Application of Liquid Phase Pre-filling Technology with Fly Ash Based Adhesive Material in Fully Mechanized Mining through Old Goaf

Aiming at the problem of severe roof subsidence caused by the instability of residual coal pillars in old goaf roadways during the stoping process of coal mines, a liquid phase pre-filling technology with fly ash based adhesive material is proposed. In the engineering geological conditions of this working face, there exists a goaf formed by historical roadway mining in the direction of advancement. There are 36 sections of old goaf roadways left in the area, and their roofs are supported by residual coal pillars, these coal pillars are prone to crushing and instability under the action of advanced support pressure, resulting in an increase in the empty roof distance of the basic roof, if the basic roof cannot remain stability on its own, sharp subsidence and other ground pressure phenomena might occur. This technology integrates the originally discrete residual coal pillars with the fractured surrounding rock to form a composite structure with bearing capacity, thereby transferring concentrated stress to the deep rock mass. Through on-site engineering geological condition analysis and numerical simulation, key filling parameters are determined. The monitoring data indicate that the intensity of mine pressure behavior is decreased by 42%, and the bracket working resistance is remained stable in the range of 24-39 MPa, achieving a fundamental improvement in the roof stability in the area of old goaf roadway.