大气作用下黄土路基水分迁移规律及增减湿变形特性研究

Loess is special in structure and sensitive to moisture. Remarkable moistening deformation occurs in large numbers of loess subgrades of highway due to the repeated effect of moistening and wetting caused by the atmosphere in the long period of execution, which has great influence on the operation safety and service life of highway. Study on the law of moisture migration and the characteirstic of moistening and wetting deformation of loess subgrade is an advanced topic in geothchnical engineering, which has important theoretical and practical significance. Through the main research methods of laboratory test, theoretical analysis, numerical simulation and in-situ monitoring, the characteristics of soil water and moistening and wetting deformation of unsaturated soil with different dry densities, variation ranges of moisture and wetting-drying cycles are studied. The expression of moistening and wetting deformation of unsaturated soil taking into account the influencing factors discussed above is established, and the relationship between unsaturated soil modulus and water content is deduced. The thermo-hydro-mechanical coupling mechanism is analyzed, and the thermal-hydro-mechanical coupling model of unsaturated loess considering the moistening and wetting deformation of unsaturated soil in the effect of atmosphere is set up. Then, the moisture migration and moistening and wetting deformation of loess subgrade are analyzed under the action of typical atmosphere such as rainfall and evaporation, etc., and the influence mechanism of moistening and wetting deformation on the characteristic of subgrade soil is revealed. Furthermore, the reliability of model and calculation results is verified according to the long-term in-situ monitoring data of subgrade in temperature, humidity and deformation. The research resluts can provide scientific references for highway subgrade design and the controlling of the moistening and wetting deformation of subgrade.

黄土结构特殊，湿度敏感，在大气作用下大量高速公路黄土路基在运营过程中饱受增湿和减湿的反复作用产生变形，严重影响公路的安全营运及其使用寿命。开展大气作用下非饱和黄土路基水分迁移规律和增减湿变形特性研究是岩土工程的前沿课题，具有重要的理论和实际意义。本项目拟以室内试验、理论分析、数值模拟和原位测试为主要研究方法，研究不同干密度、增减湿幅度和干湿循环次数下非饱和黄土土水特性和增减湿变形特性，提出考虑以上因素的非饱和黄土增减湿变形的表达式，建立非饱和土模量与含水量的关系；分析热流固耦合机理，构建能够反映大气作用下非饱和土增减湿变形的热流固耦合模型，研究降雨、蒸发等典型气候作用下路基的水分迁移和增减湿变形规律，揭示路基填筑土体特性对路基增减湿变形的影响机理，并通过原位测试采集路基温度、湿度及变形数据，验证模型和计算结果的可靠性。课题研究成果可为公路路基设计和路基增减湿变形控制提供科学依据。

受全球气候急剧变化的影响，黄土高原地区夏季高温期间降雨强度和降雨次数显著增加，致使路基在降雨入渗引起的增湿和蒸发导致的减湿的反复作用下引起增减湿变形，造成路基水毁破坏。针对黄土地区公路运营过程中迫切需要解决的降雨、蒸发等气候反复作用引起的路基变形问题，本项目对大气作用下黄土路基水分迁移规律和增减湿变形特性开展深入细致的研究。选取依托工程—西禹高速公路西安郊区某路段路基外侧20米处黄土作为试验用土，采用滤纸法开展土水特征曲线试验，获得三种干密度下的土水特征曲线，分析干密度对VG模型参数的影响。采用非饱和土三轴仪开展不同净应力下的脱湿变形试验，测得三种不同净应力下孔隙比和含水量随基质吸力的变化曲线，建立孔隙比和含水量与净应力和基质吸力的关系式，并结合非饱和土非线性弹性本构关系，获得弹性模量和体积模量与净应力和含水量的关系式，进而分析净应力和含水量对非饱和土模量的影响。分析非饱和土的热流固耦合机理，将非饱和土非线性弹性本构模型引入力的平衡方程，并组合水汽两相流运动方程和热能扩散方程，推导了用位移、水头和温度等基本变量表示的热流固耦合模型。基于热流固耦合模型和降雨入渗、蒸发边界，分析了降雨入渗作用下降雨强度、降雨模式、路基高度、初始含水量等因素对路基湿度变化的影响，研究了蒸发作用下蒸发强度昼夜更替、相对湿度、风速、太阳辐射量、气温等因素对路基水分迁移规律的影响，并引入不同降雨模式及降雨强度，对比研究了降雨-蒸发干湿循环效应下的路基湿度变化规律。最后，根据路基湿度控制标准，提出控制路基湿度的工程技术措施，以提高路基湿度的长期稳定性。该研究对于正确认识黄土增减湿变形特性，科学预测黄土路基工程病害，保证路基长期稳定性具有重要的理论意义和应用价值。