Research On Impact Energy Index And Damage Law Of Coal And Rock Mass Based On Peridynamics

In order to effectively prevent the occurrence of rock bursts and provide a safe environment for energy mining,laboratory experiments,theoretical analysis and numerical simulation are used to analyze and calculate the entire process of coal and rock mass failure under load conditions.Combined with the existing indicators for judging the occurrence tendency of rock burst:rock elastic deformation energy index(W_ET)and rock impact energy index(W_CF),the advantages and disadvantages of the two indexes are analyzed,and a new index for judging the impact tendency—actual impact is derived.Energy Index（W_X）.The more mature judgment index-roof bending energy index(U_WQS)is used to verify the accuracy of the deduced actual impact energy index（W_X）.The method of peridynamics is used to deduce the PD damage constitutive force function,based on the lammps software.The change of energy when rock burst occurs is analyzed to verify the validity of the experimental results and the deduced actual impact energy index（W_X）.The main research contents and achievements are as follows:（1）In the test of elastic energy and impact energy experiments,the impact test of a variety of materials was carried out,and the results showed that the impact resistance of fine sandstone was the weakest,followed by coarse sandstone,mudstone,bottom plate coal seam and roof coal seam;the combined structure of coal rock with a ratio of 1:2 was stronger than that of other proportional combination structures,and the corresponding upper rock and lower coal combination was the strongest,that is,the impact tendency was the strongest at the location where the ratio of the top slate layer to the coal seam was 2:1,according to the judgment criteria of W_ETand W_CF.The calculated values are greater than 7.01 and 3.44 as strong impact tendencies,and the W_Xjudgment values are 2.59,which can provide a reference for the prediction of ground pressure of different rock impacts in actual engineering.（2）In the bending energy experiment of the combined roof of different prefabricated inclination rock samples,the bending energy value of the top plate with a degree of 0 degree to the horizontal plane is the largest,followed by 30°and 60°,and the rock sample with the horizontal plane of 0°is more likely to have impact pressure,of which the fine sandstone rock layer is the most likely.The tendency to impact ground pressure calculated by the calculation of the top plate bending energy index(U_WQS)is weak impact tendency,which is the same as that of the new actual impact energy index（W_X）constructed,indicating that the actual impact energy index（W_X）constructed is valid.（3）Based on PD theory and bond-based PD theory,it is analyzed from the perspective of energy,and a PMB model is constructed.The variable energy density formula of PD theory for discrete processes in the near-field region is defined,and the problem of solution accuracy in macro-scale simulation is solved.The damage variable is established.The relational expressions of D and PD constitutive force function f are obtained through mathematical fitting to obtain the damage variables of peridynamics,and the criterion of bond fracture on the microscopic level of brittle materials is established.（4）Under the loading conditions of different specimens,the"X"type stress distribution state will occur when the coal rock monomer is destroyed,and in the coal rock composite structure,with the increase of the coal body component,the more obvious the"X"type stress distribution state.Moreover,the coal-rock composite structure is more likely to concentrate stress in the coal body;the prefabricated inclination has a greater impact on the load capacity of the simulated specimen,and when the prefabricated crack inclination angle is 0°,the impact is minimal,and the load capacity is gradually reduced with the increase of the prefabricated crack angle.The angle of the prefabricated crack will affect the distribution of the upper and lower primary cracks and the internal energy,the larger the inclination of the prefabricated cracks,the easier it is to produce the main crack at the crack tip;and the calculation of the W_Xindex of different specimens to determine the impact tendency is more consistent with the experiment,indicating that the experimental results are accurate and the actual impact energy index（W_X）constructed is real and effective,which can better predict the occurrence of impact ground pressure.