Abstract:
Aiming at the common engineering problems in deep broken soft coal seams in China, such as easy hole collapse of gas drainage boreholes and prone deformation and failure of screen pipes, this study aims to improve the bearing capacity and stability of hole-protection screen pipes under complex working conditions with high in-situ stress, strong creep and multi-field coupling. The influencing factors of compressive performance of hole-protection screen pipes in broken soft coal seams were investigated. Two types of polymer screen pipes, polyvinyl chloride (PVC) and polyethylene (PE), were selected. By adopting a rock triaxial rheological test system and the control variable method to systematically simulate the complex stress environment, the coupling influence mechanism of four key parameters including opening angle (60°, 90°, 120°, 180°), screen hole spacing (10 cm, 20 cm, 30 cm), pipe diameter (3.2-7.2 cm) and material on the radial compressive strength of screen pipes was explored. The results show that the overall compressive and deformation resistance of PE screen pipes are significantly better than those of PVC screen pipes. Under the same parameters, the maximum compressive strength of PE pipes is 27.3% higher than that of PVC pipes. The compressive strength of screen pipes increases obviously with the rise of opening angle, screen hole spacing and pipe diameter. The strength gain caused by the increase of screen hole spacing is the most prominent, with a maximum increase of 46.0%, and a synergistic amplification effect exists among various parameters. Increasing the opening angle from 60° to 180° can effectively reduce stress concentration around holes and delay structural buckling. Enlarging the pipe diameter can enhance the circumferential stiffness, while the strength gain gradually slows down when the pipe diameter exceeds 6.3 cm. Based on the optimal compressive performance principle, PE material is recommended for hole-protection screen pipes used for gas drainage in broken soft coal seams. On the premise of coordinating and unifying drainage efficiency, economic benefit and construction reliability, screen pipes with a screen hole spacing of 30 cm, an opening angle of 180° and a pipe diameter of no less than 7.2 cm are recommended.