部分飽和土壤精簡力學模式於不排水條件下之力學行為模擬

Abstract

部分飽和土壤內部的吸力會提供土壤額外的內部穩定因素，提高土壤的勁度與剪力強度。現今處理部分飽和土壤之力學模型及地工相關問題，多僅描述其排水條件下之力學行為與工程問題，甚或更僅將土壤簡化為飽和土壤來分析之。欲正確考量土壤實際之狀態與行為，有必要發展兼顧部分飽和土壤於排水與不排水條件下之力學模型。 儘管有些學者業已提出力學模型以描述部分飽和土壤之力學行為，但對於部分飽和土壤的不排水力學行為則鮮有著墨。本研究旨在建構一個部分飽和力學精簡模型，嘗試能描述部分飽和土壤在不排水條件下之基本行為特性，以便描述部分飽和土壤於不排水條件下的力學行為，進而能用於地工相關問題之模擬分析。 本研究先建構所需之理論基礎、接著撰寫程式以模擬實驗室之力學試驗。為檢討本力學模型的效能，繼以過去學者所曾發表之部分飽和土壤不排水三軸試驗作為模擬對象，用於驗證此模型描述部分飽和土壤的不排水力學行為之能力。待驗證本力學模型效能後，再將此模型之計算程序移植成大地工程分析軟體FLAC的使用者自訂模式（UDM）副程式，以供分析模擬大地工程相關之邊界值問題。本研究最後並以基礎承載分析與無支撐開挖作為應用分析範例，以展示本模式於部分飽和土壤工程問題之可應用性。

Suction in a partially saturated soil can increase the stiffness and shear strength of the soil. In many cases, the effect of suction in a partially saturated soil is ignored at all; very often, the soil above the ground water table is simply treated as a dry soil or as a saturated soil. Most constitutive modeling for partially saturated soils focused on the mechanical behavior and engineering problems in drained conditions. Mechanical behavior and modeling of partially saturated soils under undrained condition has drawn much less attention. This thesis aims to develop a concise constitutive model for describing the mechanical behavior of partially saturated soils under undrained condition, at least qualitatively. First, model simulations of mechanical behavior for various stress paths in undrained condition are presented and compared with existing published experimental data for verification. Subsequently, a series of parametric study demonstrates the simulated mechanical behavior under various conditions. Finally, engineering behavior of various geotechnical problems are examined by using numerical stress analysis with the inclusion of the proposed model.