A long strip footing was constructed on an adjacent lot approximately six feet away from the west exterior wall of the Academy Sports and Outdoors building (four feet clear between edges of concrete footings). This construction reportedly caused the entire length of the wall to uniformly settle approximately one-half inch. The relatively sudden movement caused damage to the exterior block wall, interior flooring and drywall, and led to the closing of the store until the west wall of the building could be permanently stabilized. Temporary measures to prevent wall failure and further damage to the store included lateral support with steel tube bracing and vertical support to the overhanging roof with scaffolding.
The geotechnical investigation completed for the proposed adjacent structure identified competent bearing material (medium dense to dense sand) from just a few feet below the surface to the explored depth of 20 feet below grade. Dense sand was encountered below a depth of about 6 to 10 feet at each boring location. A relatively high water table at three to four feet below grade, as is typical for the area, was also observed.
Retrofit helical piers were selected to permanently stabilize the west wall of the building. Helical piers can be installed quickly and in areas of limited or tight access, such as around the existing lateral bracing and scaffolding. Our design software was utilized with the test boring information to determine pier depth and helix plate configuration to achieve the estimated design working load of 20 kips per pier with a factor of safety of two. Mobilization to the site began just three days after the observed wall settlement. Fifty-two (52) Model 288 (2.875-inch O.D. by 0.276-inch wall) round shaft helical piers with a 10”-12” double-helix lead section were installed along the exterior wall at a six foot spacing. The piers were advanced to depths of 10 to 12 feet and to torque values of at least 4,500 ft-lb, correlating to ultimate pier capacities of at least 40 kips (FOS ≥ 2). The piers were fitted with a retrofit bracket and a 30-inch long external pier sleeve. Hydraulic cylinders were then used to uniformly load the piers and stabilize the wall without lifting. The helical pier installation was completed in only three days, just six days after the settlement was observed.