Deformation and failure mechanism of karst mountain with deep and large fissures under multi-coal seam mining: Insight from DEM simulation

Taking the Pusa Collapse in Nayong County,Guizhou Province, China as a case study, this paper investigates the impact of multi-layer coal mining on karst mountains characterized by deep fissures. Based on field investigations and employing discrete element numerical simulations, the deformation and failure mechanisms of karst mountain containing deep and large fissures under multi-seam mining conditions was investigated. The influence of the direction of coal seam extraction and the sequence of extraction between multiple coal seams on the failure modes of karst mountain with deep and large fissures was studied. The results indicate that underground mining primarily manifests in the development of mininginduced fissures in the mountain body, subsidence and deformation of slope masses, and triggering the expansion of existing fissures, further driving overall deformation and damage to the slopes. Deep and large fissures control the deformation and failure modes of the slopes, with closer and longer deep and large fissures near the slope surface exerting greater influence on the slope mass. The impact of mining in the same coal seam direction on the slopes is mainly reflected in the process of slope deformation and failure. Downslope mining directly leads to overall subsidence of the slope mass, squeezing the front and lower parts of the slope mass. Upslope mining initially causes the foot of the slope to sink and the entire slope mass to move outward, and continuous mining leads to overall settlement and downward compression deformation of the slope. The sequence of mining between multiple coal seams mainly affects the overall and local deformation values of the slope mass.Downward mining leads to increased overall subsidence of the slope mass and exacerbates the backward tilt of the slope top.