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CHAPTER 6






                        Project Considerations


                           for Pipe Replacement



                                                   Methods










     6.1 Introduction
          Existing sewer, water, and natural gas pipes can be replaced by three
          basic methods of pipe bursting—pneumatic, hydraulic, and static
          pull. In addition, there are proprietary trenchless pipe replacement
          systems that incorporate significant modifications to the basic pipe-
          bursting technique, including pipe reaming, the impactor method,
          and pipe extraction (also called pipe insertion). Pipe reaming is the
          most common method of pipe removal, where the broken pieces of the
          existing pipe are actually taken out of the ground with the use of
          slurry drilling fluids (see Sec. 6.3.1). The basic difference among these
          systems is in the source of energy, the method of breaking the existing
          pipe and some consequent differences in construction operations that
          are briefly described in the following sections. The selection of a spe-
          cific replacement method depends on soil conditions, groundwater
          conditions, degree of upsizing required, type of new pipe, original
          construction of the existing pipeline, depth of the pipeline, avail-
          ability of experienced contractors, and the like.



     6.2 Pipe Bursting
          Pipe bursting was first developed in the United Kingdom in the
          late 1970s by D. J. Ryan & Sons in conjunction with British Gas, for
          the replacement of small-diameter, 3- and 4-in. cast-iron gas
          mains (Howell, 1995). The process involved a pneumatically driven,



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