Effect of axial loading rate on mechanical and permeability properties of raw coal

The coal-rock rheometer was used to carry out conventional triaxial mechanical seepage experiments on raw coal under different axial loading rates in this paper. Volume expansion stress, peak stress, elastic modulus and deformation modulus were used as mechanical indexes of raw coal. It was found that the law of raw coal used in the experiment was the same as that of typical brittle rock. The mechanical properties increase with the increase of axial loading rate. During the loading process, the energy dissipation of coal samples can be divided into pre-peak stage and post peak stage. Most of the energy absorbed in the pre-peak stage is transformed into releasable elastic strain energy, and the rate of dissipative strain energy increasing is relatively slow. In the post peak stage, the elastic strain energy decreases sharply and a large amount is released and converted into dissipative strain energy. At the same time, the total energy at the peak stress increases with the increase of axial loading rate. The permeability strain curve generally presents a “V” shape. In the whole stress-strain process, the relationship between coal permeability and axial strain satisfies quadratic polynomial function.