Miniature tunnel equipment

Abstract

The invention relates to a drill string (32) for a micro-tunneling device (1) having a tool (21) at a distal end of the drill string (32) and an external drive mechanism (2) at a proximal end of the drill string (31). The drill string (32) is formed by a plurality of connected drill string segments (13), each drill string segment (13) having a drive shaft (33) aligned along a central axis for rotation about the central axis and an elongate sleeve (34) housing the drive shaft (33). The front end of one drill string section (13) is adapted to be connected with the rear end of the other drill string section (13) by a latching connection to form a drill string (32), the latching connection being adjustable in order to vary the tolerance between the front end of one drill string section (13) and the rear end of the other drill string section (13) when they are connected.

Description

Technical Field

[0001] The present invention relates to a microtunneling apparatus for producing a substantially horizontal borehole. The invention also relates to a drill string and a microtunneling apparatus comprising a reamer and a drill string. The term microtunneling as used in this specification refers to drilling or digging a non-vertical hole, usually not more than 1500 mm in diameter, wherein an operator does not need to enter the hole. Conveniently, hereinafter, the invention is described in this reference. Background Art

[0002] Traditionally, delivering services such as telecommunications, gas, water, stormwater, sewage, data and electricity may involve digging a trench, laying the services and backfilling the trench. This may be convenient where the trench is relatively shallow and there is no existing infrastructure above it (such as a "greenfield" site). However, as the depth of the trench increases, it becomes difficult to cost-effectively provide machinery to dig the trench to the required depth. In addition, if other existing infrastructure would be adversely affected by the open trench, such as damage or destruction to major roads or existing services, other methods of designing the conduit must be considered.

[0003] Another such method is microtunneling, which generally involves a drilling apparatus having a drill bit at the end of a drill string that rotates to bore a hole in the ground to create a microtunnel. The drill string is formed of multiple sections, each of which includes a solid drill rod that transmits torque from a drive device at the surface or at the bottom of a vertical tunnel to the drill bit underground. The drill string may also include a supply conduit to accommodate a supply fluid line that supplies pressurized fluid to the cutting head. The drill string may also include a spoil removal conduit through which cuttings and fluid near the rear of the drill bit can be moved back to the drive apparatus.

[0004] It should be appreciated that the energy required to produce a microtunnel depends in part on the volume of spoil to be removed, so the larger the tunnel, the greater the energy required. While drilling is an option, it is difficult to accurately guide the drill. Deviations from the preferred route may result in unnecessary spoil removal. One method of reducing unnecessary spoil removal is to drill a pilot hole and enlarge the pilot hole with a reamer assembly. The pilot hole can be relatively small, and as long as the pilot hole is approximately within the spoil section to be removed by the reamer, the reaming will be relatively effective in removing the spoil.

[0005] The reamer assembly will typically rotate the reamer's cutting head using drill rods in the drill string, which is held in tension as the reamer assembly is pulled back through the pilot hole. The drill rod will provide the same torque to the reamer's cutting head as it would to the drill bit, however the diameter of the work surface that the reamer's cutting head engages will be larger than the diameter of the pilot hole. Spoil is also typically removed through the pilot hole, usually using a vacuum, which is not ideal because the cutting head will produce spoil that is larger in diameter than the pilot hole. This causes the cutting head to agitate the spoil rather than cut into the work surface.

[0006] The reference herein to a patent document or other material as prior art is not to be taken as an admission that the document or material is known in Australia or that the information it contains was part of the common general knowledge at the priority date of any claim. Summary of the invention

[0007] According to one aspect of the present invention, there is provided a drill string for a micro-tunneling device, the micro-tunneling device having a cutter at a distal end of the drill string and an external drive mechanism at a proximal end of the drill string, the drill string being formed by a plurality of connected drill string sections, each of the drill string sections having a central axis, a drive shaft aligned along the central axis for rotation about the central axis, an elongated casing accommodating the drive shaft, a first cavity in the casing, the drive shaft being rotatably mounted in the casing, the first cavity extending longitudinally along the casing and offset from the drive shaft; each of the drill string sections comprising a front end and a rear end longitudinally displaced from the front end, wherein the front end of one of the drill string sections is adapted to be connected to the rear end of another drill string section by a latch connection to form the drill string, the latch connection being adjustable so as to vary the tolerance between the front end of one drill string section and the rear end of another drill string section when the front end of one drill string section and the rear end of another drill string section are connected, wherein in use, the external drive mechanism rotates the drive shaft to rotate the drill bit and remove cuttings through the first cavity. Providing an adjustable latch connection can help reduce pressure between adjacent drill string sections that might otherwise interfere with the proper operation of the latch. It also provides the ability to compensate for wear of the connection between the leading end of the drill string section and the trailing end of the drill string section due to use.

