The Britannia Modular Laboratories 4 (BML4) project, located in South San Francisco, California, consists of three existing buildings that have been renovated for conversion to laboratory and office use. This project involves demolition or upgrade of the structures, including the addition of a new pile-supported second floor mezzanine inside one building; new canopy entrances for each building; a new service yard for heavy equipment related to laboratory infrastructure; and new site work (parking lot, walkways, etc.) - all with challenging ground conditions. Geosyntec was selected by the conversion team to develop geotechnical engineering recommendations for foundations and other site infrastructure.
Geosyntec's Scope of Services
Geosyntec collected and reviewed existing data and information available for the site; conducted a subsurface field exploration and associated laboratory testing program; and performed geotechnical engineering analyses based on previously existing data. The results of this analysis were used to develop and evaluate engineering properties at the site. We also provided geotechnical recommendations for foundation design and earthwork that were used to support site preparation, paving, utility installation, and pipeline trenches. We ultimately prepared the geotechnical report summarizing the work performed and associated conclusions and recommendations, and provided construction observation and testing services during earthwork and pile installation.
A particularly challenging aspect of the project was the evaluation of the amount of additional load that existing footings could take as part of the upgrade. The site overlies non-engineered fill and soft San Francisco Young Bay Mud. With additional loads being applied to some, but not all, of the existing footings, an evaluation of differential settlements between footings was critical. Where settlements were anticipated to be excessive, recommendations for piles were provided, and a pile testing program was developed to establish target penetration lengths for Tubex piles installed in low headroom conditions.
The site was also found to have significant areas of poor quality fill, which needed to be addressed during trenching and in advance of paving. In the worst areas, subgrade improvement was achieved through lime treatment when equipment access was feasible. Where subgrade conditions would not allow lime treatment, ground improvement was achieved through over-excavation of 18 inches and backfilling with rock and cellular geosynthetics to better distribute vehicular loads.