台中卵礫石層深開挖之三維有限元素法分析

Abstract

台中地區的地質條件主要由渾厚且廣泛的卵礫石層所組成，其土層具有良好的承載力以及自立性。在台中卵礫石層進行深開挖工程時，工程師一般透過經驗公式推估的方式，以評估卵礫石層的剪力強度，但此方式並無法精確地了解現地的土壤狀況。另外，擋土柱工法為經常使用於台中卵礫石層的半經驗施工方式，此工法大多由人工挖掘所完成，因此施工過程安全性為相當重要的課題。 綜合以上問題，需要建立卵礫石層之剪力強度參數簡易區分法與評估深開挖工程於臨界狀態下之安全性。由於卵礫石層的土壤粒徑過大而難以進行土壤試驗 (例如:土壤三軸試驗)，本文將透過蒐集過去進行的現地以及室內卵礫石層土壤試驗結果，並統整為卵礫石層之剪力強度參數範圍，提供工程師後續進行設計時參考之土層參數。透過有限元素數值模型以及硬化土壤模型，進行土壤試驗模型模擬與驗證，以探討此數值方法模擬卵礫石層力學行為的適用性。最後，透過三維有限元素分析，分別針對台中深開挖工程以及擋土柱工法進行分析，數值分析結果針對擋土柱護圈間距以及土層於臨界狀態下深開挖工程的安全性進行評估，並且針對擋土柱的進行最佳化設計。

The subsurface conditions of Taichung consist of a deep layer of gravels which have a strong bearing capacity and self-supporting. Besides, engineers usually evaluate the shear strength of the gravel by the empirical equation in design for deep excavation and the shear strength of gravel is not accurate. Besides, retaining pile is designed by experienced and the excavation of retaining pile is carried out manually, the safety of excavation progress is important. Due to the above reasons, establishing the shear strength distinction method and evaluating the safety in critical condition for deep excavation are in need. In this study, due to the fact that it is hard to conduct soil tests (i.e., triaxial test) because the size of the gravel is too large to sample, collecting the soil tests results and summering the range of shear strength through previous field and laboratory test to provide the engineer a reference about design in gravel deposit. Finally, the 3D finite element numerical indicates deep excavation and retaining pile in Taichung to analyze. The numerical results evaluate the spacing of cement protection and optimize the design for retaining piles (i.e. the spacing of retaining piles)