Patent Publication Number: US-3874463-A

Title: Means for boring parallel holes

Description:
United States Patent 1191 Hicks et al.  
 [451 Apr. 1, 1975 MEANS FOR BORING PARALLEL HOLES Inventors: Charles L. Hicks; Raymond R.  
 Leon, both of 123 l-lenshaw Ave., Space 8, Chico, Calif. 95926 Filed: Aug. 1, 1973 Appl. No.: 384,468  
 Related US. Application Data Continuation-in-part of Ser. No. 239,223, March 29,  
 1972, Pat. No. 3,805,899.  
 US. Cl 175/53, 175/19, 175/62, 175/326 Int. Cl. E2lc 9/00 Field of Search 175/53, 62, 326, 1922, 175/416, 401, 420, 419; 37/193;  
 References Cited UNITED STATES PATENTS 8/1914 Pauli 3/1941 Graham .I 175/326 X 175/420 Ransome 175/401 Primary Examiner-Frank L. Abbott Assistant ExaminerRichard E. Favreau Attorney, Agent, or Firm-Ernest L. Brown [57] ABSTRACT A means for boring parallel holes in soft material such as earth, and more particularly for boring substantially parallel conduit runs in the earth between manholes or trenches, wherein a rod and piercing tool are rigidly spaced apart by a sharpened spacing element so that when the rod is forced through an existing hole, the piercing tool bores an additional hole substantially parallel to the existing hole.  
 26 Claims, 29 Drawing Figures PATENTED APR 1 9 5 SHEET 2 OF 9 PATENTED APR 1 5 SHEET 6 UP 9 PATENTED AFR 874.463 wwsqs MEANS FOR BORING PARALLEL HOLES This application is a continuation-in-part of US. Pat. application Ser. No. 239,223 filed Mar. 29, 1972, now US. Pat. No. 3,805,899 issued Apr. 23, 1974.  
 BACKGROUND OF THE INVENTION It is customary, when forming bores, between manholes or trenches, for electrical conduit or utility pipes, to drive a substantially cylindrical piercing tool through the earth with a hydraulic ram. Typically the piercing tool is attached to a string of rods. That is, the piercing tool is forced into the ground by the ram. A rod is then attached to the trailing end of the piercing tool until only the end of the rod protrudes out of the ground. Another rod is then added to the trailing end of the embedded rod, and the process is repeated until the piercing tool reaches the other manhole or trench.  
  The piercing tool is then removed from the rod string, and an enlarging broach (called a frog) is attached to the end of the rod string. The enlarging broach is, typically, a conical member which, when forced through an existing hole, enlarges the hole to the diameter of the outer diameter of the broach. In the example, the enlarging broach is attached to the rod string with its smaller end facing the string. A conduit segment may be attached to the trailing or larger end of the broach. The rod string is then drawn back through the existing hole with the broach enlarging the hole to accommodate the conduit, and the conduit following the broach. When the broach reaches the end of the hole adjacent the ram, the conduit then extends between the manholes or trenches. If needed, additional segments of conduit may be spliced onto the conduit segment being pulled through the hole.  
  The process just described is particularly useful when it is desired to place a new conduit or utility pipe beneath existing pavement, as between existing street or highway.  
  It is obvious that the earth being penetrated must be sufficiently soft or granular to allow piercing. Most compacted roadbeds allow such piercing.  
  When it is desired to place more than one conduit, it is cssential that the two conduit bores do not intersect. It is also desirable that they do not substantially diverge, for that would mean that future conduits would need to be spaced farther from the existing bores to avoid intersection.  
  Unfortunately, boring two holes substantially parallel using a piercing tool on the end of a string of rods, as described above, it is not adequately controllable, and it is the exception when two bores are substantially parallel.  
 BRIEF DESCRIPTION OF THE INVENTION The apparatus of this invention ensures that a second bore is substantially parallel to the first bore. A third bore may then be added parallel to the first two bores. Additional bores may be added as desired.  
  The apparatus comtemplated by this invention is a tool for boring substantially parallel bores in relatively soft material, such as earth, clay, sand, gravel aggregates, road fabrication material, and the like.  
  The first or pilot hole is bored, for example, as described above.  
  The apparatus of this invention has a first rod member which is contoured to be thrust into an existing bore. A piercing member is attached by a spacing member to the first rod member. In a preferred embodiment, the spacing member forms a knife edge which is inclined, like a guillotine knife, relative to the direction of travel of the piercing member.  
