Longwall Mining–Induced Damage and Fractures: Field Measurements and Simulation Using FDM and DEM Coupled Method

Comprehensive tests were conducted on a longwall face in China to study mining-induced strata movement and fractures. The first and periodic weightings of the main roof were both captured by microseismic (MS) monitoring and support resistance recording and were 64 and 20 m, respectively. Based on the fracture detection through hydrological observations in a borehole, the roof is clearly divided into three zones: water-conductive zone, horizontal fracture, and continuous zone. Following the field investigation, an innovative finite-difference method (FDM) and distinct-element method (DEM) coupled numerical simulation method was proposed, which features simulating the progressive failure of the rock mass from intact to blocky. The numerical study shows that the proposed coupled method can give reasonable explanations for all in situ tests and handle the progressive caving of the rock layers, as well as the accompanying MS activities and response of the hydraulic supports. The proposed coupled method has advantages over a continuum or discrete method in coal mining simulation. Compared with a continuum method, the coupled method can simulate the deformation and collapse of the overburden strata, whereas the continuum method is only applicable before the first weighting of the rock layer, after which it gives wrong results. In contrast, compared with a discrete method where the blocks are factitiously set before and their sizes are mandatory, the coupled method allows the blocks to form automatically based on the failure state of the rock mass.