STABILITY CRITERION CALCULATION OF LIMESTONE ROCK ROOF OF THE 15^# COAL IN WOZHUANG MINE

With the exhaustion of the 3^# coal resource in JinCheng mining area, the 15^# coal is urgently to be mining in many mines. However the roof of 15^# coal consists of thick and hard limestone. The excavation in it may form a large bare area and consequently cause sudden collapse, which may lead to a series of safety problems. According to the occurrence of 15^# coal in WoZhuang mine, the paper determines the main roof by the key strata theory, and then analytically evaluates the bending deflection of the main roof by the elastic foundation beam theory. Additionally, the Fourier integral transformation method is adopted to calculate the floor heave deformation and then the caving height of immediate roof is also calculated. The corresponding mining width is determined by the criterion that the sum of the main roof bending deflection, floor heave deformation and the caving height should equal to the goaf height, and this is used to evaluate the stability of limestone roof. The results show that the main roof rock layer will contact the collapse rock mass when the immediate roofs of 1^# and 2^# limestone immediately collapse and the mining width is up to 22.55m. This indicates that the exploitation of 15^# coal in Wozhuang mine is safe. The method employed in this paper has a reference significance for the excavation of JinCheng mining area and other coal layers with the similar hard roof condition.