Mechanical Properties And Mining Induced Failure Mechanism Of Alterated Rock And Disaster Control Under Deep High Stress Condition

High stress environment is one of the main characteristics of deep mining.Rock mass failure and instability mechanism and control are major scientific problems related to deep mining safety.Based on the exploitation of alteration rock type gold deposit in Sanshandao Gold Mine,northwestern Jiaodong area,this research take the alterated rock and engineering as research background,mainly focuses on three key scientific problems,namely,mechanical properties of alterated rock under deep high stress,failure mechanism induced by mining activity,and disaster control,are studied.In this research,it attempts to investigate alterated rock mechanical properties and failure behavior under triaxial high confining condition,mechanical properties and failure mechanism under true triaxial loading-unloading condition,failure evolution characteristics induced by mining stress of alterated surrounding rock,triggering mechanism,engineering criterion and disaster control theory and method of typical mining induced disaster systematically and deeply,by means of field investigation and measurement,rock mechanics tests,numerical simulations,theoretical derivation and analysis,and field verification.The main contents and results can be given as follows:(1)The general geology,tectonic geology and engineering geology of the mining area were investigated,and the joint fissures and the main failure modes of the roadway/stopes in deep mining area were systematically measured and investigated.It obtained the geological survey of the mining area,the statistical information of joints and fractures in the main production middle of Xishan mining area and fractures information in the depth of 900 m～1900 m in Xiling mining area and its typical failure modes of the surrounding rock induced by high mining stress.(2)The current direction in-situ stress field of mining area was determined through analyzing the formation of fault zones and the evolution of tectonic stress in the three stages of pre-mineralization,mineralization and post-mineralization,combined with the analysis results of plate movement,seismic focal mechanism solution and GPS crustal movement vector in Shandong area.In-situ stress measurement was carried out in Xishan and Xiling research areas by stress relief method,core redirection and acoustic emission method and hydraulic fracturing method respectively.The linear regression models were established according to in-situ stress field measurement results in the two mining area,and the distribution law of in-situ stress field was obtained.(3)Two kinds of conventional triaxial compression tests were carried out on typical alterated rock in deep mining area,under the conditions of the same alterated rock but different confining pressures and the same confining pressures but with different alteration degrees,namely pyritic sericite,monzonite and sericite granitic cataclastic rock.The tests obtained the stress and strain characteristics,energy features,failure characteristics,brittle-ductile characteristics with the same lithology but under different confining pressure condition,and the rock mechanical parameters,failure characteristics,brittleness characteristics under the same confining pressure but with the different alteration degree.The results revealed the nonlinear mechanical properties of alterated rock,failure behavior and its relationship with the degree of alteration in deep mining area.(4)After restoring true 3D mining induced stress environment of deep rock mass,three types of true triaxial tests including loading,loading and unloading,and cyclic loading and unloading tests were carried out by use the alterated brittle granite in the mining area.The research analyzed the strength and deformation characteristics,failure characteristics and mechanism of granite under loading condition;rock’s strength and deformation characteristics,failure mechanism and failure effect of surrounding rock under three loading and unloading paths;rock’s plastic deformation and damage characteristics,failure mechanism and failure effect of surrounding rock under cyclic loading and unloading conditions,respectively.The experimental results revealed the competitive failure mechanism between effective tensile and shear stress of microcrack element inside rock and the failure effect of intermediate principal stress under true triaxial condition.In particular,the cyclic loading and unloading effect of intermediate principal stress can promote the initiation of a large number of tensile cracks was discovered.(5)Considering the influence of intermediate principal stress and nonlinear failure characteristics of deep rock mass,a three-dimensional statistical damage constitutive model was derived based on the double shear unified strength theory.According to this constitutive model,RFPA3D numerical static loading tests of prefabricated fracture specimens with different dip angles and high-dip fracture specimens(>60°)under different crack depths and lateral pressure(0MPa,5MPa,10MPa)were designed to analyze the failure evolution characteristics of fractured rock mass under stress-induced action.Two typical alterated granite with low strength strong alteration and high strength weak alteration were selected to establish the numerical models to carry out the surrounding rock failure process numerical experiments at the moment of roadway excavation under the condition of different depth,lateral pressure coefficient,and the surrounding rock failure process under different loading stress path numerical experiments after roadway excavation,respectively.The evolution characteristics of surrounding rock failure were analyzed.After the roadway was formed,according to the failure form,severity and acoustic emission characteristics of surrounding rock in the loading process,the mining induced failure process of surrounding rock can be divided into 3-4 characteristic stages,and the distribution interval of stress-strength index corresponding to different characteristic stages were studied.This research also designed the numerical tests on loading failure of roadway surrounding rock under four working conditions:one group of parallel joints,two groups of parallel joints,two groups of parallel joints with random joints and three groups of parallel joints,and the failure evolution characteristics of jointed surrounding rock were analyzed.(6)In this research,the high stress disasters in the mining area were divided into three types:crack propagation caused instability,"instant type" disaster at the moment of rock excavation and "delay type" disaster caused by stress adjustment and loading after rock excavation,according to the results of rock mechanics test and RFPA3D numerical test and the site nonlinear failure of deep surrounding rock including collapse,slab crack(lamination)and rock burst.The inducing mechanism and necessary conditions of three kinds of typical high stress disasters were analyzed,the failure criterion of fractured rock mass was proposed,the critical stress criterion of brittle failure with different severity was perfected,and the control theory and method system starting from eliminating the three necessary conditions of high stress disasters was established.A new "three-step"energy control strategy of high stress disaster was proposed,and the control measures should be taken under different stress strength conditions were given.The mining induced stress sequential control method in large construction roadway or deep shaft was developed with the core idea of reasonably determined the empty span or height of surrounding rock and the time of permanent support so as to make the stress in surrounding rock fully released.It has important engineering practice significance.