Research on overburden and ground surface cracks distribution and formation mechanism in shallow coal seams group mining

Abstract

In order to study the coal mining cracks (or fissure) formation and development mechanism, taking the typical shallow coal seam group mining in Northern Shaanxi as the engineering background and using the method of physical simulation, numerical calculation and field measurement, it is concluded that the mining induced cracks in overburden are mainly the upward cracks along the gob edge and roof separation cracks in the caving zone. The surface cracks are mainly the permanent boundary cracks of open cut and stop mining line, periodic parallel cracks along with mining face and sectional coal pillar boundary cracks. The coal pillar boundary cracks which are the longest in distribution is the main object of the crack control. Under the coal seam group mining, the roof caving step increase by 18%-30%, and the subsidence coefficient of the ground surface is reduced. After the repeated mining of the coal seams, the boundary cracks are easily developed and are influenced by the position of the upper and lower coal pillars. By reasonably arranging the coal pillars, the stress concentration caused by the coal pillar can be decreased, the uneven surface subsidence and cracks can be reduced.