While some foundation systems are specified for particular environments, topographies and soil conditions, a designer’s preference is usually the deciding factor. That’s particularly true when it comes to auger cast piles, as many engineers consider it to be a superior, more efficient foundation system.
Shannon Bergeron, a GROUP Deep Foundations Superintendent since 2007, says many engineers feel auger casts create a better foundational footprint. “When you drill into the ground and fill it with grout, you’re eliminating any voids in the hole,” Bergeron says. “In other words, you have more side bearing pressure, more static pressure and more friction. That makes it the preferred pile for many engineers.”
Of course, there are other factors to consider. With auger casts, the contractor must precisely sequence grout deliveries as well as maneuver grout trucks within an existing industrial facility. “You have 90 minutes to use the grout on that truck,” Bergeron says. “If you don’t use it within 90 minutes of the time it was batched, you lose that batch.” The site can also become somewhat muddy, depending upon the weather and other conditions. Other times, the composition of the soil might make it difficult to stabilize a hole.
Nonetheless, many projects are ideally suited for auger cast. Projects within existing industrial plants typically use the system, as industrial vessels can be highly-sensitive to vibration (a disadvantage of driven pile systems). There are also certain geological conditions more conducive to auger cast, such as sandy soils or clay strata. “In those situations, we get more production out of drilling the piles than driving precast,” Bergeron says.
Technology Brings Greater Efficiency
With auger casts, the contractor is essentially constructing a pile within the ground. On most jobs, the GROUP project team will operate a 100- to 160-ton crane, along with associated leads, a drill head, grout pump and auger. There’s also an excavator on site to move the “spoils” coming out of the hole and a skid steer loader to transport the spoils off-site. “As we drill, we’re pumping grout into the ground,” Bergeron says. “Then, once the grout is in, we put the ‘cage’ in the ground.”
A normal crew consists of about 10 people. Equipment operators are certified through the National Commission for the Certification of Crane Operators (NCCCO), while other team members go through specialized training offered by GROUP.
Depending upon the size and the footprint of the project, there could be multiple auger cast operations under way at once, with multiple crews. For larger sites, GROUP will operate a second rough-terrain crane to set the cages. “The pile driving rig will swing over and start driving another pile while the second crane sets the steel,” Bergeron says. “That keeps the process moving.”
While the process hasn’t changed much over the years, improvements in technology have made auger cast systems more efficient. GROUP uses a Pile Installation Recorder (PIR) to calibrate the flow of grout, which in turn communicates vital information to the crane operator. “The meter precisely measures the rate of flow,” Bergeron says. “It will tell him if he needs to slow down or speed up. Otherwise, we might waste grout or create unnecessary voids.”
Auger cast systems are also adaptable to a variety of situations. In 2019, GROUP installed some 1,200 piles measuring up to 24 inches in diameter and 105 feet deep within an existing Texas industrial plant – in record time. It was, by far, Bergeron’s largest auger cast project to date.