  After the first bore is completed,-and before the rods of a first rod string in the first bore are pulled through the first bore with the enlarging broach to enlarge the first bore, the first rod portion of the tool of this invention is attached to the trailing end of the broach. The piercing member of the tool is positioned where the second bore is desired. A conduit segment may be attached to the trailing end of the first rod portion. Pulling of the first rod string by the hydraulic ram pulls the enlarging broach, the first rod portion of the tool, and the conduit through the first bore. At the same time, the piercing member of the tool is forced into the ground, forming a second bore substantially parallel to the first bore. As the piercing tool enters the ground, a second rod string preferably is attached thereto. When the tool emerges adjacent the ram, the conduit will be in place in the enlarged first bore, and the second rod string will be in the second bore. The tool and broach, with the first rod portion of the tool positioned in the second bore, may then be used to pull conduit into the second hole while the piercing tool bores a third bore, parallel to the second and the first bores, pulling a third rod string after the piercing tool.  
  The parallel bores may be set into any desired configuration, i.e. side by side, in a vertical arrangement, or the like. Further, the spacing between bores may be adjusted by piercing one or more dummy bores to the side of the desired bores.  
  In an alternative embodiment, a plurality of piercing tools are attached to a plurality of coupling members on the after end of a separating and slicing fixture for receiving a plurality of broaches, and the forward end has a coupling member which may be attached to be pulled by a rod string. The forward edges of the fixture have sharp cutting knives for slicing the earth to allow the tool to be pulled through the earth. Such a fixture, for example, may be used to place a plurality of conduits between the street and a building to carry the various service lines, gas, water, telephone, electricity, and the like.  
  The trailing end of each of the broaches attached to the fixture may be connected to strings of rods or conduits to pull the conduits directly through the ground.  
  When it is desired to pull splicedflexible conduit, such as plastic condiut, into a bore behind the broach or behind the first rod member of the tool, the conduit typically cannot be pulled without pulling apart glued splices in the conduit. It is then, in accordance with this invention, desirable to snake a line through the conduit, attaching one end of the line to a bearing cap on the trailing end of the spliced conduit and the other end of the line to the enlarging broach or to the trailing end of the first rod member of the tool, whereby the flexible conduit is pushed, rather then pulled, into the conduit bore. It is desirable to have a centering member on the trailing end of the broach or first rod member to center the pull of the line along the axis of the conduit. A preferred centering member comprises a ball-like fitting on the leading end of the conduit, and a matching cup on the trailing end of the first rod member of the tool or on the enlarging broach. The line is preferably attached at the center of the cup and penetrates through the center of the ball-like fitting into the conduit.  
  With the apparatus of this invention, a slice is made by the spacing member between adjacent bores, but the spacing member is not followed by any other member to hold open the slice. When the hole is enlarged by the enlarging broach, the sliced portion is re-compacted.  
  When flexible conduit has been placed in an adjacent bore prior to the enlarging by the broach, it is desirable to use a special broach of this invention. Alternatively, a fitting or mantle may be placed over the broach, the mantle having special characteristics to prevent crushing of the emplaced conduit. The special broach will be described herein as a special mantle which fits over the broach. The special broach or broach mantle has a second blade or stress reliever thereon which is substantially in a plane tangential to the enlarged bore, whereby stress in the earth, created by the enlarging broach, is directed away from the stress reliever. The stress reliever is preferably placed on the side of the broach or broach mantle adjacent the emplaced flexible conduit. The size of the stress reliever is adjusted so that sufficient compacting stress is directed toward theslice made by the spacer to compact the slice.  
  The broach mantle is adjustably positioned on the leading end of the first rod member, over the broach, so that the stress-relieving blade is positioned on the side of the bore toward the emplaced flexible conduit. The second blade is held in position by preventing the broach mantle from turning about the axis of the bore during the enlarging process. To prevent the turning, the trailing or large end of the broach mantle has a plurality of axially directed tines thereon, two of which straddle the spacing member.  
  It is a first process of this invention to (I) pierce a hole, drawing a rod string into said hole, and (2) pierce a second hole, holding the piercing member a fixed distance apart from said first hole, using the emplaced rod string as a guide for the piercing member.  
  It is a second process of this invention to (l) pierce a hole, drawing a rod string into said hole, and (2) enlarge said hole while piercing a second hole, holding the piercing member a fixed distance apart from said first hole, using the emplaced rod string as a guide for the piercing member.  
  It is a third process of this invention, in addition to the steps in the next above paragraph, to draw a second rod string into said second hole as said second hole is pierced.  
  It is a further process of this invention to pierce two parallel holes by l piercing a first hole, drawing a rod string into said first hole, (2) piercing a third hole, parallel to said first hole, drawing another rod string into said third hole, and (3) piercing said second hole, parallel to said third hole.  
