THE EFFECT OF SEAM INCLINATION ON SURFACE SUBSIDENCE: A PARAMETRIC STUDY

Abstract

Underground coal mining in inclined seams presents complex geomechanical challenges that differ significantly from horizontal strata, particularly regarding surface subsidence behavior. This study investigates the influence of seam inclination and panel geometry on the morphology of subsidence troughs using a 3D numerical modeling approach (FLAC3D). The model configuration is grounded in the specific operational conditions of a coal mine in East Kalimantan, Indonesia, utilizing a 16° seam inclination and site-specific lithology. A parametric study was conducted to evaluate the sensitivity of subsidence to panel width, depth, and height. The results reveal a distinct asymmetry in the subsidence profile driven by the tangential component of gravity along the bedding planes. Specifically, the locus of maximum subsidence shifts noticeably toward the down-dip direction, while the subsidence profile exhibits a steeper gradient on the up-dip side. Pearson correlation analysis quantifies the influence of geometric parameters, identifying extraction height as the governing variable (ρ = 0.671). Panel width demonstrates a moderate positive correlation (ρ = 0.395), whereas panel depth exhibits a weak inverse relationship (ρ = -0.141), functioning as a minor attenuating factor. The findings demonstrate that traditional symmetrical monitoring designs are insufficient for inclined seams. Consequently, this research suggests that subsidence management strategies in the Indonesian coal basin and similar geological settings must account for the down-dip shift of the maximum impact zone to ensure effective risk mitigation.