Numerical Simulation Research on the Spatiotemporal Evolution of Underground Combustion-affected Areas Constrained by Satellite Observations

Objectives: Underground coal fires are regarded as a "global disaster," as their combustion not only leads to the waste of coal resources but also causes severe environmental pollution and geological hazards. Understanding the morphology and spatiotemporal evolution of the combustion-affected areas formed by coal seam fires is essential for effective fire suppression and disaster prevention. Methods: We integrate satellite observation data into strata movement numerical simulations. Using surface temperature and deformation information derived from thermal infrared remote sensing and interferometric synthetic aperture radar (InSAR) as constraints, combined with thermodynamic and elastoplastic mechanics theories. We then conducted a numerical simulation to investigate the spatiotemporal evolution of the three-dimensional temperature field and morphology of underground combustion-affected areas. The methodology was applied to the Hongliang Fire Area in Rujigou, Ningxia. Results: The results indicate that satellite observation data provide more accurate surface parameter constraints for numerical simulations. Spatially, the temperature decreases gradually from the coal seam core outward, while temporally, both surface and strata temperatures rise as coal seam combustion progresses. For instance, the time series of temperatures at three characteristic points (Q1-Q3) along the profile reveal that Q1's temperature remains stable at approximately 18 ℃ during the first three months and then increases at an accelerating rate, reaching 27 ℃ after 12 months. At Q2, the temperature rises slowly during the first three months, followed by a linear increase to about 145℃. Q3 experiences a rapid temperature rise, with the rate of increase decelerating over time, reaching around 600 ℃ after one year. In the inversion process, In the inversion process, as the strata weakening coefficient decreases from 1, temperatures above the coal seam rise due to combustion, leading to the formation and continuous expansion of a plastic zone. When the strata weakening coefficient is between 1 and 0.18, no connected plastic zones are observed. However, when the coefficient reaches 0.18, a connected plastic zone appears in the coal seam roof, displaying a K-shaped profile and being significantly impacted by shear plastic deformation. In the forward simulation, the subsidence zone takes on a funnel-shaped deformation pattern, with the magnitude of deformation decreasing outward from the center, which delineates the extent of combustion influence. As the time steps increase, surface subsidence progressively increases. At time step 5 400, the maximum surface subsidence reaches 149.80 mm, with the subsidence profile showing a peak pattern. The forward and inversion simulations of the underground combustion-affected areas align well, with a standard deviation of 4.59 mm, indicating that the model can accurately represent the three-dimensional morphology and evolutionary characteristics of the combustion-affected areas. Conclusions: This study provides a novel approach and scientific basis for uncovering the spatiotemporal evolution patterns of underground combustion-affected areas, offering theoretical support for the effective management of underground coal fires.