Potholing with Precision

By Chris Thompson

When it comes to uncovering underground utilities, there is no room for error. Even a small mistake can have serious and expensive consequences. With modern underground networks becoming more complex and congested, contractors are well aware of the risks that come with damaging existing utilities. To keep crews safe and minimize costly downtime, many contractors are turning to vacuum excavators to assist in damage mitigation. Vacuum excavators have become a popular tool in the arsenal of utility contractors, allowing them to work more accurately and with greater precision. They offer an efficient, effective and safe solution to the challenge of uncovering utilities through a process known as “potholing.” To aid in damage mitigation and keep jobsites efficient, it is vital to follow proper potholing techniques. From choosing the right nozzle to ensuring the proper water pressure, adhering to best practices in potholing can help underground construction professionals improve efficiency, increase productivity and enhance jobsite safety.

EXPOSING UTILITIES TO SUPPORT DAMAGE MITIGATION
Potholing is a technique that involves using a soft excavation method – a vacuum excavator – instead of a shovel or backhoe to create a hole and remove debris. Contractors use either air or high-pressure water (hydro) to safely dig underground to expose an existing utility. It is essential to excavate to the depth of the bore, particularly when going under utilities, so that operators can physically see the drill bit and pipe safely passing under the utility. This step is crucial for preventing damage to existing utilities and ensuring jobsite success. As a best practice, contractors should start small, utilizing air or water excavating method, and expand as needed. This ensures that contractors won’t make a bigger hole than what is needed, streamlining efficiency and keeping operators productive. If contractors are struggling to expose utilities in hard soil or heavy clay, hot water heater packages are an option with most vacuum excavators. Using hot water can help break down clay without applying additional water pressure. However, operators should keep the temperature below 130 degrees Fahrenheit for best results.

QUICK TIP: The recommended pressure for potholing is no greater than 2,800 psi. Although
many vacuum excavators offer higher psi capabilities, too much pressure can damage utilities. The pressure should be reduced even further if using heated water.

EXCAVATING IN A VARIETY OF GROUND CONDITIONS
Today, most equipment manufacturers design vacuum excavators with both air- and hydroexcavation capabilities, so operators don’t have to choose between the two. For example, contractors can start excavating the ground surface with air and switch to hydro once they reach harder soil formations. The water will cut through the clay and be sucked into the spoils tank to mix with the dry spoils from the air excavation. With the ability to switch from hydro to air, operators can better adapt to changing jobsite conditions and stay productive in a variety of ground conditions. When choosing between hydro or air excavation, contractors should consider the jobsite and soil conditions. For example, pressurized water typically exposes utilities faster than air. However, air is the better choice when working in areas where contractors are worried about an overcut, next to a highway or transportation work. This is because air typically displaces less soil and reduces the worry of washouts near roadbeds. Hydro excavation uses pressurized water to do the hard work. For example, rock, cobble, clay and sandstone are a few of the most difficult soil types to excavate and, as a result, they take the most time. Operators facing rocky or sandstone conditions should use hydro excavation with hot water as it more effectively cuts through difficult soil. Because hydro excavation requires operators to dispose of liquid spoils and replenish water sources while on the jobsite, following best practices for water conservation is important. However, the ability to conquer various soil conditions quickly and efficiently makes hydro excavation the preferred method for many contractors.

QUICK TIP: If operators are not getting enough pressure from their vacuum excavator, they should check their filters, as clogs can cause issues with water pressure.

Air excavation allows operators to break up soil with compressed air and vacuum dry spoils, which can be reused onsite as backfill. This method works best on softer soils such as topsoil, sand and some clay formations. Unlike hydro excavation, which requires access to water, air excavation keeps machines running and operators on the jobsite without having to make trips to acquire water or dispose of liquid spoils. Additionally, many operators are turning to air excavation on jobsites as liquid spoils disposal restrictions tighten and certified disposal sites become more difficult to find. Additionally, air excavation doesn’t create a slurry, it keeps more of the soil together and limits the chance of the hole caving in on itself. Contractors who are looking to ensure a clean hole or who are working on an extra sensitive jobsite – like a golf course – should opt for air excavation.

QUICK TIP: Some municipalities even require air excavation to be the first option in sandy ground conditions.

TIPS FOR NOZZLE OPERATION
Operators should constantly keep the nozzle moving within the excavation and not focus the water in one specific area. One way to ensure that operators keep the water moving and efficiently digging is by using the proper nozzle. For example, when hydroexcavating, operators should use a rotating or oscillating nozzle to deliver a stream of circulating water. A stream of circulating water will help keep the water moving through and prevent excessive pressure from consistently hitting a specific area, aiding in utility damage prevention and maintaining jobsite productivity. As another best practice, operators should keep the nozzle six to eight inches away from the utility and out of the dirt. Holding the nozzle too close to the utility increases the risk of damage. To prevent the nozzle from clogging and avoid costly downtime, the nozzle should never impact the soil or be used as a shovel to dig. When using an air excavator, it’s even more important to avoid putting the nozzle in the ground, as cleaning dirt out of the nozzle can be more challenging with air excavators.

QUICK TIP: If the water pressure is low, operators should check the nozzle to ensure nothing is hindering the nozzle’s flow.

PREVENTING UNDERGROUND UTILITY DAMAGE
Contractors can prevent underground utility damage effectively and efficiently by correctly exposing utilities at the job site. By implementing potholing techniques and adhering to best practices, operators can optimize efficiency and guarantee job site safety. As the demand for underground construction projects has increased, vacuum excavators have become essential tools that assist in preventing damage and enhancing job site productivity. Understanding the distinctions between hydro and air excavation and utilizing the appropriate nozzle and PSI will ensure operators are well-equipped for success.

Chris Thompson is a product manager at Ditch Witch with responsibility over the vacuum excavation product line. Thompson focuses on providing customers with innovative, customer-driven products and solutions with the goal of damage prevention and jobsite solutions. Before taking on the vacuum excavation product line, he covered the CUE and utility locator product lines. He holds a BA in Organizational Leadership from the University of Central Oklahoma and an MBA from Oklahoma Christian University.

Article originally appeared on ExcavationSafetyMagazine.com

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