“We chopped 50 percent off the contract schedule,” states Jim Swenson, licensed professional land surveyor for Oregon Mainline Paving based in McMinnville, OR.
That’s 50 percent less worker hours, 50 percent less machine time, 50 percent less costs.
“The project was completed a year ahead of the two-year schedule,” Swenson says. “We finished the project so quickly due to long hours of hard work and our use of machine control technology.”
The project: Milling and repaving 19 miles of I-84, Baldock Slough - South Baker Interchange section located in Baker City, Oregon. The Oregon Department of Transportation (ODOT) project had a $17,949,200 contract value and Oregon Mainline Paving was the general contractor on the project. The I-84 project involves two eastbound and two westbound lanes. When completed, it is expected to improve travel on a stretch that was originally part of the Oregon Trail, which was the 2,000-mile historic east-west wagon route and emigrant trail that connected the Missouri River to valleys in Oregon and locations in between.
Project challenges
The I-84, Baldock Slough - South Baker Interchange project came with challenges.
“ODOT has implemented different surfaces for the fast and slow lanes on two-lane interstates,” says Swenson. “The fast lane has an asphalt finished surface while the right-hand lane is concrete, plus there are asphalt shoulder lanes flanking both lanes.”
ODOT took the existing road surface profile but didn't mimic that surface exactly. Instead of going all the way down to subgrade and building it back, they are requiring Oregon Mainline Paving to grind off the existing asphalt to establish the bottom for the new road surfaces.
“In the concrete lane, we were milling eight to 10 inches, and then there were some short bridge sections, where we actually went down a foot,” Swenson states. “For the fast lane surface we were milling two to four inches, the fast lane shoulder we milled zero to two inches, and the slow lane shoulder called for a three-inch grind. So, there were four different depths of asphalt ground across the road section.”
To handle this complex milling project, Oregon Mainline Paving purchased a new Wirtgen W2100 cold milling machine and then contacted SITECH Oregon, located in Portland for assistance in selecting the right Trimble machine control system.
“We’ve worked with Trimble systems before, so we knew the quality of the systems and that the dealer could help,” says Swenson. “We outfitted the new Wirtgen with Trimble 3D milling which is the GCS900 Grade Control System with a SPS930 Universal Total Station, so we could mill surfaces at variable depth and slope without stringlines.”
The technology on a mill machine is designed to control the cutting depth of the mill to minimize over-cutting, create a smoother surface, and reduce the need for additional asphalt or concrete material in the ensuing re-paving process.
Technology places project ahead of schedule
Oregon Mainline Paving received a site model and design information from ODOT, which SITECH Oregon converted for them into a 3D model using Business Center-HCE. Business Center-HCE completed the data preparation for the Trimble machine control and site positioning systems.
“We were confident that the technology would save us a year of production,” Swenson states. “When we met with the ODOT officials at the beginning of the project, they said. ‘We were hoping someone would bring in machine control but we're looking at your timetable, and there's no way you're going to get this done in a year’ and we said, ‘Yeah, we are.’"
The ODOT officials’ response was that they wanted all Stage I work completed by July 4 before commencing on Stage II work.
Stage I was to construct crossovers at the ends of the projects and the three interchanges that cross the 100 foot wide earthen median. This placed traffic traveling both directions temporarily on the eastbound side. At the incline at the south end of the project an additional temporary passing lane was constructed. The crossovers required stone embankment two feet below the existing ground with geotextile fabric under the stone embankment. The crossovers were then brought to grade and paved. The earthwork was performed using dozers equipped with dual-mast Trimble GCS900 Grade Control Systems and GPS RTK equipment. Stage I work started in March and was completed April 20.
Stage II grinding of the eastbound freeway began April 21 and was completed May 18, except where the interchange traffic was crossing the existing surface. The interchanges required that two crossovers be constructed for each on and off ramp, so the traffic could be switched onto the poured concrete lane after it had cured. Then, the blockout was ground and white paved.
After the white paving was complete the remainder of the eastbound side was paved, traffic switched back to the Stage I configuration and the crossovers were torn out and reconstructed to accommodate traffic being on the westbound freeway and crossing the under-construction eastbound freeway. This work had to be complete by the 4th of July.
Oregon Mainline Paving began grinding the eastbound freeway on July 6 and finished grinding the eastbound freeway on August 9. The company completed the 9.5 miles in 24 days of grinding. Paved concrete and asphalt were placed using Blaw Knox 220 and 5510 pavers. Oregon Mainline Paving easily met the September 30 top-lift paving cutoff date set by ODOT for the State of Oregon. Other items completed during this time were the construction of sleeper slabs and concrete anchors, guardrail, barrier, striping and signing.
This was a non-typical large scale ODOT project where a completely different finished surface was accomplished by milling the existing 14- to 16-inch road surface, leaving enough existing asphalt to be the top of the four- to six-inch base for the new concrete and asphalt surface. The project called for 66,582 cubic yards of grinding and 135,000 tons of ground asphalt.
The cross section of the 42-foot wide final roadway has four different depths from the finished surface. A two-inch deep by six foot wide fast lane shoulder, a four-inch deep by 12-foot wide fast travel lane, a nine inch deep by 14-foot wide slow travel lane and a three-inch deep by 10-foot wide slow lane shoulder.
Controlling the mill depth
The challenge for Oregon Mainline Paving was how to control the milled depth to a 0.02-foot vertical tolerance, stay on line at the different depth offsets while using a grinder with a 7-foot, 2-inch drum. The cross section required the grinder to make nine passes across the roadbed. It could have been completed in seven passes, but two additional passes were required in the nine-inch deep section.
“We wanted to grind from the lesser depths to the deepest so we wouldn’t leave ground asphalt behind,” Swenson says. “Performing this milling task over a 9.5-mile project, 19 miles of roadway, with additional milling to 12-inch depth in the concrete portion at the starting end and the bridges for the sleeper slabs and anchors was definitely a challenge.”
Once the milling was completed, Oregon Mainline Paving used 62,000 tons of asphalt and 154,000 square yards of concrete at nine inches thick to pave the road.
“It was tremendously important to have an accurate milled surface for the paving,” states Swenson. “Our pay depends on the IRI (International Roughness Index) score, which Oregon requires a score of 45. On this project, we were significantly below that mark at 35. Additionally, ODOT has a zero-out-of-tolerance expectation and measures concrete depth randomly, but always within a 200-foot section. The concrete subcontractor had estimated a three percent overrun, but in actuality they were at one percent. Needless to say, ODOT is very pleased with the results.”
The project is completed and the I-84, Baldock Slough - South Baker Interchange section of the one time Oregon Trail is handling traffic.
Swenson reflects: “This was our first job where we used a robotic total station with machine control. I’m impressed with how efficient the Trimble Universal Total Stations were and how well they worked. Think about it, in 24 days we ground 9.5 miles of highway, 9 passes across. That’s an incredible amount of grinding which we completed accurately with the help of the technology. Our schedule was a bit of a grind — pun intended — but we finished the project in one year, half the time, which was incredible.”
