Seismic Retrofit of 92/280 I/C Foundations by Micropile Groups in San Francisco Bay Area, California
Location
Chicago, Illinois
Date
02 May 2013, 2:00 pm - 3:30 pm
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
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
Momenzadeh, Mahmood; Nguyen, Tung; Lutz, Phil; Pokrywka, Tim; and Risen, Chris, "Seismic Retrofit of 92/280 I/C Foundations by Micropile Groups in San Francisco Bay Area, California" (2013). International Conference on Case Histories in Geotechnical Engineering. 28.
https://scholarsmine.mst.edu/icchge/7icchge/session02/28
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.