[0008] The latch connection may include a latch member associated with one of the front end of the one drill string section or the rear end of the other drill string section, the latch member being adjustable between an inactive position and an active position, in which the front end of one drill string section is separable from the rear end of the other drill string section, and in which the front end of one drill string section is connected to the rear end of the other drill string section. The latch connection preferably includes a pawl member adapted to interact with the latch member to retain the latch member in the active position or the inactive position. It has been found that the inclusion of a pawl is beneficial when connecting and disconnecting adjacent drill string sections. A biasing member may also be included for biasing the latch member toward the active position. Where both a biasing member and a pawl are included, it is preferred that the pawl overcomes the force of the biasing member to retain the latch member in the inactive position.

[0009] The drill string preferably includes an adjustment member, the adjustment member being adjustable to change the tolerance between the front end of one drill string section and the rear end of another drill string section when the front end of one drill string section and the rear end of another drill string section are connected. The adjustment member may take any suitable form, and in a preferred form, the latch connection includes an impact member associated with either the front end of the one drill string section or the rear end of the other drill string section, the impact member interacting with the adjustment member to adjust the position of the impact member relative to the front end of the one drill string section or the rear end of the other drill string section. It is further preferred that the impact member is an elongated member having a tapered guide. Obviously, the impact member may take other forms, however such a configuration facilitates the positioning of one end of a drill string section with the other end of an adjacent drill string section.

[0010] The drill string preferably includes a sealing arrangement between the front end of the one drill string section and the rear end of the other drill string section, such that in use, the sealing arrangement prevents cuttings from escaping from the first cavity between the front end and the rear end of the connected drill string sections. The sealing arrangement may take any suitable form, and in one form, the sealing arrangement includes at least one gasket located between the drive shaft and the first cavity on at least one of the front end or the rear end of the connected drill string sections. The sealing arrangement may also include at least one gasket surrounding the drive shaft on at least one of the front end or the rear end of the connected drill string sections. The sealing arrangement may also include at least one gasket surrounding at least one cavity on at least one of the front end or the rear end of the connected drill string sections.

[0011] According to another aspect of the present invention, a micro-tunnel device is provided for enlarging a substantially horizontal guide hole on the ground to produce a borehole, the micro-tunnel device comprising a drill string and an reaming drill assembly as described above, the reaming drill assembly having a tool rotatable about an axis, a gear box located on a first side of the tool, and a main body located on a second side of the tool, the tool having at least one cutting element on a radial peripheral portion of the tool, the gear box having a gear box input end for interacting with a drill rod, the drill rod being rotated about the axis by a driving device outside the guide borehole, the gear box also comprising a gear box output end interacting in a radial center portion of the tool, the main body being used to transmit thrust from a thrust device outside the enlarged borehole to the tool, whereby the tool rotates relative to the main body.

[0012] The gearbox is preferably configured to increase the torque between the gearbox input and the gearbox output. The degree of torque increase may take any suitable form, but preferably the gearbox is configured to increase the torque between the gearbox input and the gearbox output by more than a factor of two.

[0013] The reamer assembly preferably includes a generally cylindrical housing located on a first side of the tool, the housing housing the gearbox, the cylindrical housing including a pin for connecting to a drill string, thereby preventing the cylindrical housing from rotating relative to the drill string. The cylindrical housing preferably includes a fluid supply port for connecting to a fluid supply conduit in the drill string, the cylindrical housing and the gearbox defining a fluid path therebetween for passing fluid through the gearbox to cool the gearbox. This arrangement of the cylindrical housing protects the gearbox from wear when pushed through the borehole, while cooling the gearbox reduces wear on the gears and extends the life of the gearbox. Preferably, at least one bearing is provided between the cylindrical housing and the output end of the gearbox so that the gearbox outlet can rotate smoothly relative to the cylindrical housing.

