基于改进Green-Ampt模型的降雨入渗条件下均质土坡稳定性分析

Stability analysis of homogeneous soil slopes under rainfall infiltration conditions based on an improved Green-Ampt model

摘要

【目的】降雨入渗对边坡的稳定性分析具有很大的影响。Green-Ampt模型常用于降雨入渗问题的分析，但其部分假设条件与实际情况有较大差异。为了得到更加符合实际的计算结果【方法】在Green-Ampt模型的基础上做了一定改进：在稳定降雨强度条件下，基于分层假设，将湿润区分为饱和区、过渡区、初始区，同时考虑了有限长边坡饱和区的坡面渗流作用，以粉土为例，假设入渗初期雨水完全渗入土体中，将入渗过程中的两阶段入渗(降雨强度控制阶段、土体入渗能力控制阶段)分别进行分析，并对渗透系数进行修正，得到入渗深度随时间的变化规律曲线，称为PSGA模型。以改进的PSGA入渗模型对边坡稳定性进行分析，此处考虑降雨入渗区均处于地下水位以上，并分别选取湿润锋、饱和区-非饱和区交界面作为危险滑动面进行计算，取较小值得到边坡安全系数随入渗时间的变化。最后采用PSGA模型对张家湾滑坡进行降雨入渗和稳定性分析。【结果】结果显示：从误差分析可知PSGA模型计算结果相较GA、SGA、MSGA模型更为精确；根据边坡稳定性分析：GA模型最早达到临界安全系数(2.71 h),其次为PSGA模型(4.74 h),最后为PSGA模型(6.27 h);对张家湾滑坡进行稳定性分析：相比SGA模型，PSGA模型计算结果更接近实际情况。【结论】结果表明：PSGA模型计算精度更高，也更符合实际情况；PSGA入渗模型得到的临界失稳时间较传统GA入渗模型更长，较SGA入渗模型更短；在坡长较小时，边坡饱和区的渗流作用对湿润锋深度的影响较大；通过PSGA模型对张家湾滑坡进行分析验证了该模型的合理性。

Abstract

[Purpose] Rainfall infiltration has a great influence on the stability analysis of slopes, and the Green-Ampt model is commonly used in the analysis of rainfall infiltration problems, but some of its assumption conditions are quite different from the actual situation. In order to get more realistic calculation result, [Methods] made some improvements on the basis of the Green-Ampt model: under the condition of stable rainfall intensity, based on the stratification assumption, the wetted area is divided into a saturated zone, transition zone and initial zone, and at the same time, the slope seepage effect of the saturated zone of the finite-length side slope is considered, and the assumption that the rainfall in the early stage of infiltration completely seeps into the soil body is made by taking the chalky soil as an example. The two stages of infiltration(rainfall intensity control stage, and soil infiltration capacity control stage) are analysed separately, and the infiltration coefficient is corrected to obtain the infiltration depth change rule curve with time, which is called the PSGA model. Improved PSGA infiltration model for slope stability analysis, here consider rainfall infiltration area are above the water table, and respectively selected wetting front, saturated zone-unsaturated zone interface as a dangerous sliding surface for calculation, take the smaller value to the slope safety coefficient with infiltration time. Finally, the PSGA model was used to analyse the rainfall infiltration and stability of the Zhangjiawan landslide. [Results] The result show that: from the error analysis, it can be seen that the calculation result of the PSGA model are more accurate compared with the GA, SGA, and MSGA models; according to the slope stability analysis: the GA model reaches the critical safety coefficient at the earliest time(2.71 h), followed by the PSGA model(4.74 h), and lastly, the PSGA model(6.27 h); the stability analysis of Zhangjiawan landslide: compared with the SGA model, the PSGA model is more accurate than the SGA model, the PSGA model is more accurate than the SGA model, and the stability analysis is more accurate than the SGA model. SGA model, and PSGA model calculation result are closer to the actual situation. [Conclusion] The result show that: the calculation accuracy of the PSGA model is higher and more in line with the actual situation; the critical destabilisation time obtained by the PSGA infiltration model is longer than that of the traditional GA infiltration model and shorter than that of the SGA infiltration model; the seepage effect of the saturated zone of the slope has a greater influence on the depth of the wetting front when the length of the slope is smaller; and the analysis of Zhangjiawan landslide by PSGA model verifies the reasonableness of this model.

关键词

降雨入渗 / PSGA模型 / 渗流 / 边坡稳定性 / 临界失稳

Key words

rainfall infiltration / PSGA model / seepage / slope stability / critical instability

基金资助

国家重点研发计划资助项目(2021YFC1523400)