Research On Migration Law Of Mining Overburden Based On Particle Discrete Element Method

The coal resources in Xinjiang are abundant,but the geological environment in this area is extremely complicated.Under the influence of mining,the rock layers are prone to produce water and sand guiding channels,which induces water and sand inrush disasters.Therefore,it is of great significance to study the failure characteristics of rock mass and the development law of water flowing fractured zone of coal seam roof.In this paper,the Dananhu mining area in Xinjiang is taken as the research object.And based on the laboratory tests and particle discrete element numerical simulation,the basic mechanical properties of rocks and the evolution law of fractures are analyzed.Based on the modified bond model,the numerical model of the roof rock stratum in Xinjiang mining area is established,and the movement and breakage law of the coal seam roof under the influence of mining is studied.The main research contents are as follows:(1)Research on the relationship between particle discrete element simulation parameters and macroscopic parameters.The effect of several different mesoscopic parameters such as particle contact modulus,friction coefficient,stiffness ratio,parallel bond modulus,parallel bond normal strength and tangential strength on macroscopic mechanical properties was studied one by one.The function fitting analysis is used to analyze the influence degree of the mesoscopic parameters on the macroscopic response,and the selection of the mesoscopic parameters is proposed.(2)Research on mechanical strength characteristics and failure law of sandstone.Through the uniaxial compression and the Brazilian splitting test,the basic mechanical properties of sandstone are studied,and the corresponding numerical models are established to compare with the indoor test to verify the validity of the simulation.Furthermore,the evolution law of fractures in the failure process of the initial fracture angles of 0°,30°,45° and 90° is studied.It is found that the existence of initial fracture has a great influence on the strength and deformation law of the model.The smaller the fracture angle is,the more obvious the stress concentration phenomenon is,and the greater the influence on the strength of the model.(3)Research on damage constitutive model and PFC model modification of rock mass.Simplify the extended model of wing fracture under uniaxial compression and determine its stress intensity factor and damage variable.Based on the strain equivalence principle,the constitutive equation considering the initial damage is established,and the internal bond model is modified in PFC.The variation of the strength of rock samples and the development of fractures in different bond models were analyzed.The simulation results show that the modified bond model is easier to be destroyed and cracks are more likely to occur inside the model,which can better characterize the characteristics of weak bond and low strength of strata in Xinjiang mining area.(4)Research on movement and failure law of roof strata under mining conditions.Taking the Dananhu mining area in Xinjiang as an example,a numerical model was established to simulate and analyze the breaking behavior of the coal seam roof during coal mining.Under the mining conditions,the influences of the different coal seams mining height on the fracture development characteristics,the variation of the water flowing fractured zone height and the moving mechanism of the overlying strata are analyzed.It is found that the distribution of fractures in the roof strata presents a "ladder" type feature,and the number distribution curve of the fractures is "M" type.The development angle of the fracture is mostly vertical,and the dip angle is mostly at a high angle.With the advancement of the working face,the settlement of the roof rock layers is gradually increasing.The settlement curves all show a concave distribution with small intermediate and large ends.The closer to the middle of the goaf,the larger the settlement of the rock layers.This thesis includes 69 figures,11 tables and cites 101 references.