Numerical Analysis for Buttresses in Deep-excavation

• Main Authors: Chong-Dao Li, 李崇道
• Other Authors: 陳水龍
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/yzcxqq

碩士 === 國立臺北科技大學 === 土木與防災研究所 === 97 === Balustrades are commonly used in deep excavations in soft soil, and there have been many successful cases accumulated, indicating the installation of balustrades contributes greatly in the control of lateral displacement of diaphragm walls, differential settlement of jobsite and heaving. The behavior of balustrades is a three dimentional issue, for which single-dimensional elasto-plastic beam analysis is frequently used in engineering designs but difficult to simulate the actual mechanics of a balustrade. The 3D computer program, Plaxis 3D Foundation, was introduced for analysis of balustrades in actual cases, while the observation of lateral displacement in diaphragm wall and monitoring results from real-life cases were compared. A hypothetical case was established for investigation of the impacts of type, thickness and penetration depth of diaphragm to the stability of excavation from a microcosmic point of view, as well as the impacts of asymmetric balustrades and different spacing and length of balustrades from a macroscopic point of view. The analysis result suggested that interior balustrades that are removed as a whole perform the best in controlling lateral displacement in diaphragm walls, followed by non-T-section interior balustrades that are removed one by one, and T-section interior balustrades that are removed one by one performs the worst amongst all. The displacement of diaphragm walls stopped to decrease when the two types of balustrades that are removed in stage reach certain penetration depth. In addition, in case that there is no acceptable bearing layer at the bottom, the self-weight of balustrades will increase with thickness, resulting in increase in lateral displacement. The increase of penetration depth and thickness of T-section interior and exterior balustrades that are removed in whole helps control the lateral displacement of diaphragm wall. The establishment of asymmetric interior balustrades that are removed in stage performs better compared to symmetric establishment, but the lateral displacement on the other side of wall where there is no balustrade shows sign of increase. The result of interior balustrades that are removed in whole is completely the opposite of that obtained from balustrades removed in stage. The establishment of interior and exterior balustrades with proper length and at proper spacing provides effective control of lateral displacement.However, too many balustrades may result in high stiffness of diaphragm wall, leading to cantilever configuration. Finally, a normalized chart was developed for the maximum mid-section displacement of diaphragm walls for reference of designers.