The American Society of Civil Engineers (ASCE) recognized two California projects with their 2022 San Francisco Section project awards: Outstanding Geotechnical Engineering Award for YouTube Headquarters in San Bruno and Outstanding Seismic Retrofit Award for Riverside Elementary in San Pablo.
ENGEO, an engineering and environmental consultancy with offices in the US, Australia and New Zealand, worked on both projects. YouTube Headquarters Building 3 at 1450 Bayhill Drive includes up to four levels of underground parking. Construction of the garage required the installation of a hybrid soil nail, tie-back and cantilever support pile shoring system up to 21.3 m (70 ft) deep. The excavation was located between a Caltrans dam and two San Francisco Public Utilities Commission (SFPUC) water lines, which are the primary source of water for San Mateo County and the city of San Francisco.
Due to the proximity to sensitive infrastructure, ENGEO prepared a monitoring instrumentation plan, analyzed expected deflections using numerical modeling, and calibrated the models to measured deflections. The Company held weekly meetings with SFPUC to present measurements and forecasts of future movement and provided engineering/geological observations throughout construction. The project was successfully completed between December 2020 and June 2021. Throughout construction, the SFPUC pipelines remained fully operational and the Caltrans Dam was unaffected.
For Riverside Elementary, a Bay Area school, ENGEO provided design-build construction services for a lateral spread mitigation caused by liquefaction adjacent to the Bay Area elementary school. Overlapping deep soil mix (DSM) columns were constructed to create shear plates in the soil parallel to the direction of possible soil movement.
The company conducted analysis to design the DSM panels and created the engineering drawings and specifications in-house. The project timeline allowed just over five months to provide the design, come to terms with the school district geotechnical engineer, and obtain approval from the State of California to begin construction within the district’s required schedule. During construction, the company conducted part-time observations supporting the contractor’s quality control team and the school district team’s quality assurance observations and reviews.