All About Vacuum Excavation
Air or water? Positive displacement or fan power? We sort it out.
It’s simply good business to hire or buy a vacuum excavation unit to look for utilities. When you investigate utility conflicts by digging with a vacuum excavation truck or trailer-mounted unit, you know beyond a doubt what’s down there. But deciding on the type of equipment you’ll need is not so simple.
Vacuum excavation equipment uses high-pressure air or water to precisely control soft excavation. Spoil is sucked through a vacuum hose and is deposited into a debris tank for later disposal, or for backfilling into the hole. Models range from large dedicated truck units to small trailer- or skid-mounted units, which gained popularity in the 1990s as support machines for horizontal directional drilling operations.
The smallest units even fit into the back of a pickup truck.
As the awareness of vacuum excavation increases, the market for the method is growing. Many states require visual confirmation of the presence of utilities—through “potholing” or slot trenching—before digging with an excavator or backhoe. Vacuum excavation is cost-effective and it works faster than hand-digging. And it avoids tremendous financial liabilities. One vacuum excavation contractor said one of his former customers realized how much he was hiring the vacuum excavation rig, bought a machine for himself, and became a competitor to his former vendor.
Sucking out large water filtration vats at Farmington Hospital
Photo: Atlas Daylighting
Working a tough spot in the woods to locate an underground gas main
The variety of applications for vacuum excavation equipment is almost endless. Rockies Construction, for example, works for oil and gas companies, telecommunications owners, road contractors, construction companies, power plants and refineries. The Aztec, NM–based company even does slot trenching for irrigation pipes on lawns. It digs utility pole holes, cleans culverts and digs piling holes for footings. If the soil conditions are acceptable, crews can dig precision-cut trenches for house foundations. The trenches can be filled with concrete to make footings.
PD Units, or Air?
Vacuum excavation units pull a vacuum by either the use of a positive displacement blower or by fan-powered air. Positive-displacement (PD) machines use lobes that resemble revolving doors to move air. Fan powered units move incredible amounts of air; the fans can be staged in series so that one fan supercharges the next one.
Pacific Tek Inc., of Santa Ana, CA, builds a range of vacuum excavation units that dig with either pressurized air or water. The units have debris tanks that range in size from 66 gallons to 1,200 gallons. All units use positive displacement blowers. “We can get higher cubic-feet-per-minute rates out of a PD unit than a vacuum pump,” says Dan Skorcz, president of Pacific Tek. He’s referring to the rate of debris product movement as pulled by the vacuum.
Why does he favor PD units? “They’re simple in design, reasonable in cost, they provide high flow rates for the size of package they are, and they are pretty reliable,” says Skorcz. His smallest unit moves 325 cfm of product; middle-sized units move 525 cfm; and the standard high output machine pulls 825 cfm. “The faster you move the wet, sloppy material, the better chance you have to avoid clogging up the line,” says Skorcz.
While 825 cfm is his largest standard unit, Skorcz says he has built trucks with up to 2,300 cfm capacity. “I just shipped a couple of 1,100-cfm units,” he says.
Skorcz says some contractors and cities make a practice of locating and maintaining underground water valves. Over years of no operation, the valves become stuck, and must be exercised. Plus, the valve boxes get dirty and have to be cleaned. So Pacific Tek makes vehicle-mounted hydraulic valve operators to wrench the valves loose. A machine can do it more effectively than can a man with a wrench, Skorcz says. His valve operators range from 50 foot-pounds of torque up to 2,500 foot-pounds.
Anaheim, CA, has an aggressive program to exercise its water valves, Skorcz says.
Using Water to Dig
Rockies Construction runs nine vacuum excavation trucks, and they all use water for digging. “The air machines don’t seem to work as well in the rocky clay type soil that we dig into,” says Clayton Spurgeon, manager for Rockies.
Six of the trucks are large Tornado Hydrovacs (formerly Tornado Technologies) units with 12-cubic-yard debris tanks. Another is a 7-yard Tornado. One is a 6-cubic-yard Amerivac, and they also have a four-wheel drive truck with a 3-yard tank for getting into small areas.
Rockies once dug a 50-foot-deep hole, 8 feet in diameter, for a power transmission pole in Utah. As the unit dug down, Rockies inserted corrugated metal rings, each 10-foot tall, into the hole to support the soil.
“We’ve done quite a few pipeline projects,” says Spurgeon. “We spot all the utilities for a 5- or 6-mile stretch of pipe, and pothole down to the utility junctions. Then we dig a bell-shaped hole where the new service ties into the existing service. We slope the bell-holes according to OSHA requirements so that a worker can get in there and make the junction.”
