Criterion of Grouting Pressure in Regional Advance Grouting Treatment to Prevent Water Disaster from Karst Aquifers in Coal Seam Floors.

The deep mining of coal mines in North China faces the serious threat of water inrush from karst aquifers in the coal seam floors, and regional advance grouting technology (RAGT) is an effective means to prevent and control such disasters. However, it is difficult to choose the grouting pressure during the implementation of RAGT, and excessive grouting pressure will lead to the splitting of karst fracture and reduce the grouting effect. In this study, based on the Bernoulli equation, the relationship between the ground grouting pressure and critical grouting pressure during grouting is established. Based on the Hoek-Brown (H-B) strength criterion and a fracture mechanics analysis of hydraulic fracturing, a theoretical equation of the critical grouting pressure for fracture splitting during grouting is obtained. The determination methods of the main parameters, such as the length of the fracture, internal friction angle, and H-B constant of the intact rock and geological strength index, and their effects on the critical grouting pressure, are discussed. The results show that the joint influence of the H-B constant and geological strength index of the intact rock is the key factor influencing the critical grouting pressure. The theoretical research results are applied to the Xujiazhuang limestone grouting reinforcement project of the floor of coal seam 11 in the Zhaoguan coal mine. The critical grouting pressure of the aquifer is determined to be 14.54 MPa, which guides the smooth implementation of the project.