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Faster, Easier, Cheaper - Pyrotechnical Anchoring
by: David SmallenIt looks like a Patriot missile launcher on a yellow truck, and when the "launcher" is extended from the bed of the truck, it does fire a projectile. However, instead of shooting something into the sky, it "shoots" a pile into the ground.
This strange contraption was invented in France, and originally, there were four of them. Now only two remain, and one of them is in the United States.The one in the United States belongs to George McGinnity, a Massachusetts businessman. He says the launcher is more like a big firecracker that shoots piles into the ground to support or anchor roadside signs; noise walls; specialized foundations; traffic signals; reinforced soil structures; and light, power, and telephone poles. With this pyrotechnical technology, the delays that are inherent in current standard practices - digging holes, pouring concrete, and waiting for concrete to dry - can be avoided. McGinnity believes that his machine can cut constructions costs and construction time. He envisions that contractors who use his technology will be able to reduce their costs and underbid their competition. And, ultimately, the sponsoring public agencies will pay less.
A New Technology in France
The story of McGinnity's machine began in France in 1989 when a company named FondaTech (short for Fondations & Techniques de Pyro-ancrage) patented the technology to thrust piles into the ground using the energy released by a pyrotechnical mixture of expanding gases. FondaTech eventually mounted four of the pyrotechnical popguns on mobile bases built by the French automobile and truck manufacturer Renault and filed patents in 36 countries.
FondaTech used the machines in France for three years for heavy construction work as well as for highway signs and soil stabilization. They were also used in Belgium, Germany, and Italy.
Shortly after FondaTech began using the machine to shoot beams into the ground, venture capitalist Gordon Beatty of Zero Stage Capital took McGinnity to Albertville, France, to look at the new device. The two men saw the potential for the construction industry - and for themselves. McGinnity obtained the licensing agreement for North America in July 1997 and brought one machine to the United States.
Then, last year, FondaTech went bankrupt as a result of matters unrelated to the anchoring machine. One machine is still in France, but it is not being used. The remaining two have been dismantled.Selling Pyrotechnical Anchoring in the United States
McGinnity is now trying to demonstrate the value of his new technology to the Federal Highway Administration (FHWA), to state and local contracting agencies, and to the construction industry. The explosives have been approved by the Bureau of Alcohol, Tobacco, and Firearms.In late 1999, he approached FHWA about performing tests to determine the worth of the new technology. FHWA agreed, but even getting the machine to FHWA's Geotechnical Laboratory at the Turner-Fairbank Highway Research Center in McLean, Va., was a challenge for McGinnity. Moving the 54.5-metric ton (109,000-pound) vehicle over the roads from McGinnity's company, Foundation Technologies, in Boston to McLean took 11 hours.
He said that FHWA officials weren't quite prepared for the big yellow and blue machine that pulled up to their testing ground.
"It's a weird machine," McGinnity said. "They couldn't believe it. Then we loaded up and shot a 6.1-meter (20-foot) I-beam into the ground."
McGinnity is confident that tests will support his claims for the pyrotechnical technology.
"It meets a real need for the construction industry," he said. "It can replace highway signs at very low cost and very quickly."
McGinnity estimated that the new technology will put the foundation in place for new signs in two hours. The current digging, pouring, and waiting process now takes two to three days. "That doesn't count waiting for the concrete to be delivered," he added.
The French machine replaces that process with pyrotechnical anchoring - using firecracker-type explosives ignited by a gas generator to shoot beams into the ground at 644 kilometers (400 miles) per hour.
McGinnity is working with FHWA to get the agency to back up his claims about its value. Once that is done and the technology is accepted by the American Association of State Highway and Transportation Officials (AASHTO), he will start the process of persuading companies bidding on contracts to lower their costs by making Foundation Technology a subcontractor.
The FHWA Reaction
"It has the potential for terrific cost-savings," said Albert DiMillio, FHWA team leader for geotechnical research. "It would be another tool in our toolbox."
DiMillio said FHWA is "just in the conceptual stage. We're evaluating all the information the French have, but we're going to do our own tests."
