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"We used to hand-dig
potholes to find utilities," says O.G. Morrison, president
of Bear Contractors Inc., an underground contractor based in West,
TX. "But about two years ago, we bought a hydroexcavation machine.
Depending on soil conditions, that machine can dig twice as many
potholes in a day as you can dig by hand. Now we can't afford
not to have it. We find that it's cheaper to stop and locate
utilities than to hit them and have to pay for damages."
Utility strikes, nevertheless,
happen by the thousands in the course of underground construction.
In fact, some 12,000 strikes occurred in Colorado in 2002, says
Gregg Austin, product safety and compliance engineer with Vermeer
Manufacturing Co. in Pella, IA.
To avoid such strikes—and
prevent damage to utilities—more and more contractors are turning
to hydroexcavation or vacuum excavation machines. Indeed, Occupational
Safety & Health Administration rule 29 CFR 1926.651 requires
contractors to expose all utilities before digging or drilling—and
safety demands it.
Hydroexcavation machines
come in trailer-mounted or truck-mounted models. They rely on a
high-pressure water pump, which feeds one or more nozzles for blasting
away soil, sand, and even some types of rock. Frequently a hand-held
"water knife," working at 2,000 psi or more, is used to
dig holes or slots in the ground. The water creates a slurry, which
is sucked up by a high-powered vacuum system. In some cases, the
water nozzles are attached to the vacuum hose. The resulting slurry
of water and debris goes to a debris tank, which typically is hundreds
of gallons in capacity.
Some machines combine
both hydroexcavation and sewer cleaning by water jetting and vacuum
suction. "All of our sewer cleaning equipment can do hydroexcavation,
but not all of our hydroexcavation machines are equipped to do sewer
cleaning," says Steve Schoenberger, president of Vector Technologies
Ltd., a Milwaukee, WI–based manufacturer. Vector's combination
machine has both a 35-gpm pump for sewer cleaning and a 4-gpm pump
for hydroexcavation, but hydroexcavation needs only the smaller
pump.
Hydroexcavation has its
roots in the petroleum industry, where it has been used for years
to expose—with no damage—underground oil pipelines and
valves. "Now hydroexcavation has spread to finding all kinds
of utilities—especially fiber optics, which has a high cost
of repair," says Dan Hutchison, operations manager for Badger
Daylighting Inc. in Pittsboro, IN.
Exponential Growth
By most reports, growth in the hydroexcavation business is at least
steady and perhaps stronger. As more contractors learn what hydroexcavation
can do, they are finding that its benefits—in utility strikes
and damages avoided—more than outweigh its costs.
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| The
quiet-running FX30 Vacuum Extraction System with compact vacuum
tank |
"Hydroexcavation
is a safe way of excavating in a place where you have sensitive
utility lines," says Tom Jody, marketing manager for Vac-Con
Inc., a manufacturer based in Green Cove Springs, FL. "You
can use hydroexcavation machines for everything from digging out
curb boxes to potholing to general trenching. Hydroexcavation has
grown exponentially in the last five years because it does no damage
to underground utilities."
Recent, rapid growth
is evident at a franchise of Badger Daylighting, Badger of Western
Wyoming. Just since 2000, the number of hydroexcavation trucks owned
by the franchise has jumped from one to five, says Mike Hughes,
owner and operator of the Big Piney, WY, company. Business has jumped
fivefold. "We uncover fiber optics, electrical lines, telephone
lines—anything buried underground," says Hughes. "We've
gone down to 30 feet deep."
One recent Badger project
involved locating utilities under a potential road used to haul
in extremely heavy windmill equipment. Ultimately the project will
result in bringing 80 new power-generating windmills to Evanston,
WY. The windmill equipment was heavy enough that hauling it in could
damage underground gas lines, so the road had to be built up to
protect the underground lines.
"We took two trucks
and three days to do that job," says Hughes. "Each truck
located 16 to 18 utility lines per day. We went down 6 to 12 feet
deep, working in conjunction with the gas company."
