黄井武1,2， 王德洋3， 严振瑞1， 朱鸿鹄3,4， 施斌3
1．广东省水利电力勘测设计研究院有限公司，广东广州510170
2．广东科正水电与建筑工程质量检测有限公司，广东广州510170
3．南京大学地球科学与工程学院，江苏南京210023
4．南京大学大地探测与感知研究院，江苏南京210023
摘要：高水压作用下水工隧洞衬砌结构的承载特性及破坏机理复杂，借助现有的监测技术难以准确评价其工作状态．针对珠江三角洲水资源配置工程，开展了以“外衬管片-自密实混凝土-内衬钢管”叠合衬砌结构为研究对象的现场原位试验．采用分布式光纤感测技术对内压加载过程中叠合衬砌结构力学性能特征进行了深入探究．试验结果表明: 在内压逐步增加的条件下，隧洞衬砌的应变发展呈现非连续阶跃的特征; 内衬钢管环向应变起伏变化均匀、平缓，整体基本处于弹性工作状态; 衬砌结构中的自密实混凝土在内压作用下由弹性变形进入弹塑性变形状态，且在管片拼接缝位置处出现裂缝; 外衬管片在均布内压作用下呈现非均匀性的膨胀变形，且管片接缝张开显著区域主要分布于隧洞拱顶位置．研究结果从应变演化的角度揭示了叠合衬砌结构承载特性及破坏机理，充分验证了分布式光纤感测技术在输水隧洞结构健康监测中的巨大应用潜力．
关键词：输水隧洞; 叠合衬砌结构; 衬砌管片; 光纤传感器; 布里渊光时域反射技术( BOTDR) ;受激布里渊光频域分析技术( BOFDA) ; 应变监测
为了解决区域水资源分布不平衡问题，我国多地开始建设高压输水隧洞工程，如南湃水电站高压引水隧洞、南水北调穿黄隧洞工程、广州西江引水工程等［1-3］．这些输水隧洞具有埋深大、距离长、工程规模巨大等特点，其沿线各类不良工程地质条件和周边工程建设活动不可避免地给隧道工程运行带来严重的威胁［4-5］．此外，高压输水隧洞在运营过程中，内部高水压作用使得隧洞长期处于复杂受力状态，由此产生的附加应力场可能会对衬砌结构造成不同程度的损伤及破坏［6-7］．同时，输水隧洞还对耐久性和抗裂性有着极高的要求［8-9］．因此，亟待对其实际工作性能进行深入研究，这对于优化隧洞的结构设计方案，保证输水隧洞安全运营具有重要的意义.
目前，复杂隧洞衬砌结构的承载特性研究可分为试验及数值模拟两个方面，前者多采用缩尺模型试验或现场足尺试验．毕湘利等［10］开展了顶部加载和周边卸载模式下盾构隧道结构承载特性的足尺度试验，探讨了两种工况下通缝拼装盾构结构的变形特征及极限承载能力．针对常规试验中模型结构粗略化的不足，封坤等［11］自主设计了“多功能盾构隧道结构体试验系统”，实现了管片衬砌结构土水压力分离加载的模拟．在此基础上研究了不同拼装方式的管片衬砌结构的破坏特征．同时，何川等［12］采用该系统对狮子洋隧道衬砌结构进行了原位加载试验，发现高水压作用下结构纵缝区域易发生局部剪切破坏，相关研究结论为同类工程的设计提供了参考．然而上述的现场模型试验多采用应变片、位移计等常规的监测方法．该类方法只能测量隧洞结构某点或某几个位置的变形或应力应变，无法获取衬砌结构整体变形特征信息［13-16］．另外，传统传感器在输水隧洞的监测中很难长期存活，因此为了实现长期有效的结构健康监测，必须引入更加先进、可靠的监测技术．
近年来，光纤感测技术逐渐被应用于隧道结构的监测，并在工程实践中取得了良好的监测效果．南京大学施斌等采用布里渊光时域反射( BOTDＲ) 技术，监测了南京玄武湖隧道的运行状态，验证了光纤感测技术在隧道结构健康评估中的可行性［17］．董鹏等将分布式光纤监测技术用于浅埋隧道覆岩的变形监测，再现了开挖作用下隧道上覆岩土体力学行为的时空演化过程［18］．由于隧道施工场地环境恶劣，各类光纤传感器在安装及使用过程中易受到损伤［19］．鉴于此，魏广庆等［20］根据不同的施工环境设计了不同的传感器保护层和封装结构，并采用改进后传感器对在建隧洞初衬结构在开挖过程中的应力应变进行了实时监测，相关结果为评估初衬支护效果提供指导依据．虽然光纤感测技术在隧道结构健康监测中已有较多的成功案例，然而该技术在输水隧洞结构中的应用却鲜有报道．
在建的珠江三角洲水资源配置工程全线采用深埋隧洞方式，并主要采用了基于联合受力模式的“外衬管片-自密实混凝土-内衬钢管”的特殊叠合衬砌结构［4］．然而工程界对这类叠合衬砌结构的传力机理和损伤破坏规律缺乏充分的认识．依托于该项目，开展了输水隧洞典型段的现场内压加载试验，并基于分布式传感光纤监测系统获取外衬管片、自密实混凝土层和内衬钢管的应变分布特征，为优化叠合衬砌结构的设计方案提供参考依据．
In-situ experimental study on the behavior of water conveyance tunnel under high internal pressure using fiber optic sensing technique
HUANG Jingwu1,2, WANG Deyang3, YAN Zhenrui1, ZHU Honghu3,4, SHI Bin3
1. Guangdong Hydropower Planning and Design Institute, Guangzhou 510170, China
