Freeway Corridor Infill Apartments
San Diego, CA
Overview
Moment performed the geotechnical investigation for a 3-story apartment building on a tight triangular lot at a freeway interchange, less than a kilometer from the Rose Canyon Fault. The investigation included a liquefaction analysis, Caltrans-protocol corrosion testing, and foundation design that addressed both seismic settlement and environmental exposure from the freeway corridor.
The Challenge
The triangular lot at a freeway interchange presented multiple constraints: proximity to the Rose Canyon Fault (0.89 km, M6.6), 2–3 feet of undocumented fill at the surface, groundwater at 27.5 feet requiring dewatering consideration for deep excavations, and potential soil corrosivity from the freeway corridor environment. The site is within a mapped liquefaction zone.
Our Approach
Moment advanced two borings to 50 feet with SPT sampling at 5-foot intervals. The subsurface profile showed 2–3 ft of undocumented fill over native soils: loose to medium dense silty sands and well-graded sands (SM/SW, SPT N=12–34) in the upper 25 ft, underlain by medium dense to very dense interbedded sands, silts, and sandy clays (SPT N=20–52). Corrosion testing per Caltrans CT 643 (performed by Clarkson Laboratory) evaluated pH, resistivity, chloride, and sulfate concentrations. The liquefaction analysis confirmed the saturated sands are not susceptible, though dry sand settlement of 1.2 inches was anticipated.
Results
The investigation confirmed shallow spread footings at 24-inch depth would support the 3-story structure with a combined total settlement (static + dry-sand seismic) of 1.7 inches. Corrosion potential was classified as low to moderate — no extraordinary protection measures required beyond standard practice. The dewatering advisory for deep excavations was communicated to the contractor.
Technical Summary
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