Experimental Study on the Fracture Distribution Characteristics of the Overlying Strata in an Abandoned Gob

Abstract A lot of gas resources remain in the abandoned gob. The overlying strata of the abandoned gob are the main places for gas storage and flow. The fracture distribution characteristics of the overlying strata have a significant impact on the gas migration. The mining similarity simulation test device of a plane stress was used to study the deformation and failure characteristics of overlying strata in an abandoned gob. The caved strata of the abandoned gob formed a trapezoidal distribution, and the caving range decreased gradually with an increase in distance from the coal seam. The strata collapsed in the caved zone, whereas the strata collapsed mainly on the bending subsidence in fractured zone. The subsidence curves of caved strata showed a lower concave shape, and the maximum subsidence existed in the middle of the abandoned gob. The caved strata subsidence decreased with an increase in distance from the coal seam. The horizontal fractures were dominant in the fractured zone. The abscission rate of the end mining position was greater than that of the start mining position. Large numbers of vertical fractures existed in the caved zone. The development degree of vertical fractures near the end mining position were larger than that of the start mining position, and the width of the gas-conducting fracture was more than three times that of the start mining position. The development degree, quantity and connectivity of the fracture in the end mining position were better than those in the start mining position.