交通往复移动荷载下饱和软粘土循环弱化特性及路基长期运营沉降预测

Soft clays are widely distributed in the coastal area in China, where traffic loading has caused significant long-term pavement settlement. Focused on this issue, this project aims to explore the permanent deformation behaviors of soft clay as well as those of aggregate, and tends to develop an effective approach to prediction of long-termed pavement settlement induced by traffic loads. Firstly, an analytical method is used to obtain the dynamic stress caused by moving traffic loading. According to in-situ stress path, we use DHCA to perform a series of cyclic non-proportional loading tests on soft clay and pavement aggregate. Moreover, we use a micro-macro method to demonstrate the anisotropic fabric of aggregate under cyclic non-proportional loading, and carry out a series of large-scale triaxial tests on anisotropic-fabric aggregate. We explore the threshold and critical dynamic stress ratio based on experimental observations. Within the framework of shake-down theory, threshold and critical dynamic stress ratio are used to built an equivalent viscoplastic model that is capable to reproduce a huge number of times cyclic loadings. Finally, the equivalent viscoplastic model is integrated into FEM so that long-term pavement settlement caused by repeated traffic loadings can be well predicted. This study aims to propose a technical guideline to control long-termed settlement of pavement above soft subsoil.

围绕我国沿江沿海地区交通荷载引发软粘土地基过大的长期运营沉降问题，开展大数目非比例循环加载下软粘土及碎石料的累计变形特性研究，建立软土路基长期运营沉降的理论预测方法。基于移动荷载下成层地基-路基体系的动应力解响应得到交通移动荷载下场地应力路径，并采用动态空心圆柱扭剪仪实现软粘土非比例循环加载，揭示交通动载下软粘土累积变形特性及循环弱化规律；与此同时，采用微宏观理论分析非比例循环加载下碎石颗粒组构各向异性，进而借助于循环大三轴试验揭示交通动载下各向异性碎石土的循环塑性行为。基于试验研究获得软粘土和碎石料的门槛和临界动应力比并融入到安定理论框架中，建立等效粘塑性模型模拟大数目交通循环动载下软粘土及碎石土的累计变形，与初应变有限元方法相结合，形成交通动载下软土路基长期运营沉降预测方法，从而为软土路基长期运营沉降控制技术提供理论支撑。

针对往复交通动载下饱和软黏土循环弱化及长期沉降的动力岩土灾变问题，综合理论解析、单元试验、本构理论及有限元方法等多种研究手段，揭示交通动载下地基土变形弱化的微宏观机理，建立长期循环动载下软黏土沉降的预测方法。基于Biot动力理论，推导了高速移动荷载下三维饱和层状地基动应力响应的理论解，进而获得了移动荷载下主应力偏转(PSR)的心形应力路径；基于动态空心圆柱仪（DHCA）平台，实现了大数目心形循环动载下上海饱和软黏土的累计变形规律与安定性，获得了累计变形的显示公式并获得了安定状态分区，将显示模型与初应变有限元方法(FEM)相结合，建立了往复动载下软土路基长期变形的等效有限元预测方法。本研究成果克服传统的拟静力与经验方法的局限性，建立了交通动载诱发地基沉降的土动力学理论框架，为交通动载下软土路基沉降设计标准与交通岩土工程灾变控制提供了理论支撑。