HELICAL PULLDOWN MICROPILE
The Helical Pulldown Micropile is a system for constructing a grout column around the shaft of a CHANCE Helical Pile Foundation System.
The 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 significantly higher capacity pile system.
Developed in 1997 as an adaptation to the historic square shaft CHANCE piles, this patented innovative application of the helical pile integrates portland-cement-based grout to increase the section properties of the shaft.
The 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 flowable, expansive 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 in competent 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 but mostly in restricted access sites the installation is carried out with no machines with just handheld equipment. Continuous torque and downward pressure to applied to advance the Helical Pulldown Micropile into the soil.
Benefits & Applications
Benefits of the Pulldown Micropile
- Speed: 40-50 piles per day/per team
- High capacity
- Predictable measured load capacities during installation
- 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
- Tree root protected areas (Tree friendly piling system)
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.
Ground Sun are approved Distributors of the Deep Foundation Solution from CHANCE
• 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
- RUnderpinning & 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.