Case Study
Situation
In 2007, Cantsink was hired to provide support for the foundation of a three-story addition to downtown Savannah’s Ralph Mark Gilbert Civil Rights Museum.
The original building is a former bank built in 1914 to serve the African-American community. The renovated structure was opened as the Civil Rights Museum in 1996.
The contractor, Collins Construction Services, hired Cantsink to provide foundation support for the addition and soil testing was conducted by Whitaker Laboratory, Inc., a geotechnical engineering firm, to determine the level of support needed to stabilize the structure.
Concern for the existing structure, helical piles were recommended in lieu of traditional pile driving systems that cause vibration.
Because of the limited space required for helical pier installation, the work proceeded concurrently with excavation, saving valuable construction time in volatile coastal weather conditions.
Scope of Work
Soil testing and investigation revealed a dense layer of fine brown sand with an “N” value exceeding 50 at depths ranging from 14 feet to 22 feet.
The subsurface contained very firm, gray fine sand and stiff, gray fine sandy clay to depths of 40 feet or more. After considering the range of options, Cantsink’s patented helical piers emerged as the best choice, with the engineer’s goal for pile depths around 15 feet to 20 feet.
Because helicals are augured into the ground, the installation minimizes vibration, which was important to protecting the adjacent historic building.Also, the skid steer used to perform the installation is more maneuverable in the densely developed urban environment.
Crews used a 7,500 ft.-lb. hydraulic drive head mounted on a Bobcat S250 skid steer loader for the job.
Anchor System
During the four-day installation process, 99 helical piers – 2.5-inch schedule 40 steel shaft with a single 14-inch diameter helix – were installed to depths of 15.5 feet to 17.5 feet, along with conducting a load test for capacity verification.
Results of the load test indicated a total deflection of .462 inches at 60 kips with .185 inches of rebound. All piers were galvanized to prevent corrosion in the coastal climate.
Final pressure reading of torque for the piers ranged from 2,900 to 3,000 psi.
Results
The Ralph Mark Gilbert Civil Rights Museum remains a popular attraction for the growing tourism market in Savannah.The city now reports more than 14 million people visited Savannah in 2018, many of them drawn by its plentiful historic sites, including this museum.
Thanks to the efficiency of Cantsink helical piers, the museum addition’s foundation could be quickly and permanently secured, saving time and money in the construction process.
Twelve years after Cantsink assured lasting stability for this structure with its patented helical piers, it continues to serve museum staff and hundreds of guests who tour the exhibits five days a week.
With Cantsink’s permanent support, this facility’s useful service will continue for generations to come.
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