地温能提取对能源地下结构围岩特性与承载性能的影响研究

Energy geostructure is a novel sustainable technology that synergy geotechnique and utilization of renewable geothermal energy. It will be a new perspective growth point of geotechnical engineering. From the view of energy utilization, it has superior performance. However, the deterioration of properties of surrounding earth and mechanical performance of geostructure induced by heat exchange is not clear and worrying. It is the key issue constraining the technology. Combing with typical energy geostructure projects, the monitoring and experimental systems are under construction, which will provide important basis for this study. The heat transfer, temperature evolution and variation of pore water pressure in surrounding earth during energy extraction will be primarily discerned. Employing a series of experiment with precise control of temperature, the variation of properties of surrounding earth induced by heat exchange will be studied. The study will focus on the key variations of geotechnical properties, the threshold of temperature which induces significant variation, the mechanism of these variations and the most sensitive geomaterials. The constraint of surrounding earth on thermal deformation of energy geostructure, load-transfer function under thermal loading and correlated calculation method will be studied. In numerical simulation, ad hoc evolution laws will be set to describe the variations of geotechnical parameters and contact conditions during temperature evolution. Thermo-elastoplastic behavior of surrounding earth will also be considered by using thermal-yield function. The solving methods and parameters will be validated or modified by comparison between the numerical simulation, theoretical calculation and in-situ monitoring results. The study try to reveal the mechanism of interaction between energy geostructure and surrounding earth and the variations of mechanical performance of geostucture during heat exchange, and then develop the correlated prediction method and controlling principles. The study will provide scientific reference to the geotechnical design of energy geostructure.

能源地下结构，是岩土工程与可再生能源利用相结合的新技术和学科新的生长点。从能源利用角度其优越性突出，但可能诱发的围岩特性与地下结构自身性能变化尚不明确，成为制约该技术的关键问题。本项目拟结合以典型工程为依托正在建立的观测与换热试验系统，揭示围岩热湿传递规律、典型换热工况能源地下结构与围岩温度场的演化规律、时空特征及孔隙水压力变化；研究换热过程中围岩及围岩/结构接触特性的关键性变化、内在机制、显著变化的临界条件，并识别敏感地层；探索围岩对地下结构热变形的约束作用、热作用下的荷载传递函数特征与计算方法、考虑围岩特性变异与热塑性的模拟计算方法；对比模拟计算与原位测试结果，对求解模型与参数进行反馈分析，揭示地温能提取诱发的能源地下结构与围岩相互作用机制、地下结构承载性能等的变化规律，提出相应的预测计算方法与控制原理。本项研究将为能源地下结构的安全保证与合理设计提供理论基础和科学依据。

能源地下结构是一项具有广阔应用前景的浅层地热能利用新技术。本项目采用原位试验、模型试验、室内试验和数值模拟等方法，针对能源地下结构中的关键科学问题展开研究。为了地下能源结构的模型试验研究，研发了大型模拟试验平台。利用该平台，进行了大尺寸能源地下连续墙模型试验：通过正交试验，揭示了能源地下结构换热性能的影响因素及其影响程度；研发了地应力及能源地下结构约束条件的模型试验方法；通过模型试验与数值模拟相结合，揭示了不同换热工况、不同结构约束条件下能源地下连续墙的变形、墙-围岩接触特性变化规律。通过原位试验和数值模拟系统研究了典型换热工况下地温场的变化幅度、时空特征和演化规律，可为热热环境效应与热平衡控制提供依据。通过原位试验研究，揭示了围岩孔隙水压力变化、结构-围岩作用机制，试验表明：在恒温换热工况下温度升高会产生超孔隙水压力，其大小与围岩渗透性能、与换热管距离有关；桩土接触压力，在变形模量不同的地层中有所不同，基于此提出了围岩对能源地下结构约束度系数K：P=Ks（P-能源地下结构-围岩接触压力；s-能源地下结构径向变形；K与地层变形模量有关）；为了研究温度变化对能源地下结构接触面强度特性的影响，研发了一套控温剪切仪，对砂土-混凝土及粘土-混凝土进行不同温度剪切试验发现温度升高会提高粘土和混凝土接触面剪切强度，而对砂土接触面则影响很小，这主要是由于温度升高使接触面的粘土固结变密，增加接触面粘聚力；提出了能源桩内力与沉降变形计算的荷载传递计算方法，并编制了模拟计算程序。