Essential to ease growing pains at DIA, this $29 million project expanded the Concourse C East Apron to provide more area available to stage aircraft for deicing, while allowing open access to gates and affording overnight parking for six airliners. Designed in 6 milestones, the main project scope included 183,000 sy of 17" PCCP placed over 12" cement treated subgrade and cement treated base course, over 200,000 sy of bond breaker fabric, asphalt Vehicle Service Roads (VSR), pavement marking, electrical, including 130 taxiway centerline and edge lights, adjustment of over 27 drainage structures to final paving grades, 54 new structures installed along with 12,432 lf of drainage pipe and 3,700 lf of trench drain, 36 acres of seeding, a jet fuel distribution system for 10 gates, and a blast deflecting fence.
Project DetailsSchedule & Complexity
Bid in January of 2008, delay of grant funding from the FAA setback the notice to proceed to June. At that time, authorization was only given to construct approximately 15% of the project. The construction team including the Contractor, Subcontractors, Design Engineer and the City and County of Denver worked together to devise a plan to mitigate effects of the funding delay. Plans to expand the Concourse C Building were postponed for economic reasons, and the Owner decided to decrease the Apron project scope by approximately 40%, partially by deleting the jet fuel distribution system upgrade. Final funding approval was received in September, at which time the schedule was revised to facilitate project completion as early as possible. Construction activities were re-sequenced and localized into smaller areas to allow segmented completion of underground utilities and earthwork. This allowed paving operations the earliest possible start in late fall of 2008. Utilities and earthwork continued throughout the winter of 2008-2009, expediting the start of paving operations in spring of 2009 without negatively affecting the project budget. Milestone sequencing was changed to avoid any downtime associated with taxiway closure restrictions, allowing the project to ultimately finish ahead of schedule.
During the spring of 2009, the project experienced significantly higher than normal precipitation, challenging completion of the earthwork. Over 17,179 cy of unsuitable subgrade material was encountered, requiring removal and replacement. These efforts resulted in over-excavation of dirt to a depth of 8' below the top of pavement in an area surrounded by the existing taxiways and VSR. This large "low spot" proved especially effective in collecting rainwater runoff from the pavement, requiring frequent pumping.
Several existing underground utilities posed challenges during construction. Two water lines, 20 inch and 36 inch, too shallow to provide adequate protection, required excavation and encasement in flowfill to provide the necessary structural support for the pavement section. Stabilization of the main FAA communication duct bank providing all communication to the main airfield control tower was required, while undocumented ductwork encasing the wiring for the jet fuel distribution system was located, and needed to be lowered. All utility adjustment work was coordinated and performed without affecting any of the end users of any of the existing utility services.
Construction & Innovation
Because the 80 plus concrete structures were built or adjusted during the winter months, before any of the paving, ramps were used to track up and over the structures. The paving operation was set up to pass over in-lane structures and hand finish around the structure grates to obtain the correct elevation. This created additional burden on the paving crew already tasked with the standard slip-form paving operation. Vibration was performed around the taxiway and edge light base cans and dowel basket assemblies to ensure consistent concrete consolidation. Individual training was provided to paver operators, groundmen and finishers to assure that 90 degree vertical edges and tight "edge slump" requirements were maintained. The tracking speed of the paver was monitored and maintained to avoid unnecessary stops. A smart vibrator system was used to constantly monitor the consistency of the consolidation. Sixteen foot straightedges were utilized full time to eliminate surface deviations, particularly at the light base cans and structures, while the concrete was plastic.
The Contractor fabricated and utilized "joint plates" for the placement of the concrete trench drain. In previous experiences placing trench drain, the metal-grate framing causes cracking at every frame joint. Use of these 10" tall plates to create a dummy joint at 10' intervals effectively eliminated the angular cracking due to the frame design. This process produced an aesthetically appealing and structurally sound product that eliminated repair time and improved overall project quality.
Special header forms were utilized at each gap required for the trench drain installation allowing the paver to effectively "skim over" the area. This avoided any hand finishing, minimized bumps and any necessary grinding for the transition areas.
Surrounded by three live taxiways and the main vehicle service road supporting daily flight operations at Denver International Airport, the project was divided into six distinct and separate milestones to minimize the effect of construction activities on the operation of the airport. Each milestone involved close coordination with the airlines and the DIA Airport Operations department to close each affected taxiway, complete all construction activity and reopen to aircraft within the allotted milestone timeframe.
Completion of the project was instrumental in simplifying aircraft movement around Concourse C during winter de-icing operations. Prior to this project, aircraft on the south side of the Concourse had to switch from ground movement communications to the FAA tower and then back from the FAA to ground communications on the North Side of the concourse for staging for de-icing. This project allows movement and communications to stay under Ground Control, which significantly improves and simplifies the aircraft operations and communication.