[0014] The cutter preferably includes a mount having a plurality of cutting elements, each of the cutting elements being mounted on the mount so that each of the cutting elements is radially spaced from the axis. The mount may take any suitable form and is preferably configured to further define the fluid path as extending from the cylindrical housing through the mount, the mount having at least one fluid outlet for ejecting fluid toward at least one of the cutting elements. This arrangement assists in cooling the cutting elements while converting spoil cut from the borehole into slurry.

[0015] The mount preferably includes a plurality of grading members, each of which is spaced apart from adjacent cutting elements, and the grading members are combined with the cutting elements to screen the size of the spoil delivered to the body. It is further preferred that the grading members are spaced apart from the body by flanges, respectively, and the flanges guide the spoil when the cutter rotates.

[0016] The cylindrical housing is sized to fit within the guide hole, and the gearbox is sized to fit within the cylindrical housing. Thus, the radial dimension from the axis to the cylindrical housing is smaller than the radial dimension from the axis to the radial periphery of the tool.

[0017] The body may take any suitable form and in one form comprises a cylindrical housing positionable in use in the borehole, the housing having a spoil removal inlet adjacent the peripheral portion of the cutter, the spoil removal inlet being positioned at the bottom of the borehole. It is further preferred that the body comprises an extraction port extending from the spoil removal inlet for connection to an extraction conduit associated with the thrust device. Under the influence of gravity, spoil tends to move towards the lowest point of the borehole. This arrangement of removing spoil by the thrust device rather than the drill string facilitates extraction of more spoil from the cutter.

[0018] The body preferably includes anti-rotation means adapted to inhibit rotation of the body within the borehole.The anti-rotation means may take any form and in one form comprises at least one anti-rotation element projecting perpendicularly from the cylindrical housing.

[0019] The reamer assembly preferably includes at least one bearing between the cylindrical housing and the cutter. This arrangement provides smooth rotation of the cutter relative to the cylindrical housing.

[0020] The drill string preferably includes a hollow drive shaft to allow fluid or gas to pass through the drive shaft to the cutter in use.

[0021] Preferably, each drive shaft comprises a male end and a female end, the male end and the female end being respectively adapted to enable the male end of the drive shaft to engage with the female end of an adjacent drive shaft when connecting the drill string sections. The male end and the female end of the drive shaft may each have a complementary shape, the complementary shape providing a driving engagement between the male end and the female end for rotation in a clockwise or counterclockwise direction. A preferred complementary shape is a rounded triangle, as it has no corners, avoiding stress concentration at the corners, but other complementary shapes may also be suitable.

[0022] Preferably, the at least one cavity includes a second cavity located within the sleeve, the second cavity extending longitudinally of the sleeve and offset from the drive shaft, wherein in use, the second cavity is adapted to guide the laser beam therethrough. It is also preferred to include a thermal insulator at least between the second cavity and the drive shaft to reduce heat transfer between the drive shaft and the second cavity in use. The thermal insulator is preferably in the form of a hard or rigid foam material injected into the elongated sleeve to inhibit the ingress of water or swarf and to enhance the rigidity of the elongated sleeve, but other forms of thermal insulators may also be used.

[0023] Preferably, a channel is formed around the casing, extending longitudinally along the casing and offset from the drive shaft, wherein in use the channel is adapted to accommodate a control line, a communication line or a hydraulic line connecting the drive mechanism to the tool. The channel may be an open channel or may be closed with a cover.

[0024] The elongate sleeve and at least the first cavity may be formed by any suitable process and in a preferred embodiment they are roll formed or alternatively drawn.

[0025] Conveniently, the invention will be described in more detail below with reference to the accompanying drawings of preferred embodiments of the reamer assembly according to the invention. The particularity of these drawings and the accompanying detailed description should not be understood as superseding the generality of the preceding definition of the invention according to each aspect of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order that the present invention may be more fully understood, some embodiments will now be described with reference to the accompanying drawings, in which:

[0027] Figure 1 is a side view of an example of a microtunneling apparatus including a preferred embodiment of a reamer assembly according to the present invention.

[0028] Figure 2 From the first perspective Figure 1 A perspective view of a portion of a microtunnel device.

[0029] Figure 3 yes Figure 1 Long cross-sectional view of a preferred embodiment of a central reamer assembly.

[0030] Figure 4 yes Figure 1 A stereoscopic view of the reamer assembly from a first perspective.

