Coal is a porous medium structure. During the hydraulic fracturing process

fluids may escape along pre-existing pores and fractures

known as filtration effect

which reduces the effectiveness of hydraulic fracturing operations. Additionally

there is no established system for the relationship between pressure changes during coal seam hydraulic fracturing and fracture propagation

making it impossible to accurately assess the damage caused by hydraulic fracturing to coal. To address this issue

the Wudong Coal Mine is chosen as the research background

and theoretical analysis

laboratory experiments

and on-site tests are conducted. Firstly

the initiation mechanism of hydraulic fracturing under loss conditions is analyzed based on the stress analysis theory of surrounding rock in rock mechanics circular hole problems

coal seepage theory

and the theory of tensile fracture criterion induced by stress concentration on hole walls. Secondly

an experiment of hydraulic fracturing for steeply inclined top coal is conducted to determine the relationship between the pressure curve of steeply inclined top coal and the fracture of coal rock mass according to the crack propagation situation of the experimental coal sample. Thirdly

an on-site hydraulic fracturing test is carried out to further determine the relationship between the on-site pressure curve and the fracture of top coal. Finally

four types of pressure curve evolution patterns are summarized as a basis for judging the effectiveness of hydraulic fracturing in coal rock mass. The research results show that when the internal water injection pressure in the borehole reaches the tensile strength equal to that of the coal rock

the first crack appears at the borehole wall. During the hydraulic fracturing process

the water injection flow rate must be greater than the leakage rate

and the higher the water injection rate

the shorter the pressurization process duration. The pressure curves can be categorized into four types: (1) single initiation type

(2) fracture connection type

(3) fluid loss type

and (4) secondary initiation type. A smaller proportion of fluid loss type during the fracturing process indicates a better fracturing effect. These findings provide a basis for judging the damage effect of hydraulic fracturing on coal bodies on-site.