Cased Continuous Flight Auger Drilling: Where CCFA Fits in Foundation Construction

BAUER drilling rigs are engineered for real-world applications. In this blog series, we break down some of the most widely used BAUER foundation methods in North America, explaining where each application delivers the most value and how advances in equipment and tooling continue to expand what contractors can accomplish. Insights throughout the series are informed by Gordian Ulrich, ECA Vice President of BAUER Product Sales and Service, whose experience spans decades of foundation construction across challenging ground conditions.

What Is Cased Continuous Flight Auger Drilling?

For contractors already familiar with Continuous Flight Auger (CFA) drilling, Cased Continuous Flight Auger, commonly referred to as, CCFA starts with a familiar concept.

In conventional CFA drilling, a continuous flight auger is advanced to the required depth while the spoils are being transported upwards through the rotational movement of the auger. As the auger is extracted, concrete or grout is pumped through its hollow stem to construct the pile.

CCFA adds another critical component: a casing surrounding the auger.

That casing makes the drill string significantly more robust and helps control verticality throughout the drilling process.

“The casing determines the verticality of your wall,” Ulrich says. “With a secant pile wall, you need to maintain the overlap from top to bottom and make sure the tool doesn’t deviate to either side of the wall.”

Maintaining that alignment is particularly important when constructing secant pile walls. If a secondary pile deviates from the intended path, the required overlap with adjacent primary piles can be compromised, potentially creating gaps and pathways for groundwater.

Working steps during a Cased CFA application

Why CCFA Is Well Suited for Secant Pile Walls

Secant pile construction presents an inherent drilling challenge.

Primary piles are generally drilled into undisturbed ground. Secondary piles are different. The drilling system must cut between and overlap the previously installed primary piles.

That means the tooling encounters different levels of resistance across the same bore. There may be relatively undisturbed soil through the center while the sides of the tooling encounter concrete or grout from the primary piles.

A conventional auger naturally wants to follow the path of least resistance, creating the potential for deviation.

With CCFA, the casing helps resist that tendency and keeps the drill string aligned.

“The secondary piles are the challenge,” Ulrich says. “You have virgin ground in between and concrete or grout on either side, so you have different resistance in the hole. The casing forces that auger to stay vertical and stay in place.”

The result is greater control over pile alignment and overlap, helping contractors construct a higher-quality retaining wall with more consistent joints and improved groundwater cutoff performance.

While secant pile walls represent the majority of CCFA applications, the system can also provide advantages in unstable ground where maintaining temporary casing throughout the drilling process is beneficial.

Secant Pile Wall done with a CCFA system in England in the 2000s

From Front of Wall Drilling to Modern CCFA

The principles behind CCFA are not new.

BAUER developed Front of Wall drilling in the 1980s to install secant pile walls immediately adjacent to existing structures. Early systems paired an auger with casing to create a more rigid drill string, but the rigs and tooling available at the time limited the application primarily to granular, silty and sandy soils.

BAUER invented the FoW system back in the 1980s

As drilling rigs became larger and more powerful, the possibilities expanded.

By the late 1990s and early 2000s, BAUER was developing systems with significantly greater torque and the ability to run heavier sectional double-wall casing and more aggressive drilling tools. Heavy-duty rock augers, larger stems, stronger flighting and drilling teeth similar to those used for drilled shafts allowed CCFA systems to tackle increasingly difficult conditions.

BG 42 on BS 120 in the late 1990s – 2 KDKs and concrete pump mounted on the back

Today, CCFA can be considered for soils ranging from silty sands and gravels to clay, cobbles and, under the right circumstances, weathered or soft rock.

Ulrich recalls a 2015 project in New York City where the system successfully drilled through boulders larger than anticipated.

“The equipment has become incredibly heavy duty,” Ulrich says. “Does drilling through boulders always make sense? That’s something you have to look at case by case, but today’s equipment is capable of drilling through a very wide variety of ground conditions.”

Torque, Pullback and Stability

Modern CCFA capabilities are closely tied to the evolution of the drilling rigs themselves.

For Ulrich, three factors largely determine what a CCFA system can accomplish: available torque and rotational speed, pullback and rig stability.

Torque and rotational speed determines how effectively and how deeply the casing and auger can be advanced. But advancing the drill string is only half of the process. Once the pile reaches depth, the machine must also have sufficient pullback force to extract the casing and loaded auger.

Modern BAUER CCFA configurations can provide more than 100 metric tons of combined pullback through synchronized winch systems.

Stability becomes equally important as drilling depths increase.

After extraction, the double rotary system is positioned at the top of the mast while the casing and auger hang beneath it. The auger is also carrying several metric tons of excavated material, depending on diameter and soil conditions. That creates one of the most demanding stability conditions the rig will encounter during the drilling cycle. 

“This is where you appreciate some extra counterweight,” Ulrich said. 

Where CCFA Makes Sense

The first consideration when thinking about CCFA is depth.

Because CCFA is a single-pass method, the entire required drilling depth must be achieved without adding sections of auger or casing. Maximum depth is therefore determined by the configuration and capabilities of the rig.

Ground conditions come next.

Silty sands and gravels generally present favorable conditions. Clay can be significantly more challenging, particularly when sticky material builds up on the auger flights or drilling teeth and can be very difficult to discharge on the ejection auger. 

“People often think hard rock is the most difficult material to drill,” Ulrich says. “Certain clays can be just as challenging because they gum up the teeth, jam the flighting and don’t want to come off the auger.”

Projects involving significant boulders or extensive rock sockets require additional evaluation to determine whether CCFA remains the most efficient approach.

Diameter is another consideration. Ulrich says CCFA piles in the United States commonly range from approximately 24 to 36 inches. Larger diameters are possible, but increasing tooling weight can reduce achievable depth and affect rig stability.

Planning Is Critical to Successful Single-Pass Drilling

The production potential of CCFA is one of its greatest advantages, but that productivity requires careful planning.

Unlike Kelly drilling, where tooling can be changed as different soil layers are encountered, CCFA requires one tooling configuration to travel from the surface to final depth.

The working platform must support a larger and heavier machine. The tooling must be selected for every ground condition expected along the pile. The grout or concrete mix must remain consistently pumpable throughout installation.

If any one of those elements isn’t right, production can suffer.

“With the rewards comes risk,” Ulrich says. “Everything needs to be right, from the working platform and tooling to the ground conditions and the grout mix and of course the operator plays a key role in this application.”

That makes engineering, planning and experienced application support especially valuable when a contractor is considering CCFA for the first time.

Bringing Proven CCFA Technology to North America

Like many foundation technologies developed in Europe, CCFA experienced a delay between successful implementation overseas and broader adoption in North America.

Ulrich points to 2004 as an important breakthrough for BAUER’s torque multiplier system in Europe, while one of the first U.S. projects using that system followed roughly 11 years later in 2015.

Breakthrough in the Mid 2000s – BG 36 BS 80 and BTM in England

Today, CCFA is increasingly familiar in major East Coast markets including New York City, Boston, Baltimore and Washington, with additional opportunities in established secant pile markets such as Toronto.

Today: BG 36H BS95 in New England with a BTM System

For ECA, introducing contractors and engineers to proven foundation technologies is part of advancing the industry.

“The whole reason for us to be in this industry is to advance it,” Ulrich says. “Technology can give contractors an advantage by helping them execute jobs more efficiently, faster, safer and more productively.”

CCFA is a strong example of that philosophy. It takes the productivity advantages of continuous flight auger drilling and combines them with casing, powerful drilling systems and precise verticality control to provide contractors with another option for challenging secant pile and cased drilling applications.

The key is understanding when to use it.