Stability of end slope pillars and slope deformation under irregular loads

To study the impact of irregular loads from the overburden dumping site on the stability of the coal pillar and slope in open-pit coal mining, this study selects Laiyegou Open-pit Mine in Ordos of Inner Mongolia as a case study. Based on the irregular geometric shape of the dumping site, the Mark-Bieniawski formula is optimized. Coupled with the physical and mechanical parameters of the geotechnical body, numerical simulations of the coal pillar and slope under the load conditions of the dumping site are conducted. Rhino software is used for three-dimensional modeling and grid division, and FLAC^3D is employed for calculation and analysis based on displacement changes, plastic zone distribution, and slope sliding. The research results show that when the dumping site load is considered, the width of the supporting coal pillar is 2.9 m and the isolation coal pillar width is 8.88 m; without the dumping site load, the supporting coal pillar width is 2.8 m and the isolation coal pillar width is 8.29 m. The load from the dumping site exacerbates the deformation of the coal pillar. At a depth of 100 m during excavation, the roof subsidence reaches 7.3 mm, and the floor heave is 6.98 mm. At a depth of 150 m, the roof subsidence reaches 6.79 mm, and the floor heave is 7.63 mm. The slope displacement increases to 38.2 mm under the dumping site load, compared to 31.9 mm without the load. The load from the dumping site affects the stress and deformation of the coal pillar, especially during deep excavation, where the irregular load on the upper part causes significant deformation and stress concentration in the coal pillar, increasing the risk of instability. In areas with greater excavation depths, the load increases slope displacement, affecting the slope stability and increasing the risk of landslides. After the mining of end-slope overlying rock, a goaf is formed within the slope, leading to a dramatic increase in the plastic zone area, primarily due to tensile failure. The maximum shear strain increment is concentrated in the excavation roof area, forming a “settlement and progressive landslide” risk. In the stability analysis of this scheme, the safety factor of the slope is greater than 1.5, meeting the design specifications. In the process of end-slope mining with irregular dumping site loads, a reasonable plan should be considered to reduce the safety risks caused by coal pillar deformation and slope instability.