基于大变形理论的岩土材料热-力本构特性的研究

With the development of scientific research and engineering, study on thermal- mechanical constitutive propoties for geomaterials has become an important research field. However, because there are still some deficiencies and biases in this field, including both the theoretical research and experimental research; it is difficult to comprehensive understanding of the complex thermal-mechanical properties of geomaterials in present. In order to resolve these problems, this study will propose a systemic and in-depth study: firstly, a series of tests will be operated to investigate some important thermal-mechanical propoties for some typical geomaterials, including the short-term propoties (e.g., strength, deformation characteristics, etc.); the long-term propoties (e.g., creep, etc.); the cyclic loading behaviors under the high temperature condition. Then, based on the concept of "equivalent stress" proposed by applicant, this study will develop a simple, reasonable and natural geomaterials thermal-mechanical constitutive model in the new method; furthermore, the new model can describe properly the complex thermal-mechanical properties of materials, and satisfy the laws of thermodynamics. At last, based on the new model, a 3-D finite element program will be preparated to solve the complex thermal - mechanical boundary value problem. The study not only to deepen the understanding of the constitutive behavior of geomaterials，but also can be theoretically used for deep geologic disposal for high level nuclear waste, landslide forcast and prediction, long-term safety analysis for important traffic engineering roadbed, and so on.

随着科学研究与工程实际的发展，岩土材料热-力耦合本构特性已经成为一个新的研究领域。但是，目前相关的试验与理论研究都存在不少不足与矛盾之处，无法合理而全面的了解岩土材料复杂的热-力特性。针对这些不足，本研究拟进行系统而深入的研究：首先，进行典型岩土材料的短期（强度、变形特性）、长期（蠕变）热力特性试验，以及高温条件下的循环荷载试验，系统的认识岩土材料复杂的热-力特性；在此基础上，利用"等价应力"的概念，从新的角度建立起简单、合理而自然的岩土材料热-力本构模型，模型能够统一反映材料复杂的热-力特性，并且满足热力学基本定律；最后，基于新的模型，开发三维有限元计算程序，对复杂的热-力边界值问题进行模拟。研究不仅能够深化对岩土材料本构特性的认识，并且可以为深层地质处置核废料、滑坡预测与防治、重大交通工程路基长期安全性分析等重大工程应用提供理论基础。

在诸多岩土工程如高放核废料处置、地热资源开发等应用中需要考虑软岩的长期力学特性，而温度升高会对软岩材料的蠕变破坏特性产生复杂影响，建立能反映蠕变破坏特性的本构模型具有理论价值和现实意义。从连续介质力学入手，基于下负荷面剑桥模型和等价应力的概念，建立了能描述软岩在温度作用下蠕变过程的热弹黏塑性模型。利用自主开发的仪器，采用大谷石进行了不同围压下的三轴蠕变试验，并对模型进行了验证。多种实验结果表明，材料在不同应力状态下，存在最优温度使得蠕变破坏最慢，此外，受温升影响时存在蠕变破坏加快和减慢两种现象，提出的模型能统一描述这两种现象。分析了模型特性，总结了不同材料参数和应力状态对蠕变规律的影响。基于上负荷面模型和温度等效应力概念，提出一个考虑结构性的软岩热弹塑性模型。计算结果与试验结果表明，该模型既能够统一描述温度上升导致软岩强度上升（热增强）和强度下降（热减弱）两种现象，也能对软岩的结构性进行模拟分析。软岩初始结构性愈强，强度愈大，且初始结构性的变化可使软岩在“热增强”和“热减弱”之间相互转换。无论“热增强”或者“热减弱”，线性热膨胀系数越大或者温度越高，结构性状态变量的消散均会加快；并且，当线性热膨胀系数和温度均较高时，这种加速趋势会更为显著；相较于“热减弱”，“热增强”情况下的结构性更容易消散，即消散速度更快。