Nestled off Florida’s coast and located just offshore of Fort Myers on Florida’s southwest coast, is Sanibel Island. This remarkable island is known for the wide variety of seashells that wash up on its shores, its beautiful tropical foliage, and world renown tranquil beaches. Captiva Island, (her sister island lies to the north over a small bridge) is another enchanting tropical destination.
Accessed over land only by traversing a three-mile long causeway, Sanibel Island sends you back in time to a delightfully laid back atmosphere, with zero traffic lights.
Every pool and spa retaining wall eventually settles a small fraction, others settle significantly. Settlement is something the owner is going to have to execute measures to repair as the retaining wall has been slowly settling.
The cause of most foundation movement is settlement of the existing footing. Spread footers are a wide concrete pad that rests on the soil and reinforces the foundation wall. When the footing settles, it is a reflection the soil is shifting and it’s not supposed to. Perhaps the down spots are washing away, continually dumping water into the adjacent ground. The age and weight of the retaining wall then elects to shift or bow.
The pool contractor’s structural engineer made a preliminary site visit to determine the best course of repair. Once he reviewed the settlement issue he prepared a set of signed and sealed plans to stabilize the pool/spa retaining walls.
He prescribed helical piling to be utilized in an underpinning configuration to alleviate further settlement. Also, several helical tie-back anchors would require installation to stabilize the retaining wall.
A combination of six (6) helical tiebacks and seven (7) helical underpinning piers were chosen to stabilize the retaining wall foundation. Each tieback was installed next to the existing spa roughly four (4) feet from the top of the footing at an angle of 16 degrees from horizontal. The helical tiebacks consisted of “Chance” (1 ½” x 1 ½”) square shafts with an 10”-12” helix plate configuration on the lead sections to sustain a design working tension load of 12 kips.
The underpinning pile was a 8”10”12” “Chance” (2.875-inch OD by 0.276-inch wall) hollow round shaft. The helical piles are designed with appropriate helices and shaft size to support the foundation loads for the soil conditions. The helical piles are rotated into the soil with Caterpillar mini-excavator equipped with a hydraulic torque motor. The installation torque is continuously observed throughout the installation.
A foundation underpinning bracket was installed directly under the foundation wall and connected to the existing concrete footer. A 40 ton hydraulic jack transfers the load to the helical pile to stabilize the foundation and retaining wall.
The tie-back pile lengths ranged from 14’ to 28’ in depth. Upon completion of the helical pile installation, couplings and terminations were imbedded into a grouted column block.
Six (6) “Chance” (1-1/2-inch square bar) helical tieback anchors with a 10”-12”- double-helix lead section was installed to hold existing wall in alignment. The Caterpillar 304 CR excavator with a specialized hydraulic drive system powered by a 10k Pro-Dig drive head was utilized to install the anchors.
Eleven (11) Helical extensions imbedded the tieback anchors to lengths of 15 to 28 feet to attain final installation torques.
Seven (7) “Chance” 2 7/8” round shaft helical piles with a 10”-12” 14” triple-helix lead section were installed with a 304 CR Caterpillar Excavator. The excavator progressed the extensions to lengths on the order of 21-45 feet to achieve final installation torques. The ultimate capacities of at least twice the design working tension load of 20 kips
Nineteen (19) “CHANCE” (RS2875.203) round helical extensions were installed to corresponding capacities to secure tension load of 20 kips.
Seven (7) “Chance” Light Duty Underpinning Brackets were used to stabilize the existing concrete pool foundation and retaining wall.