Stabilizing the Ground With Help From the Sky

Mon July 21, 2008 - Northeast Edition
Mary Reed



In October 2006, Slurry Pavers Inc. (SPI) of Glen Allen, Va., landed its biggest job to date — a contract to work on the new fourth runway construction project at Washington Dulles International Airport.

The Dulles job is particularly noteworthy for SPI, not only for its use of “round-the-corner” technology, but also because not long before landing the contract, the company’s road reclamation division was facing shutdown, with its equipment due to be sold. At the time, the division was losing some $300,000 a year and management was contemplating closing it and focusing on its established, profitable divisions.

Before proceeding with such drastic measures, however, SPI decided to give the division one last chance and to this end appointed Larry Roberts as manager in August 2001.

At the time, the division was performing only full-depth reclamation (FDR), in which the machine passes over a section of pavement, pulverizing existing asphalt and the underlying materials, which are then mixed in place with cement, lime or asphalt emulsion to form stabilized base material for pavement. Using already-in-place materials this way reduces environmental impact and eliminates damage to existing roads due to hauling needed materials.

“But there wasn’t enough FDR work to keep our crews busy consistently and with low utilization rates for our equipment, we weren’t getting an acceptable return on investment,” Roberts recalled.

The solution came with a move into soil stabilization, where cement (or lime in wet conditions) is mixed with soil to form a solid base for roads. Two years later the road reclamation division was turning a profit and now accounts for 14 percent of the company’s annual income.

As part of the division’s turnaround, SPI invested in additional technology and equipment. In the latter case when crews could not find the right type of needed equipment Roberts designed a spreader to lay down cement for soil stabilization evenly and at a specified rate. This was achieved by retrofitting two World War II 6 x 6 military trucks with a spreader, and the system worked so well it is now installed on all seven of the company’s spreader trucks.

About the Job

The new runway at Dulles Airport will be approximately 9,400 ft. (2,865 m) long and 150 ft. (45.72 m) wide, with completion slated for 2008.

A major difficulty to be overcome in stabilizing the sub grade was its tendency to become waterlogged. This was caused by drainage problems that have since been corrected.

“The total job consisted of 633,000 square yards of cement soil stabilization and we have approximately 1,000 square yards of touch-up work still to carry out, which we will complete next spring,” Roberts said.

Twelve of the company’s employees have been working on-site, utilizing a Volvo G720B and a Caterpillar 12H motorgrader, a pair of Wirtgen R2500 pulverizer/mixer soil stabilizers and four Caterpillar 563 compactors. It also is using a Topcon HiPer+ rover with GNSS (Global Navigation Satellite System) capabilities used for setting up the job and checking the grade, as well as two LazerZone transmitters (PZL-1) from the same company. The latter has a working range of 2,000 ft. (609 m) and can provide measurements up to 33 ft. (10.05 m) high. Up to four transmitters can be linked to cover an area four times larger, thus rendering it particularly useful for large-scale projects.

GNSS provides signals from both the American GPS satellite system and the Russian GLONASS systems, creating more signals for 24/7 operation.

In addition, general contractor Lane Construction of Ashburn, Va., set up a GPS reference base station in its job trailer, providing a correction signal used as a point of reference to help all systems on the job pinpoint their locations. This base station was used by both SPI and Lane, who are running two Caterpillar graders and a GPS-guided concrete paver on the job.

The Wirtgen WR2500s, aptly described by John McCormick of Atlantic Laser Supply in Richmond, Va., as acting like a giant rototiller, ground up the soil and other material on which it worked and then mixed cement and water into the result. The new material was subsequently compacted and put to grade. Part of the work area is on sandstone and required two or three pulverizations before the material reached the required consistency for stabilization, which was carried out to the depth of 1 ft. (0.3 m). Once the base was prepared, brought to the desired grade, and compacted, SPI scarified the surface and spread dry cement over the work area.

“While the scale of this job is larger than most, correcting unusual soil types is our business and we have been doing this kind of work successfully for years,” said Roberts. “However, these large projects are now much easier to complete by utilizing Topcon 3D machine control with mmGPS. When you are fine grading cement you do not have time to go back and fix mistakes in grading and this system helps us to get to grade faster, easier and better, allowing for increased productivity.”

Roberts found that adapting to the new technology was not too difficult, involving a two-week learning curve wherein he worked with the equipment “a little bit” each day. “The most important thing for me was learning to trust the equipment,” he said.

Atlantic Laser Supply’s John McCormick put on a striking demonstration that helped build this trust. “With all the data loaded into one of our graders, John laid a quarter on top of one of our hubs,” Roberts recalled. “The grader operator swept the quarter off the hub — and never disturbed the hub itself.”

Ray O’Connor, Topcon Positioning president and CEO, described the Dulles runway job as the “perfect example of how adopting advanced technology in the construction industry is vitally important for company growth.”

As he pointed out, without this type of technology the bottom line is that companies cannot compete.

“Make no mistake, precise positioning technology will be at the forefront of construction developments in the coming years,” he went on. “Even though the testimonial evidence is clear-cut that cutting technology machine control can save incredible chunks of time and money on every job, some people resist leaving their comfort zone. That trend is changing rapidly. Those that do accept that change is inevitable, that embrace around-the-corner technology, are growing in number every day.”

About the Companies

With offices in Richmond and Chesapeake, Va., John McCormick and Randy Blain of Atlantic Laser Supply serve the construction and surveying industries, providing items ranging from hand tools to GPS machine control systems as well as a state of the art service center.

Slurry Pavers Inc. was founded in 1966. It offers clients milling, full depth reclamation and soil stabilization as well as striping and crack sealing. In 1984 the company began producing quality emulsion at its Richmond, Va., plant and since then has opened facilities in Manassas, Va., in 1993 and Dunn, N.C., in 2000.

Topcon Positioning Systems Inc., headquartered in Livermore, Calif., specializes in positioning technology devices for the civil engineering, equipment and construction industries. CEG