Loading-unloading experiments of coal containing gas under the condition of different moisture contents

The studied specimens are natural coals drilled from the west K1 coal bed of Ban-xi coal mine of Nanchuan- Hongneng Coal Industrial Company,China. By using self-developed “coal containing gas thermal hydrological mechan- ical (THM) coupling experimental equipment”,an experimental study on the loading-unloading test of coal containing gas was made under the condition of different moisture contents. The research results show that:① With the increase of moisture content,the bearing strength,residual strength and deformation modulus of loading-unloading coal samples all present a trend of decrease. However,the axial strain,lateral strain,volumetric strain and lateral expansion ratio all show a trend of increase;② The change of methane gas effective permeability corresponds with the damage deforma- tion of coal samples,but the curve of methane gas effective permeability lags behind the curve of stress-strain. Before coal samples damage,the higher the moisture content is,the lower methane gas effective permeability is. Conversely, after coal samples damage,the higher the moisture content is,the higher methane gas effective permeability is;③ With the increase of moisture content,the damage,fracture development and deformation of coal samples show a trend of in- crease. The total energy and the dissipation energy of coal samples present a trend of increase during the whole load- ing-unloading process,in contrast,the elastic strain energy presents a trend of decrease.