Prologis Loma Vista
Challenge
During construction of the Prologis Loma Vista EV Truck Charging station, a late design change required each of the 8 PMCI skids to resist additional uplift forces due to the anticipated seismic ground motion at the site. Each skid required 8 support locations.
Prior to construction, a geotechnical exploration consisting of the advancement of three soil borings to a maximum depth explored of 50 feet was conducted. The investigation identified 3 to 6 feet of undocumented fill soils that required remedial grading to replace them with compacted structural fill soils. The fill soils were underlain by loose to medium dense alluvial fine to medium sand, silty fine sand, and sandy silt to a depth of 37 feet. Below 37 feet, stiff to very stiff sandy clay was identified to a depth of 47 feet underlain by medium dense clayey sand to the maximum depth explored. Groundwater was not encountered at the time of the explorations.
Solution
Helical piles were selected as the preferred deep foundation option to accommodate the unanticipated design change because of their ability to work in tight areas of access and for their ability to mobilize immediately for quick installation. The Model HP287 (2.875-inch OD by 0.203-inch Wall) hollow round shaft helical pile system with a 10”-12” helix plate configuration was selected for the helical piles. The piles were installed to a minimum depth of 16 feet below grade to achieve a torque-correlated ultimate capacity of at least two times the service load of 13 kips. New construction brackets were attached to the tops of the piles leaving the top surface of the brackets exposed and flush with the concrete, allowing the PMCI skids to be connected directly to the helical pile brackets. Final location of the skids was achieved by the general contractor using steel angles that were bolted to the skid beams and field welded to the tops of the new construction brackets. The 64 helical piles were installed over a period of six days which allowed concrete to be placed around the brackets the following week, keeping the placement of the skids on schedule.
Project Summary
Products Installed:: (12) Foundation Supportworks® Model 288 Helical Piles, 10"-12" Plate Configuration, Design Working Compression Load of 10 kips, Installed Lengths of 11 to 16 feet; (24) Model 150 Helical Anchors, 8"- 10" Plate Configuration, Design Working Tension Load of 3.2 kips, Installed Lengths of 20 to 21 feet.
