Experimental Study On Energy Conversion Law Of Coal And Rock Composite Structure Failure Process

China’s coal resources are abundant,but the mining conditions are complex,and the average mining depth has reached 700 m.With the increase of mining depth,the mines and gas outbursts,impact pressure,water seepage and other dynamic disasters emerged.In shallow mining,various dynamic disasters usually occur independently.After entering deep mining,the interaction between various dynamic disasters in coal mines begins to appear,showing a composite occurrence of disasters.The interaction of various factors in the occurrence of compound dynamic disasters makes the mechanism more complicated and more difficult to control.Therefore,it is of great significance to carry out theoretical and experimental research on coal-rock composite dynamic disasters under deep mining conditions.In this paper,the combination of theoretical analysis and experimental research is used to study the energy accumulation and transformation laws of coal and rock composite structure failure process.The main conclusions are as follows:(1)In the study of the failure characteristics of the combined specimens,it is found that the strength of the combined sample is between the rock and the raw coal,and it is proportional to the lithology and rock height ratio;The damage mainly occurs in the interior of the coal body,and the cracking is the main cause,and the cracks of the coal body tend to expand toward the rock mass through the interface;At the peak damage point of the sample,the strain of the rock mass reaches an extreme value and a "strain rebound" phenomenon occurs.(2)Using the elastoplastic mechanics,mining rock mechanics and other related theories,the critical conditions for the instability failure of the combined structure are proposed.(3)Based on the elastoplastic deformation and energy theory of coal and rock mass,the calculation of the proposed research index shows that the elastic strain energy accounts for 3%-5% of the energy accumulated before the sample peak,accounting for 25%-50% of the accumulated energy of the rock itself.the ratio increases as the strength of the sample increases.(4)Based on the theory of fragmentation and the new surface theory,the new surface area and the converted diameter of the different combined samples which destroyed are calculated by the particle size analysis results of the broken coal body,and the degree of damage is characterized by the degree of fragmentation of the sample,then a quantitative way of characterizing the effect of elastic energy is obtained and an exponential relationship was found between the elastic energy and the newly added surface area.