Precise Grouting in Multi-Bed Separations of Overburden Under Curtain Protection for Isolated Coal Pillar Recovery

Traditional overburden bed-separation grouting technology often leads to issues of grout leakage and insufficient control of surface subsidence, primarily due to its poor adaptability to specific mining conditions such as isolated coal pillar recovery, the development of stratigraphic faults and fractures, or the absence of clearly identifiable key strata. To address these limitations, this study proposes an innovative multi-bed-separation precise grouting technology. The formation mechanism of multi-bed separations is analyzed, their development positions are determined, and an engineering solution for controlling surface subsidence after multi-bed-separation grouting is proposed. Key technical parameters, including grouting pressure, stability of grout-isolating layers, grouting space volume, and grout amount, are theoretically analyzed. A “three-step” precise grouting process—consisting of separation detection and verification, fracture curtain sealing, and precise grouting for subsidence reduction—was developed and applied in the 12030 isolated coal pillar panel of Xinyi Coal Mine. A total of 504,500 tons of fly ash (including cement) was grouted, of which 398,600 tons was used for precise grouting in multi-bed separations of overburden. This approach recovered 1,364,400 tons of coal resources beneath village buildings, with a grouting–extraction ratio (volume ratio) of 0.53. The technology demonstrates clear advantages: no grout leakage occurred during the process, the surface subsidence reduction rate reached approximately 75.81%, and building damage was controlled within Grade I. The results demonstrate that this technology has a significant effect on subsidence reduction and damage control, enabling safe and green mining of coal resources beneath villages under special geological and mining conditions.