Abstract:Based on the problem of impact instability of gob-side entry retaining with direct-covering thick and hard roof, taking the gob-side entry retaining of 63upper 06 working face of a mine in Shandong Province as the engineering background, the research methods of field measurement, theoretical analysis and numerical simulation were used to analyze the breaking characteristics and energy release mechanism of direct-covering thick and hard roof and energy criterion of impact instability of gob-side entry retaining. Then, the mechanism of impact instability of gob-side entry retaining with direct-covering thick and hard roof was clarified. The results show that the instability evolution of the “plate-shell” overburden structure in the stope with direct-covering thick and hard roof has the characteristics of long period, wide range of overlying strata migration control and prominent dynamic load of roof breaking. Compared with the general roadway, this kind of gob-side entry retaining is more affected by dynamic load disturbance. Affected by the large-scale hanging strata of the direct-covering thick and hard roof, the movement of the “plate-shell” overburden structure will increase the advanced static load of the gob-side entry retaining, at the same time, it will transmit severe dynamic load downward. The combined action of the static load and dynamic load causes the direct-covering thick and hard roof to break and produce super-strong dynamic load, which causes the impact instability of the gob-side entry retaining. The field case shows that the initial fracture size of the direct-covering thick and hard roof is 58m,the fracture release energy is 3.5×107 J, and the energy transmitted to the gob-side entry retaining is 8.9×105 J; the periodic fracture size is 28m, there lease energy is 1.7×107 J, and the energy transmitted to the gob-side entry retaining is 4.36×105 J, which is less than the critical impact energy 1.25×106 J of the 63upper 06 gob-side entry retaining, indicating that the initial fracture or periodic fracture of the direct-covering thick and hard roof will not induce the impact displacement of gob-side entry retaining under conventional conditions. The comprehensive prevention and control measures of “uniform or low speed mining of working face+ deep hole blasting pre-splitting of direct-covering thick and hard roof+ strengthening advanced support” were put forward, and industrial tests were carried out on the coal mine site. The research results can provide some reference for the prevention and control of impact instability of gob-side entry retaining with direct-covering thick and hard roof under similar engineering geological conditions.