The development law of surface cracks in shallow coal seam mining through double gullies terrain

In order to protect the ecological environment of the mining area in the Yellow River Basin, the mining-induced surface crack development law was summarized from the parameters of surface crack development location and development morphology during mining of the working face passing through the double gullies terrain by using a combination of numerical simulation experiments, similar material simulation experiments and theoretical analysis in the context of the working face 125203 of Anshan Coal Mine in Miaohagu Mining Area of Fugu County. Through theoretical analysis, the relative position function T of surface cracks in shallow coal seam mining through double gullies terrain and its discriminant conditions was established and the relationship between the relative location of the surface crack growth and double gullies terrain parameters was discussed. The study shows that when the working face passes through the G1 gully, there are 4 surface cracks, with the maximum crack width of 23 cm and the maximum faulting of slab ends of 11 cm. It means that the development of cracks is ahead of the working face; when passing through the G2 gully, there are 7 surface cracks, with the maximum crack width of 79 cm and the maximum faulting of slab ends of 45 cm. The development of cracks lags behind the advancement of the working face. The results indicate that the crack development shape is greatly affected by geological conditions, gully depth, slope and valley span and other factors. The relative position function T of surface cracks is closely correlated with the crack distance ahead or behind, crack width, fault table and the total number of cracks in a single gully. The degree of mutual influence of double trenches is related to the direction of working face advance. The results of the study can provide some theoretical basis for mining under valleys in shallow coal seams.