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Maryland Broadband Network Promises Major Rewards
KCI Designs, Executes Historic 1,200-Mile Design, Construction Project
The design criteria instructions furnished to the engineering teams specified the utilization of the most effective construction methodology, said Siemek. Because of significant make-ready costs associated with placing cables on existing utility poles, the percentages changed to 15 percent aerial, 85 percent underground. Eighty percent of underground cable in Baltimore was placed in existing utility pathways.
“Aerial construction costs ranged from $5,000 to $30,000 per pole, depending on the complexity of the make-ready work,” Siemek said. “KCI’s recommended alternative underground alignments saved more than $500,000 in construction costs over following aerial routes lined with severely congested poles.”
Shifting large portions of the network from aerial to underground went smoothly and did not delay construction schedules. Siemek said KCI’s knowledge of the engineering and construction permit requirements within the nine jurisdictions expedited the transition.
Open-cut construction was utilized when there were existing utilities in conflict. The project encompassed urban and suburban areas so all types of construction methods and environments were encountered. Surface conditions ranged from asphalt top coat over reinforced concrete road base to turf areas.
Horizontal directional drilling (HDD) was the predominant method of construction for underground conduit installation. Bores were made for street crossings, along street rights-of-way, water crossings and surface obstacles.
“KCI had as many as 17 drilling subcontractors operating 68 drill units and approximately 100 technicians working at the peak of construction,” said Siemek.
Bores ranged from 100 to 600 feet with the average approximately 500 feet. HDD equipment included compact models with pullback ratings from 5,000 to 9,000 pounds and medium-size machines with 20,000 pounds of pullback.
Wherever trenchless underground construction was used, test pits were excavated to visibly identify locations of all existing utilities along the proposed cable routes.
Standard duct on the project was two-inch diameter SDR11 HDPE. All pipe was rolled on reels. Mechanical connectors were made at test pits or tie-ins. Approximately 95 percent of the installation was single two-inch duct, no bundling.
KCI placed the cable using conventional pulling methods. Fifty-foot slack loops were required at each hand box placed approximately 500 feet apart. Siemek said this made pulling a more economical option compared to blowing.