A review of overburden fracturing and changes in hydraulic characteristics due to longwall mining

Longwall mining is a major mining method to extract thick, flat-lying and extensive seams. Due to the nature of this mining method, the overlying strata move continuously downwards into goaf and as a result, surrounding rocks are distressed, deformed and fractured. In the near area above the mined coal seam, both vertical and horizontal fracturing networks are evident, however within the higher zones, bed separation and slippage are the dominant displacements. The enhanced cracks alter hydraulic characteristics (porosity and permeability) of the rock mass, consequently disturbing the groundwater and surface water flow regime. There have been various techniques utilised to study mining-induced fracturing mechanisms and changes in water flow systems. They mainly include empirical, physical, analytical and numerical approaches. Of note is that due to the complexity of the issue and difficulties in the implementation of costly and time-consuming in-situ measurements, currently, numerical simulation is a popular approach. The aim of this review paper is to present the current state of the art in mining-induced goaf overburden fracturing and its interaction with groundwater and surface water