Mechanism of Ordovician limestone water inrush from the floor of caving mining face in thick coal seam and water hazard detection technology of nearly horozontal borehole

In order to study whether top coal caving can be adopted in the working face threatened by Ordovician limestone water, Huangyuchuan coal mine of Jungar coalfield was chosen to study the water inrush mechanism. The water pressure of the floor of coal seam 6^upper is 0~4.49 MPa and the thickness of water insulation layer is 54.296 m, while the average water inrush coefficient of the upper floor is 0~0.085 MPa/m which is lower than the critical water inruch coefficent. In fact, water inrush have occurred many times when tunneling across faults. It indicates that there is different water inrush mechanism in the area.The faults and fissures are developed and there are hidden karst collapsed columns in the mine, and the outflow test results in faults and karst collapsed columns shows that the dominant structural plane in the north-east direction controls the water enrichment of Ordovician aquifers. In working face 01 in 21 panel of 6^upper coal seam of Huangyuchuan coal mine, the maximum floor failure depth measured by pumping test was 34.9 m. This paper expounds the mechanism of water inrush caused by coupling coal floor damage and Ordovician strong seepage channel, which changes the traditional understanding of water inrush through vertical water-conducting from Ordovician aquifer. Nearly horizontal directional long holes have been drilled to explore and reinforce the vertical strong seepage channels, so Ordovician limestone water hazard in the process of mining is solved.