Numerical modelling of ground temperature evolution and soil subsidence as a result of underground coal fire

摘要

Coal occurs in underground seams of variable thickness and depth and in numerous cases they arernknown to be on fire. These fires can result from human activity or occur naturally. Underground coalrnfires are problematic for many reasons, including mine safety, damage to infrastructure due torncombustion-induced subsidence (e.g. Centralia, Pennsylvania, USA) and damage to the naturalrnenvironment.rnUnderstanding and predicting the temperature evolution in the ground is a key aspect when trying tornextinguish underground coal fire. A site in New South Wales, Australia, where an underground coalrnfire has been active for the past 60 years (at a depth of around 30 m) has been the subject of anrnexperimental and numerical study. In this paper, by taking Burning Mountain as an example, therngeneral formation and development of underground coal fires and their associated physical-chemicalrncoupled processes have been analysed and described. Then, a reactive model for coal spontaneousrncombustion has been implemented in a non-linear finite element code capable of simulating thermalhydraulic-rnmechanical behaviours of geomaterials. By incorporating the reactive model with heatrntransport, a thermal-chemical (TC) simulation has been conducted on an artificial simple set-up. Thernpreliminary results show that the TC model is capable of reproducing the propagation of coal fire frontrnaccompanying with reasonable temperature evolution. The next step of model development is torncouple the TC model with gas mass transport in the fractured overlying rocks. Furthermore,rnmechanical deformation will be taken into account for predicting the subsidence experienced by thernoverburden soil after passage of the burning front and the resulting collapse.