Fayette County Historic Courthouse Underpinning
Project Owner: Historic Courthouse LLLP
Lead Design Firm: K Norman Berry
General Contractor: Messer Construction Co.
MEP Engineer: CMTA
Structural Engineer: Buell, Fryer, McReynolds, Jahad Inc.
Geotechnical Engineer: GeoStabilization International
Through its underpinning strategy on the historic Fayette County Courthouse renovation project, GeoStabilization International displayed the versatility of micropiles in various applications.
“We used one method to solve multiple problems in multiple ways on a single project,” says Jarrod Hartshorn, project manager with GSI. Hartshorn says that in addition to underpinning existing structure and new construction, GSI used micropiles for permanent shoring and showed that the method could withstand buckling after creating “a vertical cut of 10 feet under the building [for contractor access] with the piles being the only thing acting as columns to hold the building up.”
The team’s scope included increasing loads on existing footings as well as dropping the basement elevation and underpinning the historic structure’s existing foundation. The team developed a micropile support solution for underpinning portions of the four-story structure and enabling access to the basement level for the expansion. Crews underpinned relevant portions of the existing structure with a combination of micropiles and conventional underpinning pits. Dubbed an “A-frame” shoring system, it allowed access to the existing basement level for the renovations and expansion of the basement while addressing challenges presented by overhead electrical hazards.
The A-frame system incorporated vertically grouted micropiles that utilized the principles of the soil’s arching parameters, which provided the necessary force to keep the soil behind the shoring system from penetrating into the excavated area. Crew used less material, as the natural elements of the subgrade soil helped achieve the system’s goal.
The underpinning micropiles had to be designed for buckling because it was the entry point for general contractor Messer Construction to expand the basement further under the existing building. Micropiles were used along the building’s foundation to ensure its structural integrity would not be compromised once the foundation system was penetrated. The value-engineered A-frame system allowed the project to proceed on time and was less costly than other systems, saving money in the budget.
GSI worked together with BFMJ Structural Engineers to design a micropile and sister footing system that would connect to the existing stacked stone footing system. Due to the lead time for the sister footing material and pressures of the overall project schedule, micropile installation had to be expedited. Analysis of existing foundation elements and design of new elements were key to keeping the project on schedule as micropiles needed to be installed with precision to connect properly with the sister beam.