结构性软土率相关解构规律及流变本构模型研究

In order to more effectively calculating and predicting the construction and post-construction settlement of structural soft clay subgrade, strain-rate-dependent and strain-rate-independent structural characteristics test of the natural soft clay as well as its consolidation and shear creep tests are respectively carried out, and its strain-rate-dependent structure destruction law is focused on (currently still using the mechanics differences of natural clay and remoulded clay to reflect the soil structural characteristic). Through the SEM test before and after loading, and discrete element numerical test analysis which can reflect its destruction process, destruction micro-mechanism of the natural soil is made a reasonable evaluation. What's more, it will guide the construction of the macro deconstruction function related to strain rate, and then the viscoplastic flow function will be established, which can consider the structural viscous parameters changing with stress level, strain rate and load times. The numerical methods based on fractional calculus will be tried to building this function, it will play this advantage which has explicitly physical meaning, and also has a good fitting to the experimental data with fewer parameters. Thereby the elastic viscoplastic constitutive model considering structural and rheological properties of soft clay can be developed. While taking use of the UMAT interface program, the established constitutive model will be implanted in the ABAQUS finite element numerical software by programming effective integration algorithm. It will be applied to calculating and predicting the three-dimensional settlement of structural soft subgrade on the complex boundary conditions. The project will eventually form a more complete set of structural soft subgrade settlement theory, experiment and numerical calculation method.

为更有效地计算和预测结构性软土路基施工和工后沉降，对天然软土分别开展率相关与率无关结构性特征试验以及固结和剪切蠕变试验，重点研究其率相关结构解构规律（目前仍以天然土和重塑土力学性状差异来反映土体的结构性），并通过加载前后SEM试验以及反映解构过程的离散元数值试验分析，对天然土体的解构微观机制做出合理评价，指导宏观率相关解构函数的构建，从而建立考虑结构性的黏性参数随应力水平、应变速率以及加载时间变化的粘塑性流动函数，并尝试利用分数阶微积分数值方法来构建该函数，使其发挥拟合实验数据好、使用参数少以及具有一定物理意义的优点，形成考虑软土结构性和流变性的弹黏塑性本构模型；同时利用UMAT接口程序，编制有效的积分算法，将其植入ABAQUS有限元数值软件，用来计算和预测复杂边界条件下结构性软土路基的三维沉降。本项目的研究将最终形成一套较为完整的结构性软土路基沉降理论、实验和数值计算方法。

为更有效地计算和预测结构性软土路基施工和工后沉降，对结构性软土的力学特征、解构软化规律、率敏性、流变本构模型以及微观机制开展了针对性研究。采取以天然软土为参照，人工制备结构性土，并开展了率相关结构性特征试验、岩土体率敏性试验和综合蠕变试验；结合SEM微结构及机理分析，并利用ESyS-Particle离散元开源程序，自主开发了接触模型和边界条件，研究了土体颗粒的率敏性微观机制，通过CFD开展了水土耦合分析，实现了宏微观相结合的多尺度数值试验，指导宏观本构模型建立。按照相对过应力理论，以下负荷面和上下负荷面为参考屈服面，建立了合理的相对过应力函数，给出了剪缩和剪胀演化规律，从而建立了三维弹粘塑性本构模型，并借助大型商用有限软件ABAQUS，利用UMAT 子程序接口，编制了有效的积分算法，用于计算和预测复杂边界条件下结构性软土路基的三维沉降。研究结果表明：1) 结构性土率敏性主要由其颗粒直接接触作用引起，而当胶结粘聚力较低时（c=100kPa），其率敏性由颗粒直接接触和胶结两者共同作用引起，而当孔隙比较大时（e=1.617），率敏性则主要由胶结作用引起；2）建立的结构性土弹粘塑性本构模型能同时描述土体的率敏性、蠕变以及结构性特征，模型参数物理意义明确、易懂可测，预测结果与试验数据吻合良好，可用于复杂边值问题的有限元计算。本项目的研究最终形成了一套较为完整的结构性软土路基沉降理论、实验和数值计算方法。