[0031] Figure 5 yes Figure 1 A perspective view of the reamer assembly from a second perspective.

[0032] Figure 6 is another long cross-section of the reamer assembly connected to the drill string and pipe section.

[0033] Figure 7 yes Figure 1 A second perspective view of a portion of a microtunnel device.

[0034] Figure 8 is a perspective view of a preferred embodiment of a drill string section from a back end perspective.

[0035] Fig. 9 yes Figure 8 A perspective view of a preferred embodiment of a middle drill string section from a front end perspective.

[0036] Fig.10 is a cross-sectional view of adjacent drill string sections.

[0037] FIG. 11 is a long cross-sectional view of a drill string section. DETAILED DESCRIPTION

[0038] Now refer to Figure 1 , Figure 1 An example of a microtunneling apparatus 1 in use is shown. Briefly, the microtunneling apparatus 2 comprises a drive apparatus 2 located in a drive tunnel 3, a thrust apparatus 4 located in a thrust tunnel 5, both of which interact with a reamer assembly 6 located between them in the ground 7. The drive apparatus 2 comprises a drive 8 located on a drive platform 9, which is movable along the drive platform. Similarly, the thrust apparatus 4 is shown as comprising a thrust mechanism 10 located on a thrust platform 11 and movable along the thrust platform 11.

[0039] from Figure 2 It can be seen that the drive platform 9 includes a guide rail 12 for linearly guiding the movement of the drive 8 along it. The drive device 2 also includes a drill string 32, which is releasably attached to the front of the drive 8. Figure 1 It can be seen that the drill string 32 includes a plurality of drill string sections 13 and is configured to be positioned in a guide hole 14 on the ground, and Figure 2 Only one of these drill string sections 13 is shown. The pilot hole 14 will be preformed by attaching a drill bit (not shown) to the front end of the drill string 32 in a manner that will be understood by those skilled in the art. Figure 1 A drill string 32 having three drill string sections 13 is shown, but this number may vary depending on the length of the pilot hole 14. The features of each drill string section 13 will be described in more detail with reference to the following figures.

[0040] from Figure 1 It can be seen that the length of the guide rails 12 on the drive platform 9 is longer than the drill string sections 13. This arrangement allows the driver 8 to be moved towards the rear of the drive tunnel 3 and allows each drill string section 13 to be disconnected from the front of the driver 8.

[0041] Figure 1 The thrust platform 11 in FIG. 1 is shown supporting two pipe sections 15 designed to transfer thrust from the thrust mechanism 10 to the reamer assembly 6. Figure 1 As shown, the thrust mechanism 10 is located at the rear of the thrust platform 11. Figure 7, shows a thrust platform 11 having a pair of racks 16 that mesh with pinions (not shown) of motors 17 of thrust mechanism 10. Operation of each motor 17 will cause rotation of each pinion to advance thrust mechanism 10 along the track. Once pipe section 15 is fully inserted into borehole 18 (see Figure 1 ), the thrust mechanism 10 can be reversed to the rear of the thrust platform 11, and another pipe section 15 falls on the thrust platform 11. Obviously, the means for advancing the thrust mechanism 10 can be different from that shown.

[0042] The thrust device also supports a portion of the vacuum duct (see Figure 1 , Figure 2 or Figure 7 ), the spoil is released from the reamer assembly 6 through the conduit to the outside of the thrust tunnel 5.

[0043] Now refer to Figure 3 , Figure 4 , Figure 5 and Figure 6 , which together illustrate a preferred embodiment of a reamer assembly 6 according to the present invention. In short, the reamer assembly 6 comprises a gearbox 20 located on a first side of a tool 21 and a body 22 located on a second side of the tool 21. The tool 21 is rotatable about an axis XX, while the body 22 is urged in the direction of the axis XX to engage a working surface 24 between the bore 18 and the guide hole 14 (see Figure 1 ).

