Trenching is Still King: 2023 Underground Report

By Jeff Griffin | Mar 15, 2023

Utility construction magazines like to publish articles about interesting projects, especially complex ones where project owners and contractors faced challenges to complete the work on time and on budget.

Utility construction magazines like to publish articles about interesting projects, especially complex ones where project owners and contractors faced challenges to complete the work on time and on budget.

Many of these articles focus on the use of trenchless construction methods, especially horizontal directional drilling (HDD), which limits excavation and the cost of surface restoration. Very few articles cover projects that employ trenching equipment, other than big machines constructing pipelines.

There was a time when electric, telephone and cable television cables were installed underground by digging a trench, placing conduit and cable in the trench and refilling it.

Vibratory plowing is an option that, depending on soil conditions, is a fast method of installing cable and conduit with less disturbance to the ground’s surface, reducing restoration time and expenses.

Is HDD replacing the need for trenching and plowing equipment? Absolutely not.

For much of today’s underground utility construction, trenching is still the fastest, most economical way to make underground installations. On many projects, trenching is the primary method used, with HDD making street crossings and drilling under other surface obstructions.


“Trenching is faster and less expensive in most cases. If there are site conditions like concrete, road crossings, creeks where trenching is not possible or practical, we will utilize HDD,” said Trent Gilmore, senior manager of electric underground construction for Consumers Energy, provider of electricity and natural gas to 6.8 million of Michigan’s 10 million residents in all 68 counties of the Lower Peninsula.

Has HDD diminished the need for excavation equipment?

“No,” Gilmore said. “HDD offers solutions to difficult sites where terrain, surface cover or other conditions make trenching impractical, but mini-excavators and trenchers are the go-to pieces of equipment for the majority of our underground construction work. Trenchers or mini-excavators are used for installing primary and secondary conductors, setting transformer bases, excavating bore pits and for site cleanup.”

Underground construction is performed by company and contract crews, Gilmore continued. Consumers Energy has a workforce that specializes in electric underground construction, including HDD. In addition, traditional LVD crews install overhead and underground electric lines. The remaining underground work that cannot be done with internal resources is contracted out.

“We use a variety of compact excavators and trenchers,” Gilmore said. “We determine what machine class to use according to the job. The heavier and higher horsepower model offers more power for moving material and digging in more difficult conditions or during winter construction.”

Gilmore explained that for primary cable used above 600V, trenches are deep enough that the top of the cable is a minimum of 30 inches below the final grade. For secondary cables, the minimum depth is reduced to 24 inches. Trench depth may increase based on terrain, sand-fill needs, joint-use needs and municipality requirements.

“Underground electric construction remains a vital alternative to overhead construction practices for a number of reasons,” Gilmore said. “Most underground construction takes place to meet regulatory requirements for subdivisions, apartment complexes and other specific service areas. In addition, having underground as an option for customers empowers them to select options that may be more aesthetically pleasing to them. There are a number of other considerations such as resiliency, safety and forestry maintenance that continue to be driving factors into evaluating underground construction strategy.

“When I think about reducing electric rates while improving reliability, underground construction plays a large role,” he said. “Companies around the nation are doing strategic undergrounding to improve reliability. Underground construction is an important and growing part of our electric construction work. Thinking about the future of the distribution grid and our goal to reduce electric rates while improving reliability and reduce impacts from storms, underground construction will be a large part of the solution.”


Terry Hahn, superintendent distribution contractor resource manager for Dominion Energy, said trenching operations play a major role in electric distribution construction for external customers, as it helps to keep installation costs down. Based in Richmond, Va., Dominion Energy provides electrical and gas services to nearly 7 million customers in 15 states.

“Horizontal directional drilling has not limited the need for trenching, as larger construction sites with multiple sets of conductors and/or other third-party joint trench communication partners make the cost of open trenching much more affordable and saves time during the installation process,” he said. “Our preference is to use standard trenching operations when the composition of the land supports the use of standard trenching methods as a way to keep installation cost down and minimize the potential for upfront costs to our customers for service.”

Several factors influence which method of construction is best and most cost-effective.

“The composition of the soil, to include terrain and soil classification, plays a major factor,” Hahn said. “In addition, equipment access, right-of-way clearing needs, environmental concerns and permitting needs for land-disturbance thresholds could impact trenching verses HDD.

