初始地下水对浅层边坡降雨入渗及稳定性影响

Rainfall infiltration and stability of shallow slope considering initial groundwater

摘要:

浙江省山地丘陵地区浅层边坡土层大多存在稳定的初始地下水,从而导致土体含水率分布复杂、降雨入渗和稳定性分析难度大。为此,根据土体非饱和特性确定考虑初始地下水影响的坡体含水率指数分布模型,根据雨强与土体饱和渗透系数的对比关系将降雨分为弱降雨和强降雨两类工况,基于Green-Ampt入渗模型及水量平衡原理推导考虑初始地下水影响的浅层边坡降雨入渗物理方程解析解；结合浅层无限边坡模型,分析考虑初始地下水影响的浅层边坡在降雨作用下的稳定性；当假定坡体含水率均匀分布时,改进模型可近似退化为传统模型；当坡体含水率呈指数分布时,通过数值模拟验证改进模型的有效性。结果表明:当浅层边坡基岩上部土层存在初始地下水时,降雨导致的失稳将发生在基岩面处,且失稳时间早于传统模型的预测结果；弱降雨工况下,雨强提高导致边坡触发失稳的时间呈近指数关系快速缩短；强降雨工况下,当不考虑坡面径流对入渗的促进作用时,雨强提高导致边坡触发失稳时间缩短,速度趋于平缓。

Abstract:

Stable initial groundwater exists in most shallow slopes in mountainous and hilly areas of Zhejiang province, which leads to complex distribution of soil water content and difficulty of rainfall infiltration process and slope stability analysis. Considering the characteristics of unsaturated soil, the exponential distribution model of water content of slope under initial groundwater was determined. The rainfall condition was divided into weak and heavy rainfall according to the relationship between rainfall intensity and soil saturated permeability coefficient. On the basis of the Green-Ampt infiltration model and water balance principle, the analytical solution of governing equations for rainfall infiltration of shallow slope with groundwater was derived for the two conditions. Combined with the shallow infinite slope model, the stability of shallow slope under rainfall was analyzed considering the influence of initial groundwater. The modified model could be approximately degenerated into the traditional model when the initial water content was uniformly distributed. When the initial water content was in exponential distribution, the effectiveness of the modified model was verified through numerical simulation. Results showed that shallow slope failure induced by rainfall occurred near the bedrock surface when groundwater existed in the soil layer over the bedrock in shallow slope, and the failure time was prior to that predicted by the traditional model. Under weak rainfall conditions, the failure time was nearly exponentially shortened with the increase in rainfall intensity. Under heavy rainfall conditions, the failure time tended to be stable when the rainfall intensity was increased, on the condition that the promoting effect of slope surface runoff on infiltration was not considered.