[0044] The gearbox 20 is located within a cylindrical housing 25 which protects the gearbox 20 while it passes through the guide hole 14. The cylindrical housing 25 has a pair of pins 26 which facilitate attachment of the cylindrical housing 25 to the drill string section 13, thereby preventing the cylindrical housing 25 from rotating relative to the drill string 32. Figure 4 As shown, the gearbox input end 27 extends from the cylindrical housing 25 for connection to a drill rod (not shown) in the drill string 13. The drill rod is rotated by the driver 8 (see Figure 1 ), thereby rotating the gearbox input 27. The gearbox 20 is preferably configured to increase the torque between the gearbox input 27 and the gearbox output 28. The preferred increase is more than two times, and a 4:1 ratio is most preferred, however, other ratios may be more appropriate depending on the operating conditions of the reamer assembly. In this case, the cylindrical housing 25 can be opened and a gearbox 20 with a more appropriate ratio installed.

[0045] Figure 3 Also shown is a pair of bearings 29 located between the gearbox output 28 and the cylindrical housing 25. The pair of bearings 29 are arranged to facilitate smooth rotation of the gearbox output 28 relative to the cylindrical housing 25. The number and location of the bearings 29 may vary. Figure 3Different than shown.

[0046] Still refer to Figure 3 , it can be noted that the gearbox output 28 is attached to the tool 21. More specifically, the tool 21 includes a mounting seat 30, and the gearbox output 28 is attached to a central portion of the mounting seat 30. Figure 4 The preferred mount 30 is further shown in Figure 3 as having a plurality of radially extending arms 31. The cutter 21 comprises three cutting elements 23 (only two of which are visible in the illustration) which are releasably attached to each alternating arm. Figure 4 It is also shown that each cutting element 23 is separated by a staging plate 32 which is remote from each corresponding arm 31 of the mounting base 30 by a flange 33. The function of the staging plates 32 is to provide a limited space on either side thereof for spoil to pass between the cutting elements 23 and the staging plates 32, thereby screening the spoil before it is extracted from the reamer assembly 6.

[0047] Figure 3 A fluid path 34 is shown in the reamer assembly, whereby fluid is delivered from the drill string 32 to the cutting element 23. The cylindrical housing 25 having the gearbox 20 is configured to partially define the fluid path 34, whereby the gearbox 20 is cooled by the fluid in the gearbox 20. The cooling of the gearbox 20 has the advantage of reducing the degradation of the gears (not shown) therein caused by overheating of the gearbox. The fluid path 34 extends through the mount 30 and is sprayed onto the cutting element 23, which assists in the operation of the cutting element 23 at the working face 24 of the borehole 18. The fluid combines with the spoil to form a slurry, which is conveniently removed from the cutter 21 through the vacuum conduit 19.

[0048] Figure 3 The knife 21 is also shown attached to the body 22 at the rear of the knife 21. Three bearings 35 are located between the knife 21 and the body 22 to facilitate smooth rotation of the knife 21 relative to the body 22. Figure 4 It can be seen that the body 22 is preferably a cylindrical housing having the same diameter as the diameter of the pipe section 15. The body 22 transfers thrust from the pipe 15 to the mounting seat 30 through the bearing 35. The cylindrical housing 22 has a spoil removal inlet 36 adjacent to the periphery of the mounting arm 31, which, in use, is located at the bottom of the borehole 18. The body 22 includes an extraction port 37 in the housing that connects the extraction inlet 36 to the vacuum conduit 19 for removing spoil from the borehole 18.

[0049] The operation of the microtunneling apparatus 1 will now be explained with reference to the overall diagram. Once the drive tunnel 3, pilot hole 14 and thrust tunnel 5 are formed, the microtunneling apparatus 1 will typically be installed on site. The drill string 32 will occupy the entire length of the pilot hole 14 and the drill bit (not shown) is removed and replaced by the reamer assembly 6. With the reamer assembly 6 in place, the driver 8 can rotate the drill rod (not shown) about the axis XX to rotate the cutter 21 relative to the working face 24 of the borehole 18. The thrust device 4 applies a thrust to the body 22 to urge the reamer assembly 6 into engagement with the working face 24. The thrust device 4 pushes the pipe section 15 into the borehole 18 and, at the same time, the drill string sections 13 are removed from the drive tunnel 3 once they have been pushed out of the pilot hole 14 by operation. Fluid is supplied to the cutter 21 along the drill string 13 through the drive tunnel 3, while spoil is drawn out of the borehole 18 and out of the thrust tunnel 5 through the vacuum conduit 19.

