雨水入渗对非饱和土坡稳定性影响的参数研究

Parametric Study of Effects of Rain Infiltration on Unsaturated Slopes

很多国家和地区的斜坡失稳与雨水入渗有密切关系。通过参数分析研究可以深化对这种关系的认识和理解，因而对滑坡灾害的预测和预防有重要意义。针对香港地区一种典型非饱和土斜坡，用有限元法模拟雨水入渗引起的暂态渗流场，然后将计算得到的暂态孔隙水压力分布用于斜坡的极限平衡分析。计算中采用延伸的摩尔－库伦破坏准则以便考虑基质吸力对抗剪强度的贡献，研究了降雨特征、水文地质条件及坡面防渗处理等因素对暂态渗流场和斜坡安全因数的影响。数值模拟结果表明：降雨强度、降雨历时和雨型对暂态渗流场及斜坡稳定性有明显的影响；土体的渗透系数，尤其是渗透系数各向异性的影响特别显著；斜坡中相对隔水层的存在以及斜坡防渗护面的效果等因素的影响均不容忽视。

Slope instability is closely related to rain infiltration in many countries. It is vital to understand this relation for prediction and prevention of landslides. Improved understanding can be gained through parametric studies. In this paper, a typical steep unsaturated cut slope in Hong Kong has been adopted for this parametric study. Transient seepage due to rain infiltration is computed using the finite element method. The computed transient pore water pressures are then used for subsequent limit equilibrium analyses of the slope. An extended Mohr Coulomb failure criterion is used to allow for shear strength variations as a result of changes in matric suction. Effects of various rainfall events, hydrogeological conditions and use of protective cover on the cut slope are investigated. The results of numerical simulation show that rainfall intensity, duration and patterns have a significant influence on the transient seepage in the soil and the stability of the slope. Anisotropic soil permeability, presence of an impeding layer and conditions of surface cover can also strongly affect the transient flows and hence the stability of slope.