Field Study on Correlation between CO₂ Concentration and Surface Soil CO₂ Flux in Closed Coal Mine Goaf

Self-heating of coal mine goaf or shallow coal seams can release an outbreak of unimaginable pollution disaster under suitable circumstances. As an indicator gas, CO₂ is always used to determine the coal spontaneous combustion state during the self-heating process. Based on this, the paper investigated the influence of abandoned coal mine goaf CO₂ on the surface environment by measuring the CO₂ concentration in the borehole connected to the goaf and CO₂ flux on the soil surface. Furthermore, rainfall and atmospheric temperature effects are discussed to illustrate the correlation between the CO₂ concentration and surface soil CO₂ flux in the closed mine goaf. Subsequently, the tracer gas experimental method is employed to analyze the effect of air leakage from an open-pit slope on CO₂ flux. The experimental results demonstrated that the distribution of CO₂ concentration in the borehole confirms the continuous diffusion of goaf CO₂ onto the surface. The value of CO₂ flux in the goaf is significantly higher than that of a normal area. Temperature is one of the primary factors that affect the CO₂ flux on the field. Air leakage from the slope promotes the surface soil-overlying goaf CO₂ diffusion. The study provides important reference data for the assessment of the mining area field environment and the determination of the spontaneous combustion risk of the residual coal in the goaf.