成层土边坡中的优势流机理及其对边坡稳定性的影响

Preferential flow are commonly triggered in the naturally and artificially layered soil slopes once the blocked-water efficiency of layered slopes loses under rainfall infiltration conditions, in which the channels are formed for water moving quickly. It is crucial to properly characterize the preferential flow process of pore water to analyze the problems related to precipitation-induced landslide in the layered soil slopes. The research results on the mechnisms of the preferential flow have been used to analyze the transport of water and solute in the groundwater pollution. However, The problem is not solved properly on the effect of preferencial flow on the mechanics and stability of unsaturated soil slope. Hence, this project focuses on the problems related to the formation of preferential flow in the layered soil slope and its effect on the slope stability. The mechanisms of the formation and its effect on the seepage processes in the unsaturated layered soil slopes are investigate based on model tests under artifical rainfall. Based on the hyraulic and strength tests on the unsaturated soils, a new seepage model is developed, which can be used to characterize the preferential flow in unsaturated soil slopes under intermittent rainfall conditions. And the shear strength model is also developed in which the effect of preferential flow is considered. By combining the proposed seepage and shear strength models and the most recent achievement in slope stability analysis, a new numerical analysis procedure is developed for analyzing the stability of unsaturated soil slopes during random rainfall events. Then the numerical procedure is implemented into a computer code. The measured data related to the seepage process and occurrence of preferential flow in unsaturated soil slopes are collected to validate the proposed theoretical models and numerical procedure. The results of this research will shed new insight into the infiltration processes and disaster evaluation in unsaturated soil slopes, while providing a theoretical basis and effective procedure for assessing the stability of unsaturated slope under complex infiltration conditions.

降雨入渗下成层土边坡中通常出现水分阻隔及穿透后的水流快速通道，即优势流现象，有效描述这类复杂的渗流过程是准确评估与预测成层土边坡失稳破坏的关键。当前主要的工作在于地下水优势流机理及对溶质运移的影响方面，然而关于优势流效应对边坡土体力学及稳定性的影响问题仍未很好解决。本研究针对非饱和成层土边坡中优势流的发生及其对稳定性的影响，通过室内模型试验，揭示非饱和成层土边坡中优势流的形成机理及对渗流过程的影响规律；结合非饱和土水力与强度特性试验，建立能够描述间歇性降雨下非饱和成层土边坡中优势流过程的渗流理论及抗剪强度模型；提出能够考虑优势流效应的非饱和土边坡稳定性分析方法，开发计算程序。利用现场实测边坡土层中渗流过程、优势流的发生及其对边坡稳定性的影响进一步验证理论模型和分析方法的实用性。本研究将为降雨、垃圾渗滤液等诱发的成层土边坡失稳及其导致的地质与环境灾害问题的预测与防治提供理论基础与分析方法。

本项目围绕降雨入渗激励下非饱和成层土边坡失稳诱发地质灾害问题的物理机制与关键科学问题展开，从理论模型建模、室内试验开展、数值模型建立及程序代码开发、稳定性分析方法建立开展了研究工作，主要研究内容：1）开展广吸力域内的土水特征关系的建模；2）构建考虑水力滞回与非平衡效应的土水特征本构关系模型，揭示动态效应与水力滞回对土体持水特性的影响机理；3）实现全含水率变化下非饱和土收缩变形特性及定量描述；4）建立考虑水力滞回与动态效应的非饱和两相流渗流理论与数值方法；5）开展水力滞回影响的非饱和土抗剪强度试验研究，揭示水力滞回效应对土体抗剪强度的影响机制；6）建立定量刻画任意含水率变化的土体抗剪强模型及非饱和边坡稳定性分析方法。获得的主要研究成果：1）建立了广吸力域内的土水特征关系模型，较为全面地揭示了从非饱和过渡到饱和状态土体含水量与吸力的动态演化规律及关联；2）建立考虑水力滞回与非平衡效应的土水特征本构关系，揭示了动态效应与水力滞回对土体持水特性的影响机理；3）提出了能够描述全含水率变化下土体收缩变形的数学方程，定量区分了毛细与吸附效应对非饱和土体收缩的贡献，4）提出了考虑水力滞回与动态效应的非饱和土渗流理论与数值分析方法，实现成层土边坡中漏斗型优势流的形成机制及对渗流过程影响规律的揭示；5）提出能够描述水力路径依赖性的非饱和土抗剪强度公式，从宏微观层次揭示了水力滞回效应对土体抗剪强度的影响机制，为土体宏观工程力学性质与微细观结构的定量关联机制的研究提供借鉴与参考；6）建立了考虑水力滞回与动态效应的边坡稳定性分析方法，实现间歇性降雨条件下的边坡稳定性实定量分析。建立的理论与方法为复杂降雨条件下非饱和成层土边坡诱发的地质灾害问题提供了定量的评价工具，并为其他有关非饱和土灾害问题的解决提供可靠的理论基础。