未飽和土壤單峰與雙峰水力特性對邊坡穩定性影響之研究

Effect of unimodal and bimodal soil hydraulic properties on slope stability analysis

黃獻廷(Tsien-Ting Huang) ； 葉信富(Hsin-Fu Yeh) ； 柯建仲(Chien-Chung Ke)

《農業工程學報》 67卷3期 (2021/09) Pp. 51-63

https://doi.org/10.29974/JTAE.202109_67(3).0005

摘要

降雨入滲是主要造成邊坡不穩定的因素，降雨入滲的過程導致邊坡土壤的含水量與內部應力改變，進而影響邊坡的穩定性。土壤持水曲線（SWRC）用來描述土壤含水量與基質吸力之間的關係與土壤的保水特性，此特性在估算未飽和土壤特性相當重要，例如未飽和水力傳導函數和抗剪強度，因此土壤持水曲線被視為描述未飽和土壤特性的重要資訊。土壤持水曲線主要受到土壤孔徑分布所影響，而具有單峰與雙峰特徵，其中雙峰土壤持水曲線適用於結構性或是具有雙孔隙介質的土壤，此方法能夠描述土體中微孔與大孔的結構，了解不同孔隙尺度中的水力行為，故該模式較為符合現地土壤特性。鮮少有研究探討土壤單峰與雙峰模式對未飽和邊坡影響之差異性，本研究考量單峰與雙峰土壤持水曲線在實際降雨狀況下進行未飽和邊坡穩定性影響評估。本研究依據現地資料建置邊坡概念模型以模擬邊坡水力行為的變化，滲流分析結果顯示雙峰模式具有較好的保水能力，故其儲水性能較佳。在相同的飽和水力傳導特性下，雙峰模式中的濕潤帶前緣向下移動速度較快，導致壓力水頭與含水量以及土壤內部應力之改變。由於保水能力的不同，結果顯示雙峰模式的含水量及吸應力變化均高於單峰模式，本研究考量不同模式之滲流分析進而評估邊坡穩定程度，其結果指出雙峰模式的潛在破壞深度高於單峰模式。

關鍵字

土壤水力特性 ； 土壤持水曲線 ； 邊坡穩定性

並列摘要

Rainfall infiltration is the main triggering factor which causes slope instability. The process of rainfall infiltration leads to changes in the water content and internal stress of the slope soil, which will affect the stability of the slope. The soil water retention curve (SWRC) is used to describe the relationship between soil water content and matric suction and the water retention characteristics of the soil. This characteristic is very essential to estimate the properties of unsaturated soils (e.g. unsaturated hydraulic conductivity function and shear strength). Thus, the SWRC is regarded as important information to depict the properties of unsaturated soil. The SWRC is mainly affected by the soil pore size distribution (PSD), and has the features of unimodal and bimodal. The bimodal SWRC is suitable for soils with structural or dual-porous media. This model can describe the structure of micropores and macropores in the soil and understand the hydraulic behavior in different pore scales. Therefore, this model is more consistent with the properties of the on-site soil. Few studies have explored the difference in the impact of unimodal and bimodal models on unsaturated slopes. This study aims to consider the unimodal and bimodal SWRC to evaluate the impact of unsaturated slope stability in actual rainfall conditions. A conceptual model of the slope is built based on the field data to simulate changes in the hydraulic behavior of the slope. The results of seepage analysis show that the bimodal model has better water retention capacity, so its water storage performance is better. Under the same saturated hydraulic conductivity function, the wetting front of the bimodal model moves down faster. It results in changes in the pressure head, water content, and the internal stress of the soil. Due to the difference in water retention capacity, the results show that the water content and suction stress changes of the bimodal model are higher than those of the unimodal model. Based on the results of seepage analysis to calculate the stability of the slope, the results indicate that the potential failure depth of the bimodal model is deeper than that of the unimodal model.

並列關鍵字

Soil hydraulic properties ； Soil water retention curve ； Slope stability