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Sandy soils and shallow bedrock present separate, different installation challenges to the HDD process. CHALLENGESĭesigners who are considering HHD as an installation option need to be aware of geological conditions along the predetermined path. After the pipe is pulled through the bore, it is typically allowed to “relax” for a period of time to self-correct any elongation that may have occurred during the installation process. A swivel is utilized between the reamer and the pressure pipe being installed to minimize torsion transmitted to the pressure pipe as it is being pulled through the enlarged pilot hole into its final position. This is accomplished by attaching the prefabricated pipeline pull section behind the reamer assembly at the exit point and pulling the assembly back to the drilling rig. The final stage involves pulling the pressure pipe through the enlarged pilot hole. Reaming tools typically consist of a circular array of cutters and drilling fluid jets and are often custom configured for a particular bore hole size or soil type. Although not required, many experienced contractors repeat this intermediate step to minimize the force required to pull the pipeline along the initial pilot hole without overburdening the drilling equipment.
#HORIZONTAL DIRECTIONAL DRILLING HDD INSTALL#
The second stage of the process involves pre-reaming the pilot hole in preparation to install the pressure pipe.
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The operator can then adjust the drill inclination as needed to come up out of the ground at the pre-determined exit point. This information is used to calculate the horizontal and vertical coordinates along the pilot hole relative to the initial entry point on the surface. During this phase of the process, the pilot-hole path is monitored, and periodic readings of the inclination and azimuth of the leading edge of the drill are taken in conjunction with measurements of the distance drilled since the last survey point. The first stage of the process involves drilling of the pilot hole. The HDD process, in general terms, follows three basic stages that are described below. Over the last 30+ years the technology has evolved from its origin as a preferred pipeline construction method for the crossing of major waterways to a technique that can be employed in very congested utility corridors along busy highway systems as well as over longer distances where traditional open-cut methods would require work hour restrictions and/or adversely impact activities along the path.Ĭurrent technology limits a single bore length to around 8,000 linear feet and pipe diameters to 48-inches or less. HDD is a trenchless method of installing pipe and cable systems underground along a predetermined path. In this article we are going to develop a basic understanding of the technique and explore some challenges and successes from the design engineer’s perspective. Until recently, the installation process has typically been more expensive than traditional open-cut methods for the same length of installed pipe because it requires highly specialized drilling equipment to complete the installation.
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Horizontal Directional Drilling (HDD) is not a new technology when it comes to the installation of pressure pipe systems for water distribution or sewage conveyance. Posted in: Public Works | Tagged with: HDD