The San Mateo Bayfront Levee Improvement (SMBL) project consisted of four separate sites requiring perimeter flood walls to protect the areas against storm surge and wave run-up. Two of the sites were earthen levees that had settled and needed to be raised and widened to provide adequate flood protection and emergency vehicle access. The SMBL project protects 8,000 properties along the bayfront of San Mateo from a major 100-year flood.
Geotechnical studies of the earthen levee systems revealed that the levees were constructed on a layer of concrete rubble over compressible Bay Mud deposits. Moreover, engineering analyses concluded that the levees would not provide adequate seepage resistance and would experience significant displacement under design seismic loading. ENGEO provided an innovative solution to mitigate seepage risk through installation of vinyl sheet piles.
ENGEO designed the levee improvements through design workshops with the City of San Mateo and the project civil engineer.
The project faced multiple challenges during construction. The primary challenge was the presence of debris within the fill, which consisted of lumber, car parts, construction debris and large concrete rubble, some of which were classified as Class I waste. This manifested into construction difficulties during the vinyl sheet pile cutoff wall construction. However, ENGEO’s field engineer worked collaboratively with the contractor in the field to troubleshoot the solution during production and eventually came up with an efficient workflow to avoid delays.
The city, ENGEO, and the contractor worked closely to separate the excavated materials and effectively isolated Class I waste from other non-hazardous debris. This waste/debris sorting effort resulted in significant reduction in Class I waste disposal costs. While the use of vinyl sheet piles for the site conditions was not ideal, after collectively coming up with a workflow to expedite the installation process, the SMBL project was completed roughly 4 months ahead of schedule and 20% below the Engineer’s Cost Estimate. At the same time, the city presented the completed project to the Federal Emergency Management Agency (FEMA) for recertification. FEMA fully accepted the SMBL project and removed a significant portion of the San Mateo Bayfront from the 100-year flood zone. The successful completion of the SMBL project would not have been possible without the collaboration of the city, the engineering team and the contractor.
The project received the 2013 CAL Geo Outstanding Project Award, Mid Size Projects Category and the 2013 ASCE San Francisco Section Geotechnical Project of the Year.
<blockquote><em>”The City’s project management team would like to thank you for he outstanding professional services provided by the ENGEO team for the geotechnical engineering design and construction support of the critical Bayfront Levee Improvements project. The constructed improvements now protect a large area of San Mateo from tidal flooding during a 100-year storm event and directly benefit over 8,000 homes”</em>.</blockquote>
Cathy Zammit, P. E