Down-the-Hole Horizontal Hammer Boring

GEONEX Helps North American Contractors Tackle Tough Conditions

When it comes to horizontal underground utility installations, methods like auger boring and horizontal directional drilling typically spring to mind. However, one company offers a solution that has demonstrated benefits for more than 30 years.

GEONEX, headquartered in Finland, offers horizontal hammer boring (HHB) equipment that is well suited for utility installations in solid rock, cobbles, boulders and other conditions. The company was founded in 2012 but its roots date back to the early 1990s when company founder Kimmo Juvani’s family-owned contacting company began implementing the use of traditional vertical down-the-hole hammer equipment to run horizontally, which at the time was the only HHB business operating in Scandinavia using this approach.

The company was sold in 2006, but Juvani stayed on to help further expand the technology, and in 2011, they completed more than 10,000 bores covering 650,000 ft using HHB.

In 2012, the concept for GEONEX was formed to be a manufacturer of HHB equipment. The equipment utilizes three main principles: a pneumatic downhole hammer, hydraulically powered components for rotating the auger, and an umbilical hydraulic power pack that would serve as the system control center.

In 2013, GEONEX made its first commercially available complete system, which is still offered today, the HZR400 and PP90 power pack. Today, GEONEX offerings include four different sized machines, two diesel power packs, and one electric power pack, allowing clients to run a range of 5.5-in. diameter holes up to 48-in. diameter casings in recorded lengths exceeding 350 lf. Today, GEONEX has 70 machines operating in 11 different countries, with 14 units operating in North America.

The company began operating in the North American market in 2017, and now has a full-time presence led by North American Operations Manager Rich Revolinsky, an industry veteran with nearly two decades of experience. GEONEX’s new base in the U.S. provides customers with a direct line to inventory, rental equipment, sales and support.

“While there are a variety of unique features incorporated into the GEONEX system, what stands out is the result,” Revolinsky says. “GEONEX equipment can bore small diameter casings through high strength solid rock and cobbles at rates of 7 to 20 ft per hour using the HHB approach. It allows for small diameters to be installed and avoids manned entry. This method also mitigates deviation from the desired path.

“Use of down-the-hole hammer components for horizontal boring is not in itself completely unique and has been used successfully within the trenchless industry. However, the hhb method utilizes specific design features of the GEONEX drill machines and modified pneumatic hammering equipment to be successful in horizontal applications. For GEONEX, this includes the use of the central control unit of the hydraulic power pack which helps adapt to jobsite requirements and decrease set-up time for launch pits. The method can and has been utilized in the HDD industry for installing washover casings.”

How it Works

GEONEX equipment is designed to utilize the HHB method. A pneumatic hammer is placed within the lead casing. The hammer actuates a center bit and peripheral bit to pulverize materials linearly instead of using rotational cutting. Release of compressed air through the center bit with each stroke of the hammer blows the subgrade back through small openings where it can be conveyed back to the launch pit by an auger string where the drill machine is located. The method does not use pipe jacking, but instead the head unit pulls the lead section of welded pipe string into place as it advances to create a straight, although unsteered, path.

This method allows contractors to break up cobbles and rock efficiently and to small sizes which avoids jamming the auger. Additionally, the linear action of the cutting head ensures that the material along the bore path is broken down, and not displaced.

For most applications the recommended installation lengths are up to 350 lf, ranging from 5.5-in. diameter up to 48-in. diameter. Ground conditions can vary as the equipment utilizes the same cutting head regardless of the conditions. While designed and intended for solid rock and cobbles, installations including sand, clay, gravel and mixtures thereof are common.

Most projects entail pressurized systems of water and gas, however electrical and telecommunication installations are becoming more common. Gravity systems with slopes of 1% or greater can also be installed.

Case Histories

While the GEONEX HHB system is relatively new in North America, contractors have been using the method with positive results. Here are a few of the recent highlights:

• Fraser, CO – 120 ft of 24-in. casing installed at 0.9% slope through granite cobbles in 12 hours continuous installation under passenger and cargo rail lines. Cobbles excavated during launch pit preparation were round, and some exceeding 20-in. in diameter. The DTH method was selected by B-Trenchless as the best solution for the project to maintain a small casing diameter despite the large cobbles.
• Lenexa, KS – 42-in. casing was installed through 380 lf of limestone. The project started with traditional auger boring but after initially boring 80 ft, the trajectory was deemed unacceptable. The Tunneling Company was hired by the boring contractor and used its GEONEX HZR1200 to complete the project.
• Marathon City, WI – EBI Drilling of Duluth, MN, was brought in to install twin 320-lf casings of 16-in. diameter through the rocky subgrade. Initially intended to be performed with their HZR400 drill machine, EBI decided to use their HZR610 and completed each bore in three days.
• Scandia, MN – Minger Construction of Jordan, MN, took maiden voyage of their recently purchased HZR1200 to install 240 ft of 36-in. diameter casing below Hwy 95 for a new culvert. Uncertain of when they would encounter rock that was visibly present on the downstream side, the bore encountered various soil conditions including about 100 ft of wet clay before hitting the boulders. The bore was completed with invert elevation on target.
• Jackson, MI – Dunigan Brothers Construction launched a 24-in. casing with traditional auger boring for the 120-ft bore only to discover the presence of large cobbles. Well versed in the area and well prepared, Dunnigan had anticipated the cobbles before boring and had GEONEX on standby. Due to launch pit limitation, the shortening section of the GEONEX HZR610 was removed to allow for a compact frame, fitting in the 20-ft long pit. 10-ft casing lengths were installed to successfully complete the bore in about three days, allowing the water main project to move forward toward completion.
• Winter Park, CO – NewTech Construction used the GEONEX system including an HZR610 drill machine to install 300 lf of 24-in. for HDD washover casing. The project highlighted the advantages of using HHB in order to pass through a 50-ft layer of cobbles at a 12 degree entry angle below a sensitive wetland and embed the end of the casing into solid bedrock. This allowed NewTech Construction to complete the 2,200 lf HDD installation successfully and maintain the tight project schedule.

With a track record spanning more than 30 years, the down-the-hole horizontal hammer boring method has demonstrated an ability to effectively construct small-diameter bores in rock and other challenging conditions. Tags: January/February 2024 Print Issue