Complex Profile Achieved on Airport Runway Rehab

Let's be clear from the start. The Ohio State University located in Columbus is not the same as Ohio University, located in Athens, Ohio. Most anyone living in Ohio—will quickly correct the mistake, if it's made. And don't forget the word "the" in front of Ohio State University. It is The Ohio State University (although curiously, it is referred to as OSU, not The OSU).

Founded in 1870, OSU is the second largest university campus in the U.S. and is one of only a few universities to have both a Department of Aviation and a busy airport. In fact, the OSU Airport ranks in the top five airports in Ohio in the number of take-offs and landings. It is located about five miles from the main campus in Dublin, Ohio.

Recently, the Columbus-based highway and heavy construction contractor, Shelly and Sands was selected to completely rehab one of the four OSU Airport runways. Considering the amount of air traffic, the university needed the project completed quickly, while satisfying the strict FAA quality requirements for grade and slope, accuracy and smoothness. This was clearly a runway that couldn't be out of commission any longer than necessary.

Shelly and Sands was up to the challenge and implemented precision construction technology from Trimble to satisfy the time deadline, smoothness, and accuracy requirements. Precision Laser & Instruments, Inc., Monroe, Ohio, their local Trimble dealer, helped them select the right system for their need.

Considered a large contractor, Shelly and Sands employs about 600 seasonal workers and has around 400 full-time employees.

Layers of Work
"We began working on The Ohio State University Airport Rehabilitation, south runway and ramp, in May 2009 and completed the project on time in November," states John Dowalter, survey manager for Shelly and Sands. "We first had to mill the existing asphalt to a variable depth of zero- to five-inches in multiple passes on the 6,000-foot runway." Shelly and Sands had a subcontractor mill the old surface to a new design using the Trimble® GCS900 3D system guided by a SPS930 robotic total station.

"After milling off the surface, we then went in and pulverized the remaining asphalt and sub-base to a 14-inch depth, then re-compacted and re-graded it," Dowalter says. "And then we cement-stabilized the pulverized material to the 14-inch depth and re-graded to sub-grade."

Between each of these processes there was grading—profile grading—to match the specs of the provided plan. The runway and ramp areas both had variable cross-slopes. "The complex grading which was required was made simple with the help of Trimble® Grade Control Systems on both of our motor graders," states Dowalter. "Both machines are equipped with Trimble® GCS900 Grade Control Systems, allowing us to match the grading to the profile plan without errors or rework." Trimble® 5600 Robotic Total Stations and R8-2 GPS Receivers with Trimble® TSC2 Controllers were used for project control and data collection.

Shelly and Sands' subcontractor used its own Trimble® GCS900 Universal Total Station system on its Wirtgen W 200 large-volume milling machine. The benefit of the 3D milling system was that the correct grade could be achieved the first time. Much of the required design spec was already cut by the mill before the grader came into the picture.

No Stringlines
"Even though string-lines were spec'd into the project, we eliminated the need for literally miles of string-line and easily saved a week's worth of staking, because we were all using Trimble systems," Dowalter says. "The engineering firm that developed the specs was, I guess, more old-school. They struggled at first in understanding the Trimble technology and its benefits. Initially, they were trying to dictate how we were to re-build the runway, but we stuck to our guns as far as using the Trimble 3D systems and proved we could achieve the grade tolerances they were requiring."

The engineering firm was not out of line with its concerns about achieving the tight grade tolerances. Understandably, the FAA is very strict in its requirements for airport runways. "We needed to hit the spec—plus or minus—a half inch," states Dowalter. "On top of that we were building a completely new profile grade for the runway that the engineers had created, which meant variable depth milling. Which meant to meet this more complex profile, we couldn't just set up the milling machine to mill four inches and let it head down the runway. We might be milling a half-inch at one point, get 500 feet down the runway and be milling three inches."

The OSU Airport south runway rehab was completed in two phases and ramp rehab project was completed in five production phases. The runway was paved in four 25-feet wide passes. The project also included ancillary work such as under-drains, perimeter under-drains and constructing burms on the sides of the runway, as well as airplane tie-down features on the ramp area for longer-term idle planes.

Dowalter reports that the timelines on a couple of phases were extremely tight. "The Trimble Grade Control Systems really helped us out since we were able to accurately hit the grade profile without needing to go back and re-grade or do any corrections."

Dowalter notes that historically when working on an area that's not graded correctly, there can be a lot of rework that will show up in the final paving. There may be pavement cut-outs where milling and repaving becomes necessary. "With the Trimble systems, we avoided those headaches—even with the variable cross-slopes for the length of the runway."

On time, Money Saved
Shelly and Sands, as well as OSU, are pleased with the results of the south runway and ramp rehab—a key runway in a very active airport. The project was completed on time, so Shelly and Sands did not incur any of the $10,000-per-day penalties for being late.

"When you think back and consider not only the amount of stringline that wasn't used and that machines and trucks didn't need to drive around the stringlines, as well as the one-pass accuracy we achieved, we're looking at very significant savings of time, money, and extra personnel," Dowalter states. "And we got everything done with smaller field crews. We had some long days, but the Trimble systems work equally well—day or night. All in all, the systems helped us to meet the tight project schedule and grade tolerances, while also controlling our material yields."