部分飽和土壤之精簡力學模式與應用

Abstract

部分飽和土壤中的吸力能夠增加土壤顆粒間的接觸應力，並造成屈服強度與勁度的上升。然而目前在部分飽和土壤相關地工問題的數值模擬中往往忽略吸力的作用，或是吸力對於變形性的影響。欲正確模擬部分飽和土壤的變形行為，必須以能夠考慮吸力效應的組合律進行數值模擬。 雖然目前學術界已提出不少的部分飽和土壤組合律，然而其中複雜的模式於實際應用上多有參數過多或參數不易率定等缺點，簡單的模式又難以表現部分飽和土壤完整的基本特性。本研究整合前人組合律理論中的各項優點，嘗試提出一套精簡的組合律理論，盡可能以最少的參數描述部分飽和土壤的各項基本行為，以利實用上的需求。 本研究並將此精簡的組合律編寫為FLAC軟體中的副程式，令該軟體在運算時能將部分飽和土壤的特性列入考量。為測試此組合律的表現，本研究模擬前人的壓密與三軸試驗結果，證實此組合律可至少定性地描述部分飽和土壤之行為。最後並以此模式應用於部分飽和土壤邊坡與土壩在遭遇降雨時的穩定分析，做為工程問題的實際應用範例。

Suction in partially saturated soils can increase the skeleton stress between soil particals and raise the yielding strength and stiffness of the soil. However, the additional stress or deformation resulted from suction was often ignored in numerical simulation. A proper constitutive model for partially saturated soils is required in numerical modeling to take the effect of suction into account. Although many models for partially saturated soils were proposed in the last two decades, some of them are too complicated in pratical application because too many parameters are required. Simple models, on the contrary, may not be able to capture the complete nature of partially saturated soils. In this thesis, a concised constitutive model that collects the merits of other models was proposed to describe major features of partially saturated soil with limited number of material parameters. The concised model was coded as a “FISH routine” in the numerical program FLAC to allow for the numerical modeling for geotechnical problem in partially saturated soil. For model verification, some triaxial tests carried out by other researchers are simulated. The comparison of the simulated and laboratory tested results confirmed that the proposed model is able to model the mechanical behavior of partially saturated soils. Finally, the stability of a slope and an earth dam with rainfall infiltration were analysed to demonstrate of applicability of this model.