採用無支撐開挖工法進行開挖時，壁體會呈現懸臂式剛性位移，最大側向變位發生於壁體頂端，其變位值可能大於容許值進而影響連續壁之強度。因此本研究之目的為於大跨距支撐下提出施工方便性與經濟性兼具之鋼支撐配置，以達如同無支撐開挖般無施工阻礙，但又能抑制連續壁頂部最大懸臂式變位之效果。首先針對臨時鋼支撐進行一系列之參數研究，研究成果顯示於基地長度小於75 m時，僅需架設一根或二根支撐即可，若架設二根支撐時建議支撐間距為6 m時有較佳配置；於基地長度大於75 m時，建議架設三根支撐且均勻地架設於擋土壁上時有較佳配置。此外支撐會因架設深度、架設層數及斷面尺寸而影響壁體變位抑制效果，支撐採架設於連續壁頂部、斷面尺寸越大及支撐層數越多，有越佳抑制效果。此外當架設大跨距支撐且同時構築內加勁版或背拉版時，有更佳抑制效果且壁體變形較為均勻。最後，將提出的大跨距支撐系統(LSS 系統)經實際案例驗證，進一步確認其合理性。

When the strut-free excavation method is used, the shape of the wall deflection is a cantilever shape, and the maximum lateral displacement occurs at the top of the wall. The displacement value may be greater than the allowable value and affect the strength of the diaphragm wall. Therefore, the purpose of this study is to propose a steel strut configuration that is both convenient and economical in construction with large-span struts, so as to achieve no construction obstacles like strut-free excavation, but also can restrain the maximum cantilever displacement at the top of the diaphragm wall. First, a series of parameteric studies on struts are conducted. The research results show that when the length of the excavation geometry is less than 75 m, only one or two struts need to be installed. If two struts are installed, it is recommended that the spacing between the struts is 6 m to have a better configuration. When the length of the excavation geometry is greater than 75 m, it is recommended to install three struts and evenly installed on the retaining wall to have a better configuration. In addition, the wall displacement restraining effect will be affected by the depth of the strut, the number of layers of the strut, and the section size. When the strut is installed at the top of the diaphragm wall, using a larger section size, and more strut layers will have better restraining effect. In addition, when the large-span strut is installed with inner cap slabs or outer cap slabs, there is a better restraining effect and the wall deflection is more uniform. Finally, the proposed configuration of large-span struts system (LSS system) is verified by actual case to confirm its rationality.

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