Airport Business

JUN-JUL 2018

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40 airportbusiness June/July 2018 AIRFIELD MAINTENANCE measures of soil- or silt-tightness to the 10.8 psi criteria for water-tightness corresponding to about 25 feet of head pressure." "In addition to the pipe joints having double gaskets to guard against potential soil intrusion," explained Tori Durliat, director of marketing for ADS. "there are fewer joints in a corrugated polypropylene pipe line because of the 20-foot long sections — the old concrete pipes had a joint every four feet. In addition to providing fewer locations for a potential joint failure, the longer HP Storm pipe section length and lighter weight also allowed the installation to proceed more quickly. Most of the work was completed well in advance of the 140 day time limit specified in the contract." The new system was designed for a five-year storm. "Typically, airfield infrastructure for storm drainage collection systems are required to meet only the five year storm," explained Duckworth. "The idea is that if it's raining so hard at an airport that it's only likely to happen once every five years, you probably don't have a lot of people flying airplanes in those conditions. "Generally speaking, the way an airport is designed, the pavement is elevated usually by more than a foot and a half or so from the areas where storm drainage collects. There are wide surrounding grassy areas with gentle slopes draining away from the pavement edges to provide the required positive drainage away from that runway. This all provides a lot of room for storm water to pond before it would get onto any pavements. If you do have a 10- or 25-year storm come across the airfield, it's only going to have an impact of a few hours of standing water before it would make its way through the drainage system designed to carry the peak five-year storm flow. "The economics just aren't there for designing and installing a system to handle a 10 or 25 year storm event that might occur, and if it does, then it's just a matter of waiting a few hours to let the five-year-storm-rated system do its job." At Tuscaloosa, as it is at most airports, workspace is at a premium. The corridor between these areas used for staging, stockpiling, and equipment operations was just 57 feet wide. "While working within a 57-foot corridor may not sound very restrictive, it was made slightly more difficult by the fact that the pipe alignment typically runs at an offset of just 10 to 12 feet from the edge of the Runway Safety Area," Duckworth commented. "In order to avoid any encroachment into the RSA, a trench box was employed, and excavated materials were stockpiled on the less-constrained taxiway side of the trench. Only removed sections of pipe were placed in the narrow space between the trench excavation and the edge of the RSA." In addition to the RSA and TOFA boundaries, a third protected area impacting the site was the Runway Object Free Area (ROFA) that spans and crosses the pipelines between the runway and taxiway centerlines. Work was permitted in this area without requiring the closure of the runway. To comply with safety regulations, the pipe and other materials were frequently brought to the site from the contractor's staging area in small enough quantities that stockpiles remained below the elevation of the adjacent pavements. This, along with assistance of the airport staff allowed the project to proceed without any operational impact from the project on Runway 4-22 or the Parallel Taxiway A system. "The HP Storm pipe is easy to move because it is light and heavy equipment is not required," Durliat offered. "So taking sections from the staging area to the field and even moving those 20-foot sections around the field can be quickly accomplished with a minimum crew." "The teamwork and cooperation among the project's stakeholders," said Duckworth, including the Tuscaloosa Regional Airport, Atkins, REV Construction and ADS, enabled the project to be completed on time and under budget, with relatively little impact to airport operations." An initial layer of crushed stone bedding material was placed on top the geotextile, which was held in place on the side of the steel trench box with magnets. Jamie Roberts, Walker Associates Inc. Runs of 36-inch diameter SaniTite HP pipe were installed into precast concrete inlet structure bases with a double compression gasket. Jamie Roberts, Walker Associates Inc. ABOUT THE AUTHOR Steve Cooper Steve Cooper has reported on a variety of storm water drainage and other pipeline projects for several decades. Based in New York, he has travelled extensively to conduct on-site news interviews with professional engineers, contractors, government officials and representatives of major companies supplying the industry. He can be reached at 516/623-7615 or steve@scacommunications.com.

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