Abstract:
A method of slitting a flexible conduit in an underground bore, the conduit having entry and exit ends thereof exposed for access, includes: (1) fitting a retainer to flexible underground conduit adjacent to the entry end thereof, the retainer securing the flexible conduit to limit longitudinal movement thereof relative to the bore, (2) passing pulling means through the flexible conduit; (3) connecting the pulling means to a pipe slitter, and (4) pulling the pipe slitter through the retainer and flexible conduit to slit the conduit, the retainer holding the flexible conduit taut as the slitter passes through the conduit. In one embodiment, the retainer is a shoring clamp assembly including a pair of ring clamps that are secured onto a split end of the flexible conduit and transfer the longitudinal forces applied to the conduit during the slitting operation to an adjacent structure such as a pit wall, thereby holding the conduit taut during the slitting operation.

Description:
TECHNICAL FIELD 
     The invention relates to an apparatus and method for slitting underground conduits, and in particular to slitting flexible underground pipes formed from plastics, thermoplastics, rubbers and ductile metals. 
     BACKGROUND OF THE INVENTION 
     A variety of systems are known for splitting rigid underground pipe made from concrete or cast iron. Typically, such methods make use of a slitting wedge or knife that is drawn through the pipe with a cable or chain attached to a winch or a piece of mobile equipment. In the case of pipe formed from relatively brittle materials such as concrete or cast iron, an impact hammer is attached to the wedge to aid in splitting and/or bursting the pipe. In some instances, new pipe is attached to the splitting tool and simultaneously pulled through the bore as the old pipe is burst or slit. 
     In one widely practiced method, a pneumatic impact boring tool such as a “Hammerhead Mole” (a registered trademark of Earth Tool Co.) boring tool is sent through the existing pipeline such that the head of the tool, which may be provided with blades that apply intense local pressure to the existing pipe, fractures or splits the existing pipe. See Streatfield et. al., U.S. Pat. Nos. 4,720,211, 4,738,565 and 4,505,302. A replacement pipe, typically made of plastic such as HDPE (High Density Polyethylene), can be drawn along behind the boring tool. Pneumatic impact boring tools are well known and are, for example, described in Wentworth et al. U.S. Pat. Nos. 5,025,868 or 5,337,837. The Streatfield et al. process has proven effective commercially because it bursts the old pipe into a multitude of fragments and replaces it with a new pipe at the same time. However, the Streatfield et al. method is less effective on ductile or non-frangible pipes such as copper, lead and certain types of plastic, such as HDPE. 
     One method for replacing existing underground pipelines is described in U.S. Pat. No. 6,171,026, issued to Crane et al. and assigned to Earth Tool Company, L.L.C., of Oconomowoc, Wis., the disclosure of which is incorporated herein by reference for all purposes. Briefly, the method includes creating open access to opposite ends of an existing pipeline to form an entry opening and an exit opening and mounting a wedge on a cable. The cable is threaded through the existing pipeline and the wedge is positioned at one of the ends of the existing pipeline after which the wedge is pulled through the pipeline from the other end of the existing pipeline so that the wedge slits the existing pipeline to form a slit pipe in the borehole. After the slit pipe is removed from the borehole, a replacement pipeline is pulled into the borehole. 
     The above described methods have not however, proven satisfactory in all cases. In some cases the methods have been ineffective in splitting underground conduits formed from relatively flexible materials such as high density polyethylene. This is especially in the case of relatively small diameter pipes, on the order of from one-half inch to about eight inches in diameter. The invention described below provides a means of alleviating and overcoming the difficulties encountered in splitting relatively small diameter underground pipes and conduits. 
     SUMMARY OF THE INVENTION 
     The invention provides method of slitting a flexible conduit in an underground bore, the conduit having entry and exit ends thereof exposed for access, including (1) fitting a retainer to flexible underground conduit adjacent to the entry end thereof, the retainer securing the flexible conduit to limit longitudinal movement thereof relative to the bore, (2) passing pulling means through the flexible conduit, (4) connecting the pulling means to a pipe slitter, and pulling the pipe slitter through the retainer and flexible conduit to slit the conduit, the retainer holding the flexible conduit taut as the slitter passes through the conduit. A slitter nose guide may be positioned on the pulling means ahead of the slitter to aid in maintaining the alignment of slitter in the pipe during the slitting operation. 
