Experimental study on the law of energy accumulation before failure of coal-rock combined body

The coal measures strata are composed of many kinds of rock strata, and the mechanical properties of each rock strata are different, and their energy accumulation capacities are also different, which leads to the uneven energy distribution in the coal-rock system.In order to explore the law of energy accumulation in the coal-rock system and determine the key layers of energy accumulation leading to rock burst, uniaxial compression tests were carried out on combined bodies with different lithology and coal-rock ratio.The results show that:① with the increase of the ratio of coal-rock, the failure area of the combined bodies gradually changes from overall failure to semi-global failure to local failure, and the failure type gradually changes from “fragmentation” complete failure, “Y type” semi-complete failure to “point type” incomplete failure.② With the increase of coal-rock height ratio, the strength and elastic modulus of the combined bodies gradually decrease, and the pre-peak energy increases gradually, and the rock component can improve the strength and elastic modulus of the combined bodies to a certain extent, and the greater the hardness of the rock component, the greater the strength and elastic modulus of the combined bodies, but the less the pre-peak energy of the combined bodies.The impact energy index of coal-rock combined bodies is between 5.164 and 6.049,which has a strong impact tendency.③ The mechanical model of coal-rock combined body was constructed, and based on the analysis of coal-rock structure and mechanical properties, with the help of the stress-strain curves of combined bodies and components, the formula for calculating the energy distribution of the same diameter coal-rock combined body and non-same diameter coal-rock combined body before failure was derived.④ The proportion of accumulated energy of coal components in fine sandstone-coal combined bodies is between 60.009% and 94.54%,and that of fine sandstone is between 5.46% and 40.005%.The proportion of accumulated energy of coal components in coarse sandstone-coal combined bodies is between 54.55% and 89.64%,and that of coarse sandstone is between 10.36% and 45.45%.The energy accumulation ratio of coal components of ternary combined bodies is 66.13% and 78.48%,that of coarse sandstone components is 19.35% and 13.29%,and that of fine sandstone components is 14.52% and 8.23%.The proportion of accumulated energy of coal components in all combined bodies is more than 50%,and coal components are the main carriers of energy accumulation.The order of energy accumulation of each component of the combined body is coal > coarse sandstone > fine sandstone, and the weak rock(coal seam) with low elastic modulus has stronger energy accumulation ability.With the increase of the ratio of coal-rock, the energy proportion of coal components also increases.⑤ The law of energy accumulation of coal-rock combined bodies was analyzed theoretically, and the prone mechanism of rock burst in deep mining was revealed.Aiming at the energy bearing structure of hard roof-coal-hard floor, from the point of view of energy accumulation layer, two energy slow control concepts and measures of direct release of energy and indirect release of energy were put forward, and the engineering practice was carried out.The results of micro-seismic monitoring and roadway deformation observation show that the direct and indirect energy release measures destroy the energy bearing structure, release the energy effectively and prevent the occurrence of rock burst.