Vacuum Excavation: A Key Component of Horizontal Directional Drilling Projects


With its ability to safely expose underground utilities and effectively remove environmentally sensitive materials, vacuum excavation is quickly becoming standard practice on horizontal directional drilling projects.

The need to connect utilities and services across roadways, rivers and congested areas has sparked the rise of horizontal directional drilling (HDD), a trenchless technology that involves using a surface-launched drilling rig to drill a lateral borehole along a predetermined path.Compared to traditional open-trenching methods, horizontal directional drilling is less invasive and more versatile; it can connect utilities and services from “point A” to “point B” with minimal disturbance to aboveground features. However, it is not without the risk for costly damages to the project site and surrounding areas: Lateral-moving drills run the risk of striking underground utilities, while the release of a slurry mixture used during directional drilling can cause significant project issues.

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The use of vacuum excavation is quickly gaining recognition as means to mitigate these risks. What follows is a brief discussion of the roles vacuum excavation can play at horizontal directional drilling sites and how it can help keep projects moving ahead.

Locating Existing Underground Utilities

Relatively recent advances in infrastructure — such as the installation of fiber-optic cables by telecom companies and upgraded power lines by utilities — have caused the ground beneath our feet to become more congested than ever. With this in mind, horizontal directional drilling operators should know exactly where underground utilities lie before drilling begins.

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Not knowing the precise horizontal and vertical location of underground facilities could result in disaster: Each year, utility strikes cost businesses, utilities and government entities millions of dollars in property damage and insurance liability. Along with interrupting service, strikes can also cause outages, explosions, fires and flash flooding. A strike near a sensitive facility, such as an airport or hospital, can disrupt life-saving systems.

Drilling operators should always call811 before starting any digging project;however, One Call marks only providethe approximate location of utility lines.

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Vacuum excavation, which relies onnon-destructive water or air vacuum technologyto safely and efficiently excavate,has become a “best practice” in the fieldof construction excavation. Many agenciesand municipalities require contactors toverify One Call utility markings by physicallylocating existing underground utilities.

Using vacuum excavation equipmentto locate utilities is much safer than usingmechanical or hand-dig methods. Accordingto the Common Ground Alliance(CGA), “non-destructive excavation andutility locate methods are consideredBest Practices in 38 states.” It’s also lessinvasive and causes less surface damage,traffic disruption and impact to surfaceactivities. Most utilities can be quicklyand efficiently uncovered. Even smaller,more complex utilities such as fiber-opticlines and cables can be located with precision,resulting in reduced risk of strikes.

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Locating utilities via vacuum excavationcan also result in substantial costsavings.Purdue University’s Departmentof Building Construction Managementpublished a study detailing how bestpractices in excavation, including vacuumtechnologies, can reduce projectcosts. According to the study, titled “Cost-Savings on Highway Projects UtilizingSubsurface Utility Engineering,” every $1spent on subsurface utility engineering(SUE) can result in $4.62 in cost-savings.

In addition to these safety and financialbenefits, knowing the exact horizontaland vertical location of utilitieswithin a project site allows drillingoperators to design borehole alignmentsaround existing utilities. If a utilitycannot be avoided, it must be relocated.Having this information at the startof a project, instead of experiencingsurprises while drilling, can reduceproject delays and expenses.

Removing Slurryfrom the Project Site

During horizontal directional drilling,slurry — a thick mixture of water, bentoniteand other chemicals — is continuallypumped through the cutting head

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or drill bit. The slurry helps to transportmaterial out of the borehole, stabilize theborehole and cool the cutting head.Drilling operators begin drilling thelateral borehole by first excavating anentry pit and an exit pit. These pits allowa safe place for the slurry to collectas it is pushed through the borehole bythe drilling pressure. Depending on thedesign of the borehole, the excess slurrymoves forward or backward through theborehole, collecting in either the entrypit or the exit pit. Once contained in apit, the excess slurry can be reclaimed.

Vacuum excavation equipment can beused to safely and efficiently reclaim theexcess slurry. Once contained in the vacuumtruck’s (or trailer’s) impermeabletank, the slurry can be transported to afacility where it can be legally disposedof. Using vacuum excavation equipmentto remove excess slurry helps keep it outof the work site — and, more important,out of drains, creeks and watersheds.

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Don Buckner is president of Vac-Tron,headquartered in Okahumwpka, Fla.

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