Page 268 - Trenchless Technology Piping Installation and Inspection
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232    Cha pte r  S i x


                             Direction of bursting
                                        Expander   New pipe
                                                           Air hose
            Existing pipe
                       Pulling eye




        Winch line
                               Pneumatic tool











                                                         Overcut

       A                             B         Expander  New PE

        A = ID of existing pipe
                                          B = OD of expander
                                   Overcut = distance between OD of expander
         B – A = Upsize
                                   and OD of new PE pipe, or annular space.
     FIGURE 6.2  The bursting head of the upsize concept. (PPI, 2008.)

          are repeated until the full length of the existing pipe is replaced. In each
          sequence, one segment of the pipe (which matches the length of the
          bursting head) is burst in two steps: first the bursting head is pulled
          into the existing pipe for the length of the segment, and then the
          head is expanded laterally to break that pipe. The bursting head is
          pulled forward with a winch cable, which is inserted through the exist-
          ing pipe from the reception pit, and attached to the front of the bursting
          head. The rear of the bursting head is connected to the new pipe and
          also hydraulic supply lines that are inserted through the new pipe. The
          bursting head consists of four or more interlocking segments, which
          are hinged at the ends and at the middle. An axially mounted hydrau-
          lic piston drives the lateral expansion and contraction of the bursting
          head (Najafi, 2005). This method of pipe bursting is not common.

          6.2.3  Static Bursting Systems
          The second common method of pipe bursting is the static pull sys-
          tem. In this method, a relatively large tensile force is applied to the
          cone-shaped expansion head through a pulling rod assembly or cable
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