Paying Attention to the Underworld
An aging underground infrastructure is presenting the potential for repair work in the near future, with much of it involving excavation that takes into account existing underground utilities.
As such, contractors look to gain efficiencies through underground location devices such as hydro- or air excavation that also will minimize the amount of destructive excavation activity.
“Infrastructure repair is a huge opportunity in the United States, as the infrastructure has deteriorated through economic downturns and just the fact that the underground infrastructure is aging,” says Tom Jody, marketing manager for Vac-Con.
To that end, the use of hydroexcavation equipment will play a critical role in its mitigation, Jody adds.
Trevor Connolly, vice president of marketing for Vacmasters, sees the market for underground infrastructure work as continuously evolving through ongoing repair and replacement work. No sooner is a road built than crews have to return to repair potholes that occur in heavy traffic conditions, he points out.
Andy Hartman, sales and marketing manager for Supersonic Air Knife, says his company has eyed the trends in the industry as regulations have increased, especially with the advent of the 811 “Know What’s Below” call system.
“It’s becoming more ubiquitous through all states,” Hartman says. “There’s been a unifying movement to where the states are trying to come closer together in what their standards are for excavation as far as recommendations for best practices for minimizing damage.”
Hartman attends Damage Prevention Alliance programs every year, many of which address 811 as well as an increasing number of regulations from state to state that govern excavation.
“Air excavation is one of the things they recommend along with hydroexcavation, and vacuum excavation—things like that that tend to be non-destructive or less destructive than heavy equipment,” he says.
Brett Hart, product manager for Vactor Manufacturing, also is noting a rapid growth in vacuum excavation.
Hart says contractors favor the technology for the use of water or air as the medium to loosen the soil surrounding buried utilities as a vacuum source removes the soil into an on-board hopper for offloading at a remote location or back into the excavation site.
“Since only water or air is being used to disrupt the ground, buried utilities are exposed without disruption or damage,” he says. “By using vacuum excavation as the preferred method of exposing utilities for repair, the user protects the asset from damage along with any other buried utility that may or may not be known to occupy the same general area. Not knowing the exact location of other buried utilities is a leading cause of unintentional utility strikes.”
Vac-Con’s Hydro Excavator truck is of the most interest to the company’s grading and excavating customers, Jody says.
“All vacuum trucks are essentially capable of sucking dirt into the tank,” he points out. “Hydroexcavators are specialized units that provide high pressure, yet a low volume of water to limit the amount of collateral damage that’s done by the excavating equipment, and promote the safety of digging under the ground by using a vacuum hose to excavate rather than using a bucket.
“You’re also using high-pressure but low-volume water to dislodge the soil,” he adds. “There’s really no impact on an underground utility. In the case of high-voltage underground utility lines, where water might be a problem because of its conductivity, high-volume, high-pressure air systems can be used to move the dirt toward the vacuum.”
Vacmaster’s Connolly says for the purposes of utility locating, air vacuuming is “by far the safest and most economical means of which to locate underground utilities. Air is non-conductive, whereas water is not. If digging around utility lines, it’s risky to use high-pressure water rather than air—it will still try to cut through utility lines.”
Using high-pressure air keeps soil dry, enabling contractors to use it as immediate backfill, he says.
“Water creates a ‘slop’ that is vacuum-dumped into your spoils tank and you have to drive to the appropriate dump and depending on the municipality or state, dump it as hazardous material, which is costly,” Connolly says.
Supersonic Air Knife has manufactured air-excavation equipment for more than 15 years. While hydroexcavation uses high-pressure water, air excavation utilizes compressed air at about 90 psi “instead of water at several thousand psi,” Hartman says.
“The air moves at supersonic speed and will pulverize the soil without creating a mud slurry,” he adds. “The main difference between the hydroexcavation and the air excavation is the pressure differential, which makes a huge difference when it comes to the safety of the person involved in digging.”
