Characteristics of coal deformation during its adsorption of He,CH4 and CO2

In order to investigate the characteristics of adsorption-induced deformation of coal,the coal defor-mation ex- periments with He,CH4 and CO2 gases were carried out. At the same time,the amount of gas adsorption under the at- mosphere of CH4 and CO2 was tested. The mechanism of isothermal adsorption-induced deformation of coal samples was discussed,and a coal isothermal adsorption-induced deformation model was established with the consideration of the effect of adsorbed gas and free gas. The results show that the compression deformation of coal samples is produced under the action of He,and the strain curve can be divided into pore compaction and elastic deformation of two stages. In the gas of CH4 and CO2 ,there is a nonlinear relationship between the adsorp-tion-induced strain and the adsorption capacity of coal samples. Under the same adsorption capacity,the swelling deformation of coal samples adsorbed CH4 is greater than that of CO2 adsorption. In CO2 ,the coal matrix is more likely to produce compression deformation than that in CH4 . The free gas not only compresses the coal matrix through pore pressure,but also promotes the swelling deformation of coal by changing the coal structure. The relationship between the deformation of coal sample and pore pressure caused by free gas can be simplified to quadratic function. Comparative analysis with related models shows that the model can accurately fit the experi-mental data,and can well describe the characteristics of adsorption-induced de- formation of coal in different ad-sorptive gases.