Experimental Study on Coal Seam Dilatancy Characteristics Under Fluid Injection

In order to more accurately understand the characteristics of coal volume expansion caused by fluid injection,a self-developed thermo-hydro-mechanical (THM) coupled with triaxial servo-controlled seepage apparatus for gas-infiltrated coal and rock was applied to carry out triaxial loading and unloading tests under different stress paths. The results show that when the raw coal is destabilized, the larger the confining pressure, the larger the volume strain at the time of its failure, and the worse the dilatancy capacity. It was found by quantitative analysis of the dilatancy factor of raw coal, compared with the stress path of triaxial compression with constant confining pressure, the dilatancy characteristics of raw coal under stress relief and fluid injection stress paths are better. The pressure relief and fluid injection stress paths cannot be completely equivalent, and there are differences in the deformation and dilatancy characteristics of the raw coal, this shows that the value of the Biot coefficient may vary greatly with the type of rock and stress state, and that capillary and adsorption between the fluid and the coal matrix after the fluid enters the coal rock may cause changes in the physical and mechanical properties of the raw coal.