Contractors have usable fill to put back in the hole that was dug out when they are finished with air excavation, Hartman points out. In contrast, hydroexcavation usually involves vacuuming the dirt with a vacuum truck into a storage tank, which then has to be taken offsite and dumped, and different fill is then brought back in, he adds.
Safety is another issue, Hartman says.
“That 90 psi makes it a lot safer for the contractor, and it’s safe to use directly on fiber optic cables, PVC pipelines, and things like that, because the pressure is low and air being nearly without mass gives up kinetic energy very easy when it encounters any structurally sound object,” he says.
“By using a lot of air moving very quickly but at a relatively low pressure, the air finds its path of least resistance to the soil and ultimately pulverizes the soil,” Hartman adds. “Any objects encountered in the ground—whether they are stones, pipelines, cables, or any other solid object—the air is diverted around that and doesn’t do any damage to what’s in the ground. You would either use a vacuum unit to remove that loosened soil, or it’s easy to shovel it out, but without the forces that digging with a shovel requires. You don’t have to jam it down in where you might cut a cable or pipe.”
Hartman says if a contractor uses the discharge hose to make a spoil pile nearby and plans to continue to dig in the same area, “You’ve got something to put back into the hole when you’re finished. Some material is still lost due to dust. You can bring a small pickup truck rather than a big truck full of dirt to fill the hole back in.”
The use of hydroexcavation equipment started in western Canada, where contractors were digging around oil and gas transmission lines, says Jody.
“It had spread throughout Canada as their exclusive means of excavation,” he says. “One of our contractors in Toronto told me that no matter what you do to excavate in the city, you have to use hydroexcavation because there are so many underground utility lines and they don’t necessarily know where they all are.”
Jody believes those regulations will begin spreading throughout the United States.
“We continue to have horrible accidents in the United States based on improper excavation of utility lines. Those accidents range from disruption to data communications and services and electrical services up to violent gas explosions that kill people as a result of digging with equipment that can damage utility lines,” he says. “Each time there is an accident like that, it just solidifies the idea that we should be using some form of vacuum or softer
Digging a test hole using vacuum excavation (Quality Level A)
Test hole exposing utility lines (Quality Level A)
Most states have a regulation mandating hand digging at a certain point after opening a hole with heavy equipment, Hartman says.
“It’s usually within 18 inches or so to expose what it is that you’re digging for,” he says. “That’s one of the places where the Air Knife is really useful. It’s faster than hand digging and it’s safer because you don’t have any of that impact force with the sharp edge of a shovel. It’s just the air coming through and you can clean things off once you expose them.”
Hartman notes that most states have come to understand that using air excavation is not the same as mechanized digging.
“The biggest thing now is getting individual work crews to understand that a well-designed nozzle applied to proper physics nozzle design equations has a lot more digging power than an air lance that they’ve put together off parts of a truck,” he says, noting that some crews have used that approach with a piece of pipe and a ball valve.
“You can make a lot of noise and a lot of dust, but I think once people use the additional power of something that is a professionally built tool rather than throwing something together to clean dirt out of a crack before paving a road, that this is the better choice.”
Vac-Con’s Hydroexcavators feature a two-engine design focused on independent vacuum and water system operations. The chassis engine drives the vacuum while the auxiliary engine for the water system delivers continuous complete water recirculation whether the truck is in motion or at rest.
The Corten steel debris tanks range from 5 to 16 yards and feature hydraulic door locks controlled from the side of the truck for safety.
Other features include an automatic vacuum breaker shutoff, a full opening rear door, the availability of a two- or three-stage centrifugal compressor and positive displacement blowers.
Vac-Con’s Hydroexcavators also include dual stainless-steel micro strainers and a centrifugal separator with cleanout and a water tank capacity of 650 to 1,500 gallons. The water tanks are constructed of cross-linked polyethylene.
The Triplex Water systems are rated at 10 gpm to 50 gpm or higher, and 2,000 psi to 3,000 psi. The front-loading boom has a 6-foot to 10-foot extension. The system also includes a 4-foot high-pressure
Vactor Manufacturing is noting a rapid growth in vacuum excavation, says Hart.
