Helical Piles Support St. Louis School

The Hickey Elementary School building was constructed in 1965. School officials planned an elevator addition to comply with American Disability Association (ADA) requirements. However, there were some challenges The soil at the proposed elevator location generally consisted of uncontrolled fill with rubble and debris beneath a sturdy clay soil. Therefore, the installation of a deep foundation system was necessary. This system needed to be installed below the fill and into the sturdier, clay soil. The deep foundation system minimizes the influence of the elevator loads on the existing shallow footings. The system also needed to be installed within the tight working space of the elevator pit excavation, which included low overhead conditions with only an eight-foot-high ceiling.

Helical piles were selected as the ideal solution for this project given their ability to be installed with relatively small equipment within the confined space of the existing building. The design engineers determined three helical piles were necessary. The design of the helical piles includes a double-helix lead section be installed to support a total service load of 80 kips in compression. A kip is a unit that measures force. One kip equates to 1,000 pounds-force. So, 80 kips equals 80,000 pounds-force. The double-helix design ensures stability.

A hand held drive unit, powered by a remote hydraulic (water) source, was used to install the helical piles to torque-correlated ultimate pile capacities of at least 54 kips. The limited overhead clearance unsurprisingly created a challenge. Shorter (5-foot) extensions were required to advance the piles to depths from 21 to 31 feet below the bottom of the excavation. New construction brackets were fitted to the tops of the helical piles to be cast into the poured mat foundation of the elevator shaft.

During installation, the team encountered old concrete foundations below the pit excavation. While the helical piles effectively churned through most of the surficial ruble and debris, they could not penetrate this large obstruction. A mini drill rig was brought in to core through the existing footing and allow for the helical pile installation.

Though the team met some challenges, the Foundation Supportworks by Woods crew successfully installed helical piles in Hickey Elementary School in St. Louis, Missouri. This foundation system will provide long-lasting support for the required elevator.