An FDM-based Dynamic Simulation Method Of Complex Mechanical Behavior Of Rock Masses Induced By Underground Mining

Underground mining could strongly disturb the surrounding rock masses and induce movement and failure of the relevant strata and ground surface,which may further result in detrimental impacts on adjacent ground infrastructure and threaten the safety of production.To control the detrimental effects,it is critical to analyze and predict the movement patterns of the overlying strata and ground surface induced by underground mining.After mining out the coal seam,the deformation,cracking,bed separation,and caving of overlying strata may occur with the formation of continuous deformation zone,surface cracking zone,fractured zone,and caved zone.The "Four zones" are dynamically developed during the mining process,and the mechanical properties in different regions correspondingly alter.The current methods of underground mining simulation are lack of sufficient consideration to adaptive adjustment of mechanical parameters of disturbed rock masses.Besides,the scopes of the "Four zones" and the location of bed separation are strongly be affected by human intervention.Thus,the simulation may bring inexact numerical results.In addition,the numerical simulation method based on continuous medium is still difficult to simulate the discontinuous phenomenon in underground mining.In this paper,we first analyze and summarize the mechanical behavior of the strata in response to underground mining.Then we focus on studying the FDM-based dynamic simulation method of complex mechanical behavior of rock masses induced by underground mining.This method is mainly composed of adaptive adjustment of mechanical parameters of disturbed rock masses,dynamic zoning and dynamic simulation of bed separation.Finally the proposed method is applied for the study site in Taixi coal mine.The following results and new understandings are obtained:(1)The method of adaptive adjustment of mechanical parameters of disturbed rock masses during underground mining simulation process is proposed and realized.The simplified complete stress-strain curve of rock mass is used to describe the process of rock mass strength deterioration in underground mining.Based on that,the relationship between the plastic strain of rock mass and mechanics parameters is established.The proposed method can adjust the mechanical parameters in the underground mining simulation based on the calculated plastic strain of the disturbed rock masses.(2)The dynamic zoning method is proposed and realized.According to the characteristics of deformation and failure of the overlying disturbed rock masses in the mining process,the zoning criterion is established.Combining with the mining process simulation,adaptive adjustment of mechanical parameters of disturbed rock masses and the zoning criterion,the dynamic zoning simulation algorithm is implemented,which is capable of reflecting the dynamic zoning characteristics of the overlying disturbed rock masses during mining simulation.(3)The dynamic simulation method of bed separation in overlying strata is proposed and realized.According to the characteristics of deformation and failure of the overlying disturbed rock masses and displacement conditions of adjacent strata in the mining process,the bed separation criterion is established.Combining with the mining process simulation and the bed separation criterion,the dynamic bed separation simulation algorithm is implemented,which is capable of reflecting the dynamic development processes of development-expansion-closure of bed separation in the underground mining simulation.(4)On the basis of the above,an FDM-based dynamic simulation method of complex mechanical behavior of bock masses induced by underground mining is formed.The proposed method is applied for the study site in Taixi coal mine to simulate the dynamic development processes of the "Four zones" and the bed separation in mining process.The simulation results achieved in this work indicates that the proposed dynamic simulation method is capable of analyzing and predicting the dynamic development characteristics of the overlying disturbed rock masses during underground mining effectively.