碎软煤层钻孔护孔筛管抗压性能影响因素研究

    Study on factors affecting compressive performance of hole-protection screen pipe in broken soft coal seams

    • 摘要: 我国深部碎软煤层普遍存在瓦斯抽采钻孔易塌孔、筛管易变形失效等工程问题。为提升护孔筛管在高地应力、强蠕变、多场耦合复杂工况下的承载能力与稳定性能,开展了碎软煤层钻孔护孔筛管抗压性能影响因素研究。选取聚氯乙烯(PVC)和聚乙烯(PE)2种高分子材料筛管,利用岩石三轴流变试验系统,采用控制变量法系统模拟复杂应力环境,探究开孔角(60°、90°、120°、180°)、筛眼间距(10、20、30 cm)、管径(3.2~7.2 cm)及材质4类关键参数对筛管径向抗压强度的耦合影响机制。结果表明:PE筛管的整体抗压、抗变形性能显著优于PVC筛管,在参数相同条件下,其抗压强度最高可比PVC筛管提升27.3%;筛管的抗压强度随开孔角、筛眼间距及管径的增大显著提升,其中筛眼间距增大带来的强度增益最明显,最高可达46.0%;各参数间存在协同放大效应,开孔角由60°增至180°可有效降低孔周应力集中,延缓结构屈曲,而增大管径可提高环向刚度,但管径超过6.3 cm后增益逐渐趋缓。基于抗压强度最优原则,碎软煤层瓦斯抽采护孔筛管宜选用PE材质;在保障抽采效率、经济效益与施工可靠性协同统一的前提下,建议选用筛眼间距30 cm、开孔角180°、管径不小于7.2 cm的筛管。

       

      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.

       

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