It was found that radial cracks were initiated from the surface of a combustion cavity into coal seam on model tests for underground coal gasification (UCG) (Kodama et al. 2018). Understanding mechanism of the crack initiation is important because initiation of the cracks is likely to change well performance of an UCG plant. In this study, process of crack initiation in coal blocks subjected to heating and cooling was observed with measuring temperature. Then, mechanism of the crack initiation is considered based on analysis of temperature dependence of crack initiation and propagation.
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