  It is a more particular process of this invention to enlarge a first hole and pull conduit therethrough while simultaneously piercing a second hole parallel to said first hole, using said first hole as a guide for said second hole.  
  It is an extended process of this invention to continue the above processes to pierce additional holes parallel to the first and second holes.  
  It is therefore an object of this invention to pierce parallel holes in materials.  
  It is a more particular object of this invention to pierce, enlarge, and pull conduit or utility pipe into parallel holes.  
  It is still a more particular object of this invention to provide apparatus for achieving the above enumerated objects.  
  More particularly it is an object of this invention to provide a tool for boring parallel bores, particularly through compacted earth, and the like.  
 BRIEF DESCRIPTION OF THE DRAWINGS Other objects will become apparent from the following description, taken in connection with the accompanying drawings, in which:  
  FIG. I shows a piercing tool, rod string, and forcing apparatus such as a hydraulic ram, according to the prior art;  
  FIG. 2 shows a first embodiment of the invention in place, ready to form a second bore parallel to the first bore;  
  FIG. 3 shows the apparatus of FIG. 2 during the process of forming the second bore, enlarging the first bore, and pulling conduit into the first bore;  
  FIG. 4 shows conduit in place in the first bore, the third bore being pierced, and the second bore being enlarged while conduit is being pulled into the second bore;  
 FIG. 5 shows an alternative embodiment of FIG. 4&#39;  
 wherein the enlarging broach carries a special mantle, and the conduit coupling mechanism is adapted for use with flexible conduit;  
  FIG. 6 shows the apparatus of this invention boring holes without the enlarging broach;  
  FIG. 7 shows an exploded view of a typical tool in accordance with this invention;  
  FIG. 8 shows a typical conduit run wherein the parallel conduits are of varying size;  
  FIG. 9 is a figure to demonstrate how variably spaced bores may be formed with the tool of this invention;  
  FIG. 10 shows a typical conduit run of identically sized holes or bores;  
  FIG. 11 is a view, partly in section of the apparatus of FIG. 7 assembled;  
 FIG. 12 is a view, taken from the bottom in FIG. 11;  
 FIG. 13 is a view, taken at 13l3 in FIG. 11;  
  FIG. 14 is a detailed view of the novel broach mantle of this invention which is used with flexible conduit;  
  FIG. 15 is a view of the enlarged end of the broach mantle of FIG. 14;  
  FIG. 16 is a view of the smaller end of the broach mantle of FIG. 14;  
  FIG. 17 shows a typical centering plug and bearing cap for laying spliced flexible conduit into a conduit bore;  
 FIG. 18 is a view, taken from the left in FIG. 17;  
  FIG. 19 is a view of a conduit attachment for flexible utility pipe;  
  FIG. 20 is a plan view of an alternate embodiment of the invention;  
 FIG. 21 is a view taken at 21-21 in FIG. 20;  
  FIG. 22 is a side view of a bracket adapted to attach to the embodiment of FIG. 20;  
 FIG. 23 is a view taken at 2323 in FIG. 22;  
  FIG. 24 is a view of the apparatus of FIGS. 20 and 21 with conduits and/or rods strings attached thereto;  
  FIG. 25 is a view of FIG. 24 with the apparatus of FIGS. 22 and 23 attached thereto and a conduit attached to the apparatus of FIGS. 22 and 23;  
  FIG. 26 is a diagrammatic view showing the manner in which two conduits are pulled by the apparatus of FIG. 24;  
  FIG. 27 is a diagrammatic view showing the manner in which three conduits are pulled by the apparatus of FIG. 24, the conduits being of different size;  
  FIG. 28 is a diagrammatic view showing three conduits of substantially equal size which are pulled in by the apparatus of FIG. 24; and  
  FIG. 29 shows a conduit configuration formed by the apparatus of FIG. 25.  
 DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows a prior art device for boring conduit holes, for example, between two trenches or manholes 20, 22. A piercing tool 24 is forced into the ground 26 by a forcing mechanism such as a hydraulic ram 28. Typically a plurality of rods 30 are attached to the trailing end of the piercing tool 24. As the piercing tool penetrates deeper, additional rods 30 are added to the string until the piercing tool 24 reaches the trench or manhole 22.  
 The piercing tool 24 is removed from the string of rods 30, and the tool 32 of this invention is attached to the end of the string of rods 30 to be pulled back through the first bore.  
  The tool of this invention, as shown in FIGS. 2 and 3, comprises a first rod member portion 34 and a piercing tool 36 attached by a spacing member 38 to the rod member 34. The spacing member 38 is, typically, a sheet of steel with a wedge blade 40 on its leading edge. The blade 40 is preferably tilted relative to the direction of motion of the apparatus 32 so that the blade 40 slices the earth 26. The tilt of the blade 40 causes the spacer 38 to be similar to a guillotine blade. The spacer 38 is preferably as thin as possible while still maintaining its rigidity of spacing.  
