A new methodology for studying the spreading process of mining subsidence in rock mass and alluvial soil: an example from the Huainan coal mine, China

Alluvial soil plays an important role in ground subsidence caused by coal mining and groundwater extraction. Coal mining areas covered with thick alluvial soil (CMATASs) are widely distributed in China, and ground subsidence in these areas exhibits unique features for instance, the maximum subsidence is greater than the extracted coal seam thickness. Consequently, studies on the regularity and mechanism of mining subsidence in CMATASs have gained much attention. However, current research methods mainly involve numerical/ physical simulation and theoretical analysis, while convincing verification using field data is lacking, leading to limited research results and weak practicability. This paper proposes a new approach for studying the spreading process of mining subsidence in rock mass and alluvial soil, as well as the response of alluvial soil to mining subsidence in these areas, through the use of field data. This approach includes the following steps and assumptions: First, the overlying rock mass and alluvial soil are regarded as a dual medium; subsidence data obtained in coal mining areas covered with thin (non-)alluvial soil (N-CMATASs) are taken as the bedrock surface subsidence in the CMATASs (the lower boundary condition of thick alluvial soil). Second, ground subsidence data obtained in CMATASs are taken as the upper boundary condition of the thick alluvial soil. And lastly, by considering the measured mining-induced overburden fracture datum and geo-mining conditions in CMATASs, we can study the spreading process of mining subsidence in rocks and soils and determine the underlying mechanism as well as the response of the soil to mining subsidence in CMATASs. A major feature of the proposed approach is that the overlying rock mass and alluvial soil can be separated and the measurement data can be obtained in different boundaries, thus compensating for the shortage of measured data in current study methods. This approach was successfully applied in the Huainan coal mining area in China, and can provide a basis for accurate calculation of ground subsidence in similar mining areas.