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Geology has a significant influence on the trenchless casing installations. One of the most challenging geology is mixed geology with abundant boulders and cobbles. This geology combined to shallow bed-rock peaks intersecting with the bore path, create very challenging conditions for trenchless steel casing installation. When the boulder size grows bigger, than casing is able to fit inside, soil is packed with cobbles not capable to displace, or bedrock contact occurs; it creates significant demands on the trenchless method. Under these conditions the Geonex Horizontal Hammer Boring is at its strongest in diameter range of 5 ½” – 48” and under 350 ft in length.

Geonex install

Selecting the proper method for these conditions, is one of the most crucial matters, when reviewing installation costs. The selection of method influences through the whole installation from engineering to final disassembly and possible surface reinstatement work. Usually, the decision between methods is made between HDD, pipe ramming, auger boring, pipe jacking / micro tunneling or Horizontal Hammer Boring (HHB).

One of the factors, when reviewing the cost efficiency in a trenchless installation, is the launch or entry pit structure. Pipe jacking and auger boring rely on jacking or thrust on casing, which requires reaction walls for the counter force. Also, pipe ramming, auger boring and pipe jacking require an accurately levelled pit base, and in some cases even a concrete base. These cause extra structural engineering and extra work phases, which lead to additional costs. With the Geonex Horizontal Hammer Boring, the casing is pulled into the hole, by an overburden drilling system and air percussion hammer. Therefore, no reaction walls are needed, and the system relies on the boring machine weight to apply the counter pressure for the hammer. The Geonex Horizontal Hammer Boring doesn’t require any accurately levelled pit base, since the boring alignment can be adjusted with the hydraulic jacklegs.

On some occasions, the casing diameter might be engineered significantly larger in diameter, than the actual conduct pipe. This is usually result, of preparing to correct possible casing misalignment or preparing for certain method, for casing to be capable to fit in rocks or hand tunneling, if rock contacts occur. If the line is not critical small grade gravitational, with the Geonex Horizontal Hammer Boring, the job can often be made with significantly smaller casing diameters. Even 5 ½” casings can be installed successfully into this difficult geology. In the same saving category is the boring length, due to pit-to-pit principle, the system does not have HDD related slope down & slope up length, and does not require space for these slopes.

One key matter in cost efficient pipeline construction is the scheduling of the whole pipeline construction, and the workflow management. Goenex Horizontal Hammer Boring has reasonably fast steady and predictable workflow in these conditions since the penetration in hard soil conditions is effective and the drill head is the same in all soil conditions. Geonex system does not suffer from down time caused by tool changes or hand tunneling. The Geonex system penetration rate in hard, for example 50,000 PSI granite, is significantly greater compared to disc cutters. Also, Geonex system drilling consumable cost is low compared to claw or disc cutters.

Even with trenchless methods, some consequences of pipe installations might require some reinstatement of surface infrastructure, which cause extra costs for the installation. The Geonex Horizontal Hammer Boring installs casing pipes with a minimal overcut and the steel casing provides a solid support, so settlement of the surface after installation does not occur. Neither does the Geonex system displace any material during, so heave does not occur in this type of geology.

If pipeline trenchless installations have critical small grades, the trenchless sections should be installed before open excavation sections. This way, small imperfections in grade, can be compensated in the open cut parts of the pipeline.

In overall, the Geonex Horizontal Hammer Boring is a very cost-efficient method for these difficult soil conditions. But sometimes the grade requirement can be challenging or even impossible to meet. To achieve the best accuracy of the Geonex Horizontal Hammer Boring, the following measure should be considered. Perform the boring downhill because the line and grade is more consistent to predict. Use as long casing elements as the application allows. This does not require jointing the whole crossing length, but usually 40 ft casing elements provide good accuracy, when properly aligned. Longer casing elements also mean less welding, which increases workflow and efficiency and lowers the cost.

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