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Effects of Change in the Support System on Temporary Secant Pile Wall
Deep excavation with a support system is required to construct various parts of underground structures like shafts, stations, entry structures, etc. These structures have to be constructed using permanent or temporary embedded retaining walls with a support system. The selection of a suitable type of retaining wall will depend upon the geological condition present in the particular location, time, cost, available equipment, etc. In Bangalore Metro Rail Project, a secant pile wall was adopted as the temporary earth retaining system with the depth of excavation of about 20 m. It was designed initially based on bottom-up construction methodology with 3 levels of struts and 3 levels of anchors, but at a later stage, due to time and other construction-related issues, it was decided to change the configuration to 6 levels of struts. Generally, in deep excavations, all the underground structures should be designed and checked for the critical forces from both permanent stage and construction stages. Since secant piles are used as a temporary retaining wall, only construction stage analysis is carried out to get the governing forces and deformation. In construction stage analysis, soil layers are defined with boundary conditions, and the surcharge during construction and surcharge from the actual building near the secant pile are considered. This paper discusses the effect of change in the support system from anchors to struts and how these changes in the support system affect the behaviour of the secant pile and subsequently adjacent buildings present in the influence zone of the excavation. As a result, in changing from anchors to struts, the wall displacement, strut forces and ground movement on the adjacent ground and buildings increase. The increase in deflection, ground movements and strut forces occurs during backfilling sequence of the underground station excavation. During backfilling, struts have to be removed and this imparts a higher magnitude in deflection, strut forces and ground movements.
Effects of Change in the Support System on Temporary Secant Pile Wall
Deep excavation with a support system is required to construct various parts of underground structures like shafts, stations, entry structures, etc. These structures have to be constructed using permanent or temporary embedded retaining walls with a support system. The selection of a suitable type of retaining wall will depend upon the geological condition present in the particular location, time, cost, available equipment, etc. In Bangalore Metro Rail Project, a secant pile wall was adopted as the temporary earth retaining system with the depth of excavation of about 20 m. It was designed initially based on bottom-up construction methodology with 3 levels of struts and 3 levels of anchors, but at a later stage, due to time and other construction-related issues, it was decided to change the configuration to 6 levels of struts. Generally, in deep excavations, all the underground structures should be designed and checked for the critical forces from both permanent stage and construction stages. Since secant piles are used as a temporary retaining wall, only construction stage analysis is carried out to get the governing forces and deformation. In construction stage analysis, soil layers are defined with boundary conditions, and the surcharge during construction and surcharge from the actual building near the secant pile are considered. This paper discusses the effect of change in the support system from anchors to struts and how these changes in the support system affect the behaviour of the secant pile and subsequently adjacent buildings present in the influence zone of the excavation. As a result, in changing from anchors to struts, the wall displacement, strut forces and ground movement on the adjacent ground and buildings increase. The increase in deflection, ground movements and strut forces occurs during backfilling sequence of the underground station excavation. During backfilling, struts have to be removed and this imparts a higher magnitude in deflection, strut forces and ground movements.
Effects of Change in the Support System on Temporary Secant Pile Wall
Lecture Notes in Civil Engineering
Adimoolam, Boominathan (editor) / I. V., Anirudhan (editor) / Basarkar, Sunil S. (editor) / Prashant, Amit (editor) / Anburaj, C. (author) / Srinivas, A. (author)
DFI-India Annual Conference ; 2021
2023-04-11
13 pages
Article/Chapter (Book)
Electronic Resource
English
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