CHANCE® Foundation Solutions Blog

We’re often asked by engineers and contractors how to bid helical pile foundations. This often happens when the geotechnical report for the project does not provide specific recommendations for the helical piles, i.e., pile type and length, helix configuration, and capacity. One of the best tools available to design helical piles based off a geotechnical report is HeliCAP® v3.0 Helical Capacity Design Software. The soil boring information can be taken directly from the geotechnical report and input into HeliCAP. Within minutes, the software will provide everything necessary to competitively bid the project.

CHANCE® helical tiebacks are a pre-engineered mechanical anchoring system for permanent and temporary shoring. The success of the helical anchor tieback system is based on decades of similar use of CHANCE anchors in the electric utility industry. Capacities up to 200,000 pounds per anchor are obtainable with this “instant” tieback shoring method. CHANCE tiebacks offer a fast, cost-effective and simple solution for any tieback project.

The Reality
A recognized challenge for geotechnical engineers designing deep foundations is utilizing information on subsurface soils from a finite number of subsurface explorations (e.g., test borings with Standard Penetration Test sampling).  If the geotechnical engineering consultant that was hired to coordinate and report on the explorations performs their work within the standard of care, the number of explorations performed at the site is appropriate and useful for characterization of a site’s soil profile.  From a well-coordinated subsurface exploration program, a geotechnical engineer is able to develop a representative understanding of the composition and strength of subsurface soils (including rock and obstructions where present) at a site.  It’s no mystery that SPT boring logs per ASTM D-1586 are routinely used in the design of deep foundations, especially considering the many empirical correlations between SPT blow count and engineering properties of soils that have been established since the test method was standardized in the mid-1950s.

All Engineers can relate to an experience we’ve had where what we designed was not how it turned out in “the real world”. Rarely does a project end up being exactly as what we put down on paper. Soil testing for foundation supports is no exception and unfortunately these differences almost never end on the positive side of a cost estimate.

Modern infrastructural design and architecture are evolving due to rapid improvements in modern technology and material science. This has raised the bar, calling for construction and engineering companies to rise to the occasion with improvements in foundation systems.

Have you ever needed to estimate the axial capacity of a helical pile? You could calculate helix bearing and shaft friction by hand, but there is a better method. Use HeliCAP® v3.0 Helical Capacity Design Software! HeliCAP is software that estimates the axial capacity of helical piles, is free to use, and accessible from any computer, smartphone, or tablet with an internet connection and a web browser. A desktop or laptop computer with the Google Chrome web browser is recommended for best results.

Helical piles are a displacement piling system that moves the soil away from the central axis of the shaft. This has many advantages that include no spoils to remove, but also comes with disadvantages as the shaft diameter increases. The helical piling industry categorizes pipe helical piles into low, medium, and high displacement. Each category has advantages and disadvantages that a specifying engineer must consider when selecting a pile that is applicable and economical for the project.

Low Displacement

The largest volume pipe shaft helical pile used in the North American market are low displacement pipe piles. Low displacement piles are defined as piles with central shaft diameters up to 4.5 inches.

On many construction projects, soil borings are not completed due to the property owner wanting to reduce costs or, quite simply, being unaware of the need to obtain soil strength data for foundation design. During the installation of CHANCE® Helical piles, monitoring torque can provide real time data defining underlying soil strength and its load capacity. As a helical pile is installed (screwed) into increasingly denser/harder soil, the resistance to installation (called installation energy or torque) will increase. The higher the torque, the higher the axial capacity. In most projects, the installation torque increases with depth, and the capacity of CHANCE helical piles can be determined at the time of installation. Regardless of whether the pile is being installed in clay or sand soil, the torque to correlation factor (Kt) for each shaft size, is multiplied by the effective installation torque (T), resulting in the ultimate capacity for each pile. The standard equation for ultimate capacity is Kt * T. The torque correlation factors for CHANCE helical piles can be found in the CHANCE Technical Design Manual-4^th Edition. The effective torque is the average torque taken over the last 3 feet of installed depth, measured in 1 foot increments.

The shaft type/size of a helical pile is critical to both the axial and lateral capacity – especially for compression in soft/loose overburden soils where lateral stability of the shaft must be considered.  The following is a brief summary of the 4 different shaft types commonly used for helical piles and their relative advantages and disadvantages based on site conditions and application.  It is very important to understand that helical pile installation must be considered in the design process.

As the concepts and design of modern structures continue to evolve, so too must the deep foundation systems on which they are founded upon. With the help of modern technology and material science, structural boundaries continue to be pushed and economic considerations are causing a trend toward the increased use of high-capacity piles. In response to the demand, helical piles have expanded beyond light and medium loaded structures and have been engineered to support heavily loaded structures subjected to both compression and tension.