Location

Chicago, Illinois

Session Start Date

4-29-2013

Session End Date

5-4-2013

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

Appears In

International Conference on Case Histories in Geotechnical Engineering

Meeting Name

Seventh Conference

Publisher

Missouri University of Science and Technology

Publication Date

4-29-2013

Document Version

Final Version

Rights

© 2013 Missouri University of Science and Technology, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

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Apr 29th, 12:00 AM May 4th, 12:00 AM

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.