ABSTRACT:
Overburden grout injection is a cost-effective technology used to control coal mine subsidence by injecting fine waste material (e.g. flyash) into the overburden during longwall mining. The injected material fills the bed separation gaps formed above the mining horizon and reduces the propagation of the overburden movement to the surface. A systematic laboratory study was carried out to investigate the flow properties of flyash grouts and their injectability into open fractures. To facilitate this study, a laboratory injection rig was designed and constructed. A series of laboratory injection tests were conducted to investigate the mechanism of grout flow and solid settlement in open fractures, and the effects of grout solid content and fracture aperture on injection process. The results of the tests are discussed in this paper. A key finding from the laboratory studies was that the flyash grout always flows in channels, breaking through the previously settled solid ashes.
1 INTRODUCTION
Overburden grout injection is a cost-effective technology used to control coal mine subsidence by injecting fine waste material (e.g. flyash) into the overburden during longwall mining. The injected material fills the bed separation gaps formed above the mining horizon and reduces the propagation of the overburden movement to the surface (Guo et al. 2007). Grout made of flyash and water is typically used for the overburden grout injection mainly due to its low cost and availability, particularly where coal firing power stations exist. However, flyash particles can settle quickly in the grout, which may lead to blockage of the injection system and limit the distance of filling in a narrow fracture. Many researchers have in the past carried out studies on using flyash for geotechnical grouting (e.g. Anon 1997, Nichols & Goodings 2000), mine backfills (Gray et al. 1997), and coal seam fire control (Colaizzi 2004).
