High Capacity Helical Piles Featured

When it comes to deep foundations and high capacity piles in general, helical piles are often overlooked by today’s engineers. Perhaps it’s due to a lack of familiarity, or simply minimal evidence supporting their capabilities. Many designers are comfortable with more traditional foundation solution methods; however, helical piles provide a cost-effective alternative to traditional deep foundations such as drilled shafts. Beyond cost, helical piles offer many benefits not available with more traditional foundation systems.

In high-capacity applications, common concerns with helical piles tend to be uncertainty of load carrying capabilities, shaft buckling, and excessive settlement. On the contrary, load test data continues to indicate large load carrying capabilities for helical piles with low deflection values. With increased amounts of test data, as well as design improvements like the addition of grout columns for lateral support, larger diameter shafts, and increased wall thicknesses; helical piles in new construction applications are becoming increasingly viable. 

Benefits of Helical Piles compared to Concrete Drilled Shafts (Caissons)

• Capacity - Helical piles offer the advantage of a known capacity once they have been installed. Installation torque measured during installation confirms the pile’s capacity. If the soil that is encountered during installation varies from the soil boring, the torque readings during installation will reveal it. The installer could then modify the helical pile by adding or subtracting extensions to make the pile deeper or shallower. A smaller lead section, the section with the helical plates, could be utilized or helical extensions could be added. Since a helical pile is modular, it can be easily modified if the soil conditions vary from what is expected. A concrete drilled shaft can only offer estimated capacity based on the data in a soil boring.
  
  
• Down-drag – Also known as negative skin friction, down-drag occurs when the soil around a shaft consolidates or shrinks as the soil dries out. A drilled shaft has lots of area in contact with the soil simply because of its large diameter and when the soil consolidates, there will be large compression forces contributing to the load on the foundation. The slender shaft of a helical pile does not experience the same negative down-drag in expansive soils simply because the shaft is smaller in comparison.
  
  
• Installation – Concrete can take 2-4 weeks to fully cure, making a displacement foundation a challenging and slow start to a project. Helical piles can be installed and loaded immediately with no cure time needed. Because helical piles can go places concrete piers cannot, they are a simple solution for sites with poor access, challenging soil conditions, rough terrain, flood plains, glacial till, sand, swamps, or bogs.
  
  
• Equipment – Concrete weighs around 4,000 pounds per cubic yard and a full concrete truck can weigh 66,000 pounds and not including the drill rig required for a drilled shaft! Helical piles in comparison can be installed with readily available hydraulic equipment, either small or large, and can be installed almost anywhere. Backhoes, skid-steer loaders and mini-excavators are easily fitted with hydraulically-driven torque motors to install helical piles in construction sites inaccessible by the larger equipment required for other deep foundation systems.
  
  
• Weather conditions – Concrete installers are limited by weather temperatures with numerous adjustments to be made to deal with freezing or hot temperatures, rain, and snow. Although concrete can be installed in some of these conditions, it often affects the cure time and can reduce capacity. Helical piles can be installed in any weather or conditions that the contractor is willing to work in. Even rock-hard caliche or permafrost conditions can be overcome with the ROCK-IT, a modified lead section. By placing load-bearing helix plates into competent bearing strata below active expansive clays or frost zones, CHANCE helical pile designs can be shorter than concrete piles for equivalent capacities.
  
  
• Environmental impact – Helical piles are environmentally less intrusive without the cleanup associated with concrete. With no spoils to dispose of, helical piles offer contractors major advantages when it comes to local disposal regulations. Since helical piles can be removed and reused in another location, construction waste is reduced, providing significant savings with the temporary foundations common in the oil and gas markets and aquaculture.

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High Capacity Round Shaft Helical Piles

High-capacity round shaft helical piles provide an excellent solution for applications in soft soils requiring considerable lateral resistance or when buckling concerns exist. Extendable, they can be installed as deep as necessary to reach the required load bearing stratum in soil. The major distinguishing features and benefits include below are reflective of round shaft piles up to 7 inches in diameter. Greater capacities can also be achieved with larger diameter shafts.

• Capable of up to 90,000 foot-pounds of installation torque
• Up to 360,000 pound ultimate capacity and 180,000 pound working load.
• Excellent option for soft soils when buckling is a concern.
• Superior lateral load resistance
• Predictable Load Capacities
• Ideal for limited access areas
• Rapid Installation
• Minimal vibration and noise during installation
• No de-watering required
• Limited or no spoils

Helical Pulldown® Micropiles

The Helical Pulldown Micropile (HPM) is a method used to form a grout column around the shaft of a standard helical pile. The installation process can employ grout only (see Figure 1) or grout in combination with either steel or PVC casing (see Figure 2). 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. Load test data for a single 2-inch square shaft HPM has shown ultimate load capacities of up to 285 kips in compression.

Learn more about CHANCE Helical Pulldown Micropiles

Multi-story Condominium Case Study - Cambridge, Ontario

Dino Vito, M.A.Sc., P.Eng., Tayler Cook, University of Waterloo

EBS Geostructural Inc., Breslau, Ontario, Canada

A 13-story condominium tower was designed for construction in Cambridge, Ontario along the east bank of the Grand River.  The site was the location of a former factory and was subject to a remedial clean up prior to construction. The soil on site was variable and had a very high water table due to its proximity to the river. Many solutions were considered for the deep foundations required including pipe piles, “H” piles, caissons, and helical piles.

To determine the most efficient foundation design, testing had to be completed. The test results indicated a 2-inch solid steel, square shaft helical pile with an 8, 10, and 12-inch helical configuration was the most efficient pile design in the soil conditions, and the most cost-effective. Additional benefits of the helical piles included eliminating the need for soil removal and vibrations that might have caused issues with surrounding structures.

Based on the test data, design criteria included a minimum pile depth of 15 feet and a minimum of 6.5 ft into a suitable sand and gravel layer. All 730 helical piles were installed complete with a 6-inch diameter grout column in just forty working days and were able to resist an ultimate load of 285 kips in compression.

The ultimate load capacities of helical piles in compression and tension make them an increasingly effective foundation solution in many new construction applications. This is only one of many case studies on record, but one that clearly indicates that helical piles can be used in high-capacity applications.

Get the CHANCE Technical Design Manual and find your local distributor