Potholing is a construction method that includes vacuum excavation for the purpose of obtaining visual confirmation of utilities and underground obstructions near or crossing the planned bore path. It is a process whereby a small, exploratory hole is dug along the proposed path of underground construction to ensure there’s no conflict with existing subsurface construction or any other feature that will interfere with the project.
Air and hydro vacuum excavators are self-contained units that use pressurized air or water to displace soil and create a dry or wet spoil. This displaced spoil is then removed from the area through a large hose using high-velocity suction and is stored in a holding tank on the vacuum. Since vacuum excavators use low-pressure air or water to remove spoil, they are perfect for potholing or identifying existing utilities during underground construction projects. Vacuum excavators may be mounted to a trailer or on the back of a truck and range in size and gallon capacity.
Originally used to clean septic tanks and car wash pits, as well as to remove slurry from horizontal directional drilling projects, contractors have discovered that this non-evasive technique has a wide range of uses, including utility potholing.
“Damaging underground utilities can be expensive in terms of project downtime and potential contractor fines,” says Randy Hawks, Director of Utility Operations for Americom Technology, Inc. “The hydro and air pressure doesn’t damage existing utilities like a heavy equipment might. In fact, the air and water are able to maneuver around the existing utilities, giving the operator a clear view of what he’s dealing with.”
Utility Line Exposure
While digital locators have become more accurate, it’s still important to see exactly where the line or pipe is located. Contractors are not allowed to dig in the safe zone, which may be from 18 inches up to 3 feet from either side of the marked line. The required distance varies state to state. Contractors are only allowed to dig by hand or use a non-destructive method like air or hydro excavators in the safe zone.
Using a vacuum or hydro excavator instead of a shovel has its advantages. A shovel against a water pipe is non-destructive, but a shovel against a fiber optic line can be extremely sensitive, especially in hard ground conditions.
“Much of Americom’s cable is installed using horizontal directional drills (HDD) rather than trenchers, so we don’t have the typical ditch line, road closures and inconvenience like in the past,” says Hawks.
Lines installed using HDD don’t disturb the ground or leave a ditch line, so the ground is the same hardness and it is difficult to know if you are getting close to the line or cable. Since the ground may be hard, you can easily cut a cable line with a shovel. Using a vacuum with air or water at a non-damaging pressure will safely expose the line.
Taking the extra steps to pothole may seem like an added expense or more time, but Hawks stresses that this safety step is vital for his workers, customers, and anyone near the jobsites.
“Hitting a gas or utility line with a backhoe, trencher or HDD could be catastrophic. A water line hit could literally put a hospital out of business for hours or days,” says Hawks. “The cost of shutting down a project for a day is sure to exceed the cost for a $3,000 locator and a little extra time to properly pothole a jobsite.” (Portions of this article are credited to Constructionequipment.com)