"I don't know if it is important," said Carl D. Ealy, FHWA geotechnical research engineer. "If the concept does work, it will be. It will be an economical way to install piles for signposts and overhead signs."Ealy estimated that the time savings from pyrotechnical anchoring could be as much as 30 to 40 percent.
"They could put in 15 a day with this technology compared to five a day with conventional method," he said. "Contractors are always looking to save money. The savings will go to the states. That's what our job is - to try and find ways for the states to save money."
According to Ealy, pilot studies were conducted at the Turner-Fairbank Highway Research Center to investigate the relationship between fuel charge, pile length, and axial capacity and to test the loads. Detailed analysis of the data is being performed at the University of South Florida.
Ealy said FHWA is trying to determine if there is any interest on the part of the states to jointly fund a six-month to one-year research project on pyrotechnical anchoring. He said that $200,000 to $500,000 would fund a series of tests similar to the pilot studies in different types of soils.
Pyrotechnical anchoring is attractive because of its cost-savings potential.
The Machine
The French invention, officially known as PAP (Pyro-Anchoring Posts) version 2 pyrotechnical anchoring machine, is called PAP 02. It uses expanding gases from explosives to launch objects at speeds of up to 50 meters (164 feet) per second and a laser to aim the objects. It is designed to shoot a galvanized metal pile into the ground to serve as the foundation for a superstructure that is laid on top of it.Shooting the pile into the ground is a four-step process:
- A piston loaded with an anchoring pile is installed in the launcher, and a gas generator is inserted into the combustion chamber in the piston.
- Combustion of the pyrotechnical mixture causes the gases to expand, setting piston and the pile in motion.
- The piston/pile combination is ejected out of the launcher. FHWA has measured the speed at 644 kilometers (400 miles) per hour. Because of its velocity, the pile enters the ground without any deviation. It stops when all of the kinetic energy has been absorbed by the friction of the pile in the ground. A stop plate allows the blocking and positioning of the pile at ground level.
- The launcher, roughly 10 times heavier than the piston/pile combination, recoils with about one-tenth the velocity of the pile. The recoil is absorbed by gravity without use of an auxiliary shock-absorbing system.
Propulsion of a pyrotechnical anchor
in a normal field setting.
PAP 02 is mounted on a Renault-built carrier truck. The mounted equipment consists of:
- An interface with a top chassis equipped with four stabilizers, an orientation turret supporting a mobile telescopic arm, and two hydraulic pistons that position the pyrotechnical anchoring device vertically.
- A pyrotechnical anchoring combination with a 4.6-meter (15-foot) launcher, recoil ramp, a system of ratchets and catches to lock the launcher in its raised position, a safety and arming device, and a striking mechanism.
- A piston with a generator-carrier and a flange that fixes the pile in place.
- A series of GGP- (Generator Gas Post-) type gas generators with pyrotechnical mixtures of varying strengths.
- Hydraulic and electrical equipment, including a remote-control panel.
- Accessories and guards.
The stabilizers, turret, telescopic arms, and other features on the interface allow the precise positioning of the pyrotechnical anchor and the planting of piles on embankments or in clearings and excavations up to 4.5 meters (14.75 feet) from the axis of the turret.
Galvanized steel pyrotechnical anchor and pole are set together using threaded rods and a welded plate. To launch the pile, the gas generator is inserted into the confining structure in the piston. The structure, known as a "generator-carrier," is pierced with calibrated orifices that allow the gases to spread.
A percussion cap is used to light black powder that causes combustion of the propergol. The gases rise through the generator, pass through the ejection orifices, and fill the thrust chamber bounded by the cylinder head and the piston.
A laser-based aiming system, installed at the end of the piles, positions the pyrotechnical anchor before firing. The system consists of a mobile support that adapts to each type of pile and of an autonomous laser diode that generates a light beam. Once the system has been installed on the pile, the pile's longitudinal axis is shown by the light beam. The laser diode, rated class IIIa, is not considered to present any particular danger.
