基于非均质材料均匀化理论的冻土弹塑性本构模型研究

In order to meet the evaluation and prediction demand of long-term service performance of Permafrost Subgrade and the inevitable trend of the sustainable development of engineering construction in cold regions, the study of the constitutive model with high precision is one of the basic subjects in the field of geotechnical engineering. Based on the homogenization theory of heterogeneous materials, the 3 aspects about the constitutive model of frozen soil are studied by using the cyclic tri-axial and CT testing technique. Firstly, laboratory tests are applied to study on the non-uniform distribution of stress and strain and the microstructural evolution of ice and soil-water mixtures in frozen soil. Secondly, the relationships between meso structure and macroscopic response are studied, and the constitutive model will be deduced considering non-uniform distribution of stress and strain. Thirdly, for validation and application of the model, the efficient and stable method are developed and adopted to solve the model, and the numerical results are compared with the test results to verify the validity and reliability of the constitutive theory and solving method, and the constitutive model is implemented in Abaqus Software. Through the implementation of this project, the quantitative description method of the meso structure of frozen soil will be established, and an elastoplastic constitutive model are proposed considering the inhomogeneous distribution of stress and strain. In order to lay a theoretical foundation for the development of dynamic design method of frozen soil engineering, this project tries to solve the basic problems in the design of Permafrost Subgrade.

针对我国冻土路基长期服役性能评价与预测需求，以及寒区工程建设可持续发展的必然趋势，发展高精细的本构模型是岩土工程领域中基础性课题之一。基于非均质材料均匀化理论，应用循环三轴与CT测试技术围绕冻土的本构模型开展3方面的研究内容：①室内试验：研究冻土中冰与土-水混合物的应力应变分布规律及细观结构演化规律；②本构模型：研究细观结构变化和宏观响应的关联，推导考虑细观非均匀的冻土弹塑性本构模型；③模型求解、验证与应用：研究模型的数值算法，开发高效、稳定的求解方法对模型求解，将数值结果与室内试验结果、现场实测资料进行对比研究，验证本构理论及求解方法的有效性与可靠性，并将本构模型在Abaqus软件中实现二次开发。通过本项目的实施，将建立冻土细观结构的定量描述方法，构建考虑细观非均匀的弹塑性本构模型。力图解决冻土路基设计中的基本理论问题，为发展冻土工程动力设计方法奠定理论基础。

土的基本特性及本构关系与强度理论是土力学及岩土工程学科的重要理论基础之一，在数值计算技术日趋成熟的情况下，本构模型研究的重要性显得更加突出，并且逐渐由静力问题发展到动力问题，建立高精细的宏-细观本构模型已经得到较为普遍的关注。随着寒区工程建设的日益增多，以冻结冰碛土为研究对象，利用冻土动静三轴测试系统对冻结冰碛土的静动三轴力学特性进行研究，基于冻结冰碛土的变形机理，将非均质的冻结冰碛土抽象为胶结元和摩擦元组成的二元介质材料，认为胶结元在外荷载下会逐渐破损并转化为摩擦元，从能量耗散的角度建立冻结冰碛土破损过程演化方程，在均匀化理论框架下，建立静动力荷载下冻结冰碛土的二元介质本构模型，并基于二元介质的概念建立描述冻结冰碛土强度特性的强度准则。将模型预测结果与三轴试验结果对比表明，建立的静力二元介质本构模型能较好地反映冻结冰碛土的应变软化现象和先体缩后体胀的力学特性，建立的动力本构模型能较好模拟循环荷载作用下冻结冰碛土的轴向应变累积特性以及先体缩后体胀的力学特性，建立的强度准则能较好模拟冻结冰碛土的非线性强度特性。该项目的实施对寒区冰碛松散堆积体长期服役性能评价与预测，以及完善寒区冰碛土工程设计理论与方法具有重要意义。