Stringless Curbs and Gutters

Contractor Summers-Taylor, Inc. holds license number 00000069 in its home state of Tennessee, U.S.A which means it's the 69th contractor of any kind to be licensed in the state.

Founded in 1932 as a general maintenance and construction company, Summers-Taylor is now the largest, heavy and highway construction contractor in the region of Northeast Tennessee, Southwest Virginia and Western North Carolina. Located in Elizabethton, Tenn., the company owns more than 400 pieces of construction equipment and trucks, five concrete plants, and four asphalt plants.

Travel an interstate or major highway in this region, it has likely been built or repaired at some point by Summers-Taylor. The family-owned company has grown from its modest start and now employs more than 375. The contractor has diversified, adding design and engineering capabilities to its core construction and paving services. Yet, road building remains at its heart.

Not surprisingly, the company is involved with the $US18 million Tennessee Department of Transport improvement and expansion of state Highway 75. The highway spanning between Washington County and Sullivan County is being widened from two to four lanes. The project is a 6.5km stretch and requires placement at various locations of concrete curbing and gutters for drainage and catch basins.

"With its long, straight highway run this is the perfect project for us to try our newly acquired 3D GPS machine control on our Gomaco GT-3600 slipform concrete curb and gutter paver," states Lee Thomson, concrete superintendent for Summers-Taylor.  "We're among the very first, contractors in America running a stringless GPS-based curbing machine - they're more commonly found in use outside of the States." 

Thompson points out that he feels comfortable "pioneering" machine control technology on the curb machine because he's followed the evolution of the technology over the past 10 years, learned how its benefiting Canadian contractors, and his company is successfully using GPS technology with its earthmoving and site grading side of the business.

The Summers-Taylor Gomaco concrete curb machine is equipped with a Topcon GPS+ receiver and an on-board graphical display. A pair of masts - each topped with a Topcon PZS-I laser sensor - are mounted on the machine to control grade elevation and steering. Because Summers-Taylor uses laser-enhanced GNSS technology, a pair of Topcon PZL-1 transmitters are positioned at control points on the site. Thompson places the transmitters 150 metres apart to track the position of each receiver on the curb machine and relay curb location and elevation data to the curb and gutter machine. As the machine progresses Thompson leap-frogs the transmitters to maintain the slip-form production flow.

The PZL-1 Millimeter GPS transmitter uses a fan beam signal that Topcon calls Lazer Zone technology and is designed to emit a fanned signal with a height of 10 meters. Summers-Taylor relied on Construction Engineering Solutions, LLC, Leopold, Ind., to help create the 3D model that was converted via Topcon Office 3D software to the files the curb machine used.

The project requires 900 cubic metres or approximately 500 linear metres of Class A, 3,000psi concrete to form the 760mm gutters with 150mm high curbs. Summers-Taylor has a six-member concrete crew, including the machine operator. The crew places expansion joints every 30 metres, muscles the heavy cast iron catch basin grids into place, smooths out any imperfections in the newly formed gutter and curb, brooms in the texture, and then moves the laser transmitter ahead as the curb and gutter machine progresses. There are 69 catch basins to be installed along the project route.

"Since this was our first time using GPS technology on a curb machine, we were nervous at first and began the project by running stringlines in front of the machine," Thompson says. "The client inspectors wanted to see the stringlines too, but when we saw the machine could run perfect without them, we stopped placing them. The finished grade is a straight line - no flutter or waves; it is very impressive. Once the client saw how good the results were, they pretty much pulled their lower jaws up off their chests and left us with one inspector."

The Highway 75 project is a two-year project and Summers-Taylor is completing its work on time. Thompson reports that adding the millimeter GPS capability to the curbing machine is improving both accuracy and speed, and virtually eliminating rework.

"In terms of accuracy, we're accustomed to achieving the already tight +/-30mm finish grade specifications with our Topcon 3D-MC2 earthmoving equipment, so achieving even tighter specs using our Millimeter GPS, with laser-enhanced GNSS technology on our concrete paving work, is more than possible," says Thompson. "In fact, our curb machine operator comes from the dirt side so he's comfortable with machine control technology and achieving quality results."

Summers-Taylor is seeing faster production with the GPS machine control on its curb and gutter paver. "Clearly, we're saving time and cost by not needing workers setting stringlines or needing to replace them if they're knocked down," Thompson states. "When you consider quicker speed, greater accuracy, and reduction of rework, we're at least 20 to 25 percent more productive with the stringless GPS curb machine."

In taking in the state Highway 75 project as a whole, Thompson concludes: "I'll remember this project as our first stringless curb and gutter project. Implementing the machine control system went exceptionally well and we had great support from our dealer, Roper Laser, in getting everything set up and running properly. My concrete crew certainly likes that at the end of the day they don't need to collect stakes and string; instead they retrieve the two transmitters, stash them in their cases, and head home."