GEOMECHANICAL ANALYSIS OF THE EFFECT OF UNDERGROUND COAL GASIFICATION ON GROUND SETTLEMENT AND THE STABILITY OF THE OVERLYING STRATA IN A COAL-BEARING FORMATION
DOI:
https://doi.org/10.32782/3041-2080/2026-7-29Keywords:
underground coal gasification, pillar stability, surface subsidence, thin coal seam gasification, safety pillar width.Abstract
Underground coal gasification (UCG) is a clean, unmanned coal extraction technology with great potential. The main environmental hazards hindering the widespread adoption of this technology include a high risk of surface subsidence, flooding, and water contamination due to the fracturing and displacement of overlying strata above the reactor cavities. The formation of cavities because of gasification causes a redistribution of stresses in the surrounding rock, triggers the growth of existing cracks and the formation of new ones, leading to the collapse of the reactor roof, inelastic deformation of the roof rock, and the inflow of groundwater into the reactors. To address these issues, it is essential to ensure the stability of the rock mass above the UCG reactor cavities. This study analyzes the impact of underground coal gasification on overlying strata and the Earth’s surface. To model the behavior of rocks during the gasification of a thin coal seam, the parallel CMBP method and the finite element method were applied in the ANSYS environment, which made it possible to determine the stress-strain state and temperature distribution in the surrounding rocks. The results showed that, provided the bearing capacity of the safety pillars is maintained, surface subsidence and rock displacement remain within acceptable limits, ensuring a minimal risk of negative impact from gasification on the surface. Under the gasification of a 1.05-meterthick formation at a depth of 392–465 meters, vertical surface settlements did not exceed 46 mm for a 3.75-meterwide section and 27 mm for a 15.0-meter-wide pillar, and the height of the stress change zone above the cavity did not exceed 70 meters. The collapse of the pillars between gasification cavities leads to a significant increase in subsidence–by 11.7 and 19.9 times, respectively–which threatens the integrity of aquifers and surface infrastructure
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