Experimental Study on Mechanical and Permeability Characteristics of Water Injection Coal Sample

In order to study the relationship between water absorption and time, mechanical properties and infiltration characteristics of coal sample, the natural water absorption test of Gaojiapu coal was carried out, and then single-axis compression test was carried out on MTS815.03 electro-hydraulic servo testing machine with natural and saturated water coal, and finally a water penetration test was conducted.The results showed that the water absorption is the secondary function of the immersion time before the coal sample is saturated, and the natural water absorption rate is 3.37% after 3.5 days of immersion to reach the saturated water state.Compared with natural coal sample, the axial strain increases with the axial stress peak in the saturated water state, and the "hysteresis" phenomenon occurs, and the Poisson's ratio and the Platts coefficient decrease by 3.36% and 9.07% respectively, compressive strength and elastic modulus decreased by 20.97% and 17.05% respectively.According to the trend of permeability curve, the change of permeability during stress and strain can be divided into compaction reduction, slowly increasing, peak appearing and residual reduction in four stages.The peak of stress is ahead of the peak of permeability.