Reasoning research on stability of room coal pillar based on cellular automata

The large area of room mining goaf remains in the shallow coal seam of the western mining area. As the only bearing system in the gob, the stability of coal pillars determines the stability of the entire gob, thereby affecting the safe mining of the lower coal seams. In order to study the evolution law of the failure and the instability of coal pillar in shallow-buried gob, the 8 Moore cell-automata model of coal pillar in shallow-buried gob was established by using the theory of cellular automata theory. Combining with the influence of confining pressure on the energy storage limit of coal and rock units，the coal-pillar cell was divided into four levels, which defines the distribution law of energy storage limit of the two-dimensional cellular model of coal pillar and analyzes the evolution law of the failure and instability of room-type coal pillars from the perspective of energy transfer between cells. The proposed theoretical model was validated by numerical simulation results of coal pillars in the coal seam type gob of No.3-1-1 of Shigetai Coal Mine and field studies.The results show that: ①There are two evolution modes for the failure and instability of coal pillars. In the I-type evolution mode, the feature of elastic core region of the coal pillar is approximately rectangular, while the elastic core area of the coal pillar is approximately a convex polygonin the type II evolution mode. ②Due to the existence of the "equivalent cell" in the typeⅡevolution model, the energy storage limit of the whole cell is higher than that of the I-type evolution mode. Under the same evolution rule and the same generalized energy applied externally, the stability of the Ⅱ-type evolution mode is relatively better. ③The numerical simulation results show that the coal pillar failure evolution law of the No.3-1-1 coal seam gob in Shijietai Coal Mine is consistent with the evolution characteristics of theⅡ-type evolution mode, and the elastic core area after the calculation balance is also convex. ④The field studies show that the morphological features of the elastic core region of the horizontal section of the coal pillar are consistent with the result of Ⅱ-type evolution mode, which verifies the correctness of the evolution model of the room coal pillar.