在一般的深開挖的分析設計,對於軟弱土層引致之連續壁潛變變位常被忽視,或者因為需要進行複雜的有限元素分析,而沒有去考慮潛變的影響性。本研究基於台北市軟弱黏土層深開挖完成且高品質觀測之施工案例,採用軟土潛變之土壤模型(soft soil creep)來進行模擬分析,而分析結果經與現場連續壁變形、背土側沉陷及擋土支撐軸力之觀測值頗為吻合,故選用作為進一步研究之基準模型,後續利用有限元素法進行一系列的模型進行參數研究,並將前述分析之結果統計歸納後,建議了之擋土壁最大變形與擋土系統勁度正規化公式、擋土壁最大潛變率與擋土系統勁度之正規化公式、擋土壁最大潛變增量與擋土系統勁度之正規化公式,以及擋土壁最大潛變速率與擋土系統勁度之正規化公式。本研究建議之簡化計算方法,經與觀測資料比對,顯示可以得到不錯的預測結果,根據相關建議之公式,可以簡單利用開挖深度及支撐系統勁度等基本參數,用來評估軟弱黏土層開挖之最大壁體變形量,以及由土壤潛變引致之最大壁體變形量、潛變率、總潛變率、潛變速率及潛變量,本文研究結果期盼可以提供作為對日後類似工程規劃、分析及設計時之參考。
Analysis and design of diaphgram wall displacement due to creep of soft clay has traditionally been ignored, probably due to the ignorance of its significance or the needs for complicated finite element analysis. Using data retrieved from a diaphragm wall supported soft clay excavation site in Taipei city, a finite element study that adopted the soft soil creep model has been employed to back-analyse the instrumented data and calibrate the appropriate use of the soft soil creep model, its material parameters and modelling process. The soft soil creep model together with the material parameters were then used in a series of parametric study to evaluate the relation between support stiffness and wall displacement due to undrained soil creep and the associated creep rate of the wall. Simple equations, in terms of the maximum excavation depth and support stiffness that is a function of support spacing and flexural stiffness of the wall, were then obtained. The result of this study provide valuable reference information for future design of diaphragm wall in similar ground.