     In one aspect of the method, the retainer comprises a shoring clamp assemble adapted to be secured to the end of the flexible conduit and the method includes securing the clamp assembly onto the conduit. In this aspect the method may be implemented by splitting the entry end of the pipe with a saw or similar tool after which the shoring clamp is clamped onto a split end of the pipe. The clamp assembly may comprise a two piece assembly, such as a pair of ring clamps wherein at least one split end of the flexible conduit is positioned between the pieces which are clamped onto the split end by bolting or screwing the clamps together. An expander may be used with the slitter to expand the bore, and in some cases multiple passes through the bore may be made with larger expanders to further increase the size of the borehole. A replacement pipe may also be attached to the slitter, in which case the replacement pipe is pulled behind the slitter through the retainer and the bore in a single pass application of the method. 
     In yet another aspect of the invention, an apparatus for slitting a flexible conduit in an underground bore includes a pipe slitter and retaining means adapted to be fastened to an entry end of the flexible conduit. The retaining means includes an opening therethrough for passage of the pipe slitter therethrough and into the conduit and serves to limit longitudinal movement of the conduit relative to the bore as the pipe slitter is pulled through the conduit. A pulling apparatus such as a winch or a piece of mobile equipment is positioned adjacent to an exit opening of the conduit to pull the slitter through the conduit. A flexible pulling means for connecting the slitter to the pulling apparatus through the conduit may comprise a cable, rope, chain or rod. 
     In this aspect, the retaining means is preferably a pair of ring clamps adapted to be secured on the end of the pipe, although clamps have other geometries that may be used. The ring clamps are adapted to clamp a split end of the conduit between them to limit longitudinal movement of the flexible collar by transferring longitudinal forces applied to the flexible conduit to a wall of a pit adjacent to the entry end of the flexible conduit. The clamps are configured with a central opening that is large enough to accommodate the slitter, allowing it to pass through the opening into the pipe to be slit. The slitter may also include an expander and/or adapter for attaching a replacement pipe if the replacement pipe is to be pulled behind the slitter through the bore. Additionally, the slitter may be provided with a hollow, cylindrical nose guide for maintaining the alignment of the slitter in the flexible conduit during the slitting operation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings, like numerals represent like elements except where other wise indicated: 
     FIG. 1 is a schematic diagram of a pipe slitting operation in accordance with the invention; 
     FIG. 2 is a cross sectional view of an existing underground pipeline with a slitter pulling cable passing therethrough; 
     FIG. 3 is a cross sectional view of the pipeline of FIG. 2 after the pipeline has been slit and a replacement pipe pulled into the bore; 
     FIG. 4 is a side view in partial section of a pulling apparatus suitable for use in the invention; 
     FIG. 5 is a front perspective view of a shoring retainer or clamp installed on the split end of a pipe to be slit with slitter positioned to being the slitting operation; 
     FIG. 6 is a rear perspective view of a shoring retainer or clamp installed on the split end of a pipe to be slit with slitter positioned to being the slitting operation; 
     FIG. 7 is side view of the shoring retainer or clamp of FIGS. 5 and 6; 
     FIG. 8 is a second side view of the shoring retainer or clamp of FIG. 7 rotated 90° from the position in FIG. 7; 
     FIG. 9 is a cross sectional view taken along line A—A of FIG. 7; 
     FIG. 10 is an end view of the shoring retainer of FIG. 8; 
     FIGS. 11-13 are front, side and back views of a back ring-shaped half of the shoring retainer of FIGS. 5 and 6 including a pair of threaded apertures positioned 180° apart; and 
     FIGS. 14-16 are front, side and back views of a front ring-shaped half of the shoring retainer of FIGS. 5 and 6 including a pair of bolt holes positioned for alignment with the threaded apertures illustrated in FIGS.  11  and  13 . 
