A Closer Look
As our easements and roadways become more congested with utility lines, it’s vital to visually identify the location of these utilities — gas, fiber, water, telecommunications and sewer — to ensure the safety of your workers and reduce third-party utility strikes.
“Not taking the time to visually locate underground lines can have detrimental effects on the safety of your crew and could impact your company finances with heavy fines and repair expenses for hitting an existing underground line,” says Jeff Wage, Vice President for McLaughlin Group.
The nationwide One Call system has helped to make identifying infrastructure easier. However, the vast and complex array of underground lines means that One Call contractors’ marks may not be as accurate as your underground project demands. This is where potholing with vacuum excavation comes in.
Potholing has been around for years, but not everyone takes the time to visually identify underground lines before digging. Potholing is a technique to expose a utility prior to excavation and allows the contractor to know exactly where the utility is located, right to left, as well as depth. This information can help avoid construction damage to the utility or to the people around the utility.
There are a number of ways to pothole existing utilities.
“One method is to use a shovel, post-hole digger or digging bar and carefully remove the soil until you find the lines,” says Wage. “The only problem is each has a cutting edge and can damage the line you are trying to identify. A second method used sometimes in rural and at times urban areas is excavating with a mini excavator or backhoe. This is clearly a much more productive and less physically demanding approach, but also very risky for damaging lines and requires a great deal of restoration costs. A more efficient and nondestructive method is to use vacuum excavation.”
Vacuum excavation is rapidly becoming the preferred method for exposing utilities. The technology is a fast, surgical, nondestructive and safe way to quickly expose a utility, whether in wet or dry soil conditions. Another benefit — the process is clean and does not leave a pile of dirt in a homeowner’s yard.
Vacuum Excavator 101
Vacuum excavators are self-contained units that use pressurized air or water to displace soil and create dry or wet spoil. The displaced dry or wet spoil is removed from the area through a hose using high-velocity suction and stored in a holding tank on the vacuum. Vacuum excavators can be mounted to a trailer or the back of a truck and range in size from 100 to 3,000 gal of capacity.
Since vacuum excavators use low-pressure air or water to remove spoil, they are perfect for potholing to identify existing utilities during underground construction projects. In fact, the air or water move around the existing utilities, giving the operator a clear view. Operators can select the amount of air or water pressure depending on the utility.
For most soil conditions, operators will confirm water is a more effective method for digging and works better in different types of soil. “It’s quicker than air in reducing the soil, but the downside is that you’re left with spoil that’s muddy,” says Wage. “Air, on the other hand, is not as fast, but is neater. You’ve got dry material to put back into the hole, but not every soil can be dug as efficiently with air.”
In the past, contractors had to choose between water or air units. Now, several vacuum manufacturers have introduced units that offer the choice of air and water in one machine — allowing you to select the best excavation method depending on the ground conditions and the task at hand.
Before purchasing a vacuum, the size of the spoil tank is a consideration; how often do you want to go between emptying it? The larger the tank, the more potholes you can accomplish. Portability is an issue as well. A smaller tank gets into the areas where the bigger units don’t reach as easily. A larger cfm unit has the ability to remove more material at a much higher rate of speed, which speeds up the vacuuming process.
Safety Considerations
On any jobsite, safety is paramount. Wage offers some tips to keep the site and your crew safe when potholing.
“First of all, you want a clear work area and no clutter,” he says. “Secondly, you need to be wearing dielectric boots and gloves. A vacuum excavation system is not going to damage the cable. But, if the cable already has damage to it, you’ll want to avoid any possible danger there. Hard hat, eye and ear protection is a must, as well as proper traffic control equipment when working along a street.”
It’s important that the air knife or water lance have a covered tip so as not to damage the cable or line. A sharp tip may slice or puncture a line.
Potholing at J.F. Electric
Ray Pour with J.F. Electric in Edwardsville, Ill., understands the importance of potholing. He oversees the overhead and underground transmission and distribution crews in the state of Missouri for the family-owned company.
“It’s becoming tougher to find an area where there isn’t something underground,” says Pour. “In subdivisions it’s common to find second- and third-generation electric and cable lines. Bore paths are more cluttered and companies are becoming more protective of their facilities.”
This makes Pour’s job of managing the installation of underground distribution lines tougher. Pour oversees a fleet of 16 horizontal directional drills (HDD) and five vacuum excavators spread all over the state. The vacuums work ahead of the drills to complete the potholing process since the company takes potholing seriously, as does the state of Missouri.
“In Missouri it’s a law to pothole if your bore will cross an existing facility,” he says. “But this is also a policy for our crews whether we are working in Missouri or Illinois.”
Missouri requires that the facility to be crossed must be visually located to determine the exact elevation. If the facility cannot be located, then the contractor can open the bore window by 2 ft on either side of the locate and excavate 2 ft below the intended bore depth.
“If we pothole down 5 ft and cannot find the facility, the crew can bore at a depth of 3 ft, but must visually watch the head pass through the pothole to ensure the new facility does not interfere with an existing line,” says Pour.
Potholing is a very basic function, but a recent project in St. Charles, Mo., required J.F. Electric to cross nine utilities. The challenge: The nine lines were located under 9 in. of solid concrete. So in order to pothole, the crew working on the project brought in a core saw, and within 30 minutes two of the six plugs had been created and pulled — allowing the potholing crew to do their job.
“It’s a tool [vacuum excavator] that is here to stay, and it’s an integral part of our system,” says Pour.
Greg Ehm is a Technical Writer for Two Rivers Marketing.