“The method is increasingly becoming the preferred alternative to conventional excavation practices,” he says. “The costs of strikes to buried utilities is a risk most construction companies, utilities and cities are no longer willing to accept.
“As a result, there is a desire to seek alternative means, such as the Vactor HXX HydroExcavator and Vactor HXX Prodigy vacuum excavator to locate, inspect and repair buried assets. Vacuum excavation offers the means to safely and effectively perform the work without the risks associated with conventional mechanical digging. Vacuum excavation is true damage prevention.”
For the past 20 years, contractors have been using Vacmasters air-vacuum excavation systems for potholing with an eye to safety, avoiding damage to underground utilities and taking advantage of using the dry spoils for immediate backfill use.
Vacmasters manufactures four systems:
System 6000, featuring a 250-horsepower, six-cylinder engine and 350-cfm, 250-psi air compressor and a positive displacement blower rated at 1,866 cfm at 15 inches HG. It has trenching capabilities and a wireless remote hydraulic boom. Other features include a 950-gallon tank with a full opening door, an interceptor canister separating dry and wet spoils with a rear mount to facilitate backfilling, a self-purging filtration system and an enclosed power head.
- System 4000 is Vacmaster’s highest-capacity, non-CDL system, which operates in soil that is tough, wet, sun-baked, compacted or including ground frost. It operates at 300 cfm, 220 psi. It has a 155-horsepower, six-cylinder John Deere turbo diesel engine and features an Air-Tec nozzle. Other features include an interceptor canister, self-purging washable filters, hydraulic-powered dumping, enclosed power head, high-efficiency absorption chamber silencer, and a slurry vacuum mode. It also has a 450- to 800-gallon spoils tank.
- System 3000 is a mid-priced air vacuum excavator operating at 165 cfm, 180 psi. Other features include a 100-horsepower, four cylinder John Deere turbo-charged diesel engine and a 300-gallon spoils tank.
- System 1000 is a low-cost, small air vacuum excavation system with a skid-mount design allowing it to be trailer or truck-mounted. It operates at 100 cfm, 150 psi. It features a 68-horsepower, four-cylinder John Deere diesel engine that drives the vacuum, air and water systems, a two-stage cyclonic filtration system with particulate element, and hydraulic-powered dumping of a 300-gallon or optional 500-gallon spoils tank.
All systems have selectable air or water, with air being used 95% of the time; remote operation from up to 200 feet away; a supervisory control panel with auto shutdown; slurry vacuum mode, and low-maintenance design.
Supersonic Air Knife offers several options:
The X-LT and the X-ST2—Hartman describes them as two versions of the same tool, using the same nozzle and compressor, but different in materials and weight. The X-LT is lightweight aluminum and the X-ST2 is made of industrial strength stainless steel and brass and can take more of a “beating” on the job site, Hartman notes.
- The X-HFA is a larger-scale version of the X-LT: aluminum with a larger compressor that puts out twice the air and produces five times faster the digging power under the same soil conditions as standard tools.
- The VAC-H1 and H2 is a small vacuum powered by an air compressor. It uses a Venturi effect to direct materials upward through the tube and deposit them near the end of a 3.5-inch or four-inch flexible discharge hose.
“That makes it a lot more smooth for the contractors to finish their job without impacting the utility, hitting a gas line or shutting off a phone service, for instance.”
Geotrack uses equipment such as ground-penetrating radar from Mala, radio detection equipment by Subsite, and vacuum excavation trucks from Pacific Tek or Vacmasters.
Gas and telecommunication lines are the two most common lines hit by construction activity because they are the most shallow, says Tan.
Tan is noticing a call for different applications for vacuum excavation.
“Gas companies might use it to encapsulate gas lines that need repair,” he says. “We’ve got a project in Washington DC where they want to put utility monitoring points along a sewer for a wastewater plant. They’re building a deep tunnel and they want these utility monitoring points in the future, so if something happens they can reference it to a certain point on the line along a 2- or 3-mile stretch.”
