You Can't Dig Too Carefully

By Jeff Griffin | Aug 15, 2020
You Can't Dig Too Carefully




Preventing accidental damage of buried utilities is everyone’s business, no matter what the project or industry. An accidental utility hit can cause injury or death while disrupting services that can result in costly repairs and financial losses. After a hit, the project owner, contractor and subcontractors may face litigation, no matter who ultimately is found responsible.

In the last decade, the Common Ground Alliance has made much progress in efforts to prevent utility hits by educating industries and the general public and developing and coordinating programs to reduce accidental utility damage. Even so, figures released last fall based on 2018 data documented that 509,000 excavation-related damages to underground facilities occurred that year.

An initial step in preventing utility hits is to find and mark locations of buried infrastructure before excavation or any earth-displacing work begins.

The March issue of Electrical Contractor covered basic methods of locating underground pipe and cable, which included electromagnet and ground penetrating radar tools. The article also discussed potholing, uncovering underground utility lines to visibly confirm their exact locations.

How better to know exactly where a buried line is than to see it?

Potholing with a shovel, backhoe or compact excavator has been a common practice for years, but any mechanical method of digging to find a buried utility risks damaging it with the potential of injuring an equipment operator and nearby personnel. 

Vacuum excavation is the faster, safest way to pothole. While vacuum excavators have been around for years, they only began appearing on utility construction sites in the early 1990s. Compact models were ideal for keeping job sites clear of drilling fluid escaping directional drilling pilot holes. Their “soft” excavation capabilities were perfect for potholing by greatly reducing the risk of damage to in-place infrastructure.

Vacuum excavators dig either with high-pressure water or high-pressure air. Advocates of water (hydro) excavation say high-pressure water penetrates most types of soil, and the equipment generally is less expensive than air models. Those who prefer air excavation point out there is no need to have a water supply tank to excavate with air, that spoil stays dry and can be reused and that air cannot damage a plastic pipe or cut a cable.

Hydro advocates would counter that air units are not effective in some dense soils. They also raise dust and cost more. When properly used, hydro units will not damage utilities.

A final point from air proponents is that technology has evolved so that air units work in most soils, and many air units also have a backup hydro capability.

In addition to potholing, M.L. Chartier excavating and environmental service company workers use hydro vacuum excavation while installing a utility pole.

Vacuum excavator equipment today ranges from compact trailer-mounted models to powerful, high-production truck-mounted units. Basic specs for vacuum excavators include the trailer-or truck-mounting method of excavation, vacuum ratings in CFM and inches of mercury, compressor ratings in cfm and psi, storage capacity of spoil tank and water supply tank for hydro models.

Dual-purpose vacuum excavators are among the most versatile in a utility construction fleet. They are well-suited for multiple tasks for utility providers. 

Potholing is required in many states and other jurisdictions when construction is going to disturb the earth within a specified distance of an existing buried utility. In Michigan, the state law requires that any time excavation is planned within 4 feet of an existing utility, the utility must be “spotted,” that is uncovered and its location visibly verified, said Pietro Grillo of Consumers Energy, Jackson, Mich., a public utility that provides electricity and natural gas service to two-thirds of Michigan's 10 million residents. 

“Safety is the foundation of everything we do at Consumers Energy, and potholing by vacuum excavation improves the safety and quality of work," Grillo said. "It also allows for work to be completed faster and efficiently."

Consumers Energy subcontracts all potholing work.

However, potholing is not the only job vacuum excavation equipment performs for the utility company.

“In addition to spotting utilities, our excavation contractors utilize vacuum excavators to clean up drilling mud, set electric poles and to do slit trenching,” Grillo said.

One of the contractors providing potholing for Consumers Energy is M.L. Chartier, Fair Haven, Mich., an excavation and environmental service company that specializes in hydro excavation.

“Vacuum excavators are an essential part of our day-to-day operations,” said Kyle Wesch, hydro-vac manager. “In order to perform traditional excavation methods safely, we rely on vacuum excavation to locate buried infrastructure. It’s the most crucial piece of the entire process of an excavation job. The entire purpose is to excavate safely, and if that can’t be accomplished, people are going to get hurt, utilities will get damaged and job costing increases drastically.”

