Riverside Avenue Crossing - Jacksonville, Florida
The 36-inch diameter HDPE pipeline crossing was done after two previously failed attempts by another contractor that created several sink holes in the heavily traveled state road. Pre-project investigations determined that a layer of hardpan existed at a depth of 22-ft below the ground surface. Upon receiving this information, the profile was adjusted to penetrate the hard pan and proceed to the sandy marl formation that was present beneath the solid formation. The hard pan acted as a barrier between the sandy marl and the loose sand that existed above the hardened formation. This enabled the drilling operations to proceed with minimized risk of jeopardizing the roadbed integrity.
Once the pilot hole exited the ground, reaming activities commenced by operating 24 hours per day to maintain hydraulic fluid pressure in the loose sand formations of the entry and exit zones above the hard pan layer. Reaming operations were conducted flawlessly en route to pipe pullback. Pipe pullback operations had to commence during the nighttime hours to allow for a road closure of a highly traveled arterial roadway along the pipe layout location. A buoyancy control fill line had to be installed in the larger product pipe to allow water flow into the pullback pipe to reduce positive buoyancy forces caused by the fluid displacement of the 36" HDPE product pipe. The water placed in the pipe during pullback greatly reduced pullback forces and allowed the installation of the HDPE pipe to occur without problems.
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