During a large flood event in downtown Cedar Rapids, an underground diesel storage tank was compromised and began taking in water. The owners decided to relocate the fuel tank and support it above ground in the lower level of an existing parking garage. A geotechnical investigation discovered approximately 12 feet of clayey fill with crushed limestone, over medium stiff to stiff sandy clay/clayey sand to depths of at least 35 feet where weathered limestone bedrock was identified.
Helical piles can be installed quickly with relatively small equipment, making them the obvious choice to provide the deep foundation support for the fuel tank in its new location. A 26 kip design working load was specified for each helical pile. The pile configuration consisted of Model 288 (2.875-inch OD by 0.276-inch wall) hollow round shaft with an 8”-10”-12” triple-helix lead section. The leading helix plate was fabricated to have a V-style cut on its leading edge to help the pile penetrate the dense fill and bear on or within the underlying bedrock. Standard extensions advanced the piles to depths from 35 to 47 feet to achieve torque-correlated ultimate capacities of at least twice the design working load (FOS ≥ 2). The piles were fitted with standard new construction brackets to be cast within two concrete tank supports. Despite tight working conditions with low headroom, even helical piles were installed within two days.
Certified Pile Installer: MidAmerica Basement Systems
Products Installed: (7) Foundation Supportworks HP288 Helical Piles, 8"- 10"-12" Lead Sections, Installed Depths from 35 to 47 feet, Design Working Load of 26 kips