Location

Chicago, Illinois

Session Start Date

4-29-2013

Session End Date

5-4-2013

Abstract

The Route 92/280 interchange (I/C) connectors are the latest major bridge structures to be retrofitted in the San Francisco Bay Area, California, United States. The presence of poor quality rocks and high groundwater due to the proximity of the San Andreas Fault at this site combined with low overhead of the connectors superstructure at some of the existing bents led to the use of micropile foundation system instead of a conventional Cast in Drill Hole (CIDH) pile system. The existing CIDH foundations were retrofitted at 5 bents by micropile group with very heavy column steel reinforcement additions and 11 bent columns were retrofitted by steel enclosure without foundation retrofit. This case history describes the project development, foundation investigation, construction method of the micropile foundations including the performance and proof testing conducted for the piles and the issues encountered and lessons learned during the project. For micropile projects in poor ground conditions and with high structural load demands similar to this project, it is essential to develop design parameters estimates such as pile tips and bond stress achievable for the site conditions and the project design loads and consider various aspects of constructability issues seriously and not rely solely on the performance testing role. Otherwise constructability and cost increase can be significant issues. For retrofit projects with cyclic load reversal from tension to compression due to rocking the pile displacement at the tension design load shall not exceed the elastic elongation of the pile significantly otherwise there is high risk of pile failure in tension or the subsequent compression loading where there is limited pile end bearing.

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

Seismic Retrofit of 92/280 I/C Foundations by Micropile Groups in San Francisco Bay Area, California

Chicago, Illinois

The Route 92/280 interchange (I/C) connectors are the latest major bridge structures to be retrofitted in the San Francisco Bay Area, California, United States. The presence of poor quality rocks and high groundwater due to the proximity of the San Andreas Fault at this site combined with low overhead of the connectors superstructure at some of the existing bents led to the use of micropile foundation system instead of a conventional Cast in Drill Hole (CIDH) pile system. The existing CIDH foundations were retrofitted at 5 bents by micropile group with very heavy column steel reinforcement additions and 11 bent columns were retrofitted by steel enclosure without foundation retrofit. This case history describes the project development, foundation investigation, construction method of the micropile foundations including the performance and proof testing conducted for the piles and the issues encountered and lessons learned during the project. For micropile projects in poor ground conditions and with high structural load demands similar to this project, it is essential to develop design parameters estimates such as pile tips and bond stress achievable for the site conditions and the project design loads and consider various aspects of constructability issues seriously and not rely solely on the performance testing role. Otherwise constructability and cost increase can be significant issues. For retrofit projects with cyclic load reversal from tension to compression due to rocking the pile displacement at the tension design load shall not exceed the elastic elongation of the pile significantly otherwise there is high risk of pile failure in tension or the subsequent compression loading where there is limited pile end bearing.