    
    
     DETAILED DESCRIPTION 
     While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention. 
     Buildings supplied with municipal water or natural gas are typically connected to a main pipeline that supplies gas or water to the general area with a small diameter pipe known as a service connection. These connections are typically made with a flexible conduit or pipe such as plastic, copper, steel or lead pipe. As used herein, the term “flexible conduit” includes pipes made from synthetic materials such as plastics, rubbers and thermoplastics possessing sufficient flexibility so that each half of a split end portion of the pipe may be bent at an angle sufficient to allow the split portions of the pipe to be clamped in a retainer as described hereinafter without breaking. “Flexible underground conduit” also refers to ductile metal pipes such as copper, steel and lead having a similar degree of flexibility as the plastic conduit described above. 
     Replacement of service connections is common and may be required for a number of reasons. Water lines may develop leaks as the pipe forming the service connection deteriorates over time. Water lines may also lose flow capacity due to calcium buildup in the pipe. Older residential connections in the U.S. or Europe were typically made with plastic or copper for gas and plastic, copper or very commonly lead for water, in which case replacement of the line is required. Additionally, many HDPE gas line pipes installed in the 1960&#39;s proved to be defective and are now failing. These service lines are typically relatively small diameter pipes, for example a gas pipe may have an inside diameter as small as 0.38″. 
     Referring now to FIGS. 1-5, one method for replacement of an existing pipeline  10  generally includes the steps of creating open access to opposite ends of the pipeline to form a bore bole entry opening (entry pit)  12  and a bore hole exit opening (exit pit)  14 . Segments of the pipeline  10  in pits  12 ,  14  are removed to create an entry or front end opening  20  in pit  12  and an exit or rear end opening  21  in pit  14 . A cable  16  is threaded through the existing pipeline  10  and positioned in entry pit  12  near one end of the existing pipeline for installation of a wedge-like cutter or slitter (not shown). The cutter is pulled through pipeline  10  from front end opening  20  of the existing pipeline  10  with a winch  15  so that the cutter slits the existing pipeline  10 . A pulling apparatus including winch  18  suitable for the slitting operation is shown in FIG.  4  and described in detail in U.S. Pat. No. 6,171,026, incorporated herein by reference. A replacement pipe  22  may be pulled behind the cutter or the slit pipe  24  and may be removed from the borehole  26  and a replacement pipeline  22  pulled into the borehole after the slit pipe has been removed. 
     A problem frequently encountered in replacing flexible underground conduits in the manner described above is jamming and/misalignment of the pipe slitter in the pipe to be replaced. When the slitter jams in the flexible conduit, the pulling force on the slitter tends to break the conduit and or cause the slitter body to break through the conduit. It was determined that the jamming problem was the result of the flexible conduit flexing in the bore ahead of the slitter as the slitter was pulled though the pipe. Such flexing occurs when force created by the wedge splitting the pipe is greater than the frictional and compressive forces holding the pipe in place. This is especially the case in loose and or soft soils which allow the pipe ahead of the slitter to move laterally during the slitting operation or where a small diameter pipe passes through a larger diameter bore, also allowing the pipe to flex laterally. It was discovered that the jamming problems resulting from the pipe flexing could be overcome through the use of a retainer or shoring device that secures the entry end of the pipe, restraining the pipe against the forces tending to move the entry end of the pipe longitudinally. 