[0050] Now refer to Figure 8 , shows a preferred embodiment of a drill string section 13 having a drive shaft 33 configured to rotate about a central axis XX for attachment to a gearbox 20 (see Figure). It can be noted that the drive shaft is hollow along the central axis XX in order to allow fluid or gas to be driven from the drive device 2 (see Figure). Figure 1 ) is transmitted to the cutter 21 through the drive shaft, but this is not required. The drill string section 13 also includes an elongated casing 34 that accommodates the drive shaft 33 and a first cavity 35 and a second cavity 36. The first cavity 35 can be used to remove the vacuum conduit 19 that has not been removed from the working face 24 (see Figure 1 ) to remove the chips and fluid. The second cavity 36 can be used to aim (sight) the laser beam passing therethrough to facilitate guiding the drill bit.

[0051] In an alternative embodiment not shown, the drive shaft 33 may be solid and gas may be supplied to the cutter 21 through the second cavity 36. In this alternative configuration, the supplied gas not only helps to force the chips out through the first cavity 35, but also helps to cool the space where the laser beam operates. It will be appreciated that the drill string section 13 will heat up when in use, and the more the space in the second cavity 36 heats up, the greater the distortion of the laser beam. Therefore, by keeping the space cool, the distortion of the laser beam is reduced.

[0052] Figure 8 The rear end 37 and the front end 38 of the drill string section 13 are shown. The terms front and rear are used herein only to aid explanation and do not impose any limitation on the features. The rear end 37 includes a pair of elongated members 39 adapted to be positioned within holes 40 formed in the front end 38. A pair of latch members 41 ( Figure 8The drill string section 13 is connected to the elongated member 39 to form a connection between the front end 38 of one drill string section 13 and the rear end 37 of an adjacent drill string section 13 (see the adjacent section 13 for examples). Figure 1 ).

[0053] Fig.10 The front end 39 is shown with a pair of latch members 41, with the left latch member 41 in an open state and the right latch member 41 in a closed state. The latch members 41 may be biased toward the closed state so that the elongated member 39 may engage with the latch members 41 in a snap-fit ​​manner. However, a pawl 42 may also be included to hold the latch members 41 in the open or closed state, thereby requiring manual adjustment of the pawl 42 and the latch members 41 before the latch members 41 can adopt the closed state.

[0054] Now refer to Figure 8 and Fig. 9 , which respectively show the rear end 37 and the front end 38 , showing a drive shaft gasket 43 around the drive shaft 33 , a first cavity gasket 44 around the opening of the first cavity 35 , and a second cavity gasket 45 around the opening of the second cavity 36 . Figure 8 and Fig. 9 Also shown is an adjuster 46 at the rear of the elongated member 39, which can be rotated to adjust the length of the elongated member 39. Although it is generally desirable that the front end 38 of one drill string section 13 is parallel to the rear end 37 of the adjacent drill string section 13, the adjuster 46 allows for fine adjustments within tolerance. This can be used to allow adjustment of the angle of one drill string section 13 to the adjacent drill string section 13. The adjuster 46 can also be useful in reducing the pressure on the latch member 41 that may have become stuck in the closed position after use. In addition, the adjuster 46 can also increase the tension in the connection that may have been reduced over time, thereby extending the working time of the drill string 32.

[0055] Figure 8 The male end 48 of the drive shaft 33 is shown, which is complementary in shape to the female end 49 (see FIG. Fig. 9 ). Fig.10 It can be seen that the complementary shape is a rounded triangle. This shape was found to be an improvement over the hexagonal shape because it avoids stress concentrations at the hexagonal corners and is easier to disconnect from the adjacent drive shaft 33.

[0056] FIG. 11 shows a long cross section of the drill string section 13 to show that the elongated sleeve 34 is supported by a plurality of spaced apart ribs 50. An insulating foam 51 may be located between the elongated sleeve and the ribs to isolate heat from the drive shaft 33 from at least the second cavity 36 (see FIG. Figure 8 ). The insulating foam is preferably relatively firm / hard so as to provide structural rigidity to the drill string section 13.

[0057] Refer again Figure 8 , it is shown that the elongated sleeve 33 is formed with a channel 52, which can accommodate communication pipes, hydraulic lines, etc. for communicating / interacting with the cutter 21. Although the figure shows an open channel 52, it can be a closed longitudinal cavity similar to the first cavity 35 and the second cavity 36, or can be surrounded by a removable cover. Adding a removable cover can provide additional protection for pipes and pipelines.

