Vacuum excavators are an economical solution where a high risk of damage prevents the use of mechanical trenching machines and where worksite conditions make traditional excavating methods impossible.
Manual and mechanical hydraulic digging are not as efficient as using vacuum excavators for economic and safety reasons. Manual digging is slow and costly, and hydraulic excavators are risky in a congested infrastructure.
Risks and costs associated with striking underground infrastructure:
- Insurance liability due to death or serious injury to employees or public
- Lost man hours
- Damage to equipment
- Lost machine productivity
- Fines and cost to repair site
- Utility service disruption
- Litigation and lawyer fees
- Lost revenues and company reputation
Using vacuum excavators improves overall efficiency and productivity for municipalities, utilities and contractors. They are used in:
- Underground construction work
- Frozen ground excavation
- Sewer pipe cleaning and pipe rehabilitation
- Directional drilling
- Pole and sign installation
- General landscaping
- Fiber optic for telecommunications maintenance and repair
- Removing soil pollution
- Demolition work sites
- Daylighting or potholing underground infrastructure
- Long distance, vertical or horizontal accessibility
- Gas lines excavation
- Underground utilities excavation
- Maintenance and repair of railway tracks
- Slot trenching and excavation
- Sewer pipe cleaning and catch basin cleaning
- Broken water main repairs
- Laying of new gas, water, cable, or, waste disposal vacuum pipelines
- Accessing and repairing pipes and cables in tight areas
- Non-destructive excavation
This equipment can quickly access and non-destructively expose underground utilities, and decrease traffic congestion and reduce environmental impact.
How Vacuum Excavators Work
A high velocity water or air stream penetrates, expands and breaks up soil. A high speed vacuum fan generates an air current producing a vacuum within the vacuum tank. A vacuum hose attached to the vacuum tank resting on a hydraulically operated boom, is guided by the operator, and a suction nozzle collects the loosened debris.
Best Practices Study Conducted and Ensuing Results
In the late 90s, a NY state agency put together a project team to study the facts to see if vacuum excavation technology worked on project sites. They solicited interest from contractors, offering them to cover vacuum excavator unit rental expenses to verify the accuracy of utility markings and to study and verify the locations of test holes.
The benefits of using this technology became immediately clear to the excavators. All of them said that using vacuum excavators to locate utilities made the task easier and more efficient. The entire group of participants responded that vacuum excavators saved time, and all but one participant said that vacuum excavation saved them money.
When asked whether they had avoided damages, 7 out of 8 indicated that they had. It should be noted that about 120 vacuum excavations were performed during the project, only two minor and unavoidable damages occurred to unknown and unmarked facilities that would likely even been damaged by hand digging.
Participants felt that these machines were better suited to some projects than others. Examples cited were;
- Utility location verification, potholing or daylighting
- Directional bore projects, specifically across other utilities and definitely around natural gas lines
- Locating existing utilities for reroute or repair
- Work sites where surface disturbance is a factor
All of the excavating contractors participating in the study expressed considerable interest in purchasing or renting vacuum excavator equipment for future projects.
The study concluded qualitatively that vacuum excavators had distinct and clear advantages over hand digging to locate utilities. Vacuum excavators save design, excavation and construction time, and as a result saves money. It minimizes the potential of damages to underground infrastructure and has far less impact on the surrounding environment than standard methods of excavation.
The main benefit of hydro excavators is the relative ease and speed of excavation. The higher density of water produces a powerful jet that penetrates and loosens virtually all types of soil. Water acts as a lubricant during excavation, helps control static electricity, and can be heated to do winter digging. During this project many hydro vac excavation holes were performed in less than 15 minutes.
Hydro Vacuum Excavators
Hydro-vacs require large trucks or trailers with sufficient capacity to handle the volume and weight of the water. Hydro excavators usually have a tank for clean water and another tank to store the soil. Hydro vacuum excavators are limited to the amount of water held in their tanks. When the water is depleted, the tanks must be refilled before continuing work.
The soil slurry or sludge from the hydro vac excavation may be difficult to dispose of. For instance the slurry may not be suitable for backfill after the utility has been exposed, requiring the procurement of backfill by the contractors.
Winter digging with water in cold or freezing temperatures is challenging. Hydro jetters equipment lines can freeze requiring environmentally friendly antifreeze solutions and heaters to provide hot water to help cut through the frozen ground.
Hydro excavation systems are also disadvantaged by the very advantage that makes them desirable - the high-pressure water. Over compressed water can damage underground utilities therefore variable water pressure control is required, depending on soil conditions. Water is also a conductor of electricity thereby requiring construction site safety plan when excavating near buried electric utilities.
Hydro vacuum excavators work best in mild temperatures with easy access to soil disposal, and a nearby source of water to refill tanks.
Air Vacuum Excavation
Air vacuum excavation systems penetrate and expand soils, blowing the soil apart so it can be vacuumed up. On board air compressors generate an unlimited supply of air during vacuum excavator operations. The soil from air excavation is usually used for backfill and is easily disposed of.
Though air excavation may not be as quick as hydro excavation the air vacuum excavators are quite often smaller, lighter and more economical. They are best suited to sand or gravel soil conditions. Air machines require more work in clay or harder, dense soil conditions.
Since compressed air is a gas, it will flow around utilities without damaging the utilities surface. Highly compressed air in very dry conditions can produce dust clouds, possibly one of many causes of air pollution. Additionally, using compressed air to excavate and locate utilities is non-conductive, reducing the electrical hazard to operators.
Pros and Cons
|Will not damage utilities||Slower excavation|
|Will not damage roadwork||Slower progress in frozen ground|
|Units are small and portable||Slower progress in and dense soils and heavy clays|
|Will not damage trees|
|Air is non-conductive|
|Excavated soil remains dry to use for backfill|
|Limitless supply of air|
|Very effective in all soil types, including frozen ground||Wet soils more difficult to dispose|
|Faster progress in harder soils||Potentially abrasive or damaging to utilities|
|Can damage roadwork|
|Limited water supply|