     Referring now to FIGS. 5-16 a pipe retainer  30  for use in connection of the method of the invention includes a pair of collar shaped shoring ring clamps  32 ,  34  adapted to grip the ends  36  of a split flexible pipe  38 . Shoring ring clamp  32  includes a plurality of treaded holes or apertures  40  positioned in spaced apart relationship on ring clamp  32 . Ring clamps or collars  32 ,  34  are fastened together with a plurality of fasteners such as bolts  42  that pass through holes  46  in shoring ring clamp  34 . Bolts  42  engage threaded apertures  40  in shoring ring clamp  32 , pulling shoring ring clamps  32 ,  34  together to compress and grip ends  36  of pipe  38 . As shown, two bolts  42  positioned 180° apart are used to secure shoring ring clamps  32 ,  34  on ends  36  of pipe  38 , however it will be appreciated that a greater or less number of fasteners  42  may be used to secure the shoring ring clamps together. It is also anticipated that alternative methods of fastening shoring ring clamps  32 ,  34  together may be employed. For example, shoring ring clamps  32 ,  34  could be clamped together with C clamps or a similar device or the central opening  44  in shoring ring clamps  32 ,  34  could be threaded so that the shoring ring clamps could be screwed together on a threaded rod or pipe nipple (not shown) having an outside diameter equal to the diameter of openings  44 . 
     After pipe  38  has been slit, and ends  36  clamped between shoring ring clamps  32 ,  34 , a pulling means such as a rope, chain or cable  52  is threaded through pipe  38 , shoring ring clamps  32 ,  34 , slitter pilot nose  54 , wedge-shaped slitter  56  and expander  58 . Slitter  56  is sized to pass through central opening  44  and is provided with a hollow cylindrical pilot nose  54  through which cable  52  passes. Pilot nose  54  aids in aligning slitter  56  in pipe  38  to prevent the slitter from catching on any joints, breaks or similar irregularities in pipe  38  in which case the pulling force applied to the slitter to slit the pipe may increase to the point that pipe  38  breaks instead of slitting. As shown, slitter  56  includes a wedge-shaped cutting end or blade  64  and adapter  66  for attaching a replacement pipe  68  to the slitter that can be pulled through a bore as pipe  38  is slit. A bead, knot or clamp  53  (FIG. 9) is used to retain cable  52  in place on cable  52 . Alternatively, an insert (not shown) may be inserted into a loosened, enlarged diameter portion of the cable  52  to form a stop as described in U.S. Pat. No. 6,171,026. 
     Slitter  56  also includes an expander retaining flange  74  that extends around the circumference of the slitter between the wedge shaped cutting end or blade  64  and the threaded adapter  66 . Expander  58  comprises a generally cylindrical body including a central opening  60  adapted to fit over slitter  56  and an annular retaining ring  62  that abuts flange  74  when the expander is slipped over slitter  56 , retaining the expander on the slitter. Expander  58 , which defines the size of the bore is generally cylindrical with a diameter longer than the length of the cutting edge of blade  64  and the diameter of replacement pipe  68 . The slip on design of the expander allows the operator to select different sized expanders, depending upon the size of the replacement pipe and the ground conditions, in order to minimize the force required to pull slitter  56  through pipe  38  during the slitting operation. This design also allows the operator to make a first pass through pipe  38  with a first expander, re-thread cable  52  through pipe  38  and reinstall slitter  56  with a larger expander  58  and make a second and, if necessary, additional sequential passes to increase the size of the bore. Subsequent passes through the bore may be made as necessary to further increase the size of the bore. A small diameter rope, cord or string  50  may be clamped to the slitter as illustrated in Figure to aid in rethreading the cable  52  through the bore in the case where a second or multiple passes are desired or necessary. 
