Construction of the YouTube HQ garage required installation of a hybrid soil nail, tie-back and cantilevered soldier pile shoring system up to 70-ft. deep. The excavation was located between a Caltrans embankment and two San Francisco Public Utilities Commission (SFPUC) water transmission lines that are the main source of water to San Mateo County and the city of San Francisco. (ASCE photo)

American Society of Civil Engineers (ASCE) has awarded two California projects its San Francisco section 2022 project awards: outstanding geotechnical award for YouTube's HQ in San Bruno and outstanding seismic retrofit award for Riverside Elementary in San Pablo.

ENGEO, an engineering and environmental consultancy with offices in the U.S., Australia and New Zealand, worked on both projects. YouTube HQ's Building 3, located at 1450 Bayhill Dr., includes up to four levels of below-grade parking facilities. Construction of the garage required installation of a hybrid soil nail, tie-back and cantilevered soldier pile shoring system up to 70-ft deep. The excavation was located between a Caltrans embankment and two San Francisco Public Utilities Commission (SFPUC) water transmission lines that are the main source of water to San Mateo County and the city of San Francisco.

Due to proximity to sensitive infrastructure, ENGEO created a monitoring instrumentation plan, analyzed expected deformations using numerical modeling and calibrated the models to measured deflections. The firm led weekly meetings with SFPUC to present the measurements and predictions of future movements and provided engineering/geology observation throughout construction. The project was successfully completed between December 2020 and June 2021. Throughout construction, the SFPUC pipelines remained fully serviceable and the Caltrans embankment was unaffected.

For the Riverside Elementary, a Bay Area school, ENGEO provided services for the design-build construction of a mitigation of liquefaction-induced lateral spreading adjacent to the Bay Area elementary school. Overlapping deep soil mix (DSM) columns were constructed to create shear panels in the ground parallel to the direction of possible soil movement.

The firm performed analyses to design the DSM panels as well as preparing the construction drawings and specifications in-house. The project schedule allowed for slightly more than five months to provide the design, get in agreement with the school district's geotechnical engineer and gain approval by the state of California to start construction in the district's required timeline. During construction, the firm took part-time observations supporting the contractor's quality control team and the quality assurance observations and testing by the school district's team.

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