逆打工法樓板軸向勁度之研究

The Slab Axial Stiffness in Top-Down Construction

錢立豪(Li-Hao Chien)

指導教授 ： 陳水龍

國立臺北科技大學/工程學院/土木與防災研究所/碩士(2013年)

https://doi.org/10.6841/NTUT.2013.00659

摘要

台灣都會區高樓大廈林立，幾乎都與鄰房相距甚近或貼近，進行地下深開挖施工時必需考量鄰房安全。其中逆打工法於深開挖工程中可有效地減少工時及損鄰情況，尤其適合都會區有地下室工程之建築物或地鐵捷運等地下工程，今已普遍的被運用。本研究先採用Plaxis 2D數值分析軟體來進行實際逆打深開挖工程案例分析，並以此案例作為基準案例。再使用Plaxis 3D數值分析軟體來模擬逆打工法中不同寬長比情況下樓板所產生的軸向勁度及變形量。最後由分析之實際軸向勁度與一般所預估之軸向勁度以比例的方式來轉換2D程式分析時所需輸入的參數，將轉換後之軸向勁度進行基準案例程式模擬與比對，繪製出K值比與位移δ比之正規化曲線圖，及不同樓板寬長比下，各開挖階段時之位移比曲線圖及K值轉換圖表。
分析結果顯示，轉換後的連續壁側向變位量會比原基準案例的連續壁側向變位量小，隨著開挖深度越深該現象越趨明顯，在同一寬長比模型中，中心點位移變化量為最大，而越靠近樓板邊緣的位移變化量越小即軸向勁度越大，代表抵抗連續壁側向變位量的力量也越強，最後統整來看樓板寬長比越小時，與基準案例連續壁側向變位量的位移比相對越小，樓板寬長比越大時，位移比會越大越趨近於1，代表會越接近基準案例之側向變位量。此與實務上的經驗相同，證明本研究所提出之方式可供參考，未來在設計上就不需要如此保守，該結果也可應用於3D數值分析簡化為2D數值分析上，提供更方便之分析模式並節省程式分析時所需時間，以達到最佳化與更具安全性的開挖工程設計。

關鍵字

深開挖 ； 逆打工法 ； 連續壁 ； 樓板 ； 變形量 ； 軸向勁度 ； PLAXIS

並列摘要

In metropolises in Taiwan, high buildings stand in great numbers and are usually very close to neighboring buildings. Therefore, for constructions related to deep excavations, it is important to consider the safety of neighboring buildings. Among the construction methods, the top-down construction method can efficiently reduce man-hours required and damage to neighboring buildings in cases of deep excavations. This method is especially suitable for underground constructions such as basement constructions of buildings and subway/MRT constructions. It has been widely used nowadays. This study first used Plaxis 2D, a numerical analysis software package, to perform a case analysis of an actual top-down deep excavation construction as the benchmark case. Then Plaxis 3D, another numerical analysis software package, was used to simulate the axial stiffness and deformation of floor slabs of different aspect ratios using the top-down construction method. Finally, based on the ratio of the actual axial stiffness and the predicted axial stiffness, the input parameters for the analysis using the 2D software were transformed. The transformed axial stiffness values were used for simulations by computer programs and comparison with the benchmark case. The diagrams of normalized curves of the rations of the K values and the displacements δ were obtained, as well as those diagrams with different floor slab aspect ratios in various excavation phases.
According to the results of the analyses, the lateral displacements of the diaphragm wall after transformation were smaller than those of the benchmark case. This phenomenon was more significant as the depth of excavation got deeper. Under the same aspect ratio, the displacement of the center was the largest. The displacements closer to the edges of the floor slabs were smaller, in other words, the corresponding axial stiffness values were higher, meaning stronger resistances against lateral displacements of the diaphragm walls. To sum up, when the floor aspect ratio was small, the displacement ratio based on the benchmark case would be relatively small. When the floor aspect ratio was large, the displacement ratio would be large and closer to 1, in other words, the lateral displacement was closer to that of the benchmark case. This finding was consistent to the practical experience, and proved that the method proposed by this study can be used as a reference. Future designs can be less conservative. This finding can also be applied to cases of simplifying a 3D numerical analysis into a 2D numerical analysis by providing a more convenient analysis model. The time required for analyses using computer programs can also be reduced. The purpose of designing an optimized and safer excavation construction can be achieved.

並列關鍵字

deep excavation ； top-down construction method ； diaphragm wall ； floor slab ； deformation ； axial stiffness ； plaxis

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