Control technology of direct passing karstic collapse pillar in longwall top-coal caving mining

Karstic collapse pillar (KCP) is a special geological structure caused by the palaeo-karst subsidence in carbonate areas, and it directly affects the safe and efficient production of the coal mines. In this article, in order to improve the recovery rate and reduce relocation of the longwall panel, the water-scarce KCP in 8203 longwall face, Jinzhuang Colliery was directly passed through. Based on the field conditions of KCP and above initial mining problems, a stress changes model including four stress zones in the surrounding rock is established. They are crushing zone, plastic stress-decreasing zone, elastic stress-increasing zone and in situ stress zone from inside out in turn. A variety of measures were taken to ensure that the longwall face safely and efficiently crossed the KCP. These measures contained intensive arched shed instead of bolt-mesh-spurting supporting technique, injection of cement and marithan, respectively, into longwall face in KCP and developmental plastic coalwall at the end of KCP, hard rock blast, reduction of mining height and increase in the working face drainage ability. During the face's passing through the KCP, working resistance of the support indicated that four-stress-zone model of the surrounding rock with the KCP conformed to field observations.