為了避免地面鐵路對都會區開發的影響，有將地面鐵路移入地下或高架化的需要，而深開挖為鐵路地下化的重要工具。本研究以台南市區鐵路地下化為例，以台鐵永久軌里程UK356 + 320 ~ UK 356 + 840段的地下化開挖工程為研究對象，針對深開挖工程細節、土壤試驗、監測資料進行整理。深開挖的過程常引致擋土壁體的側向變位、開挖區外地表沉陷等問題，本研究首先探討二維與三維單元寬度在模擬平面應變條件下的差異，再對二維與三維全模模擬結果進行探討，最後針對考慮鄰房加載與否進行更深入的討論。分析所使用的軟體為PLAXIS 2D與PLAXIS 3D。
考量實際監測資料的不完整，本研究數值模擬跟監測結果比對，就變位增量及支撐軸力改變來驗證各開挖階段壁體變形變化的趨勢，模擬結果顯示，三維模擬能考量到整體分區施工的情形，相較於二維模擬在平面應變限制下的結果，三維模擬整體開挖所引致的地盤反應可以更好的表現，再者，鄰房加載與否對於最大壁體變位並無造成顯著增加。

In order to avoid the interruption from the at-grade railway on the development of the urban area, it is necessary to move it underground or elevated it, and deep excavation is an important tool for the construction of an underground railway. In this study, the Tainan underground railway project, at the chainage of UK356+320~UK356+840, was taken as the research background. The details of deep excavation (cross-section, ground profile, and construction sequences), soil test, and monitoring data are collected and studied. During the delivery of deep excavation, several issues such as lateral displacement of retaining wall and surface subsidence outside excavation area are often caused.
In this study, the difference between results from 2D and one-unit length 3D is firstly investigated. Further, 2D and full-scale 3D simulations are carried out and results are discussed. Finally, discussions on the impacts from adjacent buildings are undertaken. The software Plaxis 2D and Plaxis 3D are adopted for the study. Due to the absence of monitoring data, the wall-displacement increment and the variation of supporting axial force from both numerical analyses and available monitoring data were used – to verify induced wall deformation at each excavation stage.
Through the results of this study, it is concluded that the 3D simulation can take into account the impacts of zoning construction. So 3D simulation could perform better in a comparison with a 2D simulation which is only applicable to plane strain conditions. It is also concluded that the impact from adjacent buildings does not affect the maximum wall displacement induced by the deep excavation.

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