Connecticut Basement Systems Case Studies: Surfside Motel Renovation - Helical Piers
Challenge
The Surfside Motel was originally constructed in the mid-1950's on a foundation supported on timber piles. The building is located adjacent to an ocean inland waterway that causes the groundwater table to fluctuate several feet throughout the day. During the construction phase of a neighboring property, a sheet pile wall was installed adjacent to the Surfside Motel's end wall. This end wall is a support wall spanning an opening in the motel to allow vehicle access to a back parking lot.
After the sheet pile wall was installed, the neighboring property was dewatered to allow for excavations to proceed. Reportedly, the dewatering process effectively lowered the groundwater table and caused the end wall of the Surfside Motel to settle. Deflection of the sheet pile wall may have also contributed to the end wall movement. Square bar retrofit helical piles were quickly installed in the hopes of stabilizing the wall from further movement. Upon completion of this repair, creep movement continued until work on the adjacent site was completed.
In the fall of 2010, the owner of the Surfside Motel began a renovation project, which included the construction of an additional third floor level. The original foundation design of the building theoretically allowed for the additional floor to be added. However, the design consultants and owners were concerned whether the end wall could handle additional loads considering the past history of movement. Since the adjacent property was built just a few feet from this end wall, load tests or other evaluations of the existing foundation did not appear feasible. They instead decided to install additional retrofit helical piers along the wall to ultimate design capacities of 60 kips per pile.
Solution
The retrofit pier design included 11 Model 350 (3.5-inch OD by 0.313-inch wall) helical piers. The new helical pier configuration consisted of 10"-12"-14"-14" quad-helix blade, ten-foot long lead sections. Meticulous site layout was required as the new helical piers would be installed between the existing square bar helical piers and the original timber piles. The leads were installed at a slight angle to allow for the uppermost 14-inch helix blade to extend past the bottom edge of the footing. Once the lead was installed, extensions were added to advance the piers to an average depth of 24.5 feet. The piers were installed to torque-rated ultimate capacities ranging from 60 to 64 kips. Foundation Supportworks Northeast installed the 11 retrofit helical piers in two days.
Project Summary
Architect: T.F. Cusanelli Architect
Structural Engineer: Hayman Foundation Engineering
Certified Pier Installer: Foundation Supportworks Northeast
Products Installed: (11) Model 350 Helical Piers, 10"-12"-14"-14" Lead Sections, Installed to an average depth of 24.5 feet, Design Ultimate Load of 60 kips.
