砂土液化大变形的热力学机理与本构模型研究

Study on liquefaction and large post-liquefaction deformation of saturated sand is one of important and difficult topics in research on soil dynamics and geotechnical earthquake engineering. Based on the non-equilibrium thermodynamics, the proposed research project focuses on the saturated sand. The main contents are: firstly, considering the saturated sand as a solid-liquid two-phase continuous medium, and constructing its theoretical framework of non-equilibrium thermodynamics, to get the partial differential equations that control the liquefaction and large post-liquefaction deformation behavior of it; secondly, exploring reasonable free energy model and transport coefficient model, reproducing the liquefaction and large post-liquefaction deformation behavior of saturated sand, calibrating right parameters, providing the constitutive relation of sand under the seismic load; thirdly, based on large amounts of experimental data of Zhang Jianmin, as well as a series of complex stress path tests, acoustics tests, creep tests and relaxation tests, verifying the validity of the model; finally, using COMSOL Multiphysics software to analyze the liquefaction behavior of sandy soil foundation under the seismic load. The research project aims to explore and reveal the soil dynamics behavior and its inherent laws under different conditions, to develop and improve the calculation models and methods, in order to enrich the basic theory of soil dynamics, to provide more systematic, comprehensive and scientific theoretical basis for liquefaction and large post-liquefaction deformation of saturated sand.

饱和砂土地震液化大变形问题，是岩土工程抗震领域研究的重点和难点之一。本研究采用非平衡态热力学方法，以饱和砂土为研究对象。首先，将饱和砂土简化为固液两相连续介质，构建其热力学理论框架，得到砂土液化大变形行为的控制偏微分方程组；其次，探索合理的自由能和迁移系数模型，再现砂土液化大变形的基本规律，建立其与热力学模型参数之间的内在联系，标定模型参数；以张建民等的大量的试验数据为基础，再辅助开展一系列复杂应力路径试验和砂土材料声学、蠕变试验，检验模型参数的正确性；采用COMSOL Multiphysics 软件进行砂土地基震动液化行为分析。旨在探究和揭示不同条件下的砂土动力学行为及其内在规律，发展和完善计算模型和方法，以期丰富饱和砂土液化问题的动力学理论体系，深化其热力学理论基础，为饱和砂土地震液化大变形分析和预测提供更加系统、全面和科学的理论依据。

饱和砂土地震液化大变形问题，是岩土工程抗震领域研究的重点和难点之一。本研究采用非平衡态热力学方法，以饱和砂土为研究对象，构建了饱和砂土固液两相热力学理论框架，得到了砂土液化大变形行为的控制偏微分方程组。研究了自由能参数和耗散参数对饱和砂土力学行为的影响，给出了合理的应变能模型，该模型得到的弹性波速表达式能够揭示密度和各向异性对波速的影响，同时能够反映各向异性条件下剪切波的劈裂现象，并通过声速试验对模型参数进行了标定；分析了砂土材料蠕变和松弛行为，通过非平衡态热力学基本框架，给出了研究砂土材料的流变行为的简化模型，得到了如下结论：a.该模型能够较好地反映和预测砂土侧限压缩和各向同性压缩条件下的蠕变和松弛行为；b.砂土在外力加载过程中，颗粒熵（颗粒温度）被激发不断增大直至稳定值，在停止加载后的流变过程中，颗粒熵（颗粒温度）逐渐衰减，排除外界扰动引发的颗粒熵波动，理论上最终衰减为零；c.颗粒熵衰减过程，伴随着颗粒温度引起的弹性弛豫，引发的不可逆变形宏观上表现为砂土的流变行为，随着颗粒熵衰减到零，理论上流变最终停止在一个稳定值。本研究给出了砂土流变行为的热力学机理并标定了耗散模型参数，可以为砂土流变行为的研究和工程实践提供理论依据。初步揭示了饱和砂土液化大变形行为的热力学机理，饱和砂土在循环剪切作用下，砂土颗粒熵（颗粒温度）被持续激发，颗粒温度引发的不可逆体积变形、球应力压缩体积变形以及剪切引起的可逆体积变形共同作用，控制了饱和砂土液化后大变形力学行为。