Utilisation of surface subsidence measurements in assessing failures of rigid strata overlying extracted coal seams

摘要

In the region around a mined-out area, there is always an increase in stress in the exploited rock masses. Compression of rocks occurs around the goaf due to the increased stress [1-3]. This compression often causes measurable subsidence at the surface. Determining the amount of surface subsidence with respect to the extent and thickness of the mined-out faces is important for understanding the conditions under which the deformation of the rigid overlying strata occurred. In many cases, a strutting arch is formed over the mined-out area, and the unfaulted, rigid overlying strata do not fail. Stress concentrations and anomalous geomechanical phenomena can occur in the rock during the formation of the strutting arch. However, even in cases where the overlying strata are broken, the area of complete failure is not always extended by subsequent mining. During a complete failure of the rigid overlying strata, failure will not occur in the entire area over the goaf; rather, some of the overlying strata (overhangs) over the gob will remain unbroken. The resulting overhangs of unfaulted strata contribute to the large stress concentrations in the system [4]. The deformation of the overlying strata is caused by changes in rock mass and may include plastic, elastic, or brittle deformation. Deformation of the overlying strata produces a subsidence trough on the surface.