Benefits of Higher Lateral Capacities Using Large OD Crossovers Sections on Smaller Diameter Helical Piles-PPT Presentation

PPT Presentation

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The Taylor Farms mixed-use project in Salinas, California, required foundations for a three-story addition in a vibration-sensitive historic district. Liquefiable soils, high seismic base shear, existing foundations, limited access, and just 22 feet of overhead clearance ruled out many conventional options.<br /><br />Small 2.875-inch helical piles could be installed with available compact equipment and short sections, but their predicted axial capacity was slightly below the 100-kip ultimate design target, and their lateral resistance fell short of the 3-kip requirement. Static axial load tests confirmed adequate performance, with back-calculated torque factors of 8.9–9.5, higher than the empirical value of 8.4 used for the initial estimate.<br /><br />The design addressed the lateral shortfall with a 4.5-inch-diameter crossover section in the upper 15 feet, transitioning to a 2.875-inch shaft below for axial resistance. This combined the larger upper shaft’s lateral capacity with the smaller shaft’s installation and axial-design advantages. Lateral testing and LPILE analysis supported acceptable performance for production piles with fixed heads.<br /><br />Using compact equipment, the contractor installed about 900 feet of pile per eight-hour shift—typically 10 piles per day—with pile depths of 75–95 feet. The approach required no spoils and avoided vibration concerns, while allowing pile locations to shift around obstructions.<br /><br />The presentation concludes that static load testing can reduce design uncertainty and that large-diameter crossover sections can provide greater lateral capacity without requiring large-diameter piles along their full length. This solution can be especially useful where access, overhead clearance, and protection of nearby structures constrain foundation construction.

Keywords

Taylor Farms

Salinas California

mixed-use project

helical piles

foundation design

vibration-sensitive district

static load testing

lateral resistance

crossover section

seismic soils