A flange serves as the interface between the piston and the pile to be anchored. For each kind of pile, there is a corresponding flange. There are two families of flanges that are based on the way they secure the pile. Transversal bars are inserted through holes pierced in the wings of the pile and through two braces placed on either side of the pile. Threaded rods are welded longitudinally to the pile.
In certain very precise instances, it is sometimes necessary to add flange raisers to fix the pile at a certain height. These raisers are bolted directly onto the flanges.
To avoid the risk of gravel, mud, or other material being projected during firings, a gravel guard must be set up under the launcher before every firing. The guard, consisting of two metallic half shells attached together, essentially surrounds the area where the planting of the pile is to take place.
PAP 02 can generally anchor piles ranging from 150 to 400 kilograms (330 to 882 pounds). The size of the load in the gas generator can vary from 280 to 700 grams (10 to 25 ounces), depending on the soil characteristics; the shape and length of the pyrotechnical anchor; and possibly, the depth of penetration of piles previously fired.
Operation of PAP 02 requires an accessory truck with an auxiliary crane capable of lifting one ton up to seven meters (23 feet) using a highly secure claw grip. In addition to transporting the piles, the accessory truck is used to assemble the pile in the piston's flange. The auxiliary crane also facilitates the loading of the system into the pyrotechnical anchoring device's chamber and the disengagement of the piston from the anchor after firing. An additional vehicle is needed to carry the gas generator.
The launcher is positioned through operation of the turret, the telescopic arm, and two cellarage jacks, which adjust the verticality of the firing axis. Following propulsion into the ground, the launcher returns to the ramp and is refolded. The piston is disengaged from the pile.
When used properly, PAP 02 can install as many as 14 piles per day. At least four people are needed to operate the machine - one at the PAP controls; a second at the auxiliary crane controls; a third on the platform to load the piston; and a fourth to help, in turn, to position the PAP, disengage the fired piston, and assemble the next piston to be fired.
PAP 02 is a loud machine, reaching 150 decibels at peak use. Operation requires the use of hearing protection.
Outlook
Pyrotechnical anchoring is part of a growing trend to use new technologies for traditional construction processes. In this case, the technology has been used successfully in Europe but has not yet been used commercially in the United States.McGinnity is negotiating with Spandeck Inc. of Franklin, Tenn., the maker of Mantis Crawler Cranes, to mount the PAP 02 on a standard construction undercarriage that would make the machine easier to use. John Cliff, Spandeck vice president of marketing, said a bulldozer-like undercarriage would reduce the weight from 54.5 metric tons (109,000 pounds) to 32 to 36 metric tons (70,000 to 80,000 pounds), making it easier to move around the country. It could be moved on a machinery moving trailer.
Cliff said the bulldozer treads make the machine more efficient on the job site. The crawlers can telescope to the sides, providing better stability for the launching of the piles. The Spandeck undercarriage also has more axles, reducing the pounds per square inch that must be supported by ground that is frequently soft.
The potential for reducing cost and construction time is likely to lead FHWA and the states to continue research and tests. If the tests bear out the claims of McGinnity and his backers, subsequent approval from AASHTO could lead to much more widespread use of pyrotechnical anchoring.
If that happens, American drivers may be surprised more and more often to see a "missile launcher" on the highways.
David Smallen is the president and chief executive officer of David Smallen Associates, a consulting/writing/editing company in Washington, D.C. For 14 years, he served on Capitol Hill, first as press secretary and then as director of communications for the House Committee on Public Works and Transportation and as senior staff member of the House Subcommittee on Investigations and Oversight. Before that, he was a newspaper and news service reporter. He has a bachelor's degree from Duke University, and he attended the graduate school of journalism at the University of North Carolina.
Other Articles in this Issue:
Using Monte Carlo Simulation for Pavement Cost Analysis
Studying the Reliability of Bridge Inspection
Ultrasonic Inspection of Bridge Hanger Pins
The Northwest Transportation Technology Exposition
Faster, Easier, Cheaper - Pyrotechnical Anchoring
Practical Research Answers Real-Life Questions
A Nondestructive Impulse Radar Tomography Imaging System for Timber Structures
Strategic Work-Zone Analysis Tools
