Interaction between vertical stress distribution within the goaf and surrounding rock mass in longwall panel systems

摘要

Four main longwall panel systems are used in China: conventional longwall top coal caving (CLTCC), multi-slice longwall mining (MLM), high-seam longwall mining (HSLM), and longwall mining with split-level gateroads (LMSG). Theoretical analyses and physical modelling studies were carried out to investigate the interaction between vertical stress distribution within the goaf and surrounding rock mass in these systems. These studies were supported by numerical analyses and validated by field observation. The difficulty in numerical analysis for longwalls lies in goaf modelling, and research on this is rare. Reasonableness and correctness of numerical modelling is highly dependent on goaf behaviour. A complete and detailed numerical model of stress distribution within the goaf and surrounding rock mass is presented in this paper. A double-yield constitutive model, which is best fitted by Salamon's model that was obtained through laboratory tests, is used to simulate the goaf. The angle of break obtained through physical modelling was also incorporated into numerical modelling, which is closer to practice. The modelling shows that: (1) the more load the goaf bears, the less the abutment pressure and vice versa; (2) the abutment pressure, stress concentration factor, and yield zones would be larger without considering goaf behaviour; (3) goaf pressures in the curved section employing HSLM and LMSG are larger than in MLM and CLTCC; (4) when one slice is being extracted in MLM, the goaf pressure is greater than with any other methods, and the high-stress zone and yield zone are smaller; (5) the goaf edge is the most destressed zone in the entire panel system of the four mining methods. Field observation shows that the intake entry in LMSG has a favorable stress environment. Ground control problems such as severe deformation and bursts in the entry are therefore minimized, which in turn validates the theoretical and modelling analyses.