[0058] The elongated sleeve 34, first cavity 35 and second cavity 36 may be formed in any suitable manner, and one preferred configuration is to form these components by roll forming or drawing.

[0059] As will be appreciated from the foregoing, the reamer assembly 6 as described above provides a relatively simple means for increasing the torque of the cutter 21 at the working face 24 of the borehole 18. Cooling the gearbox 20 using a water supply that may have been provided to the drive apparatus 2 when making the pilot hole 14 provides another beneficial result. Furthermore, the removal of spoil at the spoil removal inlet 36 adjacent the peripheral portion of the cutter 21 and through the pipe section 15 rather than through the drill string 13 allows for more efficient removal of spoil.

[0060] Various modifications and / or additions may be made to the drill string components as described above without departing from the spirit or scope of the invention.

Claims

1. A drill string for a microtunneling apparatus having a cutter at a distal end of the drill string and an external drive mechanism at a proximal end of the drill string, the drill string being formed by a plurality of connected drill string sections, each of the drill string sections having a central axis, a drive shaft aligned along the central axis for rotation about the central axis, an elongated casing receiving the drive shaft, a first cavity within the casing in which the drive shaft is rotatably mounted, the first cavity extending longitudinally along the casing and offset from the drive shaft; each of the drill string sections comprising a front end and a rear end longitudinally displaced from the front end, wherein the front end of one of the drill string sections is adapted to be connected to the rear end of another drill string section by a latch connection to form the drill string, the latch connection being adjustable to vary the tolerance between the front end of one drill string section and the rear end of another drill string section when they are connected, wherein in use, the external drive mechanism rotates the drive shaft to rotate the drill bit and remove cuttings through the first cavity.

2. The drill string of claim 1 , wherein the latch connection comprises a latch member associated with one of the leading end of the one drill string section or the trailing end of the other drill string section, the latch member being adjustable between an inactive position in which the leading end of the one drill string section is separable from the trailing end of the other drill string section and an active position in which the leading end of the one drill string section is connected to the trailing end of the other drill string section.

3. The drill string of claim 2, wherein the latch connection comprises a pawl member adapted to interact with the latch member to retain the latch member in the active position or the inactive position.

4. A drill string according to claim 2 or 3, comprising a biasing member for biasing the latch member towards the active position.

5. The drill string according to any one of claims 1 to 4, comprising an adjustment member adjustable to change the tolerance between the leading end of one drill string section and the trailing end of another drill string section when they are connected.

6. A drill string according to claim 5, wherein the latch connection includes an impact member associated with either the front end of the one drill string section or the rear end of the other drill string section, and the impact member interacts with the adjustment member to adjust the position of the impact member relative to the front end of the one drill string section or the rear end of the other drill string section.

7. The drill string of claim 6, wherein the impact member is an elongated member having a tapered guide.

8. A drill string according to any one of claims 1 to 7, comprising a sealing device between the front end of the one drill string section and the rear end of the other drill string section, so that in use, the sealing device prevents chips from being discharged from the first cavity between the front end and the rear end of the connected drill string sections.

9. The drill string of claim 8, wherein the sealing arrangement comprises at least one gasket located between the drive shaft and the first cavity on at least one of the leading end or the trailing end of a connected drill string section.

10. A drill string as claimed in claim 8 or 9, wherein the sealing means comprises at least one washer surrounding the drive shaft at at least one of the leading end or the trailing end of a connected drill string section.

11. A drill string according to any one of claims 8 to 10, wherein the sealing arrangement further comprises at least one gasket surrounding the at least one cavity on at least one of the leading end or the trailing end of a connected drill string section.

12. A drill string as claimed in any preceding claim, the drive shaft being hollow to allow fluid or gas to pass through the drive shaft to the cutter in use.

13. A drill string according to any one of the preceding claims, wherein each drive shaft comprises a male end and a female end, the male end and the female end being respectively adapted to enable the male end of the drive shaft to engage with the female end of an adjacent drive shaft when connecting the drill string sections.

14. The drill string of claim 13, wherein the male and female ends of the drive shaft have complementary shapes, respectively, the complementary shapes providing driving engagement therebetween for rotation in a clockwise or counterclockwise direction.