  The pointed end 41 of the piercing member 36 is positioned to start a new hole in the wall 42 of the trench or manhole 22.  
 An enlarging broach. 44 is attached to the string of rods 30 and to the tool 32, as shown. The broach 44 (sometimes called, in the trade, a frog) is substantially conical in shape, having a smaller diameter, at the contact with the rods 30, substantially equal to the diameter of the rods 30. (It should be noted that the piercing tool 24 may have the same diameter, or slightly larger, as the rods 30). The larger diameter of the broach 44 is sufficiently large to create a bore accommodating the conduit or utility pipe 46. The conduit or utility pipe 46 is preferably attached to the trailing end of the rod member 34.  
  As the rods 30 are drawn back toward the ram 28, the tool 32 is also drawn toward the ram 28. The broach 44 enlarges the first bore, and the conduit or pipe 46 is drawn into the enlarged bore. The piercing member 36 pierces a second bore substantially parallel to the first bore, and the spacer 38 cuts a slice 48 between the bores 50, 52. The slice 48, however, is not held open and the dirt fills in slightly behind it. Compaction of the bore 52 on the next pass of the tool 32 completes the compaction of the slice 48, completely filling it. A second string of rods 54 is pulled behind the piercing member 36.  
  During the cutting of the earth by the tool 32, the resistance ofthe earth 26 to the piercing tool 36 produces a torque, about an axis perpendicular to the sheet of the FIG. 3, to be placed on the tool. The torque is resisted by the string of rods 30 in the first bore, and the apparatus moves through the earth without binding.  
  FIG. 4 shows how the second bore may be used to guide the tool 32 through the ground 26 to form a third bore 60 which is substantially parallel&#39;to the second bore 52 and, hence to the first bore 50.  
  It should be noted that, as shown in FIG. 8, the different bores in a conduit run may be of different size. The bores may be formed with different sized broaches 44 or with no broach at all in the smallest size.  
  It should be noted, as shown in FIG. 9, that the spac ing between adjacent usable parallel bores 126, 127 may be varied by forming one or more auxiliary bores such as 128. The bore 126 may be formed first. The bore 128 is formed next. Then the bore 127 is formed parallel to the bore 128. The spacing between bore 126 and bore 128, and the spacing between bore 128 and bore 127 is the length of the spacer element 38. Note however, that the spacing between bore 126 and bore 127 may vary up to a dimension equal to twice the length of the spacer element 38. The unused bore 128 is usually compacted by the broach being pulled through the bore 127.  
  If the spacing between bores 126 and 127 is desired to be greater than twice the length of the spacer element 38, additional unused bores (not shown) can be formed between the bores 126 and 127.  
  When a bore is to be unused, preferably an entire rod string is not pulled behind the rod member 34 of the tool. Instead, as shown in FIG. 6, a single rod 86 is used to counter the torque on the piercing member 32.  
  A typical conduit run of six identical bores is shown, by way of example, in FIG. 10 wherein the bores are formed in sequence 131, 132, 133, 134, 135, 136.  
  FIG. 5 shows the tool of this invention in combination with apparatus for pulling flexible conduit and a special broach mantle with a novel stress reliever 72.  
  When a spliced plastic conduit is used, it is preferable not to pull in the conduit, but to push it. Such a flexible conduit is attached to the tool 32 by a cable or other flexible tension member 76. The cable 76 extends down the central axis of the conduit 74, and it is attached to a bearing cap 78 on the trailing end of the conduit 74. Motion of the tool 32 pulls the cable 76 and the bearing cap 78 which pushes the flexible conduit 74. The conduit 74 is centered on its leading end by a ball centering cap 80 which fits into the leading end of the conduit 74. A matching cap 82 is attached to the trailing end of the first rod member 34. The cable is preferably attached to the center of the cup 82 and extends through a central aperture 8-1 (see FIG. 17) in the ball cap 80.  
  The basic tool 32 is shown in exploded view in FIG. 7. In FIG. 7, the string rods 30 screw onto the leading end of the conical broach or frog 44. A coupling screws onto the stud 92 on the trailing end of the broach 44. The rod member 34 comprises a rod 94 which screws into the coupling 90 and the coupling 96. The rod 94 forms a sliding fit into the sleeve 98 so that the angular position of the piercing member 36 about. the axis of the rod member 96 is adjustable, allowing choice in positioning before a bore is commenced. The conduit coupler 100 is adapted to grasp a conduit or utility pipe 46, as by screw threads. On the forward end of the coupler 100, an car 102 fits between a pair of matching ears 103, 104. A pin 105 (FIG. 11) is adapted to fit into the transverse holes in members 102, 103, 104 to carry the pull on the coupler 100.  
