Accurately distinguishing the stability of the residual coal pillars formed by the room-and-pillar mining method is significant for the safe mining of adjacent coal seams. In this study, the correlation between the rapid decrease in vertical stress and the connectivity of the internal dissipative energy core during the instability of coal pillars is revealed. Then, a new method for distinguishing the stability of coal pillars based on the above correlation is proposed, overcoming the shortcomings of previous studies that only used the plastic zone range to determine the stability of coal pillars. Based on this discriminant index and simulation method, the mechanism of residual coal pillar failure as well as the dynamic instability and expansion characteristics of multi-pillars have been revealed. The engineering method of grouting and filling to enhance the bearing capacity of coal pillars is proposed, and an in-depth study is conducted on the improvement effect of different strength filling materials on the bearing capacity of coal pillars. And the reasonable filling body strength is determined to be greater than 3MPa. The new discrimination method has important guiding significance for the analysis of coal pillar stability and the formulation of safety protection technical measures on engineering scales.

Fracturing hard roofs by ground hydraulic action is an important control technology for the strong mine pressure in the stope. In this paper, a new simulation method, “separate + interface,” is proposed, and two physical simulation experiments are conducted; the phenomenon of increased goaf pressure and decreased front abutment pressure is discovered after fracturing in the key strata, and then the influence of different fractured crack shapes on the front abutment pressure and the goaf stress is revealed. The results are as follows: Firstly, the separation under the high-level hard strata blocks the transmission of overburden load to the goaf, leading to the high-stress concentration of the coal seam, which is the main reason for the large deformation of roadways and the breakage of a single hydraulic prop in the roadway. Secondly, the weakening effect of mine pressure differs when hard rock strata are fractured artificially with different types of cracks. The peak value of abutment pressure is reduced from 24.91 to 20.60 MPa, 17.80 MPa, and 16.13 MPa with the vertical crack spacing of 20 m, 15 m, and 10 m, respectively, and the related goaf pressure is increased from 2.61 to 3.54 MPa, 3.91 MPa, and 4.34 MPa, respectively. The peak value of abutment pressure decreased from 24.79 to 22.08 MPa, 19.88 MPa, and 17.73 MPa. The related goaf pressure increased from 2.61 to 3.39 MPa, 3.81 MPa, and 4.43 MPa, respectively, with the key strata also fractured into two horizontal layers, three horizontal layers, and four horizontal layers with horizontal fractures. Thirdly, after the hard roof is fractured above the No. 8202 working face, the first breaking step distance of the main roof decreased from 112.6 to 90.32 cm, while the first breaking step distances of KS2 and KS3 decreased from 106.3 and 135.8 cm to 93.5 cm and 104.8 cm, respectively, and the goaf pressure also increased. Compared to the adjacent unfractured No. 8203 working face, the mine pressure intensity of the No. 8202 working face is significantly reduced. The research results can provide useful guidance for the treatment of strong mine pressure.