"John N. Puder was contacted as our choice for a difficult job. We have done some very tricky, high profile projects with John which were finished on time and on budget. To do the impossible takes a team that can work together, communicate, and give and take what is necessary. JNP is a sterling example of the type of contractor needed to do the impossible." ~ Geotechnical Professional Engineer
Holmes Correctional Institution Project Bonifay, FL |
Augercast & Drilled Piles
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| Top: Augercast piling underway for excavation
support. Bottom: Following the augercast work and installation of drilled underpinning piles, a custom designed system was installed that supported the three suspended columns during pit excavation and new foundation construction. |
Creation of the Orange County Regional History Center within the Orange County Courthouse, originally built in 1927, included the installation of a centrally-located elevator to comply with the American Disabilities Act. Excavation for installation of the elevator pit mat foundation would extend seven feet lower than the existing floor slab. This presented the design and construction team with several distinct challenges: sieve analysis had indicated that the level of fines in the subsurface soils precluded the use of chemical grouting which had been the originally anticipated method of earth stabilization for pit excavation; existing footings that intruded into the excavation area needed to be underpinned; and three steel columns supporting the 4-story steel frame and concrete structure were completely within the excavation area, requiring a temporary support system until their foundations could be demolished and the column loads transferred to the new foundations.
In close cooperation with the design and construction team, John N. Puder (JNP) developed a turnkey solution that involved an augercast pile earth retention system, drilled helical underpinning piles for footing support, and an innovative, custom-designed support system for the interior columns.
Augercast Excavation Support
The pit excavation was 38 feet by 28 feet in plan. The 12-inch diameter semi-continuous tangent pile support system was designed to extend to approximately 15 feet below working grade. In the low overhead conditions, sectional augering was required to reach embedment tip elevation. High-strength grout was pumped from outside the building to the basement level work area. Sixty eight reinforced piles were installed in this first stage of JNP’s subcontract.
Drilled Underpinning Piles
After the augercast piles had cured to 4,000 psi, general contractor Turner-PSA excavated to bottom of footing at a depth of 3.5 feet below existing floor level. At the three footings that impinged the excavation zone, JNP then installed helix-drilled steel piles to a competent stratum at five feet below the tip of the augercast wall. The piles were connected to the footings and hydraulic rams used to transfer the loads to the new foundations.
Customized Column Support System
By far the most challenging part of the work lay in supporting the three main columns. JNP designed, and fabricated on location, a system consisting of three pairs of 50-foot long, wide flange support brackets welded to the existing columns and reinforced with stiffeners, and steel frame bracing. All of the materials, including the 3,300-pound beams, had to be brought into the building through window openings.
With the support system in place, six calibrated hydraulic rams were positioned between the beams and reaction plates that were welded onto the existing steel columns. The hydraulic rams were activated simultaneously to lift the columns off the foundations. Short steel support pipes were then welded into position and the ram were removed. Once footing demolition was complete, excavation advanced to design depth and the new reinforced concrete foundations were poured and allowed to cure. The jacks were then repositioned and the column load lifted for support pipe removal. Controlled release of the hydraulic pressure then allowed load transfer of the columns to the new foundations.
For the successful and on-time resolution of this complex, critical-path portion of the overall project, JNP was recognized by the Associated Builders and Contractors with a Subcontractor Eagle Award.
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| Cross-section showing the three components of JNP’s work
– augercast piling, drilled underpinning piling, and column support system. |