Air-Vacuum Excavation Systems: Exposing Buried Utilities Before You Drill

As the use of horizontal directional drilling (HDD) continues to increase in popularity in today’s growing underground infrastructure industry, the concern for accidental utility strikes has demanded that very strict safety protocols are implemented and firmly adhered to.

An age-old problem facing anyone involved with the HDD industry is that they are not certain of exactly where all underground utilities are located in relation to the proposed path of their bore-head. Historically, methods for digging have ranged from simple hand-digging practices to expose the utility to just using a backhoe to make the job “easier.”

The problem with these two methods is that both can still present dangerous consequences if a buried utility is accidently struck. Although vast improvements have been seen in the past few years in the development of better and more accurate ground penetrating radar (GPR), there is still plenty of skepticism about the accuracy of the depths of utilities that those GPR units can accurately determine. In fact, there are several U.S. states that have developed ordinances requiring specific amounts of potholes, depending on the length of the HDD run, to be created so the operators can visually watch the bore-head pass over or under any utility lines in its path.

As an alternative solution to these methods mentioned above, the development of air-vacuum excavation systems, machines developed specifically for the purpose of safely and economically exposing utilities, are now offering utility professionals a faster, more economical and much safer method of potholing before HDD commences.

Air-vacuum excavation systems use high-pressure air in combination with a powerful vacuum to first break up the soil and then remove it. This process enables a pothole to be dug quickly, easily and — most importantly — safely. After the utility is exposed, its exact location is marked and then the removed spoils can be placed back in the hole as backfill or, as mentioned above, the HDD contractor can visually see their bore-head safely passing the located utilities. Air-vacuum excavation systems eliminate the back-breaking labor involved in hand digging potholes and, since spoils stay dry for use as backfill, there are no spoil disposal costs.

It is important to understand that it takes a significant amount of horsepower to dig a hole with air as opposed to other methods.  This is because air is a “soft,” compressible gas and requires a large amount of kinetic energy in a high-velocity air stream to penetrate, expand and break up soil. Air systems work by delivering supersonic air from the air lance while still in a compressed state. The compressed air than travels into all the porous spaces in the soil and begins to expand. This process breaks apart, or literally explodes, the soil from within while the operator is simultaneously vacuuming up the spoils. In this way, a hole is created to the desired diameter and depth as required herein.

One of the major problems with water is that it is indiscriminate in what it cuts: Water can cut through either the soil or a buried utility.

A simple, comprehensive way to consider the benefits of air-vacuum excavations systems used in conjunction with horizontal directional drilling projects is as follows:

(A) In most soils air is much faster than water
(B) Spoils stay dry for use as backfill
(C) The HDD contractor will also now have a vacuum system on hand for the directional boring mud clean-up.
(D) Air won’t damage the road base
(E)  And, of course, air is much safer (no damage claims or injuries)

There are three important reasons in considering the use of vacuum excavation. First, it has the potential to reduce the actual time to expose utilities prior to drilling and, on larger projects, it can also reduce the cost, as well (if performed during the same mobilization as the horizontal drilling). Secondly, it reduces the potential damage claims, as well as the risk of physical injuries that are far too common results of a bore-head hitting and damaging a buried utility. Third, potential ergonomic and or personal injuries as a result of hand excavation (hand auger, posthole digger, etc.) may be reduced and or eliminated.

Implementing the use of vacuum excavation prior to any directional drilling work as precautionary measures are recommended for all subsurface pre-investigation work for any underground intrusive or construction activities performed.

In a recent report put together by a national energy company, there have recently been an unacceptable number of instances of cable damage or destruction due to HDD contractors not locating exact placements and depths prior to drilling. This report showed conclusively that for every $1 spent on potholing activities prior to directional drilling application, the overall project experienced an average savings of approximately $4.75. With the costs of some of these HDD jobs today, that can mean big saving for contractors and customers alike.

If certain safety practices such as potholing with air-vacuum excavation equipment are not developed and adhered to, there is always the ever present potential of encountering, puncturing, compromising or disrupting service to buried on-site utility service lines, municipal or third party owned off-site utility services, UST system components and other subsurface property service lines or systems during intrusive activities being performed. These “disruptions” can very easily lead to large claims against the contractor or planner.

All major metropolitan cities are constantly busy with large HDD projects to keep up with the demand for new utility installation to support our much needed economic growth. It is literally impossible to do any type of excavation within thirty feet of an area where utilities are expected without experiencing a conflict of one type or the other. If a project involving directional drilling is called for, air vacuum excavation for potholing provides the safest and most economical answer to locate the underground utilities.

Trevor Connolly is vice president of sales and marketing for Vacmasters.