Risk assessment of Ordovician limestone water inrush in No.9 coal seam of Yangdong coal mine and its prevention and control measures

With the increasing of mining depth, intensity, scale and speed, Ordovician limestone water has become the biggest threat to the safety production of the low group seam. Based on the existing geological data, the hydrogeological characteristics of Ordovician limestone water are analyzed; the risk of Ordovician limestone water inrush is evaluated by using the method of “five maps and double coefficients” and considering the importance of effective protective thickness of floor protective layer in the evaluation results. The results show that there are no non straight through relative safety area (Area I) and non straight type relative risk area (Area II), only non straight type water inrush risk area (Area III) and straight through water inrush risk area (Area IV). According to the evaluation results, the floor grouting reinforcement is directly adopted in Area IV, and the Ordovician limestone may need to be modified in the strong water rich area; in Area III, the grouting transformation of the floor is carried out after the area with water inrush is identified first, but the Ordovician limestone is not needed. Other prevention and control measures should be subsidiary.