Calculation Formula Derivation of Grouting Reconstruction Depth at the Top of Ordovician Limestone and Its Application

Based on the feasibility analysis of grouting at the Ordovician limestone roof,starting from the water inrush coefficient formula,the formula about depth of the grouting reconstruction at the top of Ordovician limestone is deduced,and Feicheng Mining Area under the water threat from 7,8,9,10 coal seams is analyzed respectively;7 coal mainly adopts five ash grouting reconstruction and dewatering depressurizing mining measures;8,9,10 coal layers grouting reconstruction is in accordance with the elevation of three levels. Through an example of seam grouting reconstruction, the formula of the Ordovician limestone roof grouting has played a guiding role.