Helical Pulldown Micropile
The use of helical micropiles has long been established as a viable, cost-effective method for use in high capacity applications.
The Chance® Helical Pulldown Micropile is a composite pile combining Chance® Square shaft Helical Pier anchors with a grout column formed around the extension sections. Chance® Helical Pulldown Micropile increases lateral loading in poor soil conditions and adds a frictional component to end bearing capacities.
The Chance® Helical Pulldowns are used to install high-capacity foundations in soft soils where support on a slender steel shaft is a potential problem, or when the installer wishes to incorporate the friction capacity or other advantages of this high capacity helical pile.
First, a helical anchor/pile is placed into the soil by applying torque to the shaft. The helical shape of the bearing plates creates a significant downward force that keeps the foundation advancing into the soil. After the Lead Section with the helical plates penetrates the soil, a Lead Displacement Plate and Extension are placed onto the shaft. Resuming torque on the assembly advances the helical plates and pulls the displacement plate downward, forcing the soil outward to create a cylindrical void around the shaft. From a reservoir at the surface, a flowable grout immediately fills this void surrounding the shaft.
The process typically doubles or triples the ultimate compression capacity of the slender shaft when the helices are placed in adequate bearing at some depth below very soft soils. Additionally, the technique allows for protection of the anchor shaft by encapsulating the shaft with fibre reinforced grout coating as it goes through possibly aggressive environments.
ADVANTAGES OF THE CHANCE® HELICAL PULLDOWN MICROPILE:
- Capacity of each pile is accurately measured using the installation torque
- End-bearing/friction composite pile
- High-capacity-tested to 410 kips
- Transfers load through weak soils to high end bearing capacity helical plates
- No vibration during installation
- Achieves design loads in given soils
- No excavation spoils to remove
- Low mobilization costs
- Installs in any weather
- Installs in limited access situations – can be hand-installed if necessary
- Ability to be installed in close proximity to underground services