Another project by Badger
of Western Wyoming entailed cutting a slot 12 ft. deep and 6 in.
wide in the shape of a football field. For a natural-gas plant expansion,
Williams Field Service wanted to find all utilities crossing the
boundary into the football-field-sized area, Hughes says.
"We reslotted the
area," he continues. "After we excavated, we found some
gas lines that prevented [Williams Field Service] from putting the
new plant where [it] had planned. So we cut a new area about half
the size of a football field. We'd use a mirror to reflect
the sunlight down into the slot to see the utilities."
Costly Utility Damage
Hydroexcavation contractors say the process is considerably more
costly than using a backhoe—but a lot less expensive than utility
damage. "You've got to have a potholing machine," says
Craig Cleveland, vice president of Diversified Underground Inc.,
a contractor in Fayetteville, GA, "because if you hit something,
you may as well just leave your machine where it sits. You're going
to lose a big chunk of what you've got." Cleveland's choice
is a Ditch Witch FX30 hydroexcavation machine.
Just how much does hydroexcavation
cost? At Hydrovac Inc., a contractor based in Boca Raton, FL, Jim
Derks owns two Vac-Con hydroexcavation trucks. One has an 80-gpm
water pump, a 1,300-gal. water tank, and a 12-yd.3 debris tank.
The other is a smaller machine with an 8-yd.3 debris tank. Derks
says one truck can cost up to $2,000/day, depending on soil conditions
and the situation. "Our hydroexcavation business has probably
increased 20% to 30% in the past two years," he notes.
Not long ago, Hydrovac
was called upon to install an underground pump room for stormwater
drains at a condominium building in Deerfield Beach, FL. Because
the site was close to the ocean, the water table was just 4 ft.
below grade, yet the pump room was situated 22–24 ft. down.
Hydrovac stood a section of 96-in.-diameter concrete pipe on end
and then used hydroexcavation to carve out the sand around and inside
the pipe. As the pipe section sank into the sand, a tower crane
would hoist another pipe section into place atop the previous one,
and the process was repeated until design depth was reached.
"We worked mostly
on the inside of the pipe," says Derks. "The water volumes
were so high that we used a 6-inch hydraulic water pump to assist
the hydroexcavation machine. When we got down to depth, we poured
an 18-inch-thick concrete floor into the bottom of the shaft—under
water—and then pumped the water out. That was their pump room.
It took about five days to place the pipe."
Derks cites another challenging
project at the Diplomat Hotel in Hollywood, FL. The task was to
dig a number of holes for 20-ft.-long light poles. Each light pole
required a 48-in.-diameter base reaching about 4–6 ft. deep.
"It was like a bowl of spaghetti underground," says Derks.
"You could not dig without destroying one utility or another.
We would hydroexcavate a hole, and if we found a utility, we would
move the hole over. It was a huge hotel, and we were on-site for
three months. Seldom did we dig a hole that we didn't have to move
more than once. Even though it was an expensive operation, we saved
[the hotel] a fortune in utility repairs."
He also recalls the time
Hydrovac worked for an electric utility that had been auguring a
48-in.-diameter hole for a light-pole base in Stuart, FL. "They
got down to 24 feet, and the hole caved in and broke off the auger
bit," says Derks. "They called me, and we took a 20-foot-long
by 6-foot-diameter pipe and stood it on end over the spot. We vacuumed
out the ground inside of it and sunk this 20-foot pipe until we
found the auger. We lowered a man inside the pipe, he wrapped a
choker around the auger, and we pulled the auger out.
"They put the light
pole in the same hole. We got down 24 feet, and the light poles
were 200 feet long. The project took two days. They just filled
the shaft with concrete." For that project, Derks used his
smaller machine, a Vac-Con unit with a 50-gpm, 2,500-psi water pump.
Mounted on an International chassis, the machine has a 1,000-gal.
water tank.
