Experimental study on longitudinal wave velocity of water-bearing coal：taking Guhanshan bituminous coal and Zhaogu anthracite as examples

Due to factors such as groundwater and hydraulic permeability improvement technology，coal seams have different water content in the coal body. Coal seams with different water content have a great influence on their mechanical properties and gas flow in the coal seam，thus causing difficulties in gas extraction.In order to solve the difficult problem of water-bearing gas extraction，this paper adopted the Guhanshan bituminous coal and Zhaogu anthracite to conduct the acoustic wave test of coal samples with different water-bearing saturation in the experiment，and analyzed and studied the law by combining the Gassmann equation assumed by Wood theory and the kuster-toksoz theoretical equation.It is found that the water saturation of both ancient hanshan bituminous coal and zhaogu anthracite is 60%. The parallel bedding water saturation before 60% conforms to Gassmann equation assumed by Wood theory，and after 60% conforms to kuster-toksoz theoretical equation. However，vertical stratification pores and fractures are relatively developed，and the water saturation before 60% is inconsistent with Gassmann equation assumed by Wood theory. Therefore，the author established a modified formula to calculate wave velocities of different water saturation，which is basically consistent with the actual wave velocities. After 60%，it conforms to the kuster-toksoz theoretical equation. It provides a theoretical basis for defining the wave velocity variation rule of coal body under different water saturation.