Vacuum excavation is being used to dig down to the top of the utilities, which are an average of 15 feet deep.
“There are different applications now for this service,” Tan says. “It’s a safe method of digging. It’s more efficient than digging by hand and it’s less damaging than using a backhoe as a traditional way of excavating.
“You’re seeing more of those types of applications when resources are scarce and they’re trying to find new ways of doing things better,” he adds.
Tan notes regulations regarding the preference of hydroexcavation and air excavation are becoming more stringent.
“The American Society of Civil Engineers has standards where engineers are now liable if they know about this service and don’t use it,” he says. “If damage occurs, the engineer will be to blame.”
Tan would like to see the vacuum excavation become an integral part of the 811 ‘one call’ system.
“Especially in urban areas where the potential for gas lines that would be critical for businesses and homes were damaged that they would require vacuum excavation before they dig,” Tan says. “Simply marking out the utilities is good, but it doesn’t eliminate entirely the hits on utilities.”
There are still more than 250,000 hits on utilities in the United States alone, says Tan, adding that before the ‘one call’ system, there were more than a half-million.
“It’s cut in half, but it hasn’t eliminated them,” he adds. “If they integrated the vacuum excavation into that ‘one call’ system, there would be a huge savings.”
One utility hit can cause billions in damage, Tan points out.
“In 1995, a powerline was hit and shut down the airport in Newark, New Jersey,” he says. “Because it was down for the day, flights were cancelled all over the country and it cost the airline industry more than two billion dollars. Utility hits can be very, very costly.”
The need to repair underground infrastructure is being stymied by the lack of money to do so, Tan points out.
“Municipalities are obviously struggling with budgets and lower tax revenues,” he says. “The whole country is suffering because we haven’t had an infrastructure bill since [President Bill] Clinton. Until that goes into place, it’s a chicken and egg question. That needs to go into place first so there’s money to repair the infrastructure.”
And none too soon.
“By next year, over half of the nation’s bridges are going to be more than 50 years old, which is basically the lifespan of a bridge,” Tan says. “Water systems are in terrible shape, roads in many communities are worse than Third World country conditions.”
Tan says he believes the effort must start with the federal government.
“Eighty percent of the roads in terms of mileage are owned by the states, but they are all struggling,” he says. “A highway bill is necessary with regulations that require this sort of safety in place. Anytime you have a construction project that goes over budget, 99% of the time it’s because they hit utilities. They didn’t know where they were.”
Multi-Construction Services (MCS) in Toronto, Canada, has been using Vac-Con equipment since its inception 11 years ago. The company does hydroexcavation with 15 Vac-Con units. Clients include municipalities, utility companies, sewer and water main companies, and other specialized companies.
“The main purpose of using this type of equipment is in how it works,” says Mario Musto, MCS vice president. “It uses high-pressure water and a powerful vacuum to loosen the ground soil. It deposits the ground soil into a self-contained debris tank for transport.
“It’s very safe and it can get into unique spots where most conventional equipment can’t get into. When you’re digging around very sensitive underground infrastructure, whether it’s gas, electrical, phone, fiber optics or cable, you would rather do that than rip it out of the ground.”
Musto points out that hydroexcavation will not cut through pipes and his workers are able to clean what’s been dug up with the hydroexcavator so that which is underground can be exposed with damage.
Musto says that Toronto laws are become more stringent to the point where there can be no excavation without mapping out the area with a vacuum truck to do the locates.
“It’s not to the point where they’re banning bucket excavation,” he says. “They’re taking certain safety precautions before they let a company start to dig. Usually a company like ours will be the first ones on site after they do the locates to verify all of the locates and verify all of the depths and find and expose everything before they actually start digging.”
MCS maps out an area every 10 to 20 feet with hydroexcavation.
“A lot of times when you’re working with a gas main, when you locate it, they’ll let you dig with conventional equipment until about three feet off the pipe and then the rest of it has to be done through hydroexcavation,” Musto says.