  The piercing member 36 is attached to the sleeve 98 by a spacing member 38 which keeps the piercing member 36 a fixed distance from the sleeve 98 and causes the bore being formed to be substantially parallel to the existing bore which carries the rods 30. The leading edge 40 of the spacer 38 is sharpened to a wedge to penetrate the earth. The blade 40 may be substantially perpendicular to the axis of the bore of the rods 30, but it is preferably angled, after the fashion of a guillotine, as shown in FIG. 11, relative to the direction of travel of the tool 32, to aid in slicing the earth.  
  The leading end 41 of the piercing tool 36 is pointed to penetrate the ground. The trailing end of the piercing member 36 carries ears 108, 109 which straddle the ear 110, on the leading end of coupler 112, to which they are attached. The assembled tool 32 is shown in FIGS. 11, 12, 13.  
 The apparatus of FIGS. 24 through 29 are used, for  
 example, to pull service conduits from the street into an adjacent building. Typically, for example, the configuration of FIG. 29 might have the gas service pulled through the conduit 200, the electric service through conduit 202, the telephone service through conduit 204, and television cable through conduit 206. Other permutations may be used, if desired, and other services such as water, steam, and the like may be pulled through the conduits. If one of the conduits requires a larger hole, it may be positioned as shown at 200 or, alternatively, as shown in FIG. 27 at 208. For mechanical reasons it is preferable to have the larger or off-sized hole at the position 208 while keeping the holes or conduits 210, 212 substantially the same size. In this fashion, the apparatus drag is balanced and the apparatus of FIGS. through is pulled straight without a tendency to skew. Of course, three conduits may be pulled as shown at 214, 216, 218 of FIG. 28 where the conduits are identical. If only two conduits are needed, a pilot hole may be used as shown by the dashed line 220 in FIG. 26, and the apparatus, due to the side push of the dirt, fills the hole 220 when the holes or conduits 222, 224 are placed in the ground.  
  The apparatus of FIGS. 20 through 25 are used to produce the hole patterns of FIGS. 26 through 29.  
  A fixture as shown in FIGS. 20, 21 comprises, typically, a substantially fiat plate 300, preferably steel, having a pair of slicing blades 302, 304 on the front end thereof. Although the plate 300 is shown as substantially flat, it may, if desired, increase in thickness by a gradual taper from the front end 306 to the back end 308.  
  The direction of travel of the tool through the earth is shown by the arrow 310. The blades 302 and 304 are preferably swept from the forward end toward the rear end 308 to provide a slicing action of the blade. The angle of sweep is not specified, and that angle, designated A, may in fact be zero degrees. Further, the angle A may be increased so that the rearward end 312 of the blade 302 and the corresponding rearward end of the blade 304 may extend clear to the rearward end 308 ofthe fixture 300.  
  The structure 300 is preferably symmetrical about the center line 314 so that resistance to force applied to the fixture 300 produces only minimal torque on the apparatus.  
  The blades 302, 304 are sharp blades and are wedge shaped to facilitate cutting through the earth.  
  A coupling member 316, which may have screw threads thereon, is adapted to receive a rod string or an enlarging broach 318 as shown in FIGS. 24 and 25. The fitting 316 is preferably symmetrical about the center line 314. A  
  On the rear end 308 of the fixture 300 are a plurality of coupling members 320, 322, 324 which are aligned, generally, in the direction of the movement arrow 310 and the center line 314. The fitting or coupling member 320 is preferably symmetrical about the center line 314, and the additional fittings or coupling members 322, 324 are preferably even numbered and balanced about the center line 314. Although only two of the offcenter-line fittings 322 and 324 are shown, it is obvious that additional fittings may be used. It is also obvious that the additional fittings need not be even in number, although the use of an odd number of fittings causes some problem of increasing torque upon the fixture 300.  
  The fittings 320, 322 and 324 are adapted to be attached to rod strings such as those shown in FIGS. 24 and 25 at 326, 328, 330. Enlarging broaches 332, 334,  
 336 are preferably placed on the leading ends of the,  
 rod strings 326, 328, 330.  
  The broaches 332, 334, 336 may be of the same size to produce the hole pattern shown in FIG. 28. Alternatively, the broach 332 may be larger than the broaches 334, 336 to produce the hole pattern shown in FIG. 27. If desired, the entire rod string 326 and broach 332 may be eliminated to produce the hole pattern shown in FIG. 26 wherein the dotted hole 220 is the original pilot hole through which the rod string attached to the broach 318 is pulled. The enlarging broaches 334 and 336 then cause the hole 220 to be refilled.  
