From: Municipal Sewer & Water

By:  Doug Day

Hydroexcavation is gaining ground as a safe, precise and efficient alternative to conventional digging.

Hydroexcavation has been popular in Canada for 50 years, but it only started gaining traction in the U.S. about 15 years ago. It’s still not as widely used as it should be, according to Vac-Con Marketing Director Tom Jody, and there is huge potential for growth.

Ordinances requiring vacuum excavation in certain situations are common in Canada, and Jody says that demonstrates how much growth potential there is in the U.S. “Most communities in Canada require utility location with vacuum excavation or some sort of potholing before you’re allowed to excavate,” he says. “In some cases, you’re not even allowed to excavate with a conventional bucket machine; you have to use vacuum technology to do it.”

Many people may view hydroexcavation simply as a method for safely exposing underground utilities, but there are many other uses, especially in confined areas. “There are some situations where it’s a necessity because it’s impossible to get an excavating machine into a location,” says Jody. “Take for example getting behind a home in a residential neighborhood to expose the foundation to repair a utility line or drain tile.”

There are also times when hydroexcavation is the easiest method. Besides daylighting (potholing), it is useful for things like excavating for water valve replacements, trenching and cold-weather digging, as well as pipeline locating, identification and rehabilitation. “It is very precise; think about excavating a trench between someone’s prized flower garden and the wall of their house,” Jody says. “That’s something you can do with hydroexcavation that you couldn’t do with even the smallest of excavators. The applications are myriad and the equipment is relatively simple.”

Karl Lassberg works in sales and marketing for T-Rex Services Hydro Excavation and Industrial Vacuum Services, which owns the largest fleet of hydroexcavators in Texas. T-Rex, founded with one truck in 2001 by former NASCAR driver Bobby Hillin Jr., now has a fleet of more than 38 hydroexcavation and vacuum excavation trucks. “At the time, there wasn’t a lot of hydroexcavation going on in the southern Gulf region,” Lassberg says. “He just went out there and hustled, and the popularity of hydroexcavation has grown over the last decade as the awareness of the technology has grown.”

Lassberg cites one recent job as a good example of the versatility of hydroexcavation. The excavation was only 4- by 4- by 6-feet but required hand digging because the location was inside a parking garage. “It would have taken several days to dig and carry out 3.6 cubic yards of dirt by hand,” he says. “We ran a remote hose down a stairwell and it took us less than three hours. Our bill was much cheaper than a hand dig.”

He adds that hydroexcavation is also a good alternative to an auger for digging holes. “If you have only a couple of holes to dig with an auger, hydroexcavation can be competitive because the material is sucked straight into the truck and dumped off site,” Lassberg says. “You don’t have to worry about additional equipment to scoop it up and haul it away.”

The advantages are even greater when it comes to utility pole holes, usually 18 inches in diameter and 8 feet deep. Two people with posthole diggers will need about two hours to do a single hole, while it’s a 10- or 15-minute job with hydroexcavation.

Lassberg says electro-mechanical work has led to a lot of hydroexcavation work in recent years, such as grounding wire trenches, 6 inches wide and 18 inches deep, that used to be dug by hand. “We can hydroexcavate 300 to 400 feet of that in one day and cover it with a skid-steer instead of putting five guys trying to dig for days at a time.”

One such project was at a lighting conduit project at the Galleria Mall in Houston in September 2010 — 700 feet of trench (2 feet wide and 2 feet deep) underneath a sidewalk bordered by a long line of historic oak trees. “With all those tree roots, you have to dig a little differently and more conscientiously,” Lassberg says. “If you even skin a tree root you can kill the tree, so digging by hand is very tricky business.”

In this case, all the roots crisscrossing through the excavation area made any other sort of excavation impossible. Since tree roots can also be damaged by high-pressure water, the excavators used lower pressure and kept nozzles well way from the roots. The job also had to be done in 48 hours in a high-traffic area of the city. T-Rex brought in five trucks. “We started Friday at 9 p.m., and finished 40 percent ahead of schedule,” Lassberg says. “Two years later, the trees are still in great condition.”

Consider the options

Lassberg says there are three main issues to think about when considering hydroexcavation. Is there a source of water on site? Can the spoils be dumped on site? And how close can the truck get to the excavation?

“Most trucks require a water source, whether it’s a fracking tank, water truck, hydrant or a pond,” he says. “Dumping on site usually makes a job much more productive. Dumping offsite means driving to a dump site and back; sometimes there are dumping fees. Access within 15 or 20 feet from the dig site allows for the greatest productivity but we can work 300 to 400 feet away from the truck when necessary.”

The key pieces of equipment are a vacuum hose and a line for pressurized water. Compressed air can also be used, in which case it is called vacuum excavation (the generic term for the process). The water or air loosens the soil, and the vacuum removes the soil. “It creates a very accurate excavation and less impact on the surrounding environment with a much neater work space because you’re removing the soil into the debris tank,” Jody says.

Using air or water greatly reduces the possibility of damage that is common with a metal bucket. “It’s very easy to sever a fiber-optic cable with an auger or backhoe,” Jody says. “You could be shutting down the transfer of information to and from an entire city.”

Such accidents can happen even when underground utilities have been marked or mapped. “We’ve been on jobs where we had diagrams showing the precise locations of utility lines and after we expose them, they’re 3 feet off from where they were supposed to be,” he says. “There’s a huge amount of wiring and utilities underground in this country, to the point where you see dizzying pictures of all kinds of cables, wires and pipes crisscrossing each other in one excavation.”

So why hasn’t there been a greater shift toward hydroexcavation? Jody isn’t sure, but he has several examples of contractors who could have avoided incidents if they had chosen it over conventional techniques. “Part of it is just not knowing that the technology exists, but there are organizations around the country building awareness, including the Common Ground Alliance and local one-call groups that can help contractors become more familiar with it.”

With the right tools, hydroexcavation can be used in a myriad of specialized applications, Jody says. “Anywhere you need precision digging is a good application for hydroexcavation.”