     In one application, entry pit  12  is dug at an outside wall of the residence, structure or building  28  at a location at which an existing pipe, for example gas line  10  enters a residence, structure or building, generally at gas meter  11 . A first segment (not shown) of the gas line  10  which adjoins the residence  11  is cut with a pipe cutter or saw and manually removed to expose an open front end  20  of the gas line at one side wall of entry pit  12 . A second pit  14  is dug at the location where the gas line  10  connects to the gas main  13  and a second segment (not shown) of gas line  10  which adjoins the gas main  13  is removed to expose a rear open end  21  of the gas line. One of shoring ring clamps  32 ,  34  is slipped over the front end  20  of the pipe and positioned against the side of pit  12 . Front end  20  of pipe  10  is then split longitudinally with a saw or similar tool to form ends  36  (FIG. 1) of sufficient length to fold outwardly over ring claim  32 . Preferably, the ends  36  are cut sufficiently long so that the ends extend beyond the outer edge of ring clamp  32  as shown in FIGS. 1 and 2. After the ends  36  are folded outwardly over ring clamp  32 , ring clamp  34  is then bolted to ring clamp  32 , clamping pipe ends  36  between the ring clamps. To aid in clamping pipe ends  36  between shoring ring clamps  32 ,  34 , opposing faces  78  of ring clamps  32 ,  34  may include a series of ridges and grooves  80 ,  82  as shown in FIGS. 11-16. Additionally, while shoring ring clamps  32 ,  34  are illustrated as having ring-like geometry, it will be appreciated that shoring clamps with a different geometry, for example rectangular, C-shaped or U-shaped clamps could be used in the practice of the invention. 
     Before or after pipe retainer  30  is installed on pipe  10 , winch  18  is installed in exit pit  14  in the manner described in U.S. Pat. No. 6,171,026. Cable  52  is then threaded through pipe  10  between pits  12  and  14 . A free end of the cable in pit  12  is then threaded through slitter pilot nose  54 , wedge-shaped slitter  56  and the expander  58  selected for the particular pipe  10  and replacement pipe  22 . A stop  53  as previously described is formed in cable  52  to retain slitter  56  in position on the cable. Winch  18  is then actuated, taking up any slack in cable  52 . Preferable blade  64  of slitter  56  is aligned with the cuts in pipe  10  previously made to form ends  36  as the slitter is pulled through shoring ring clamps  32 ,  34  to facilitate the initial entry of slitter  56  into pipe  10 . As pipe  10  is slit, slitter  56  pushes against the pipe, exerting a longitudinal pushing force against the pipe between the slitter and exit pit  14 . Slitter  56  simultaneously pulls the slit pipe behind the slitter in the direction of travel of cable  52 . The pushing and pulling forces thus applied to pipe  10  tend to cause the pipe to flex in front of slitter  56 , causing the slitter to become misaligned and jam in the pipe. In the practice of the invention however, the forces applied to the pipe are transferred to shoring clamp assembly or retaining device  30  which transfers the forces to the wall of pit  12 , holding the flexible conduit taut during the slitting process. Shoring clamp assembly  30  thereby holds entry end  20  of pipe  10  in place, preventing the segment of pipe  10  behind slitter  56  from moving longitudinally in the bore with slitter  56 . Restraining the entry end  20  of pipe  10  with pipe retainer  30  in this manner prevents the pipe in front of the slitter from being compressed and flexing, allowing the slitter to progress without jamming. 
     After pipe  10  has been slit, replacement pipe  22  is installed in bore  26  in one of several ways. One approach is to couple the replacement to adapter  66  of slitter  56  and pull the replacement pipe through bore  26  with the slitter, either in a single pass or if conditions dictate, in a final one of a series of successive passes through the bore. The slit pipe is left in the bore. Alternatively, after pipe  10  is slit, a replacement pipe is coupled to an end of the slit pipe, or a longitudinal slit section of the pipe. The slit pipe is then pulled from the bore, pulling the replacement pipe into the bore. Yet another alternative is to connect cable  52  to an end of the slit pipe, pull the slit pipe from the bore with the cable, connect the replacement pipe to the cable and pull the replacement pipe into place. Once installed, the replacement pipe is reconnected at ends  20  and  21 , the shutoff valves are opened and service is resumed. Although the method as described utilizes a winch for pulling the slitter through the pipe, it will be appreciated that other means, such as a truck, tractor or backhoe may be used to pull the slitter. Also, under some instances, it may be desirable to place shoring between the wall of the pit and pipe retainer  30  to aid in holding the conduit taut during the slitting operation. 
     While certain embodiments of the invention have been illustrated for the purposes of this disclosure, numerous changes in the method and apparatus of the invention presented herein may be made by those skilled in the art, such changes being embodied within the scope and spirit of the present invention as defined in the appended claims.