Abstract: When coal is recovered by mining, or fluid recovered or injected, complex interactions of stress, gas sorption and thermal expansion have a strong influence on the mechanical and transport properties of coal. In this study, intact coal with endogenetic gas, collected from Baijiao mine and Zhangshuanglou mines in China, were treated by thermal-mechanical loading under different isothermal conditions. A special apparatus is used to measure mechanical parameters of solid and gaseous products released from specimen. It is observed from thermal deformation-time curves of the coals that both the deformation of coals and associated gas desorption are significantly controlled by applied thermal conditions as expected. The results show that Baijiao coals with highly in-situ gas content tend to swell below 35 ℃. And above 35 ℃, the coals first swell and then shrink. For Zhangshuanglou coals with lowly in-situ gas content, the coals exhibit swell, followed by shrinkage of coal matrix under isothermal conditions below 60 ℃. However, the coals tend to expand on the whole when the isothermal conditions are set above 60 ℃. The results indicate that the coal deformation is dominated by competition between thermal expansion and shrinkage of coal solid by the applied temperature. Meanwhile, more thermal-induced desorbing gas flow into pores and cleats of the coal. In this case, the stressed coal is characterized by complex coal-gas interaction under different isothermal conditions. Existing pore gas may be squeezed out during initial compaction of pore and cleat of coal. Ebb and flow of desorbing gas is observed from elastic deformation to failure. In comparison with the data of the two coal samples, both uniaxial compressive strengths and Young’s modulus of the coal samples are found to deteriorate with increasingly temperature conditions. It may help us to gain an insight into temperature dependency of mechanical property of gas-bearing coal.

Key words: coal, desorption, strength, temperature