AB CHANCE HELICAL PULLDOWN MICROPILE
The AB Chance Helical Pulldown Micropile system is a method of constructing a grout column around the shaft of a standard helical anchor/pile, designed to enhance its load-bearing capacity. The installation process offers flexibility, allowing the use of grout alone or in combination with steel or PVC casing.
To initiate the process, a helical anchor/pile is inserted into the soil by applying torque to the shaft. The helical bearing plates exert significant force or torque to drive the pile deeper into the ground. Once the lead section with the helical plates has penetrated the soil, a lead displacement plate and extension are added to the shaft. Applying torque to the assembly causes the helical plates to advance, which pulls the displacement plate downward, pushing soil outward and creating a cylindrical void around the shaft.
A flowable grout is then introduced into this void surrounding the shaft from a reservoir at the surface. The grout fills the void immediately, providing additional support to the pile. Further extensions and displacement plates are added until the helical bearing plates reach the required minimum depth or competent load-bearing soil. Importantly, this displacement pile system eliminates the need to remove excavated soil from the site.
The Helical Pulldown Micropile system was developed in 1997 as an adaptation of the square shaft AB CHANCE piles, and it incorporates a patented innovative application of helical piles and portland-cement-based grout. This integration enhances the section properties of the shaft and combines end-bearing on the helical plates with skin friction along the rough surface of the grout column. Consequently, the system provides a significantly higher capacity pile, capable of supporting heavier loads.
Compared to ungrouted helical piers in similar soil conditions, the Helical Pulldown Micropile can increase capacity by an additional 50-100%. (See Capacity Charts). The installation of AB Chance Helical Foundations is efficient in various weather conditions. It typically involves mounting a hydraulically powered torque motor on standard construction equipment like digger-derrick trucks, line trucks, rubber-tired backhoes, track-hoe excavators, or front-end skid-steer loaders. However, in restricted access sites, the installation can be carried out using handheld equipment, without the need for machinery. Continuous torque and downward pressure are applied throughout the process to advance the Helical Pulldown Micropile securely into the soil.
Benefits & Applications of the Pulldown Micropile
- Speed: 40-50 piles per day/per team
- High capacity
- Predictable measured load capacities during installation
- Cost-effective
- Labour-saving – smaller teams
- 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
- Commercial / Industrial
- High capacity / Greater than 100 tons
- Underpinning applications
- New construction
- Build on weak soil sites
- Limited access
- Bridges
- Tree root protected areas (Tree friendly piling system)
Ground Sun Ltd is an approved Distributor of the Deep Foundation Solution from AB CHANCE
Main Characteristics:
• Faster construction and best piling solution near trees
• Building on weak soil sites
• High-capacity applications
• Limited-access installation
• Underpinning foundations
• New construction foundations
• Authorised installation contractors are trained and certified by A.B. Chance
Benefits of this system include:
• Resistance to buckling in very weak surface soils
• Stiffer pile (deflects less at a particular load)
• Additional corrosion protection in aggressive soils
What is a Helical Pulldown® Micropile?
The Helical Pulldown® Micropile is a system for constructing a grout column around the shaft of a standard Helical Foundation pile. To begin the process, a screw anchor is placed into the soil by applying torque to the shaft. The helical shape of the bearing plates creates a tremendous pulling force that keeps the anchor advancing downward into the soil. After the lead section with the helical plates penetrates the soil, a Lead Displacement Plate and Extension, are bolted onto the shaft. Resuming torque on the assembled shaft advances the helical plates and pulls the displacement plate downward, forcing soil outward to create a cylindrical void around the shaft. From a reservoir at the surface, a flowable grout immediately fills this void, surrounding and encapsulating the shaft. Additional extensions and displacement plates are added until the helical bearing plates reach competent, load-bearing soil. This displacement pile system does not require removing spoils from the site.
History of A.B. Chance in Civil Construction
Since 1912, A.B. Chance engineering research and development have advanced the unique advantages of helical anchors to meet today’s construction challenges.
A.B. Chance is the world leader in screw anchor technology. Regardless of the application, Chance ®products and methods are efficient and predictable. They give a cost-effective alternative to traditional construction foundations
Chance® helical anchors extend bearing plates into stable strata under soft, loose or expansive surface soils without significant disturbance.
Standard Applications of the Helical Screw Pile
- Underpinning & New Construction Foundations for Extensions and Buildings
- Retaining Wall Tieback Anchors
- Pipeline Buoyancy Control Systems / Substation Foundations
- Transmission & Telecoms Tower Foundations
Standard Construction Equipment
Installation of the micropile is completed quickly and easily with a hydraulic torque motor mounted on readily available equipment. Challenging sites, even with limited access, are overcome with the Helical Pulldown® Micropile.
Extensive Load Testing underpins the Chance Piles!
| Helical Pulldown® Micropile: Tested to 205 tons | Helical Pulldown® Micropile extracted for visual inspection | Close-up of Helical Pulldown® Micropile extracted from clay soil | Cross-section of extracted micropile |
The Helical Pulldown® Micropile also develops additional 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.