  When it is desired to produce a hole pattern such as that shown in FIG. 29, the fittings 400 of FIGS. 22 and 23 is attached, as shown in FIG. 25 to the fixture 300.  
  The fixture 300 may, optionally, have a plurality of holes 350 therethrough and, preferably, positioned in two rows symmetrically about the center&#39;line 314 as shown more particularly in FIG. 20. The holes 350 are preferably threaded to receive screws 352 which are shown more particularly in FIG. 25 to attach the fixture 400 to the fixture 300.  
  The fixture 400 is an upstanding vane or fin, preferably of steel, having a knife edge 402 on the leading end thereof. As shown more particularly in FIGS. 22 and 25, the knife 402 is substantially vertical. It may be desired that the knife 402 be swept in a direction opposite to the direction of motion to produce a better slicing action. The sweeping backward of the knife edge 402 is within the spirit of the invention.  
  On the bottom end of the fixture 400 are a pair of wings or shoulders 404, 406 which are attached to the fixture 400 and which carry holes therein to receive the screws 352. The screws 352 then go through the holes 408 and into the holes 350, attaching the fixture 400 to the fixture 300.  
  Riding on the top end of the fixture 400 is a piercing member 410 having a pointed forward end 412 and a fitting or coupling member 414 on the rearward end thereof to which a rod string 416, preferably having an enlarging broach 418 on the forward end thereof, may be attached. The fitting 414, in a preferred embodiment, has a screw thread for receiving a rod string 416 or a broach 418.  
  The upstanding fitting 400, together with the piercing member 410, places a torque on the member 300 which is resisted by the surfaces of the fitting 300. That torque may also be relieved by having an additional fitting, substantially identical to the fitting 400, downstanding from the bottom surface of the fitting 300 and an additional piercing member, such as the member 410, upon the bottom end thereof.  
  It is also within the contemplation of this invention that a plurality of vanes may be used, which are radially directed from the center line 314, with a cutting edge such as the edges 302, 304, 402. The trailing edge of each of the vanes, as well as the trailing edge of the intersection of the vanes, may each have a fitting for pulling a rod string and an enlarging broach. The ends of the vanes may, optionally, each have a piercing tool such as the piercing tool 410.  
  It should be noted that a piercing tool such as the piercing tool 410 may, optionally, be positioned ahead of the enlarging broaches 334 and 336.  
 It should also be noted that the enlarging broach 418 could have been positioned behind the blade 402 in the same manner that the enlarging broach 336 is positioned behind the blade 302 and the enlarging broach 304 is positioned behind the blade 304. i  
  It should also be apparent that more than one enlarging broach such as the broach 418 may be positioned on the fixture 400.  
  It should also be apparent that other means for attaching the fixture 400 to the fixture 300 may be used. For example, the fixture 400 could be welded to the fixture 300.  
  If desired, the forward end of the wings 404, 406 could be stream lined. In the shown embodiment, such stream lining is not necessary because the wings 404, 406 are immediately behind the enlarging broach 318, whereby the wings 404, 406 do not impede the motion of the apparatus through the ground.  
  The apparatus of FIG. 24, therefore, may be characterized as an apparatus having two radially directed fins, each having a cutting edge on the forward end thereof, adapted to be attached to the end of a pulling apparatus and to have enlarging broaches attached to the trailing edges thereof, including a broach positioned substantially on the axis thereof.  
  The apparatus of FIG. 25 could be characterized as a three-vaned apparatus, not necessarily symmetrically arranged, having slicing blades on the forward ends thereof, including at least one piercing tool and adapted to pull enlarging broaches and rod strings.  
  An embodiment of the broach mantle of this invention for use to prevent damage to flexible conduit in adjacent bores is shown in FIGS. 14, 15, 16. The mantle 70, preferably made of rigid material such as metal, fits like a skin over the broach 44. The broach 44 has a threaded stud 140 projecting from its leading or small end, and a coupler screws onto that stud 140, holding the mantle 70 onto the conical broach 44 and for attachment to the string of rods 30. A stress reliever 72 is attached by a plate 142 to the mantle 70. The stress reliever 72 is a plate which is tangential to the enlarged bore formed by the broach mantle 70. Stress in the earth, caused by the forcing of the broach mantle 70 through the earth, is directed away from the direction of the plate 72, whereby flexible conduit in adjacent bores, in the direction of the plate 72, are protected. To aid the stress reliever 72 and the attaching portion 142 in penetrating the earth, the leading edges 144, 146 are sharpened into blades.  
