In this study, we investigate the application of 3D discrete element modelling (DEM) to assess the subsidence effects over a coal basin. This work focuses on the calibration of the input data for a 3DEC model (Itasca, 2013) able to predict the subsidence over three exploitation panels in a Spanish coal mine.?? This calibration was carried out by taking advantage of some valuable surveying measurements carried out in the past during the exploitation of two former panels. Firstly, the empirical method proposed by the UK National Coal Board (NCB, 1975) was used to predict conceptual subsidence profiles. After some improvements, it was used together with 2D preliminary models as a touchstone, prior to the development of the final 3D numerical model. This calibrated 3D model was used to predict the subsidence due to the exploitation of three recently exploited panels, and to assess the potential damage in a village located on the surface, close to the vertical of the panels.??Even though the calibration of this kind of models is a rather complex and time-consuming task, it was concluded that 3D discrete element methods are very strong tools to analyse and predict subsidence effects resulting from the exploitation of coal seams by longwall mining techniques.
Mining subsidence is understood as ground sinking due to the extraction of valuable materials, such as orebodies or fluids, which are located beneath and contribute to the natural support of the overlaying strata. A crucial fact associated to subsidence is the effect that ground sinking causes on buildings, farmlands, aquifers, and any other structure located above.
Due to the broad distribution of coal mines worldwide, the mechanisms and effects associated with subsidence caused by the exploitation of coal seams have been addressed for over a century. The earliest reports on subsidence date from 19th century, and are related to the extraction of flat and inclined coal seams involving relatively large extraction areas. During the first years of the 20th century, some theories were developed in order to understand the subsidence associated with mining works and to mitigate risks. The most relevant developments and understanding of subsidence effects were introduced by the UK National Coal Board's (NCB) Subsidence Engineers' Handbook. The updated methodology (NCB, 1975) is based on field observations and still used worldwide as the most widely spread empirical subsidence-prediction method.