高应力高渗压环境下深埋洞室围岩卸荷渗流特性及结构演化规律研究

Permeable fracture always emerges from unloading and relaxation by surrounding rock excavation under high stress, high permeability pressure intensifies the permeability evolution of unloading fracture network in the surrounding rock and induces to damage of lining structure. So, both high stress and high permeability pressure are often serious threat to the safe operation of deep buried water cavern. Taking the diversion tunnel of Jinping secondary power station as the study background, unloading seepage characteristics and structure evolution law of the surrounding rock and non-uniform contact deformation between the lining structure and the surrounding rock in deep buried cavern were studied under both high stress and high permeability pressure environment. A laboratory test was carried out to simulate the high permeability pressure setting of the unloading fracture network. The law of pore structure change was offered by the nuclear magnetic resonance. Besides, the 3D evolution mechanism of fracture plane morphology was obtained by Three Dimensional Contactless Surface Profiler ST500. The THMC multi-field coupling triaxial test system with PAC acoustic emission was used to obtain mechanical parameters and deformation-fracture characteristics. A numerical model was built for mechanism analysis and engineering verification based on the sub-element method and contact analysis. The Non-Darcy seepage model of unloading crack in the surrounding rock and seepage model of multi-level fracture network were also established. Both proposed models were applied to explore the seepage deformation mechanism and structural evolution law of the unloading fracture network in the surrounding rock. Moreover, the mechanical mechanism of non-uniform contact deformation between the lining structure and the surrounding rock was also interpreted by both above models. The research results would provide a scientific basis for the prediction of surrounding rock permeability deformation and the design of seepage control under high stress and high permeability pressure.

高应力下围岩开挖卸荷松弛形成导水裂隙，高渗压加剧了围岩卸荷裂隙网络渗透演化，导致衬砌结构破坏，严重威胁深埋输水隧洞的安全运行。以锦屏二级电站引水隧洞为背景，研究高应力高渗压环境下隧洞围岩卸荷渗流力学特性与结构演化规律和衬砌与围岩非均匀接触变形特征。实施模拟卸荷裂隙网络高渗压赋存环境的室内试验，依托岩土核磁共振分析孔隙结构变化规律，借助ST500三维非接触式表面轮廓仪研究破裂面三维形态演化规律，利用配备同步PAC声发射测试设备的THMC多场耦合三轴试验系统获取力学参数及变形破裂特征，基于子单元法和接触分析建立数值模型并开展机理分析及工程验证。建立围岩卸荷裂隙非达西渗流模型和多重裂隙网络渗流模型，探究围岩卸荷裂隙网络结构渗透变形机制及演化规律，阐释衬砌结构与围岩产生非均匀接触变形的力学机理。研究成果可为高应力高渗压环境下深埋洞室围岩渗透变形预测及渗控设计提供科学依据。

长大深埋水工隧洞卸荷围岩的变形破坏特征及渗流力学特性，是关乎高应力高渗压环境下水工隧洞安全运行的重点问题。基于钻爆法施工技术开挖所得卸荷围岩，极易在高应力环境下形成导水裂隙；隧洞场区动态内外水压力的潜蚀作用，易于加剧卸荷围岩裂隙网络的结构演化；受衬砌与卸荷围岩及原岩三者之间强度与变形特性的影响，容易产生以卸荷围岩为变形诱导介质的衬砌及围岩变形破坏问题。本课题以锦屏二级电站引水隧洞为背景，采用工程类比法并结合项目申请书内容，开展了如下试验工作：①基于钻爆法施工技术的分级卸荷试验及力学特性研究，②考虑卸荷诱发结构演化的卸荷围岩渗流力学特性研究，③介入高渗压作用的卸荷围岩再加载力学特性试验研究，④卸荷与渗压作用下隧洞围岩宏细观特性测试及分析，⑤考虑卸荷分区效应的隧洞围岩卸荷渗流特性分析思路研究。类比参考既有水工隧洞资料，综合试验方案制定与试验理论研究成果，得出如下初步结论：①模拟高深压环境的孔隙水压力作用，其介入时间与卸荷量级较大的影响着卸荷试样的力学特性，是工程中评价卸荷围岩承载力与后续变形的必要参考；减少动态高渗压的水力侵蚀作用，有利于围岩与衬砌结构的协调变形及变形收敛。②既定卸荷量级条件下，卸荷岩样的宏细观结构特征决定了介入孔压条件下卸荷岩样的蠕变特性及循环加载过程的力学特性，是促发承压过水隧洞衬砌变形甚或破坏演化的根本因素之一；卸荷围岩与衬砌、原岩接触部位，是内外水压力作用下诱发水力潜蚀的核心区域;受卸荷围岩与衬砌在材料及其变形特性方面的影响，必然产生因卸荷松弛圈压缩或鼓胀而导致的衬砌撕裂与结构破坏。③基于内外水头压差考虑卸荷松弛圈的变形问题的思路，存在忽略衬砌与围岩之间间隙的缺陷；采用先分析渗流再作为荷载引入衬砌与围岩相互作用分析的思路，存在计算附加荷载引起卸荷围岩先期屈服的不足；依托卸荷分区与卸荷渗流力学试验开展围压卸荷裂隙非达西渗流模型与计算方法研究，是本课题后续需要更加深入的关键点。研究成果有望为长大深埋水工隧洞卸荷围岩变形分析与衬砌结构设计提供有益参考。