Challenge

The Kingsmill Resort planned to remove the existing one-story marina and restaurant building and replace it with a new two-story building. The project also included salvaging the existing deck that wrapped around the rear of the existing structure. A soil test boring completed on the property near the existing building encountered loose to medium dense silty sand to a depth of 22 feet with Standard Penetration Test (ASTM D1586) blow counts, N-values, ranging from 9 to 16 blows per foot. Medium dense silty sand (N = 27-28 bpf) was then sampled to a depth of 32 feet over loose to medium dense silty sand (N = 9-13 bpf) to the maximum depth explored of 50 feet. Groundwater was measured at a depth of 13 feet, but was understood to fluctuate with tidal surges and seasonal flows of the James River. Deep foundation support was proposed for the new building due to the relatively weak surface soils and the potential for erosion and scour along the shoreline.

Solution

Helical piles were ultimately selected over timber piles due to the smaller equipment required and the relative ease of pile installation in the limited working space adjacent to the existing deck. The helical piles were designed for a tension service load of 10 kips and compression service loads ranging from 13 to 55 kips. The Model 288 (2.875-inch OD by 0.276-inch wall) round shaft was selected to support compression service loads up to 34 kips and the Model 350 (3.5-inch OD by 0.313-inch wall) round shaft was selected to support compression service loads from 38 to 55 kips. Both pile configurations included 10”-12”-14” triple-helix lead sections. The Model 350 piles also included a 14” helix plate on the first extension. A calibrated electronic torque transducer was utilized to monitor pile installation torque directly, or to establish the differential pressure to torque correlation. Piles were installed to depths ranging from 21 to 31 feet and to torque-correlated ultimate capacities exceeding the service loads by a factor of safety of at least two. A compression load test (ASTM D1143) and a tension load test (ASTM D3689) were completed on sacrificial Model 288 piles installed to their respective torque requirements for the intended loads. Total pile head movement, including elastic shortening or lengthening, was measured at 0.39- inch for a compression load of 33 kips and 0.28-inch for a tension load of 10 kips. Both measurements were within the tolerable limits specified.

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Project Summary

Architect: OZ Architecture

Structural Engineer: The Structures Group

Geotechnical Engineer: GET Solutions; ECS Ltd. Mid-Atlantic

General Contractors: Brasfield & Gorrie, LLC; Tauer Group

Certified Pile Installer: JES Construction, Inc.

Products Installed: (15) FSI Model 288 and (14) FSI Model 350 Helical Piles, 10”-12”-14” Lead Sections, 14” Plate on First Extension of Model 350 Piles, Installed Depths from 21 to 31 feet, Design Working Compression Loads from 13 to 55 kips, Design Working Tension Load of 10 kips