Weather proved to be a formidable foe, creating another problem for the crew. “Work was delayed two days because of the dense fog on the Mississippi River,” he says. As the tugs were mobilizing the barges, the tug captains were unable to move because of low visibility. “We utilized tug boats and two 150-foot by 60-foot barges with 50-foot spuds in order to position grid wire at the intersect point,” says Boyd Simon, P.E., division manager of Ranger Field Services. “A project such as this involves establishing an early and constant line of communication with the governing USACE district throughout the engineering, permitting and construction processes,” Sauls says.Īnother challenge of the project was the predetermined design point of intersect under the Mississippi River. The result would be undermining erosion that could ultimately compromise levee stability and lead to catastrophic flooding and devastation. “If this occurs under a regulated levee, the fissure can create the potential for the water to seep from the flood side and under the levee to the protected side during a future flood.” “During HDD construction, the drilling fluid pressure required to remove cuttings from the drilled hole had the potential to fracture the soil, creating a pathway for drilling fluid release to the ground surface, commonly referred to as inadvertent drilling fluid returns,” Sauls says. The USACE reviewed the HDD design and construction plan, including the installation of the casing and the usage of the intersect method, and required documentation of all the construction activities. Drilling under the levees was a highly regulated engineering and construction process. One of the biggest obstacles of the project was the crossing under the two USACE levee systems. Once it was completed, Ranger Field Services began their reaming activities, and multiple crews were utilized during reaming and swab pass activities. The pilot hole intersect was completed in about 50-feet of water and 115-feet below the mudline of the river. With hard work and hole preparation, the pipe was successfully pulled in hole with a pre-installed PVC liner and a maximum pressure of 140,000 pounds. The 12-inch diameter pipeline was assembled on 137 pipe rollers in preparation for the pull back. Both pilot holes used a 97⁄8-inch roller cone mill tooth bit. Ranger used two barges anchored in the Mississippi River to position secondary survey coil wires, which were used to locate the two pilot hole bits for the pilot hole intersect. The entry side rig was responsible for drilling 3,848 feet for the pilot hole as the exit side drill rig drilled 3,830 feet for the pilot hole. Thankfully, the observed downhole annular pressures remained below the allowable drilling fluid pressures prescribed by the USACE permit. The casing on the entry side was approximately 278 feet long and the exit side around 259 feet long. The casings were installed between 65 and 70 feet below ground surface through soft clay and into dense sand. Ranger jetted the pilot holes, reamed them and then rotated the casing into place using the drill rigs. The machines boasted 330,000 pounds of pullback and 50,000 foot-pounds of rotary torque. They used two Vermeer D330x500 drill rigs for the pilot hole operations, powered by 426-horsepower engines. An entry side drill rig was positioned approximately 1,700-feet from the water’s edge, and on the other side of the Mississippi River, the exit rig was around 1,500-feet from the edge. They began construction of the HDD by installing casing on both the entry and exit sides. Ranger Field Services, a Louisiana-based drilling contractor, was elected to take on the execution of the project. “This was achieved by targeting stronger soil layers at depth while installing steel casing through the softer near-surface soils.” Sauls, P.E., senior principal and geotechnical engineer of GeoEngineers. “The HDD design was completed with the understanding that the USACE would only permit the HDD installation if the risks of hydraulic fracture and creation of flow paths for under seepage and levee failure were mitigated,” says David P.
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