15. The drill string of claim 14, wherein the complementary shapes are rounded triangles.

16. A drill string according to any one of the preceding claims, wherein the at least one cavity comprises a second cavity within the casing, the second cavity extending longitudinally of the casing and offset from the drive shaft, wherein in use the second cavity is adapted to direct a laser beam therethrough.

17. A drill string as claimed in claim 16, comprising thermal insulation at least between the second cavity and the drive shaft to reduce heat transfer between the drive shaft and the second cavity in use.

18. The drill string of claim 17, wherein the thermal insulation is a hard foam material injected into the elongated casing to inhibit the ingress of water or cuttings and to enhance the rigidity of the elongated casing.

19. A drill string according to any preceding claim, comprising a passage formed around the periphery of the casing, the passage extending longitudinally along the casing and offset from the drive shaft, wherein in use the passage is adapted to receive a control line connecting the drive mechanism to the cutter.

20. A drill string as claimed in any preceding claim, wherein the elongate casing and at least the first cavity are roll formed.

21. A micro-tunneling device for enlarging a substantially horizontal guide hole on the ground to produce a borehole, the micro-tunneling device comprising a drill string and a reaming drill assembly according to any one of the preceding claims, the reaming drill assembly having a tool rotatable about an axis, a gear box located on a first side of the tool, and a main body located on a second side of the tool, the tool having at least one cutting element on a radial peripheral portion of the tool, the gear box having a gear box input end for interacting with a drill rod, the drill rod being rotated about the axis by a driving device outside the guide borehole, the gear box also comprising a gear box output end interacting in a radial center portion of the tool, the main body being used to transmit thrust from a thrust device outside the enlarged borehole to the tool, whereby the tool rotates relative to the main body.

22. The microtunnel apparatus of claim 21, wherein the gearbox is configured to increase torque between the gearbox input and the gearbox output.

23. The microtunnel apparatus of claim 22, wherein the gearbox is configured to increase the torque between the gearbox input and the gearbox output by more than a factor of two.

24. A microtunneling apparatus according to any one of claims 21 to 23, comprising a generally cylindrical housing located on the first side of the cutter, the housing housing the gearbox, the cylindrical housing including a pin for connecting to a drill string to prevent the cylindrical housing from rotating relative to the drill string.

25. The microtunneling apparatus of claim 24, wherein the cylindrical housing includes a fluid supply port for connection to a fluid supply conduit in the drill string, the cylindrical housing and the gearbox defining a fluid path therebetween for passing fluid through the gearbox to cool the gearbox.

26. A microtunnel apparatus as claimed in claim 24 or 25, comprising at least one bearing between the cylindrical housing and the gearbox output.

27. A microtunneling apparatus according to any one of claims 24 to 26, wherein the cutter comprises a mount having a plurality of cutting elements, each of the cutting elements being mounted on the mount so that each of the cutting elements is radially spaced from the axis.

28. A microtunneling apparatus according to any one of claims 24 to 27, wherein a radial dimension from the axis to the cylindrical housing is smaller than a radial dimension from the axis to the radial periphery of the cutter.

29. The microtunneling apparatus of claim 27, wherein the mount is configured to further define the fluid path extending from the cylindrical housing through the mount, the mount having at least one fluid outlet for ejecting fluid toward at least one of the cutting elements.

30. A microtunneling apparatus according to any one of claims 26 to 29, wherein the mount includes a plurality of grading members, each grading member spacing adjacent cutting elements, the grading members in combination with the cutting elements to size spoil delivered to the body.

31. The microtunneling apparatus of claim 30, wherein the staging members are each spaced apart from the body by a flange, the flange directing the spoil as the cutter rotates.

32. A microtunnel apparatus according to any one of claims 21 to 31, wherein the body comprises a cylindrical housing positionable in the borehole in use, the housing having a spoil removal inlet adjacent the peripheral portion of the cutter, the spoil removal inlet being positioned at the bottom of the borehole.

33. A microtunneling apparatus as claimed in any one of claims 32, wherein the body includes an extraction port extending from the spoil removal inlet, the extraction port being connected to an extraction conduit associated with the thrust apparatus.

34. A microtunneling apparatus as claimed in claim 32 or 33, wherein the body includes anti-rotation means for inhibiting rotation of the body within the borehole.

35. The microtunnel apparatus of claim 34, wherein the anti-rotation means comprises at least one anti-rotation element protruding perpendicularly from the cylindrical housing.

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