Location
Chicago, Illinois
Date
02 May 2013, 2:00 pm - 3:30 pm
Abstract
A deep excavation was to be carried out adjacent to a fragile building in weak ground. An underpinning scheme utilizing 250kips capacity micropiles socketed into the bedrock was designed to provide stability to the building during the excavation. In adopting the micropile system, the interior of the basement had to be retrofitted with a new reinforced concrete structural system of walls, slabs and beams to provide rigid framing for transfer of loads between the existing structural walls and the new micropiles. The micropiles were installed from inside the basement of the adjacent building under low headroom conditions. A preliminary load test on a sacrificial test pile was carried out to confirm the design assumptions for the rock socket bond strength achievable in the rock. The test pile was instrumented with five levels of strain gages to determine the load distribution along the pile. Evaluation of the load test results indicated that the rock socket bond strength achieved was 186.7psi and a minimum factor of safety of 2.15 was achievable for a 9ft long and 8.5ins diameter rock socket. The bedrock levels encountered during production drilling were highly variable. The maximum difference in the toe level of installed micropiles was 6.8ft.
Department(s)
Civil, Architectural and Environmental Engineering
Meeting Name
7th Conference of the International Conference on Case Histories in Geotechnical Engineering
Publisher
Missouri University of Science and Technology
Document Version
Final Version
Rights
© 2013 Missouri University of Science and Technology, All rights reserved.
Creative Commons Licensing
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.
Document Type
Article - Conference proceedings
File Type
text
Language
English
Recommended Citation
Ho, Chu and Pena-Iguaran, Adrian, "Underpinning Using Micropiles for Fragile Building Adjacent to Deep Excavation in Manhattan, New York" (2013). International Conference on Case Histories in Geotechnical Engineering. 33.
https://scholarsmine.mst.edu/icchge/7icchge/session02/33
Underpinning Using Micropiles for Fragile Building Adjacent to Deep Excavation in Manhattan, New York
Chicago, Illinois
A deep excavation was to be carried out adjacent to a fragile building in weak ground. An underpinning scheme utilizing 250kips capacity micropiles socketed into the bedrock was designed to provide stability to the building during the excavation. In adopting the micropile system, the interior of the basement had to be retrofitted with a new reinforced concrete structural system of walls, slabs and beams to provide rigid framing for transfer of loads between the existing structural walls and the new micropiles. The micropiles were installed from inside the basement of the adjacent building under low headroom conditions. A preliminary load test on a sacrificial test pile was carried out to confirm the design assumptions for the rock socket bond strength achievable in the rock. The test pile was instrumented with five levels of strain gages to determine the load distribution along the pile. Evaluation of the load test results indicated that the rock socket bond strength achieved was 186.7psi and a minimum factor of safety of 2.15 was achievable for a 9ft long and 8.5ins diameter rock socket. The bedrock levels encountered during production drilling were highly variable. The maximum difference in the toe level of installed micropiles was 6.8ft.
