Product Profile – Solving Difficult ‘Hard’ Geology Projects
For trenchless contractors, it is not just the hardness, but rather the varying densities and unpredictable inconsistencies of rock formations, that makes projects so difficult.
Geonex Horizontal Hammer Boring (HHB) has no penetration problems in any soil classes, even in blasted rock filling. The grade is maintained even if boulders, hard bedrock, soft soil or any combination of the above are encountered.
Trenchless technology faces great challenges in hard inconsistent ground formations globally. Scandinavia’s soil consists mainly of shield and mountain formations, and the challenging hard geology projects have mainly been solved with Horizontal Hammer Boring, with nearly 30 years of experience. This experience and knowledge are now been spread to central Europe and North America by Geonex.
In North America, Geonex equipment have been used since 2017. First casing projects in the United States were carried out in 2019 in Wisconsin by EBI Drilling, where water main and gravitational sewer were crossed under highway, after jack and bore encountered problems. Now, Geonex Horizontal Hammer Boring is also utilized in pipelines in Kansas by The Tunneling Company.
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Revolutionizing the Principle of Pit-launched Methods
Looking at the concept, it is easy to understand why the drilling process is turned around. Instead of pushing from behind, the pipes are pulled from the front by a powerful air percussion hammer.
“Pushing the rope and expecting it to stay on target is impossible without steering. But pull it, and it has no option but to keep on a straight course. It’s as simple as that,” says Geonex Oy senior advisor Jouni Jokela.
The air percussion hammer is located inside the casing in front of the boring string. Attached to the hammer, is an overburden drilling system, which transfers the impact energy of the hammer to pulling the casing and crushing the bored soil material and rock with carbide buttons. Since casing is pulled, no significant jacking force is required. Therefore, there is no need for thrust or reaction walls or concrete foundations. Consequently, the hole is completed with a single pass, as the pipe is pulled in along the advancement of boring.
All necessary operations are made in the launch pit, where extension augers and casing elements are attached and welded. Auger rods also convey the air for the hammer, and vice versa augers convey cuttings through the casing into the launch pit, so this method does not displace or expand any soil around the casing pipe. Footprint on the exit side is small, or even blind holes are possible, leaving passage through the casing. Casing elements are welded together in full material thickness, providing a strong protection for product pipes.
Pulling the casing leads to a relatively good accuracy in supporting ground materials. Experience has shown that there is either no deviation or the casing has settled slightly during the drilling.
Due to the accuracy and straightness, less friction is produced, allowing the pipe to reach even over 400 ft lengths. Due to a small overcut in the process, no settlement of surface level is encountered. As the pipe is pulled by the integrated drillhead and cutting removed through the casing, no ground pressure deformations or heave are produced by the force of excessive jacking.
Clean Tech Case Bex, Switzerland
No drilling fluids are required to reduce the friction or support the hole. The steel casing can be pulled through the ground simply by the energy provided by the hammering, and the steel casing supports the hole as it is bored. Benefits include the reduction in disruption caused to roads, rails and other nearby infrastructure, allowing for shallow installation depths in hard ground conditions and no need for excessive cover as with horizontal directional drilling (HDD).
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This clean drilling is a clear benefit for sensitive locations and projects, an example of which is the horizontal groundwater well drilled in Bex, Switzerland. As the aim of the project was to collect alpine water for bottling and sale, the use of bentonite or drilling fluids was prohibited, as any foreign material would be seen as a contaminant. Bex was textbook example showing, that boring under water table was successful with 16-in. steel casing reaching 500 ft in hard moraine. As hammer drilling only requires air, it was ideal for the purpose. The impact of the small amount of biodegradable hammer oil needed for lubrication was tested in this project. The oil was found to remain in the drill cuttings, so the soil was kept completely clean as the cuttings were collected.
Cost-efficiency in Key Role
For contractors, the Geonex HHB permits the same tools and drill head can be used in all geological conditions, leading to eventually lower investment. Higher production can also be achieved since down time for tool changes is minimized and simple tooling also enables easy logistics.
Significant cost-savings can also be achieved in smaller diameters in hard ground conditions; a casing diameter can be bored with smaller diameters, as encountering rock does not require hand tunneling. Geonex HHB works in diameter range of 5 to 48 in.
Drilling hard granite and hard mixed soil frequently proves expensive, but even in these conditions Geonex HHB can be cost-efficient. When projects do not demand per mill accuracy grades, Geonex HHB has proven to be superior in total cost efficiency, since initial survey and building costs are minimal, and production rate in boring is high.
Special Applications Conductor Barrels for HDD Projects
Conductor barrels for HDD can be drilled with Geonex HHB to reach solid bedrock. This enables safe and stable starting for actual HDD drilling ensuring the return of the drilling fluids.
Efficient Method for Solid Hard Rock
In hard solid rock DTH is the most cost-efficient method to drill. If the rock is solid and consistent, drilling can be done without steel casing. This means simultaneously that the hole length is not limited by casing friction, and that the drilling can be also steered. This Geonex system is a ready and proven solution for this task. Typical pilot hole is Ø 6 ½ in. , which can be reamed up to Ø 48 in.