Finding the Leaks
Randy Yeager tells the story of how hydroexcavation helped rescue
a broken sewer line at a major shopping mall in the Denver, CO,
area. Last March, Yeager's company, Badger Daylighting Rocky
Mountain in Brighton, CO, was called in to find the leak—under
the mall's interior—in a 6-in. sewer line. Badger used
a hydroexcavation machine to bore a 2-ft.-wide by 6-ft.-deep trench
under the mall, along the alignment of the sewer pipe.
"The tunnel was
80 feet long," Yeager recalls. "We used shoring and temporary
lighting and the whole works. We could only work at night. It took
55 hours of hydroexcavating, and at $200 an hour, our bill was $11,000.
"[The sewer line]
had several leaks," says Yeager. "We found one at 30 feet,
and then we ran a camera into the sewer line to inspect it and found
several more bad spots. We ran the trench back to competent pipe
and replaced all of the bad pipe."
Yeager, whose company
operates four Badger trucks, has also done hydroexcavation at the
$1.67 billion T-REX project in the Denver area. It's a combined
highway and transit construction project and requires drilling foundation
caissons in areas with underground utilities. "An auger digs
the caissons to within 10 horizontal feet of a utility line, and
then we do the ones where there's a utility conflict,"
Yeager says.
"We'll do caissons
3 feet in diameter and 20 feet deep. We've probably dug 15
to 20 caisson holes." In tough digging, he adds, each caisson
hole costs up to $3,200 because such holes take longer to dig.
Care With Water Pressure
Tougher digging naturally demands higher water pressures, Yeager
notes, but once the line is reached, high pressures for an excessive
dwell time can damage certain utilities. In tests of water pressure
against certain utilities, Yeager has discovered that, say, blasting
1,500 psi of water for 10 seconds can injure the old rubber asphalt
coatings used on gas lines placed in the 1950s and 1960s. But for
new polyethylene pipe covering new phone cable, blasting 2,200 psi
of water for 30 seconds does no damage.
"Lower pressure
is always better," says Yeager. "We have a pressure pop-off
valve that won't let pressure go above 2,200 psi. If we've
got hard shale, we'll turn the pressure up. The three-jet system
that Badger has is less likely to damage a utility than [is] a single-jet
system."
Sand is easy to hydroexcavate
and requires lower water pressure. "You can almost vacuum it
up without any water, but you need the water to help it flow,"
Yeager says. "For sandy clay, you'd set it at 1,000 to
1,500 psi. And here in Denver, we have some hard shale, which takes
2,200 psi, and even that doesn't do very well. You have to
flake it off, and it takes a lot of water. It's taken us a
day to dig 20 feet in shale.
"Some people can
go to 5,000 psi, but they don't have any better luck in shale
than we do," Yeager observes. Badger, it is noted, makes larger,
truck-mounted hydroexcavation machines and is a franchise operation.
Badger's vacuum trucks move 5,000 cfm of air. "Our machines
can suck up 10 cubic yards of pea gravel in eight minutes,"
he adds.
As evidence of hydroexcavation's
growing popularity, industry officials point to the fact that both
Vermeer Manufacturing and The Charles Machine Works (i.e., Ditch
Witch)—which are major underground-equipment manufacturers—now
make hydroexcavation machines. Both companies make two trailer-mounted
units.
At Ditch Witch, the FX30 was introduced in January 2002, and the
FX60 came out a year later. Both machines feature water tanks of
either 500, 800, or 1,200 gal. and offer water pressures up to 3,500
psi. The difference between the two is that the FX60 has a much
more powerful vacuum system that can move 950 cfm.
Vermeer offers the E550
and E900 potholing machines. The two are capable of delivering 1,000
cfm, and with a multinozzle wand system, both vacuum excavation
units can pothole using a 4.5-gpm, 3,500-psi onboard pressure pump.
Vermeer says its systems can be skid- or trailer-mounted.
Yes, hydroexcavation
is expensive, says Badger's Dan Hutchison. "But what cost
can you put on an accident?" he wonders. "As word spreads
about hydroexcavation, more and more people will use it to avoid
damage to utilities."
Daniel C. Brown is
the owner of TechniComm, a communications business based in Des
Plaines, IL.
GEC
- January/February 2004
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