高级检索

多元扰动行为下深部高应力煤体扩容与压实特性

Dilatancy and compaction characteristics of deep high-stressed coal under multiple disturbance behaviors

  • 摘要: 深部煤体处于高地应力环境中,其在外界扰动作用下的力学与变形行为不同于浅部煤层。由此进行了多种扰动模式(高压注水、卸压钻孔和循环加卸载)下高应力含瓦斯煤体加载破坏试验。研究表明:高应力煤体趋向延性状态转化,未出现明显的峰后应力降。以剪切和拉伸型破裂为主的深部高应力煤体表现出峰后线性扩容行为。相比纯力学破坏,含水平孔和高压注水煤体的强度分别降低了29.1%和4.1%,它们对煤体力学性能和强度的劣化机制不同,前者是由垂向变形持续增加引起钻孔塌陷和压实区形成所致;后者是由于高压注水抵消了裂隙面法向应力,促使水平向煤体快速膨胀,导致其扩容失稳,诱发剪切破断所致。含水平孔煤体在峰值应力处的剪胀系数β=−1.524<0,也表明其处于压实状态,利用单屈服面模型证明了其在峰后出现体积压实行为的合理性。等幅加卸载扰动对弹性高应力煤体力学性能起着循环强化作用,其强度提升了18.0%~27.0%,出现了显著的峰后扩容行为。由于卸荷作用对煤体变形影响更大,其各向不可恢复压实应变(ΔεH、Δεv和Δεh)随加载次数增加而增大,表现为各向呈压缩趋势的应变硬化现象,这与循环加卸载对岩石产生疲劳损伤现象相反。研究成果可为深部高能煤层解危、立体缝网改造和渗流评估等工程问题提供借鉴。

     

    Abstract: The mechanical and deformation behavior of deep high-stressed coal seams under ambient disturbance is different from that of shallow coal seams. Based on this, the effects of various disturbance schemes i.e., high-pressurized water injection, depressurized borehole and cyclic loading-unloading, on failure mechanical behavior of gas-bearing coal under high confining pressure constraint are investigated experimentally. The results show that high-stressed coal tends to ductile state transformation without significant post-peak stress drop. Deep high-stressed coal dominated by shear and tensile fracture exhibited post-peak linear dilatancy behavior. Compared with the pure mechanical failure, the strength of coal with horizontal borehole and pressurized water is decreased by 29.1% and 4.1%, respectively, and their degradation mechanisms for coal strength and mechanical properties were different. The former is induced by the continuous increase of vertical deformation, resulting in borehole collapse and compaction zone formation. The latter is induced by pressurized water counteracting the normal stress of fracture surface, which promotes the rapid expansion of coal in horizontal direction, resulting in its dilatancy instability and subsequent shear failure. The dilatancy coefficient β=−1.524<0 at peak stress of coal within horizontal borehole also indicates that it is in a compacted state. The single yield surface model is used to prove the rationality of the post-peak compaction behavior of high-stressed coal within horizontal borehole. The loading-unloading disturbance at constant amplitude plays a cyclic reinforcement effect on the mechanical properties of elastic high-stressed coal, and its strength is increased by 18.0%−27.0% with significant post-peak dilatancy. Due to the greater influence of unloading on coal deformation, the irreversible compaction strain (ΔεH, Δεv and Δεh) increases with the increasing loading times, and manifests as strain hardening with the compression trend in all directions, which is contrary to the fatigue damage induced by cyclic loading-unloading on rock. The research results can provide reference for major engineering issues such as deep high-energy coal seam risk solving, three-dimensional fracture network reconstruction and seepage assessment.

     

/

返回文章
返回