Hdd Insights

What to consider when choosing between dual-rod and single-rod HDD

Vermeer HDD tooling

Dual-rod horizontal directional drills (HDDs) like Vermeer D40x55DR S3 and D23x30DR S3 Navigator® HDDs represent the latest technology for drilling rock. But as with any new technology, many HDD contractors may be wondering: Is a dual-rod machine a better option than a single-rod machine?
Tod Michael, product manager for trenchless core products, offers the following advice: HDD utility contractors who perform 50% or more of their bores in soft- to medium-density rock, up to 24,000 psi (165.5 MPa) compressive strength, should consider investing in a dual-rod HDD. For contractors boring in rock less than 25% of the time, there is probably a more economical single-rod tooling setup to meet their needs. And for anyone whose rock-boring work falls between those two ranges, other factors should be considered before deciding if they will benefit from adding a dual-rod machine.

First things first
Before diving into whether or not you should invest in a dual-rod machine, you need to know a little bit about the technology and its advantages for drilling in rock. “Dual-rod systems use two independently controlled drill rods — one within the other — during operation,” explained Michael. “While drilling out the pilot bore, the outer rod provides rotation for steering, and the inner rod supplies torque.” 

Rock density
“Dual-rod drills are efficient in light- and medium-density rocks,” explained Michael. “If consistently above 20,000 psi (137.9 MPa) compressive strength, a contractor may want to consider using a utility drill with an air hammer or a mud motor.”

“Dual-rod machines can often be transported on the same trailer as their similar single-rod counterpart, are convenient to set up and don’t require any additional space,” explained Michael. So, if your crews typically perform several drill shots a day, a dual-rod machine has several advantages over other rock drilling tech.
Operator capabilities on the drill is another critical factor to consider. “Running an air hammer takes more training and talent,” Michael explained. “In solid rock, they have to get the drill path right the first time because it can be a real challenge to back up and adjust. There aren’t any extra steps with the dual-rod drill. There is an extra connection, but the machine handles that on its own.”

Operational costs
Dual-rod machines work in rock, clay, sand and loamy soils. Still, that versatility comes at higher upfront investment. With single-rod machines, you can use a rock bit or an air hammer, but over the long run, it may or may not be more cost efficient than the dual rod.  “Every contractor’s situation is different, which is why it’s not always an easy decision,” said Michael. “If a contractor isn’t sure which solution is right for their needs, they should talk to their local Vermeer dealer.”

You can also learn more about the entire Vermeer utility HDD product lineup by visiting our showroom.

Vermeer D40x55DR

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