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.