Page 220 - Trenchless Technology Piping Installation and Inspection
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184    Cha pte r  F i v e


           Rig side     Pilot borehole   Pipe side

                     Drill pipe  Drill bit


                  Rig side       Reaming        Pipe side

                            Drill pipe
                                    Reamer

                           Rig side       Pull back     Pipe side


                                      Drill pipe  Product
                                             Swab
                                                   pipe
                                                  Swivel
          FIGURE 5.1  Generic HDD installation. (Source: Trenchless Engineering
          Corporation.)




          intermediate to the Mini- or Maxi-HDD categories may utilize appro-
          priate “Midi” equipment of intermediate size and capabilities.
             Due to the high importance and large expense associated in accom-
          plishing Maxi-, and possibly Midi-, HDD operations, such as major
          river-crossings, experienced engineers are typically engaged to help
          plan and design the overall installation, including use of appropriate
          hardware and software programs and navigational equipment. Mini-
          HDD is relatively a low-cost procedure, which typically does not
          employ the services of professional engineers. Nonetheless, since
          improper Mini-HDD procedures, including incorrect bore planning,
          pipe loading, and equipment setup, can lead to problematic installa-
          tions, including inadvertent return of drilling fluids and possible dam-
          age to nearby buildings and facilities, the second portion of this chap-
          ter (Secs. 5.4 and 5.5) presents relatively an easy-to-understand bore
          planning guidelines and pipe loading calculations for such operations.
          Same concepts can be utilized for Midi- and Maxi-HDD operations.



     5.2 Method Description
          Directional drilling methods utilize steerable soil drilling systems to
          install both small- and large-diameter pipes. In most cases, HDD is a
          two-phase process. Phase 1 involves drilling a pilot borehole of
          approximately 2- to 6-in. diameter along the proposed design center-
          line. In phase 2, the pilot borehole is enlarged by use of a backreamer
          to the desired diameter to accommodate the pipeline. At the same
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