Damage Mechanism And Stability Analysis Of Stope Surrounding Rock Under Deep High In-situ Stress Condition

With the continuous exploitation and utilization of metal minerals,many mines at home and abroad have entered the stage of deep mining,and the problem of "three heights and one disturbance" in deep mining has gradually become prominent.It is of great theoretical and engineering significance to study the rock-breaking mechanism of deep rock under the high in-situ stress environment and the impact combination action caused by blasting to ensure the safety of deep mining of metal mines and improve the production efficiency.Therefore,this paper takes the-1005m deep mining of Xishan mining area of Sanshandao Gold Mine of Shandong Gold Group as the research background.Firstly,the in-situ stress measurement and the measurement of physical and mechanical parameters of rock foundation were carried out to obtain the data of in-situ stress and rock mechanical properties.Then,by means of theoretical analysis,laboratory test and numerical simulation,the damage process and strength weakening law of rock under the synergistic action of dynamic and static loads are studied.Finally,the law of damage weakening of surrounding rock strength was introduced into the numerical simulation process to study the stability of stope under the combined action of high in-situ stress and blasting impact.The main contents are as follows:(1)According to the basic principle of the stress relief method,the hollow inclusion strain gauge was used to measure the original rock stress from-690m to-1005m depth of Sanshandao Gold Mine,and the law of the evolution of the original rock stress with depth was obtained.Through laboratory tests on samples collected in the field,the parameters such as compressive strength,tensile strength,shear strength and wave velocity of deep rock are obtained.(2)Combined with the actual situation of deep stress distribution,a reasonable axial pressure-confining pressure ratio was set,and a confining pressure Hopkinson pressure bar(SHPB)test device was used to carry out cyclic impact tests under different confining pressures on samples collected from the engineering site.The effects of different impact strength and confining pressure on mechanical parameters such as stress,strain,strain rate,peak stress and elastic modulus of rock are analyzed.The law of transmission,reflection and absorption of energy carried by stress wave under cyclic impact is analyzed.(3)The impact damage model considering voidage and the crack propagation theory in damage mechanics are introduced,and the relationship between single impact damage and cyclic impact damage is established.According to the characteristic stress of different stages in the process of single cyclic damage,the cyclic impact was divided into five damage accumulation grades,and the damage accumulation mechanism was analyzed from the perspective of the evolution of internal cracks by combining with the theory of damage mechanics.The stress threshold division method based on the evolution of energy absorption rate was established,and two important stress thresholds of original crack closure stress and crack steady growth were defined.The effects of different confining pressures and different impact loads on the two thresholds were studied.(4)Based on the energy absorption calculation in the Hopkinson test,the damage variable in the cyclic impact process was obtained,and it was found that the evolution trend of the damage variable in the cyclic impact with different peak stresses was significantly different.The damage process under the cyclic impact condition is divided into two types:the weak damage cumulative failure,in which the crack expands steadily and becomes connected gradually,and the strong damage cumulative failure,in which the crack expands stably and then accelerates.The polynomial fitting and the inverse function fitting of Logistic function were used to fit the damage variables in the process of weak damage accumulation and strong damage accumulation,respectively.Good fitting results were obtained,and the evolutionary relationship between the damage variables and the impact times was established from the perspective of energy absorption.(5)Stress numerical simulation software,on the basis of static analysis to introduce blasting impact damage on the strength of surrounding rock weakening.According to the room-pillar mining process of Sanshandao Gold Mine,three kinds of chamber with section sizes of 6m*6m,9m*9m and 12m*12m are set for simulation.Different mining sequences of 54m span single pressure free arch and 27m span double pressure free arch were set from the perspective of constructing pressure free arch to simulate the mining process.Thus,it provides a theoretical basis for optimizing the mining process and realizing the goal of high efficiency and low waste mining.