A.B. Chance Helical Pulldown Micropile
The Chance Helical Pulldown Micropile does not require removing spoils from the site. 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.
Developed in 1997 for sites with especially weak surface soils, this patented innovative application of the helical pile integrates Portland cement-based grout to increase the section properties of the shaft.
The A.B. Chance Helical Pulldown Micropile (HPM) brings the advantages of the pre-engineered helical pile to higher load applications. The Helical Pulldown Micropile can provide an additional 50-100% capacity when compared to an ungrouted helical pier in the same soil conditions.
By “pulling down” a special flowable grout as the foundation is screwed into the soil, these micropiles create a deep foundation with both a friction-bearing central shaft and end-bearing helical plates incompetent substrata.
Chance Helical Foundations install quickly in any weather condition. A hydraulically powered torque motor is mounted to standard construction equipment such as a digger-derrick truck, line truck, rubber tired backhoe, track-hoe excavator, or front end skid-steer loader. Continuous torque and crowd is applied to advance the Helical Pulldown Micropile into the soil
Benefits of the Chance Helical Pulldown Micropile
Benefits of the Pulldown Micropile
- Speed: 40-50 piles per day/per crew
- High capacity
- Predictable results
- Labor-saving – smaller crews
- No pre-drilling
- Resistance to buckling in weak soils
- Stiffer pile (deflects less at a particular load)
- Additional corrosion protection in aggressive soils
Deep Foundation Applications
- High capacity/greater than 100 tons
- Underpinning applications
- New construction
- Build on weak soil sites
- Limited access
How it Works
Chance Helical Pulldown Micropiles are used to form a grout column around the shaft of a standard helical anchor/pile. The installation process can employ grout only or grout in combination with either steel or PVC casing. To begin the process, a helical anchor/pile is placed into the soil by applying torque to the shaft. The helical bearing plates require significant force or torque to advance the helical pile into the soil.
After the lead section containing helical plates penetrates the soil, a lead displacement plate and extension are placed onto the shaft. Torque is again applied on the assembly to advance the helical plates, which pulls the displacement plate downward, forcing soil outward and creating a cylindrical void around the shaft.
From a reservoir at the surface, a flowable grout immediately fills this void surrounding the shaft. Additional extensions and displacement plates are added until the helical bearing plates reach the minimum depth required, or competent load-bearing soil. This displacement pile system does not require removing spoils from the site.