Horizontal Directional Drilling (HDD) has been widely accepted and used for installing gas and water lines, telecommunication cables, etc. However, one area where HDD has been used with only limited success is in the installation of gravity flow sewer lines. One primary reason is the difficulty with maintaining critical grades essential for gravity-flow sewer systems when using conventional HDD tracking methods. Recently, advancements made in tracking systems, electronics, and operational techniques have made HDD technology a technically feasible and an economically attractive method for installing on-grade underground pipes in many situations. The newly developed technology illustrated in U.S. Patent 7510029 is one of representative techniques for accurate identification and tracking of the vertical location of the drilling head. This paper evaluates technical capabilities and the economic feasibilities of this new on-grade HDD technology using actual project data. The accuracy of the installed pipe placement is shown, along with a comparison of project costs compared to a theoretical open-cut installation in the given soil type for the sample project.
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