温度及湿度循环作用下非饱和路基黄土的静动力特性及本构模型

Loess is a widely distributed soil in China, covering an approximate area of 630,000 square kilometers. Due to the metastable structure of loess, pavement engineers are continuously facing major challenges on the design of transportation networks founded on loess deposits. Various types of pavement failures (e.g. excessive ground settlement and slope failure) are reported every year which is detrimental to the economy and road traffic safety. Furthermore, subgrade soil in pavements are also typically subjected to moisture and temperature cycles, but coupled thermal and suction effects on loess soils have been fully understood. To improve the current pavement design methods, this project aims to understand the monotonic and cyclic behavior of unsaturated loess at various temperatures and suctions. Four interrelated research constituents are proposed: (1) microstructure analysis of unsaturated loess pore structure subjected to moisture and temperature cycles; (2) laboratory testing of wetting-induced collapse, shear strength, small strain stiffness and cyclic behaviour of unsaturated loess at various suctions and temperatures through a newly developed temperature and suction controlled triaxial device; (3) development of a constitutive model which is capable to simulate monotonic and cyclic behavior of unsaturated loess with consideration to effects of temperature and soil microstructure; (4) implementation of the newly developed model into a finite-element code and simulation of various numerical scenarios. Based on the experimental and theoretical results, design guidelines for pavement construction founded on loess deposits will be proposed. The success of this project will have significant benefit to the construction of transportation networks and economic development of areas founded on loess deposits.

黄土在我国分布广泛，覆盖面积达63万平方公里，居世界首位。在中西部的交通运输网建设中，直接穿越黄土覆盖区经常不可避免，成为当地路基设计的重大挑战之一。黄土地区路基沉陷和边坡垮塌等问题屡见不鲜，严重影响行车安全，导致巨额的经济损失。一个重要原因在于黄土具有湿陷性等特点，并处于冷热循环、干湿循环和车辆周期荷载的复杂服役环境之中。目前，温度和湿度耦合作用下非饱和黄土的微观结构、变形和强度规律尚不明确，迫切需要进行研究。本项目基于非饱和土的先进理论和方法，引入温度效应，通过室内试验研究温度和湿度循环对黄土微观结构和静动力特性的影响，并建立和验证新的非饱和黄土本构模型，开展数值模拟分析工程实际。基于试验和理论研究，确定不同气象条件下非饱和黄土路基服役性能的控制指标，对我国现有路基设计规范提出改进建议。成果能提高非饱和黄土力学的理论，指导黄土路基和其他基础设施建设的科学设计，间接推动经济与社会发展。

黄土在我国分布广泛，覆盖面积达63万平方公里，居世界首位。在中西部的交通运输网建设中，直接穿越黄土覆盖区经常不可避免，成为当地路基设计的重大挑战之一。黄土地区路基沉陷和边坡垮塌等问题屡见不鲜，严重影响行车安全，导致巨额的经济损失。一个重要原因在于黄土具有湿陷性等特点，并处于冷热循环、干湿循环和车辆周期荷载的复杂服役环境之中。温度和湿度耦合作用下非饱和黄土的微观结构、变形和强度规律尚不明确，迫切需要进行研究。在此背景下，开展了室内实验和理论建模研究工作，主要取得了以下成果：(1) 自主研发了一套温度和吸力控制的非饱和土动三轴仪，已申请中国发明专利；利用新仪器系统研究并揭示了黄土以及其他代表性土体（作为黄土的参照与对比）在不同温度和湿度条件下的静动力特性、湿陷性、循环温度应变和强度规律；(3) 通过压汞实验实验和电镜扫描实验确定了土体微观结构特征及其演化规律，并用来解释黄土的宏观力学特性；(4) 提出了考虑土体微观结构效应的热-力耦合本构模型; (5) 确定了不同气象条件下黄土的变形和强度规律，分别为分析黄土路基的变形特性和稳定性提供了科学依据，提出了适合工程设计的强度和变形简化计算公式。 本项目研究成果成果能提高非饱和黄土力学的理论，指导黄土路基和其他基础设施建设的科学设计，间接推动经济与社会发展。