Spurgeon recalls the time he was called upon to clean out the crawl space under a house in Dallas. The house had flooded, leaving the crawl space full of silt. “We ran 80 feet of pipe into the house to do that one,” he says.
Another time Rockies ran 120 feet of extension pipe into a hospital in Farmington, N.M., to suck out two large water filtration vats. The vats each held about 200 gallons of sand to filter water, and the sand had become plugged up with deleterious material.
We asked Spurgeon how he likes the Tornado trucks. “I like them a lot,” he says. “They’re the quietest of all those trucks and they seem to break down less than the others. I think the Tornados have the best reputation for simplicity and reliability.”
Tornado Hydrovacs builds four models of vacuum excavation trucks. All have PD blowers and all dig with water pressure. The blowers range in size from 2,400 cfm to 6,500 cfm and debris tanks range in size from 4 cubic yards up to 13 cubic yards, says Mark Gilkyson, a salesman with Tornado. Water tanks range in size from 550 US gallons up to 2,300 gallons aboard the truck.
Vactor offers two models of vacuum excavation trucks: the new Vactor HXX Prodigy and the full-sized Vactor HXX. The Prodigy uses either air or water as a non-destructive digging medium. The machine pulls 16 inches of mercury with a 3,200 cfm PD blower. Like the full-sized Vactor HXX, the Prodigy uses hydro-excavation, blasting away soil with jets of 10 to 20 gallons of water per minute under pressures of 1,500 to 2,500 psi, depending on the pump selection, pressure adjustment and nozzle tip configuration. The Prodigy can carry up to 600 gallons of water, which allows for 3.5 hours of continuous operation between refills.
The full-sized Vactor HXX Hydro-Excavator can handle potholing, water line repair, slot trenching, sign and pole installation, pipe and line installation and other large-volume excavations. The machine provides up to seven hours of continuous operation with the on-board water supply. Features include a 12-cubic-yard debris tank, a 1,300-gallon stainless steel water tank and a 320-degree rotating boom.
Diversifying Into Sewer Work
Atlas Daylighting of West Lafayette, IN, operates multiple types of vacuum trucks, including two Tornado units, both with PD blowers. One is a 5,800 cfm truck, and it’s among the largest in the nation. The second Tornado is a 3,600 cfm unit on a smaller chassis to get into tighter places. Atlas’ third unit is a Vac-Con truck with a 4,200 cfm blower. The company also runs a Vactor 2100 with a two-stage fan to create the vacuum.
|Photo: Atlas Daylighting
Working in muddy conditions, a Vactor 2100 truck cleans out a sewer for Atlas Daylighting.
“As the hydro-excavation work has slowed up with the economy, we’ve diversified,” says David Kerper, general manager for Atlas. “We’ve been doing a lot of inspection, mapping, and cleaning of underground sewers and utilities.” For the inspections, Atlas bought a van with closed-circuit television (CCTV) capability. A TV camera, driven by a small remote-controlled vehicle, moves along inside the sewer and transmits video photography of the sewer walls back to a display screen in the van. (At the completion of this story, Dave Kerper was leaving Atlas Daylighting to go to Clear Crossing LLC, a hydro-excavation, water jetting and CCTV inspection company in Lebanon, IN.)
In a combined 36-inch storm-sanitary sewer in Indiana, Atlas found that large tree root balls were obstructing flow and had to be cleaned out. “We use a high-speed cutter,” says Kerper. “It’s an attachment on the end of our jet-hose; high-pressure water drives the blades that cut the root ball. We have cutters that can work up to 42-inch-diameter pipe. Then we vacuum the debris at the downstream manhole.
“Once it’s all clean we run the closed-circuit TV camera through the sewer to inspect it for any remaining debris,” Kerper says. “That camera rides on wheels or tracks, depending on the size of the pipe.
“We cleaned approximately 15,000 feet of 36-inch diameter concrete pipe,” says Kerper. “There were many root balls, and in places the sewer was one-fourth full of dirt.”
In February Kerper was preparing to inspect and clean 3,000 feet of 66-inch diameter pipe. It’s a combined storm and sanitary sewer in Indianapolis, and Kerper says it’s very dirty. Cleaning the sewer will require two workers to enter the pipe; one will handle a digging wand while the other controls the vacuum hose. “Our extensions allow us to go 300 feet from the truck,” says Kerper.
