction structure by the mine release process is revealed.Combining the above theoretical studies,it is revealed that the service life of extraction structure with Teniente type and Henderson type arrangement(the undercut direction forms an angle arrangement with the outgoing vein)is higher than that of herring bone type and branch herring bone type arrangement.(5)Applying FLAC3D numerical simulation software,the influence law of bad undercut,undercut way and change of undercut level burial depth on the stability of extraction structure was analyzed.According to the numerical simulation results:the conclusion that the theoretical analysis of forward undercut is more beneficial to the extraction structure stability than the backward undercut is verified;the conclusion that the theoretical analysis of the deeper the horizontal burial of the undercutting is,the more unfavorable to the extraction structure stability is verified;the conclusion that the bad undercutting will cause the stress state of the upper part of the mine column under pressure and the lower part under tension,and is unfavorable to the extraction structure stability is analyzed.(6)Based on the theoretical analysis and numerical simulation results,we provide theoretical basis for the support of the undercut level and extraction level of the Pulang copper mine,and carry out the test of FRP anchor support and the test of undercut roadway collapse treatment method in the field and achieve good results,providing theoretical support for the application of block caving.