增湿-剪切耦合作用下非饱和滑带黄土的劣化机制研究

The wetting-induced loess landslides have become the frequent geologic hazard in loess area. The precondition and key to solving this kind of problem is to ascertain the deterioration mechanism of slip loess. However, it is still lacking for quantification research and mechanism analysis of the deterioration of slip loess induced by wetting at constant shear stress. Firstly, the unsaturated slip loess is taken as the study object. A series of the continuous wetting test at constant stresses along two loading paths including isotropic compression and conventional triaxial shear are carried out. The development process of matrix suction and deformation during wetting at constant stresses are analyzed. The effects of both net confining pressure and principal stress ratio on water retention and deformation during wetting are discussed. The requirements for the initial stress and matrix suction are clarified if the wetting-induced slip loess failure occurs. Secondly, the water retention model considering wetting-shearing coupling is proposed based on the van Genuchten model. Both skeleton stress and matrix suction are adopted as constitutive stress, and an elastoplastic constitutive model reflecting the water sensitivity is proposed based on BBM model, for describing the mechanical behaviors of the slip loess during wetting at dead load. Finally, scanning electron microscopy and mercury intrusion porosimetry tests are also conducted to obtain the evolution behaviors of the microstructure and its characteristic parameters in slip loess during loading or wetting. The correlation between microstructure characteristic parameters and water retention as well as mechanical behaviours are investigated. The deterioration mechanism of the slip loess under wetting-shearing coupling is revealed. The research results will provide a solid theoretical support for further revealing the mechanism of wetting-induced loess landslide.

水致黄土滑坡成为黄土地区频发的地质灾害，解决的前提与关键是厘清滑带黄土的劣化机制，恒定剪切应力下水的增湿诱发滑带黄土劣化的量化研究与机理揭示亟待开展。首先，以非饱和滑带黄土为研究对象，开展等向压缩和常规三轴剪切两种加载路径的常应力连续增湿试验，分析常应力增湿时基质吸力与变形的发展过程，探讨净围压、主应力比对增湿时土水特征与变形特性的影响，明晰发生湿剪破坏时基质吸力与初始应力满足的必要条件。其次，基于VG模型构建考虑增湿-剪切耦合作用的土水特征曲线模型；采用骨架应力和基质吸力为应力变量，基于BBM模型构建反映水敏性的弹塑性本构模型，描述恒载增湿时滑带黄土的力学行为。最后，开展电镜扫描与压汞试验，研究增湿和加载过程中滑带黄土的微结构及其特征参数的演变规律，探究土水特征及力学行为与微结构特征参数之间的关联，揭示增湿-剪切耦合作用下滑带黄土的劣化机制。研究成果可为揭示水致黄土滑坡机理提供理论支撑。

水致黄土滑坡成为黄土地区频发的地质灾害，解决的前提与关键是厘清滑带黄土的劣化机制。本项目紧紧围绕恒定剪切应力下水的增湿诱发滑带黄土劣化量化研究与机理揭示展开，主要在以下4个方面的研究内容上取得了研究成果：1）揭示了应力对滑带黄土以饱和度与吸力关系表征的土水特征曲线的影响，主要体现在进气值这一特征参量上，构建了净围压、主应力比与进气值三者之间的关系，提出了考虑增湿-剪切耦合作用影响的修正van Genuchten (VG)模型。该模型最大特点之一是模型参数皆是在常应力下确定，之二是模型中以应力作为直接参量，更便于工程应用；2）揭示了滑带黄土的湿压变形特性与屈服特性既取决于施加的净等向应力大小又取决于水力路径，当试样在初始屈服应力下增湿时，增湿湿陷达到最大；湿剪破坏行为取决于剪应力水平、吸力的丧失程度以及水力路径，且可以通过莫尔-库仑强度理论的线性形式很好地描述；提出了发生湿剪破坏的剪应力水平阈值与湿剪破坏时吸力阈值的定量化表达式，前者可用于描绘导致滑带黄土破坏开始的初始应力条件，后者可用于描述发生湿剪破坏时所需的吸力丧失程度；3）选用有效平均应力p'(=p+Srs)与偏应力q及吸力s作为本构应力，基于提出的剪切与湿剪临界状态线方程、剪胀方程、s-p'与q-p'平面上的屈服面函数及非关联流动法则，在BBM模型的基础上提出了适合于描述滑带黄土水敏性的弹塑性本构模型，并利用带误差控制的自动子增量步显式算法将本构模型数值化。该模型能够再现滑带黄土的湿压与湿剪特性，揭示了水敏性的力学行为；4）基于电镜扫描试验，初步揭示了增湿-剪切耦合作用对滑带黄土微观结构的影响机制，建立了微观的界限孔隙与宏观的土水特征之间的联系。研究成果为进一步揭示水致黄土滑坡机理提供理论支撑。