GCWW Horizontal Directional Drilling Project

AMERICAN Ductile Iron Pipe Provides Key Benefits for Greater Cincinnati Water Works Horizontal Directional Drilling Project

The Greater Cincinnati Water Works executed another successful horizontal directional drilling (HDD) project with the installation of a 350-foot ductile iron water main supplied by American Cast Iron Pipe Company (AMERICAN) of Birmingham, Alabama.

The utility selected flexible, restrained-joint ductile iron pipe for the HDD pull-through project because of its higher pressure rating, deflection capabilities, and durability. Also, Cincinnati approved a novel method of ensuring the integrity of polyethylene encasement applied to the pipeline.

"This was our first HDD project with AMERICAN Ductile Iron pipe, and it certainly addressed our needs," said Mark Raffenberg, a project engineer with the Greater Cincinnati Water Works (GCWW). "This job called for a higher pressure rating and deflection capabilities to allow for a rather dramatic dip in the pipeline route under buried obstructions. The strength of the pipe and its flexible restrained joints were ideal for this project."

The pipeline route was centered down the middle of Reading Road, a busy four-lane street. All of the work to install the water main took place within and under the two center lanes while one-way traffic in each direction was maintained in the outside lanes. The obstacles along the pipeline route were an 80-foot-long bridge culvert and a 24-inch sewer pipe laid directly under the culvert's foundation.

Prior to the pull-back through the pre-drilled bore path, the contractor chose to pre-assemble all of the pipeline's 18 pipe joints and stage the pipe down the center of Reading Road. The entire work site spanned 800 feet, allowing 450 feet for assembling and staging of the pipeline.

Larry Smith Contractors of Cleves, Ohio, installed AMERICAN 12-inch Flex-Ring Ductile Iron pipe with up to 23 feet of cover. Cincinnati had used HDPE pipe on two previous trenchless highway crossings, but the HDPE was limited to a pressure rating of 150 psi. AMERICAN Flex-Ring pipe was chosen for the Reading Road project because it is pressure-rated at 350 psi and could easily handle the system's operating pressures.

In addition, AMERICAN Ductile Iron pipe's 5° deflection per joint provided an impressive radius of curvature — 230 feet for the 350-foot pipeline. That allowed for an aggressive curve in the water main's profile alignment. AMERICAN Flex-Ring's joint integrity, strength, and pulling capacity provided substantial safety factors for the pipeline and peace of mind for the owner.

Another key part of the project was the challenge presented to Larry Smith Contractors (LSC) to develop an encasement procedure that would withstand almost any condition. LSC designed a system that called for a double layer of polyethylene encasement to be tightly wrapped to the pipe, followed by a layer of stretch-wrap plastic covering the polyethylene. This method successfully maintains an intimate contact between the pipe and the encasement.

The contractor also wrapped the bell end of each joint with a wide strip of rubber to cushion the bells. More stretch wrap was then added to the rubber around the bells.

To reduce frictional drag during the pull-back, the contractor spread a thick strip of polyethylene sheeting in the middle of the road so that workers could slide the pipeline along the street to the bore path's entry point. The friction was further reduced by covering the polyethylene sheet with drilling mud. Where necessary, further steps were taken to ensure the effectiveness of the polyethylene encasement.

Larry Smith Contractors utilized a Vermeer Navigator 80x100 drilling rig, DCI Eclipse locating system and a Tri-Flo International MC2500 soil reclamation system. "We selected the equipment that we did because it provided the most assurance that the project would be completed successfully," said Jay Smith, vice president of LSC. "Along the same lines, AMERICAN's Flex-Ring pipe allowed the owner to have a flexible alternative to traditional jack and boring.

"The contractor and the owner both benefited from there being no excavation, which allowed a safer work environment; a flexible installation path that increased design possibilities; and cost savings, depending on actual site conditions."

The GCWW first performed a horizontal directional drilling project in 2001-2002 with a 36-inch water main installed under the Ohio River. It currently is installing AMERICAN 16-inch Ductile Iron pipe as part of another HDD job.

Said Raffenberg: "AMERICAN's service for the Reading Road project was excellent. They provided a review of the contractor's engineering design drawings and supplied other technical assistance in answering our questions on this new venture.

"We are pleased with the success of this project and are excited to have a new, cost-effective, time-saving, ductile iron solution in our back pocket to overcome future challenges in the distribution system."

Trend Construction of Cincinnati served as general contractor for the Reading Road project.