He plans to use three trucks, with a combination of hydro-excavation and water jetting, to equip the job. The primary unit will be the big 5,800-cfm F3 Tornado truck. When that one gets full, the 4,200-cfm Vac-Con truck will roll into action.
Finally, Atlas will run a Vactor 2100 with a water jetter through the sewer to clean the pipe out finally. The jetter pulls itself into the pipe by the force of water shooting backwards, and then the hose reel brings it back.
Kerper says he expects the hydroexcavation work to begin coming back. “We travel all over the United States to get to jobs,” he says. “We’re looking at a job in North Dakota, and we’ve been to Missouri, Illinois, Ohio, and Kentucky.”
Sewer Equipment of America, Glenview, IL, offers three trailer-mounted vacuum excavation units and four truck units. All units feature positive-displacement blowers, which enable the vacuum units to dig deeper, and at further distances from the base machine, says Brandon Shelton, marketing manager. “With a PD blower, you create between two and three times the vacuum power that you get with a fan-powered unit,” says Shelton.
“Our 3,000-cfm machines pull about 16 inches of mercury—and the HX 1227, our largest truck-mounted unit, pulls 27 inches of mercury,” says Shelton. “We do both air and water digging, but we recommend water over air. Water is more productive than air in nearly every case. But in certain soil types, like sand, air does just as good a job. You also might have to use air if you’re working with a toxic material that you don’t want to spread any further in the soil.”
USI Prefers to Use Air
Dave Munson, business development manager for Underground Solutions Inc. (USI), says his company prefers to excavate with air, not water. USI can do both, however. USI operates five Vacmaster 4000 vacuum excavation trucks. “Air is safer to deal with, it’s cleaner, and it’s more environmentally sensitive,” says Munson, who is based in San Diego.
“Water is not compressible, it can damage underground utilities,” says Munson. “Air is compressible; it will flow around an object without causing damage. Plus, with air you don’t create that muddy slurry that requires import soil for backfill. Air alleviates the need for following the environmental best management practices that are required with slurry. With air you can usually put back the same soil that was air/vacuum excavated.”
USI just completed a large project for the Port of Los Angeles, which is expanding its facilities and putting in new railway lines. “USI air/ vacuum excavated about 130 potholes to confirm utility depths and locations prior to future grading of the site,” says Munson. “The utilities ran from 2 to 8 feet deep. We used ground-penetrating radar (GPR) to locate unknown objects underground. The GPR picked up images; we would then pothole those target images to confirm what’s down there. This project area was loaded with fuel and oil lines.”
For another USI project, the company potholed a proposed cable alignment to determine potential utility conflicts with the construction of the 230-kV cable designed to bring power from the Imperial Valley area to San Diego County. The large cable requires junction vaults, measuring about 10 feet wide by 20 feet long by 10 feet deep. USI potholed 11 feet deep in three locations on a diagonal at the proposed vault locations per the clients request to confirm clearance of those sites.
Within the City of Carlsbad, USI recently completed air/vacuum excavation potholing of approximately 30 sites to determine exact locations and depths of existing casing pipes carrying utilities underneath the railroad tracks. This project was for the planned addition of new rail lines serving Amtrak and another rail company. Special measures were taken while working within the railroad right-of-way.
Vacmasters offers its System 4000 vacuum excavation trucks with the ability to dig with air or water, but says operators will usually use air. The company says its Air-Tec nozzle combined with high pressure/high volume air “can break up the hardest soils in record time.”
Vacmasters says potholing with air offers the following benefits:
- Digs faster than water in most soils
- Keeps spoils dry for fast, efficient backfilling
- Eliminates mud disposal problems
- Is safer for the utilities and the operator
- Won’t damage a road base
The Vacmasters 4000 features a 155-horsepower John Deere diesel engine. One engine drives all systems aboard the unit—vacuum, air and water. The 4000 has a 1,000-cfm vacuum that can pull 15 inches of mercury. The air lance works at 300 cfm and 220 psi of pressure. To hold spoils, the System 4000 features a 450-gallon tank with a hydraulic hoist for fast and easy emptying. An 85-gallon water tank stores water for digging or cleanup.
Vacmasters says the System 4000 can operate up to 200 feet away from the truck to reach difficult areas.
The popularity of vacuum excavation is sure to grow as the awareness of the technology expands. The financial risk and dangers are simply too great to avoid taking advantage of this exciting, relatively new technology. And as more competitors enter the field, it’s entirely possible that costs will come down, or at least level out.
Author's Bio: Daniel C. Brown writes on safety and technology in the construction industry.