The site consisted of interbedded layers of Coastal Plain silty/clayey sand, sandy silt, clayey silt, and silty clay (Coastal Plain) underlain by weathered rock. Medium dense sands and/or very stiff to hard silt/clay was encountered in the upper 15 ft of the borings. Very soft to stiff clay/silt was then encountered to the top of the weathered rock. The weathered rock was encountered at depths ranging from approximately 25 to 40 ft.
The geotechnical Engineer of Record – NCDOT Geotechnical Engineering Unit – recommended wick drains for embankments where very soft to stiff clay/silt was encountered. Due to upper medium dense sands and very stiff to hard clay/silt, approximately half of the designated wick drain locations required up to 15 ft of pre-auger to facilitate installation. To address pre-drilling, Menard used a new, experimental variable displacement drill. The drill was selected for its ability to act as both a high-speed, low-torque drill and as a high-torque, low-speed drill. The unique feature of the drill is that torque and speed of the drill is dictated by the resistance of the soil conditions. The drill features a 2-in-1 predrilling motor, capable of performing the services of predrill setups
typically done with the EX-12 and the EX-25 drills used by Menard.
Menard installed 5,746 wick drains totaling 174,357 LF to an average depth of 22 ft. and a maximum depth of 40 ft. The drains were installed using 4-ft triangular spacing. A challenge Menard faced was working within proximity of busy I-95. At mobilization, wick drain locations had been laid out within 6 ft of the highway. By collaborating with Barnhill Contracting and the NCDOT, Menard created 15 ft of clearance to avoid working so closely to the highway. A crash truck was also mobilized by Barnhill and traffic barriers were installed at the site by to ensure safety of the crew.
For a major expansion of I-95 in North Carolina, Menard successfully installed wick drains to support two roadway embankments and two bridge approach embankments.