Vacuum Excavation: A Key Component of Horizontal Directional Drilling Projects
Don Buckner Feb 02, 2013
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.
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 UtilitiesRelatively 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.
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 call 811 before starting any digging project; however, One Call marks only provide the approximate location of utility lines.
Vacuum excavation, which relies on non-destructive water or air vacuum technology to safely and efficiently excavate, has become a “best practice” in the field of construction excavation. Many agencies and municipalities require contactors to verify One Call utility markings by physically locating existing underground utilities.
Using vacuum excavation equipment to locate utilities is much safer than using mechanical or hand-dig methods. According to the Common Ground Alliance (CGA), “non-destructive excavation and utility locate methods are considered Best Practices in 38 states.” It’s also less invasive and causes less surface damage, traffic disruption and impact to surface activities. Most utilities can be quickly and efficiently uncovered. Even smaller, more complex utilities such as fiber-optic lines and cables can be located with precision, resulting in reduced risk of strikes.
Locating utilities via vacuum excavation can also result in substantial costsavings. Purdue University’s Department of Building Construction Management published a study detailing how best practices in excavation, including vacuum technologies, can reduce project costs. According to the study, titled “Cost- Savings on Highway Projects Utilizing Subsurface Utility Engineering,” every $1 spent on subsurface utility engineering (SUE) can result in $4.62 in cost-savings.
In addition to these safety and financial benefits, knowing the exact horizontal and vertical location of utilities within a project site allows drilling operators to design borehole alignments around existing utilities. If a utility cannot be avoided, it must be relocated. Having this information at the start of a project, instead of experiencing surprises while drilling, can reduce project delays and expenses.
Removing Slurry from the Project SiteDuring horizontal directional drilling, slurry — a thick mixture of water, bentonite and other chemicals — is continually pumped through the cutting head
or drill bit. The slurry helps to transport material out of the borehole, stabilize the borehole and cool the cutting head. Drilling operators begin drilling the lateral borehole by first excavating an entry pit and an exit pit. These pits allow a safe place for the slurry to collect as it is pushed through the borehole by the drilling pressure. Depending on the design of the borehole, the excess slurry moves forward or backward through the borehole, collecting in either the entry pit or the exit pit. Once contained in a pit, the excess slurry can be reclaimed.
Vacuum excavation equipment can be used to safely and efficiently reclaim the excess slurry. Once contained in the vacuum truck’s (or trailer’s) impermeable tank, the slurry can be transported to a facility where it can be legally disposed of. Using vacuum excavation equipment to remove excess slurry helps keep it out of the work site — and, more important, out of drains, creeks and watersheds.
Don Buckner is president of Vac-Tron, headquartered in Okahumwpka, Fla.