Abstract: Chenghe No. 2 Coal Mine is located in Chenghe mining area of Weibei. Deep mining is seriously threatened by
water disaster of strong aquifer in karst fissure of Ordovician limestone. With the depletion of the shallow resources,the mining
level of the mine continues to deepen,the water pressure on the floor of the working face increases,the thickness of the floor of
the water-resisting layer decreases,and the safety mining of the mine is affected. Aiming at the water disaster of floor in mining
process,the horizontal directional drilling technology is used to reconstruct the top aquifer of Ordovician limestone. In order to
further improve the reliability of Ordovician limestone aquifer reconstruction by grouting,considering that the floor failure zone
has a certain water-blocking capacity and that the mechanical properties of the floor rock have an influence on the water-blocking
capacity,based on the theory of grout diffusion,the drilling hole layout is designed by calculating the grouting treatment
layer on the top of Ordovician limestone with the improved water inrush coefficient method. After the completion of grouting,the
analysis of grouting,geophysical and drilling comprehensive evaluation of treatment effect and the feasibility of mining under
pressure was done. The results show that the top of the Ordovician limestone aquifer is rich in water,but the relative water-resisting
layer is transformed after grouting,which cuts off the hydraulic contact between the working face and the Ordovician
limestone aquifer. The maximum water inflow of the verification hole is 8 m³ / h,and the grouting transformation effect is good,
which can achieve safe and pressurized mining of the working face.

Key words: grouting reconstruction,treatment layer,floor water inrush,mining under pressure,water inrush coefficient