Although Tan finds that technology is serving him well on the job site, he sees a need for continuing research and development.
“We have to be constantly improving our technology in terms of locating underground utilities because there still are imperfections in the technology,” he says. “No two ground conditions are the same. Ground-penetrating radar is limited, electromagnetics are limited, so you end up digging. Vacuum excavation is key because it’s a safe method of digging. Many times you cannot see underground with the technology you have, so you are digging these test holes in order to see what’s down there.”
Technologies come with a price tag that bureaucracies—with their own inherent inefficiencies—are unwilling to pay despite the ‘pay now or pay later’ consequences, Tan says.
Case in point: a sensor programmable to sense any gas that can be affixed to gas lines and integrated into a GIS or utility repair system.
“If it detects a leak, it can immediately notify the right people and they can get it repaired right away,” Tan says. “There are technologies like that, but you don’t see anybody integrating these things into their systems. From a cost standpoint, everyone is running from such a slim margin—those types of capital improvements are now not possible.”
Soft excavation methods do have limitations.
The Supersonic Air Knife does not replace a backhoe or any other heavy digging equipment, but rather precedes its use, notes Hartman. The tools are most useful when a contractor is doing the initial locating to verify the markings made for underground utilities and pipes to ensure there is nothing else there, he says.
“In the past, the choices were usually to go in with a shovel or do some manual digging first,” he adds. “If you go in now with an Air Knife, you can pot hole down and locate those items faster and know where you can go in and dig with the heavy equipment.”
Jody says the only limitation in using hydroexcavation equipment is “depending on how the excavating is done, it may not be possible to use the material that’s recovered from the excavation for backfill.
“But in most cases, the machines are designed to minimize the amount of water that’s used to excavate and at that point, the soil remains relatively dry and can be used for backfill. If the soil becomes like a slurry, then it cannot be used to backfill the excavation.”
On significantly large excavation sites, “you’d use the vacuum excavation equipment to locate underground utilities and then determine a level at which those utilities exist, then you have the excavation equipment to dig down to within a certain distance of the utility line and then you use the vacuum excavation equipment to do the detail work around the utility,” Jody points out.
Jody says he sees the future for hydroexcavating to be significantly important as more companies are installing utility lines underground and the infrastructure is renewed or expanded.
“It becomes more important that we don’t damage those utilities by digging,” he adds. “In our company, we feel that this has the potential to be the biggest part of our business.
Of an increase in underground infrastructure work, Jonathan Tan, president of Geotrack, a subsurface utility engineering firm, says: “In lieu of a highway bill that would see a much bigger increase in all construction work, we are seeing an increase in our type of work.”
The impact of utilities in excavation work is always going to be significant and is the primary reason for construction delays, Tan points out. His company has been locating and mapping underground utilities since 1989.
“There are increasing opportunities with facility owners who either have capital plans for their facilities or public works projects,” Tan says. “Budgets are limited and they need to find safe trenching or safe digging to locate utilities so they don’t hit them during construction.”
Geotrack employs a number of methods to get the job done, including ground penetrating radar and electromagnetic locating, which Tan describes as the “mainstay” of what locators use for underground utilities.
“That will help you determine a horizontal or two-dimensional view of what’s underground and based on that, the above ground is marked out and you will know what’s in conflict with whatever you are building,” says Tan.
The location and mapping of underground utilities involves aboveground markout, including the use of electromagnetics, ground-penetrating radar, and sonar-based locating instruments.
At a point of conflict, Geotrack uses air, pneumatic, or water excavations to pinpoint the depth of the utilities, which then provides the most accurate information as to their location, Tan says.
“The aboveground is accurate to within 18 inches on either side of the utility, but once you’ve opened up and exposed the utility safely using the vacuum excavation method, then you have precise data—not just horizontal, but now vertical,” says Tan. “Now the contractor can avoid that utility and know if he needs to relocate it. A path for that storm drain line, for instance, can be determined in terms of depth and horizontal placement.
Carol Brzozowski specializes in topics related to stormwater and technology.
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