Written by CHANCE Foundation Solutions on November 17, 2022
Because of the ability to transfer the structure load to deep, stable soils, engineers are increasingly relying on helical piles for new construction applications. In the case of this new condominium construction, the geotechnical investigation conducted at the project site revealed layers of medium dense, loose, and very loose sands to a depth of approximately 18-feet below grade, followed by a layer of dense sand. The soil then became loose again at depths of 30 to 34-feet. A deep foundation system was needed to transfer the structure’s loads through the shallow loose layers and into the dense sand layer found at approximately 18-feet.
The CHANCE Helical Pulldown Micropile (HPM) was chosen as the preferred deep foundation system for this project for several reasons. The main reason being the limited access to the project site and the close proximity of adjacent structures. Helical piles can be installed with relatively small construction equipment and produce no vibrations during installation; therefore, they are ideal for limited access, heavily congested construction sites.
The piles would need to be installed to a final tip elevation of approximately 21 to 23-feet, therefore, the design team wanted a deep foundation system that did not rely solely on end bearing to achieve capacity due to the loose layer of sand encountered in the borings at approximately 30-feet. The CHANCE HPM derives its capacity by combining both end-bearing on the helical plates and skin friction along the rough surface of the grout column, the result is a higher capacity pile system. By using the HPM rather than a standard helical pile, the design team was able to reduce the number of piles needed for this project by 25%.
Prior to production pile installation a load test was conducted on site to verify pile capacity. A total of 95 CHANCE model SS150 Helical Pulldown Micropiles were installed by veteran CHANCE Installers at Mason Grady Foundations. Each pile was installed to support a working load of 30-kips in compression. Pile installation and load testing took approximately one and a half weeks to complete.
^ Proven- Load test
CHANCE Helical Pulldown Micropile is a deep foundation solution that constructs a grout column around the shaft of a standard helical pile foundation system. This time- and labor-saving product is installed directly into soil eliminating the need for excavation and spoil removal from the job, allowing for 40-50 piles to be installed per day with smaller crews and equipment.
The unique design combines both end-bearing on the helical plates and side resistance along the rough surface of the grout column, which results in a higher capacity pile system (greater than 100 tons possible) that is ideal for weak soil sites with limited access.
CHANCE helical foundations install quickly in any weather condition. To install, a hydraulically powered torque motor is mounted to standard excavating equipment. Continuous torque and crowd is applied to advance the HPM into the soil. Soil displacement plates create an annulus around the shaft by pushing soil laterally. Cement grout is poured into the annulus around the shaft to form a composite column. Once cured, the grout column stiffens the pile shaft and provides additional lateral capacity.
Watch the Helical Pulldown Micropile video to learn more:
• Increase buckling capacity
• Increased compression capacity
• Provides additional corrosion protection
• Stiffens the load/deflection response
• Maximum Ultimate Capacity = 300 kips
Ideal for projects where increasing capacity and providing predictable results is a must, the HPM provides a stiff pile that resists buckling in weak soils while also providing corrosion protection in aggressive soils and high water tables. A proven engineered system, bearing and side resistance is combined to bring a no pre-drill solution to a wide variety of applications for new construction, remedial repair, and limited access areas with minimal site disturbance.
Mason Grady Foundations is a family owned and operated deep foundation construction company and CHANCE Certified Installer with locations in Georgia and Florida. With construction services for commercial, institutional, and residential clients, MGF provides a foundation to build on through strong working relationships, trust, ethics, pride and a safety-focused culture.
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