Challenge

CSL Plasma planned renovations to a vacant end unit of a strip mall. The rear left corner of the unit had settled as much as two inches, evident by a large diagonal crack in the concrete block veneer covering the exterior CMU block wall. It was discovered that the entire strip mall had been constructed over an existing parking lot which was supported by up to 20 feet of fill soils. The new owners wished to permanently stabilize the settling portion of the building and lift the corner of the unit back toward level, if possible. The renovation would also include the construction of a freezer addition on the side of the building for blood plasma storage. A geotechnical exploration was not performed at the site; however, based on the findings of the presence of underlying fill materials, deep foundation support was specified for both the repair of the existing building and support for the proposed freezer.

Solution

A system of hydraulically-driven push piers was chosen to stabilize and lift the existing structure. A total of fourteen (14) Model 288 (2.875-inch O.D. by 0.165-inch wall) push piers were installed at a five-foot maximum center-to-center spacing along the intersecting walls of the settling building corner. The continuous wall footings were notched to allow the side-load retrofit brackets to extend beneath the foundation wall. The push piers were driven to approximate depths from 20 to 39 feet to achieve a target drive pressure of 3,000 psi (drive load of 28.8 kips). After the piers were each driven individually, they were connected in series with hydraulic lift cylinders and simultaneously loaded to lift the corner of the structure as much as 1.5 inches toward its original elevation.

The foundation design for the proposed freezer included nine (9) Model 287 (2.875-inch O.D. by 0.203-inch wall) round shaft helical piles with an 8”-10” double-helix lead section. A 16 kip ultimate capacity was originally specified for the helical piles; however, at the engineer’s request, the piles were advanced to depths from 19 to 25 feet below the ground surface to achieve a final installation torque of at least 2,500 ft-lb, correlating to an ultimate capacity of at least 22.5 kips. Installation of the push piers and helical piles was completed in just four working days.

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Project Summary

Architect: Novus Architects

Structural Engineer: Britt Peters and Associates, Inc.

General Contractor: Pro-Tech General Contractors

Certified Pier/Pile Installer: Foundation Supportworks® of Georgia

Products Installed: (14) Foundation Supportworks® PP288 Push Piers, Installed to Depths from 20 to 39 feet; (9) Foundation Supportworks® HP287 Helical Piles, 8"-10" Lead Section, Installed to Depths from 19 to 25 feet