2. Guangdong Kezheng Hydropower and Civil Engineering Quality Inspection Co. Ltd, Guangzhou 510170, China
3. School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
4. Institute of Earth Exploration and Sensing, Nanjing University, Nanjing 210023, China
Abstract: The deformation behaviors of water conveyance tunnels under high internal pressure can scarcely ever be accurately evaluated using existing monitoring technologies. A full-scale experimental test, based on the project of water resources allocation in Pearl River Delta, was conducted to investigate the deformation mechanism of the superimposed linings consisting of a concrete segment, self-compacted concrete, and steel tube. The distributed fiber optic sensing was used to monitor the performance of superimposed linings under high internal pressure. The test results show that the strain development of the linings presents the character of discontinuous variation during loading. The steel tube generates elastic deformation, and the strain change is small. The deformation process of self-compacted concrete can be divided into two stages: elastic deformation and plastic deformation. The plastic zone gradually expanded from the concrete surface to the deep layers forming several cracks at the segment splicing joint. The spaces between some segments on the crown of the tunnel are prone to enlarge under high uniform internal pressure. The deformation characteristics and failure patterns of the superimposed linings were revealed in the view of strain measurement. This study verifies the great application potential of distributed fiber optic sensing in the water conveyance tunnel.
Keywords: water conveyance tunnel; superimposed linings; fiber optic sensor; Brillouin optic time-domain reflectometer (BOTDR); Brillouin optical frequency domain analysis (BOFDA); Strain monitoring
结论：
本文开展了珠三角高压输水隧洞的原位试验，基于分布式光纤监测技术揭示了复合式衬砌结构在内压作用下的真实承载性能及传力规律，得到以下结论：
（1）分布式光纤感测技术可以准确捕捉到隧洞结构的变形特征，为掌握高水压作用下隧洞衬砌变形破坏模式提供了一种新的方法。
（2）复合式衬砌结构中内衬钢管处于弹性工作状态，且仍具有较大安全储备；自密实混凝土在0.45MPa内压作用下出现了微裂缝，且裂缝大多处于外衬管片的拼接缝位置；管片接头在纵向刚度上存在差异，使得试验中顶部管片出现较大的环向应变。
（3）在内水压达到0.75MPa的过程中，复合式衬砌结构始终保持稳定。但应当注意的是，在管片接头处的自密实混凝土一旦开裂，将发生地下水内渗、钢管外弧面腐蚀等一系列问题。
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