考虑湿胀异性效应下膨胀土路基边坡变形失稳机理研究

The deformation of subgrade slope instability is one of the most serious, the most vulnerable and difficult common geological disasters to deal with in the expansion highway construction land area. It is an important way to study the mechanism of expansive soil slope deformation in revealing the effect of the stress and strength change caused by soil wet-expanding and rationally analyzing the comprehensive effect of slope stress and strength change caused by soil wet-expanding. This project focuses on studying the expansive soil wet-expanding anisotropic problems, starting from the quantitative characterization of microstructure, revealing the micro and macro structure, stress condition and other factors on the effects of the three direction wet-expanding deformation, studying on the micro and macro mechanism of wet-expanding of expansive soil through the three direction expansion test, based on the theory of isotropic wet-expanding deformation of expansive soils, introducing the anisotropy index and the three direction expansion coefficient to characterize the microstructure and macro - wet-expanding anisotropy of expansive soil, establishing a wet-expanding model for the unsaturated expansive soils, which is based on the mechanism of water swelling and water softening, and then doing calibration and verification of the theoretical model; on this basis, establishing a multi field coupling numerical analysis method for the moisture field expansion deformation field stress field of expansive soil slope, simulating the effect of wet-expanding anisotropy and combining with physical model test, to study the influence rule and mechanism of wet-expanding on the deformation failure of expansive soil slope under rainfall condition and to provide a theoretical basis for designing effective slope treatment.

路基边坡变形失稳是膨胀土地区公路建设中常见的一种最严重、最易发生且难以处治的地质灾害。揭示膨胀土湿胀异性规律，合理分析由土体湿胀所导致的边坡应力、强度改变等综合效应是研究膨胀土边坡变形失稳机理的重要途径。本项目重点研究膨胀土湿胀异性问题，从微结构特征的定量化入手，通过开展三向膨胀试验，揭示微、宏观结构、应力状态等因素对三向湿胀变形的影响规律，探寻膨胀土湿胀异性的微、宏观作用机理；基于现有膨胀土各向同性湿胀变形理论，引入各向异性率指标和三向膨胀系数来表征膨胀土微结构异性和宏观湿胀异性特征，建立考虑湿胀异性和吸水软化机制的非饱和膨胀土湿胀模型，并对理论模型进行校正与验证；在此基础上，建立膨胀土边坡湿度场-膨胀变形场-应力场的多场耦合数值分析方法，模拟边坡湿胀异性效应，并结合物理模型试验，研究降雨条件下湿胀异性效应对膨胀土边坡变形失稳影响规律及机理，为开展有效的边坡处治设计提供理论依据。

降雨条件下，膨胀土坡体吸水后体积膨胀和物性软化导致的应力场和强度改变是触发边坡变形失稳的重要诱因，因而，揭示膨胀土湿胀异性规律，提出基于湿胀效应的边坡稳定分析方法，是研究膨胀土边坡变形失稳机理的重要途径。本项目以广西地区6种膨胀土为研究对象，从膨胀土微结构入手，基于自研仪器的三向膨胀试验，揭示了膨胀土微、宏观结构、应力状态等因素对膨胀土湿胀异性影响规律，并建立膨胀土三向湿胀模型进行理论描述，开展膨胀土边坡数值模拟和室内小型模型试验，提出了膨胀土边坡分析法。研究结果表明：6种膨胀土重塑立方体试样的两个横向的膨胀率、膨胀力基本相当，且竖向均大于横向，试样三向膨胀率、膨胀力随干密度的增大而增大，且竖横向比值则趋近于1，但原状土试样与相同密度重塑土试样的三向膨胀率和膨胀力数值并不相当，外部荷载对三向膨胀有抑制作用；南宁灰白膨胀土重塑立方体试样的三向膨胀率与干密度、空隙率、土颗粒粒径等宏、微观因素存在较好的相关性，干密度越大，横、竖向孔隙率越小，土颗粒粒径越大，三向膨胀率越大，竖、横向差异则越小；通过建立由无荷膨胀模型、软化模型和吸水软化压缩模型三部分组成的非饱和膨胀土三向湿胀模型能较好的描述膨胀土三向变形规律；最后通过仿真模拟和室内模型试验结果分析认为，湿胀效应是导致膨胀土边坡变形失稳的重要因素，不仅改变了坡体内的应力分布还导致了浅层和坡脚处的变形破坏形式，最终使得边坡安全系数明显降低。本项目研究成果将为膨胀土边坡设计和处治提供理论依据。