基于多频次短周期冻融循环的寒区隧道防冻理论与应用

With the put into operation of a large number of tunnels in cold region of China, especially the operation of lots of high-speed railway tunnels, increasingly urgent demand has occurred to solve the mechanism of frost damage of tunnel. According long-term continuous site monitoring, tunnel structure in cold region may undergo tens to hundreds times of short freeze-thaw cycles in one year, which provide a new ideas for study the mechanism of frost damage of tunnel. Based on long-term continuous site monitoring of temperature in different kinds of tunnels in more regions, this project will study the characters and influential factors of the short-term fluctuations of temperature, and establish its quantitative models. Materials tests of natural unsaturated concrete and model tests of tunnel structure will be carried out to research the effect of these numerous short-period freeze-thaw cycles. Thorough researches will concentrate on the performance degradation of the unsaturated concrete considered with the numerous inadequate frost-thaw processes, and the additive effects caused by the repeated frost heaving of interlayer water between the initial and secondary lining, as well as the tunnel structure and surrounding rock. Criterion of effective freeze-thaw cycles will be developed to identify those may cause material or structural damage. According to the generation mechanism of frost damage, the standard and methods to prevent frost damage will be built based on the times of effective freeze-thaw cycles or fluctuation characteristics of air temperature, and new measures will be developed to decrease the effective freeze-thaw cycles.

随着我国高寒地区各类隧道特别是高铁隧道大量投入营运，破解寒区隧道冻害形成机理的需求日益紧迫。申请者前期对实际隧道衬砌温度的长期连续实测表明寒区隧道每年可能经历数十至上百次短周期正负温交替，可为寒区隧道冻害机理研究提供新思路。本项目将立足多区域多类型寒区隧道开展衬砌温度连续实测工作，分析隧道衬砌温度短周期波动的振幅、周期特征及其关键影响因素，探索建立其量化模型。在此基础上，在室内模拟气温的短周期正负波动，对自然服役状态中衬砌混凝土与隧道结构的冻融损伤过程进行模拟研究，揭示多频次短周期不充分冻融对非饱和混凝土材料性能劣化的影响机制，以及复合防水层普遍淤塞积水、隧道结构外侧围岩富水的反复冻胀对隧道结构造成累积损伤效应，提出引起材料或结构损伤的有效冻融循环判据。根据上述冻害产生机制，提出基于有效冻融循环次数、依赖气温波动特征的寒区隧道设防标准和方法，研究抑制和减少衬砌有效冻融循环次数的防冻措施。

水害和冻害问题长期困扰我国高纬度、高海拔地区的各类隧道，传统的水害冻害防治理论不能解释隧道水害冻害经时发展、恶化的特征，导致相关研究一直无法取得突破。本项目基于前一基金发现的短周期冻融现象，从昼夜短周期冻融的视角和防水防冻措施的实际工作条件出发，对温度场波动特征、材料与结构冻融损伤机制、水害冻害防治方法与措施等方面开展了系统研究。主要研究内容及成果包括：（1）开展了多类型隧道全覆盖的洞内温度场连续实测，获得了超百万条极为珍贵的寒区隧道温度连续实测数据，采用数值模拟和模型实验验证方法，掌握了隧道洞内温度场波动的影响因素及规律，提出了洞内正负温波动次数的计算方法；（2）开展了衬砌混凝土、层间聚氨酯保温板、复合防水层的性能演化模拟实验，分析了非饱和混凝土冻融损伤的发展特征和影响因素，揭示了工程条件下层间聚氨酯保温板的性能退化机制和层间复合防水层横向排水能力的经时失效过程；（3）开展了隧道围岩-结构体系的冻融模拟试验，结合实体工程调查，阐明了围岩和初期支护的约束刚度是冻融损伤进程的主要控制因素，衬背积水和施工缝渗漏造成的宏观结冰是冻融损伤的主要原因；（4）基于上述理论研究成果，开展了冻害防治方法与技术研究，提出了基于区域气象资料推算有效短周期冻融次数的防冻设计方法，研发了基于分布式压密传感器的隧道拱顶防脱空监测技术、衬砌施工缝可维护型防水抗冻消冰结构与施工方法、衬背供热强效排水防冻方法。研究成果获得了中国铁路总公司以及相关设计单位的认可和重视，入选2017年铁路重大科技创新成果，获得省部级二等奖1项、三等奖1项，衬砌拱顶防脱空监测方法在铁路隧道全面推广，强效排水型衬砌结构和复合防水层量化设计方法初步得到应用，助推了既有铁路隧道宏观冰冻预测预警研究与应用。项目对我国各类隧道的水害防治，严寒地区隧道防冻设计、冻害预警与诊治提供了重要理论支撑，为深化研究和彻底解决寒区隧道冻害问题奠定了基础。