  To prevent the broach mantle and the plate 72 from turning, during use, about the axis of the rods 30, bifurcated pairs of tines 150, 151, 153, 154, 156, 157 are directed axially from the trailing end of the mantle 70 and spaced apart to straddle the spacer element 38 as shown particularly in FIGS. 14 and 15. Two positions of the mantle 70 and stress reliever plate 72 are shown in FIG. 15. The dotted lines 36a and 38a show a second position of the piercing member 36 and the spacer 38 relative to the mantle 70.  
  The bearing cap 78 for the flexible conduit 74 is shown in detail in FIGS. 17 and 18. The cap 78 has a slot 159 formed therein through which the cable or chain 76 extends. The cable or chain 76 is snubbed on the upstanding tab 160.  
  The cap for the leading end of the flexible conduit 74 is shown in FIG. 17. It has a ball surface on its leading end. The ball surface 170 is perforated on the axis of the conduit 74 to allow the cable or chain 76 to extend therethrough.  
  Recently utility pipe is available in flexible rolls. A typical pulling coupler which may be used to pull in flexible pipe is shown in FIG. 19. The coupler fits into the interior of a flexible pipe 190. A loop 191 on the leading end of the coupler is adapted to be pulled. The loop 191 is connected to a bolt 192 which extends axially through a plug 193. The interior end of the bolt 192 is attached to a bearing plate 194. A resilient (such as rubber) collar is positioned between the plug 192 and the plate 194, whereby pulling on the loop 191 and bolt 192 causes the plate 194 to compress the collar 195 which frictionally grips the inner wall of the pipe 190. 1  
  It may therefore be seen that with this invention, precisely parallel bores may be formed through compacted materials for emplacing conduit and utility pipe.  
  The invention further contributes particular structure and method for pulling in rigid and flexible conduit and pipe while forming parallel runs for such conduit and pipe.  
  Particular structure of the tools allows enlarging of the bores while piercing new, parallel bores, protecting emplaced flexible conduit, and the like.  
  With the apparatus and method of this invention, conduit and utility pipe may rapidly be emplaced under streets and between manholes, materially reducing the cost ofsuch operations while producing a better quality run.  
  Although the invention has been described in detail above, it is not intended that the invention should be limited by that description, but only by that description taken together with the appended claims.  
 We claim:  
  1. A tool for forming substantially parallel first and second bores, each of said bores defining separatefirst and second axes, respectively, comprising:  
 . a first rod member, having a third axis defined there along and contoured to fit into an existing bore with said third and first axes substantially coaxial;  
 a pointed piercing second rod member having a fourth axis therein along said piercing member;  
 a spacing and cutting member attaching said piercing rod member in predetermined spaced relation,  
  1 1 with said third and fourth axes substantially parallel to said first rod member; and  
 broach means on said first rod member for enlarging said existing bore.  
  2. A tool for forming substantially parallel first and second bores having first and second axes, respectively, defined therealong comprising:  
 a first rod member, having a third axis and a leading and trailing end, contoured to fit into an existing bore;  
 a piercing second rod member having a fourth axis defined therein along said piercing rod member and through its point, and having a leading, penetrating end on the pointed end and a trailing end;  
 a coupling member on the trailing end of said piercing rod member for connecting said piercing rod member to a rod string;  
 a spacing member attaching said piercing rod member in predetermined spaced relation with said third axis substantially parallel with said fourth axis; and  
 a second coupling member on the leading end of said first rod member for connecting said first rod member to a rod string.  
  3. A tool as recited in claim 2 and further comprising an enlarging broach on the leading end of said first rod member for enlarging said existing bore.  
  4. A tool as recited in claim 3 and further comprising a third coupling member on the trailing end of said first rod member for connecting said rod member to a conduit.  
  5. A tool as recited in claim 4 in which said third coupling member comprises a centering member for centering said third coupling member on the leading end of a conduit; a tension member, attached to the trailing end of said first rod member and adapted to extend through a conduit; and a bearing cap, removably attachable to the trailing end of said tension member and adapted to fit over the trailing end of a conduit.  
  6. A tool as recited in claim 5 in which said centering member comprises a cap, with a central opening therein for said tension member, adapted to fit over the leading end of a conduit, having a centering, substantially hemispherical protrusion thereon; a socket attached to said first rod member to center on said protrusion; and means for attaching said tension member to substantially the center of said socket.  
  7. A tool as recited in claim 5 in which said tension member is flexible.  
  8. A tool as recited in claim 3 and further comprising a stress relieving blade, attached to said broach and tangential to said enlarged bore, including a sharpened leading edge thereof; and aligning means for aligning the plane of said second blade relative to said spacing member.  