“The customer may also be willing to pay the extra cost for HDD installation if Dominion Energy agrees the request is operationally feasible. We also have joint trench contracts established with third-party communication companies that allow us to share the cost of the trench between all parties involved, which greatly reduces the initial cost of construction and allows for multiple facilities to be buried together, saving easement space for future use,” Hahn said.

He said the most common application for standard trenching methods is new residential subdivision developments, as joint trench agreements allow for a shared cost for the trench and encourage new subdivision developers to install other communications infrastructure earlier in the construction process.

Trenching is the preferred method in any new construction requests on customer-owned property (residential, commercial or industrial) where the land composition (i.e., green space) and clear access support the use of standard trenching equipment, which greatly reduces the potential for customer cost associated with the initial installation.

Equipment varies depending on job requirements.

“Most contractors utilize mini-excavator track equipment ranging from 23 horsepower for secondary service lateral work to 35 horsepower for larger subdivision joint trench projects and commercial three-phase projects,” Hahn said. ”Some contractors also use larger backhoes or track excavators (100–116 horsepower) for projects with rock excavation and for handling larger materials on the job site.”



All of Consumers’ electric distribution facilities are installed per the National Electrical Safety Code (NESC). Therefore, buried secondary facilities with a phase-to-phase voltage of 0–600V are installed with a minimum cover of 24 inches from grade at time of installation and after final grade.

For Dominion Energy, “All buried underground facilities with phase-to-phase voltage of 601–50,000V are installed with a minimum cover of 30 inches from grade at time of installation and after final grade. Additional depth may be necessary when working in Virginia DOT rights-of-way or within established franchise agreements, and reduced depth may be allowed when appropriate barriers are put in place. But at no time would we allow facilities to not meet the minimum requirements of the NESC,” Hahn said.

The horsepower range and equipment size is very task-specific. For electric service installations, the track excavators used do not exceed 12,000 pounds and the horsepower ratings vary depending on the manufacturer. Within Dominion Energy’s service territory, very few chain-drive trenchers are used due to soil conditions and the presence of existing utilities. The majority of this type of work is being completed with wheeled and tracked excavators.

All HDD work is performed by contractors, but some trenching and plowing is done by company crews on a case-by-case basis and is mainly isolated to rural offices. Most trenching, HDD, conduit installation and cable-pulling operations in metro/urban areas are done by contractors.

“With a good quality control process in place, facilities are installed per the NESC and built to our Dominion Energy specific design and construction standards,” Hahn said. “The use of underground construction practices for electric distribution provides a reliable service to our customers, is aesthetically pleasing and allows Dominion Energy to concentrate on other areas during restoration events. Not all facilities should be placed underground, but where it is feasible and solid design principles can be utilized to ensure reliability and minimize outages, a good combination of overhead mainline and residential underground can make you a very efficient company during restoration events.”

Equipment for installing underground electric cable

A variety of equipment is used to install electrical cable and conduit. Some is designed specifically to install underground utilities, while other equipment is multipurpose, used for a variety of tasks on construction projects.

Dedicated underground equipment includes chain-type, disc or wheel trenchers, vibratory plows and basic construction equipment such as backhoes/loaders, excavators of various sizes and skid steer equipment with trenching attachments.

Two companies—Ditch Witch, Perry, Okla., and Vermeer Corp., Pella, Iowa—dominate the market for equipment specifically designed to install underground infrastructure. Each offers a selection of trenchers, vibratory plows and horizontal directional drills.

Trenchers are available in various sizes, from walk-­behind to large riding models. Some walk-behind models have a trencher on the front and vibratory plow on the back. Larger four-wheel-drive and track models can be equipped for various applications, with attachments for rock and pavement trenching, vibratory plowing, backfilling, real carriers and utility backhoe work.

Compact and larger excavators, backhoe loaders and skid steer loaders are available from numerous manufacturers.


Vermeer’s compact dual-purpose model has a trencher on front and a vibratory plow on the rear.
Ditch Witch’s medium-size riding trencher

Ditch Witch / vermeer


Header Image: / Stramyk Igor / Boudikka

About The Author

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





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