Most of M.L. Chartier’s locating clients are major utility companies and contractors. Common jobs are locating utilities for their road-building crews that can’t locate existing utilities and assisting with the installation of new utility services to commercial and residential locations. 

“The biggest advantage of vacuum excavators is the increased safety factor,” Wesch said. “Without a doubt, it puts our crews and client crews at less risk of injury, and safety above all else is always a priority. Other benefits of soft excavating are a smaller environmental footprint. It’s a noninvasive technology and gives a broader ability to access less-common job sites. We work in both indoor and outdoor areas, larger open spaces as well as smaller spaces that need require services. 

“When we work inside a substation, we often excavate trenches for new conduit in various sizes. [The] trench may be anywhere from 100 to 2,000 feet long. Once conduit is installed, we backfill the trench with Class II sand and then compact it. Then we restore the site so it is completely remediated. Depending on the scope of work and the length of trench, these projects can run from one day to two months.”

Compact, trailer-mounted vacuum excavators dig potholes and also keep job sites clear of escaping drilling fluids.

Wesch said his crews dig holes for new utility poles with vacuum excavators every day. 

“We arrive on the job site and dig a 12-by-36-inch hole designated by the utility provider,” he said. “If a hole is not stable, we put in a culvert to prevent cave-ins. If the pole is set, we will stay on standby to fix any cave-ins. If a pole won’t be set that day, we will fence it off to keep pedestrians and crews safe.”

M.L. Chartier operates 27 truck-mounted Ramvac and Vactor hydro excavators, one hydro excavation track-mounted unit, and an air/water truck unit.

Wesch said the company is built on a foundation of versatility and the variety of services it provides. Vacuum excavators fit well into that versatility model.

“We use them for daylighting, cleaning up drill mud, cleaning catch basins for electrical vaults, excavating new trenches inside substations to run conduit, exposing pipe and valve sites and sloping it so guys can work in the hole,” he said. “We also find ourselves utilizing them for emergency spill work for the Department of Transportation on roadsides, as it gives us an advantage to do the work fast and efficiently.”

Ultra Engineering Contractors, Winchester, Calif., provides underground utility locating and mapping and subsurface engineering (SUE) services. Much of its potholing work is part of a larger contract to provide complete locating services for clients using multiple locating technologies.

“A lot of our clients are engineering firms doing preconstruction planning,” said John West, Ultra vice president. “In addition, we work for a wide variety of clients, including electric and underground construction contractors, school districts, military, hospitals and utility providers including power, water, gas and communications and amusement parks.”

Ultra Engineering contractors use an air vacuum excavator to uncover a buried utility.

Clients include Southern California Edison, San Diego Gas and Electric and the many contractors who serve them.

“Anytime a contractor is going to be trenching near transmission lines and other utilities, they first need to safely find the package,” he said. “There is no safer way to positively locate and identify underground utilities than potholing using air/vacuum excavation. With well-trained technicians, there is virtually no way to damage any underground utilities. Any other method, including hand digging, is much more susceptible to line strikes and damage.”

All Ultra’s vacuum excavation units are mounted on trucks and excavate with high-pressure air.

“Currently, we own nine Vacmaster air vacuum excavation trucks in four different sizes,” he said. “Air is safer, faster and doesn’t undermine the road base. We can use the same spoils we excavate to backfill, which eliminates the need to transport and dispose of spoils or import fill. We do have hydro excavator backup, but we use air about 95% of the time.”

Clients also hire Ultra to vacuum excavate around utility poles that are going to be replaced.

West said there has been a steady rise in demand for vacuum excavation services, and Ultra recently added two units and plans to add two more this year. 

The coronavirus pandemic has not affected Ultra’s workload, West said.

“We do a lot of work for the school districts,” he said. “They all want to get as much work performed as possible before school resumes. We have strict measures that our crews must abide by during this crisis to protect themselves and our clients. We keep the same teams working together, have them drive separately, wear face masks at all times and continually wash and sanitize their hands. We already wear full face shields all the time while potholing.” 

About The Author

GRIFFIN, a construction journalist from Oklahoma City, can be reached at [email protected].





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