  11. A tool as recited in claim in which said aligning means comprises a plurality of axially directed tines attached to the trailing edge of said mantle for straddling said spacing member to prevent turning of said 5 mantle about the longitudinal axis of said first rod member.  
  12. Apparatus for forming substantially parallel bores comprising:  
 a first rod member, contoured to fit into an existing bore;  
 at least one piercing member;  
 at least one spacing member, equal in number to said piercing members, attaching said piercing members, respectively, in predetermined spaced relation substantially parallel to said first rod member; and  
 broach means on said rod member for enlarging said existing bore.  
 13. Apparatus for forming substantially parallel bores comprising:  
 a first rod member, contoured to fit into an existing bore and having a leading and a trailing end and a first coupling member on the leading end of said first rod member for connecting said first rod member to a rod string;  
 at least one piercing member, each having a leading and a trailing end;  
 at least one coupling member attached to the trailing end of at least one of said piercing members for connecting said piercing member to a rod string; and  
 at least one spacing member, equal in number to said piercing members, attaching said piercing members, respectively, in predetermined spaced relation substantially parallel to said first rod member with their leading ends in the same direction.  
  14. Apparatus as recited in claim 13 and further comprising an enlarging broach on the leading end of said first rod member for enlarging said existing bore.  
  15. Apparatus as recited in claim 14 and further comprising a third coupling member on the trailing end of said spacing members, alined with said first rod member for connecting said spacing member to a conduit.  
  16. A plurality of rigid vanes intersecting at a common axis which extends from the forward end to the rearward end of said vanes;  
 the forward end of said vanes having a cutting edge thereon;  
 coupling means for attaching apparatus for pulling said vanes and apparatus to be pulled by said vanes; and  
 piercing means having a coupling means on its rearward end and a pointed forward end, attached to the radially-outward edge of at least one of said vanes.  
 17. In combination:  
 a plurality of rigid vanes intersecting at a common axis, said axis extending from the forward end to the rearward end of said vanes;  
 the forward edge of said vanes having a cutting edge thereon;  
 first coupling means for attaching apparatus for pulling said vanes, symmetrically positioned on said axis at the forward end of said apparatus;  
 second coupling means for attaching apparatus to be pulled by said vanes, positioned on the rear edge of said apparatus and symmetrically positioned relative to said axis;  
 at least one of said vanes having a piercing means, having a pointed forward end and a coupling means on its rearward end on its radially-outward edge.  
 18. In combination:  
 a plurality of rigid vanes intersecting at a common axis, said axis extending from the forward end to the rearward end of said vanes, said vanes being substantially flat vanes which extend in diametrically opposed directions from said axis;  
 the forward edge of said vanes having a cutting edge thereon, said cutting edge being swept from the forward end of said axis in a rearward and radially outward direction;  
 first coupling means for attaching apparatus for pulling said vanes, symmetrically positioned on said axis at the forward end of said apparatus;  
 at least three coupling means for attaching apparatus to be pulled by said vanes, positioned on the rear edge of said apparatus, one substantially upon said axis and the remaining plurality substantially symmetrically positioned relative to said axis.  
 19. Apparatus as recited in claim 18 in which said vanes are substantially identical.  
  20. Apparatus as recited in claim 19 in which said vanes are three in number, two of said vanes being substantially coplanar and extending from said axis and a third vane, upstanding from one side of said first two vanes and said third vane having a piercing member with a pointed forward end and a coupling member upon the rearward end of said piercing member, said piercing member being on the radially outward edge of said third vane.  
  21. Apparatus as recited in claim 20 in which the cutting edge of said third vane is substantially perpendicular to said axis.  
  22. Apparatus as recited in claim 21 in which enlarging broaches are attached to at least one of the said coupling means on the rearward edge of said apparatus.  
  23. Apparatus as recited in claim 22 in which conduit means are attached to the rearward end of said enlarging broaches.  
  24. Apparatus as recited in claim 23 and further comprising pulling means attached to said forward coupling upon the forward end of said apparatus.  
  25. Apparatus as recited in claim 24 and further comprising an enlarging broach attached between said pulling means and said forward coupling.  
  26. Apparatus for forming substantially parallel spaced-apart, non-coaxial bores comprising:  
 a first rod member, having a leading and trailing end and defining a first axis between said leading and trailing end, contoured to fit into an existing bore;  
 at least one piercing member, each having a leading and trailing end with a point on its leading end and defining axes parallel to but non-coaxial with said first axis;  
 at least one spacing and cutting member, equal in number to said piercing members, attaching said piercing members, respectively, in predetermined spaced relation substantially parallel to said first rod member; and  
 broach means on said first rod member for enlarging said existing bore.