Mountain Valley Contracting reduces milling time by 20% on Colorado stretch of interstate highway with Trimble® GCS900 Grade Control System

Overview:

Customer Profile 

Mountain Valley Contracting is contractor headquartered in Grand Junction, Colorado. The company specializes in milling and paving work and has successfully completed several roadwork projects for the Colorado Department of Transportation (CDOT) as well as for private companies. Project Challenge 

Mountain Valley Contracting was hired to complete a milling project for a 4.5-mile (7.2 kilometer) stretch of Interstate 70 in Glenwood Canyon in Colorado’s Rocky Mountains. Mountain Valley Contracting adopted Trimble’s advanced 3D milling capabilities to meet the project’s deadline and tight tolerances, and to maximize the yield of concrete. Solution

The team used the Trimble® GCS900 Grade Control System for milling along with the Trimble SPS930 Universal Total Station

Benefits:

• In half-mile increments, the team successfully milled the entire stretch of highway in 18 days total, nine days per side (east and west-bound lanes) with Trimble technology.

• Shaved four days — or 20% — off the project timeline and delivered significant manpower savings over the scope of the project.

• More competitive bidding for road mill projects with Trimble grade control, which brings significant net savings for this project and in the future.

• 3D milling helped in meeting ‘ride incentives’ from CDOT and others that provide extra compensation for completed roadways with extremely smooth rides.

Why Trimble?

Mountain Valley Contracting was selected for a 4.5-mile (7.2 kilometer) milling project for a stretch of road on Interstate 70 in Glenwood Canyon, Colorado. Lane Johnson, Mountain Valley Contracting’s construction manager, explains that the milling process is used for road surface profiling to eliminate wash board surfaces that are created from folds in the road. As a result of this work, a smoother road surface is created. Along with heavy civil contractor partner Interstate Highway, Johnson determined the Trimble 3D milling system was a must-have for this I-70 initiative. The Trimble GCS900 Grade Control System with the Trimble SPS930 Universal Total Station was installed on milling machines to deliver highly accurate milling at variable depth and slope without the need for stringlines.

“In the world of milling, there are really two types: profiling milling and asphalt removal,” said Johnson. “For this particular project, the owners wanted the road to be milled to that exact profile, so we knew we needed to use 3D milling. The traditional method of running stringlines and surveying would have been way too labor intensive. Trimble’s 3D milling technology let us mill to that exact profile. We were able to place a consistent 6-inch (15.2 centimeter) layer on top to give the best ride possible and ultimately reduce the amount of concrete needed during the paving process.”

The project started in June 2013 with the first step of creating a profile of the road surface. A survey crew was hired to take a topographic survey, and the profile for both the east and west-bound stretch of road was shared with Interstate Highway and the CDOT so that all parties could come to an agreement on the intended road profile.

Next, the Mountain Valley Contracting team worked with its construction technology partner SITECH Rocky Mountain to train machine operators how to use the milling system. SITECH Rocky Mountain also installed the milling machine and set up control points at 700-foot (213 meter) spacing.

Johnson and his team spent the first day testing and calibrating the mill to make sure it was performing correctly and accurately. Once they began to mill, the crew started at one end of the 4.5-mile (7.2 kilometer) stretch and milled in half-mile (.8 meter) stretches, averaging about three inches (7.6 centimeters) of milling across the entire road. Operators completed one pass on the outside edge and then turned around to come back down the other side in a U-shaped pattern.

Throughout the project, surveyors used the Universal Total Station to spot-check the grade to ensure the crew was staying within tolerance. The project was completed in September 2013 and took nine days per side (east and west-bound lanes), or 18 days total, reducing the overall milling time by 20%.

“The thing that is unique about a mill versus a dozer is that you really only get one opportunity with a milling machine,” said Johnson. “You can’t just add more material like you can with road base and make another pass across it. Your first pass has to be your final pass, and the 3D milling solution from Trimble makes that possible.”

Johnson and his team were ecstatic about the productivity gains achieved using the Trimble milling system. Johnson estimates 3D milling from Trimble shaved four days off the project timeline and delivered significant manpower savings, which enabled him to move some of his workers to other jobs.

In addition to greater milling accuracy and productivity, Johnson believes the Trimble system will continue to deliver ROI because it makes the company’s bids much more competitive.

He explains that typically as a milling subcontractor, Mountain Valley Contracting would not complete a survey in-house, prior to performing milling work, instead they would subcontract it out.

“Now we are able to use the Trimble SPS930 Universal Total Station with a rover system to complete the survey ourselves, in a fraction of the time. I would estimate that we can generally reduce a surveyor’s scope of work for profile milling by as much as 90% using this technology,” said Johnson. 

He also believes 3D milling will help meet ‘ride incentives’ from CDOT and others that provide extra compensation for completed roadways with extremely smooth rides. “Not only is there a big net savings, but after they got comfortable with the 3D technology everyone on the job became a big fan, especially our surveyor,” said Johnson. “Now he thinks every road should be built this way because it’s exact. In fact, there’s no guesswork and it’s a lot less work than pounding blue tops, or painting marks on the asphalt every 7.5 feet (2.3 meters) to represent the required elevation. He absolutely loves it.” Happy with the results on this 1-70 milling project, Mountain Valley Contracting has continued to use the Trimble milling system on several other projects. The company recently used 3D milling on an emergency spot repair job on I-70 near Eagle, Colorado. Mountain Valley Contracting was brought in mid-project because the original contractor was unsuccessful at this particular complex super elevation job. The original contractor wanted a cut and a cross-slope painted 25 feet (7.6 meters) on the upper edge of the curve. After this was milled, the crew tried to maintain this with paving, so they added level course to get back to where the surface needed to be; then they added a final mat. After this work, they then took a profile graph which was rejected by CDOT.  “We were brought in and worked for a few days to build a model, and our surveyor put in a control network,” said Johnson. “The next evening we went to work and fixed the super elevation curve. In fact, the pavers that went out the next night to repave it said it was perfect,” said Johnson. “With the Trimble 3D milling system it’s always going to be right on target.” Looking ahead, Johnson believes the milling solution will continue to open up new opportunities for Mountain Valley Contracting. Trimble technology makes the company well suited to save project owners significant money in asphalt and labor costs. For instance, Mountain Valley Contractors is working on an engineering plan for a project on I-76 in eastern Colorado. The job itself is 18.5 miles (29.8 kilometers) long and Johnson believes that by using 3D milling capabilities from Trimble, his team can generate a profile, mill to that profile and produce an extremely smooth roadway. With 3D milling capabilities, Johnson estimates a net savings of $1.5 million to the project owners and ultimately the Colorado taxpayers. “With Trimble 3D milling we can save our customers a significant amount of money,” said Johnson. “We’re showing project owners that by using 3D milling technology we can mill with better accuracy and less rework― all at a reduced cost.”