WorldWide Drilling Resource

25 MARCH 2022 WorldWide Drilling Resource® Continuous Flight Auger Method Effective in Marshy Soil Adapted from Information by Balfour Beatty The $95 million Military Cutoff Road Extension project in Wilmington, North Carolina, involves 170,000 square feet of sound wall on each side of the roadway. Balfour Beatty is constructing this part of the project in land which is quite marshy. At an elevation of 12 feet above sea level and the water table at ten feet, setting concrete piles for the sound wall, including securing each hole from water and soil seepage, is challenging. Since this issue is prevalent along the North Carolina coast, the North Carolina Department of Transportation (NCDOT) found it difficult to attract bidders for the complex installations. However, Balfour Beatty’s southeast team saw it as a unique opportunity to find a solution. Jay Boyd, operations manager for the project said, “The NCDOT standard requires control of the water coming into the pile hole and sets the flow rate at less than six inches of water seepage in ten minutes before you pour concrete. He added, “The rate of seepage along the coast of North Carolina is much higher than this, so the method used for installing the concrete piles before the Military Cutoff Road Extension project was driving a casing the full length of the hole. This method poses a lot of risk for a contractor.” The temporary steel casing method is time-consuming, involving multiple steps, as well as requiring costly equipment and materials. After driving the casing and drilling the hole, the concrete post is placed in the casing, the casing is filled with concrete, then the casing is pulled out of the hole to be reused. The company learned of a more efficient method to construct concrete piles on coastal sound wall projects in Florida, traveled to view the Florida Department of Transportation process, and decided to present the continuous flight auger (CFA) method to NCDOT and the Carolina Associated General Contractors of America. The CFA post system uses a hollow auger drill to drill the hole. Then concrete is pumped through the auger and down to the bottom as the shaft is removed. As soon as the auger is removed from the hole, the pile is inserted. This prevents water and soil seepage, is completed in one step, as well as requiring less equipment and a smaller crew. NCDOT accepted CFA as an alternate specification in their special provisions but decided the design would need to be professionally engineered and approved by the NCDOT engineer. Taking the Florida model and altering it slightly, the design team lengthened the pile panels from 15-foot spacing to 20-foot spacing, which made the materials more economical. The states had two different standards regarding how the pile is placed in the concrete grout. Combining the two standards, the new design uses a rebar base with a larger diameter and number of bars to maximize the connection throughout the entire concrete section. By leaving the rebar uncovered at the base, the concrete grout fills the spaces within the rebar and creates a bond equal to the NCDOT requirement with less concrete waste. Using a REV Drill with an auger mounted to a CAT® 336 hydraulic excavator for the pile installation, the team drilled holes ranging from 30-36 inches in diameter and 12-25 feet in depth. The Military Cutoff Road Extension is the first NCDOT project to use the CFA post system method, and it resulted in significant time and cost savings. Setting up to ten piles per day, the team previously averaged an installation of only six piles per day. The team estimated it saved up to 20% on cost and 20% on schedule compared to the casing installation method. C&G Groundwater Week 2021 Dealmakers Darren with SIMCO Drilling Equipment of Osceola, Iowa, was pleased to have the crew from Earnest Well Drilling of Milford, Nebraska, show their SIMCO rig. SIMCO Drilling Equipment A duo from Claverack Pump Service of Claverack, New York, were in Nashville to show off their pump hoist with Albin and Randy of Pulstar/Preferred Pump. Pulstar/ Preferred Pump