FIELD OF THE INVENTION

The present invention relates to a subterranean excavation machine, and in particular to a subterranean excavation machine comprising a cutting head at an end of a cable.

BACKGROUND OF THE INVENTION

Subterranean excavation machines have several application purposes, for example mining, drilling, or tunnel boring. Many such machines utilise mechanical blades or wipers to cut into the subterranean substrate so the substrate can be removed. However, such machines are typically high- maintenance and the mechanical cutting parts need replacement at regular intervals.

Mining of mineral resources normally requires removal of large volumes of soil and/or rock before the depth of the resources is reached, and historically very large areas of the landscape have been excavated to reach relatively small areas of mineral deposits. The deeper the deposit, the further beyond the edges of the deposit the higher layer of soil/rock must be excavated to reach the deposit, often causing widespread damage to the local environment.

Publication US 4,319,784 discloses an apparatus for subterranean drilling and mining, in which water jets are used to loosen and remove soil, and generally assist with the drilling and mining process. A casing pipe is used to drill vertically downwardly through the soil to the mineral deposit, and the water from the water jets returns back up the casing pipe along with the mineral deposits. The use of water jets reduces the wear on the mechanical cutting parts of the machine, but the mechanical cutting parts are still required to help break up the substrate, particularly for tough substrates.

This apparatus avoids the need to excavate large areas of soil above the mineral deposits, however the area of the deposit that can be reached with the casing pipe is limited, and the casing pipe typically needs to be withdrawn and moved to a slightly different location to access different areas of the deposit on a fairly regular basis. Accordingly, once the deposit has been fully mined, a large number of holes from the surface down to the level of the deposit may be left behind.

It is therefore an object of the invention to provide an improved subterranean excavation machine.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a subterranean excavation machine comprising a cable and a cutting head at an end of the cable. The cutting head comprises a plurality of nozzles which receive cutting fluid from one or more cutting fluid conduits passing along a length of the cable, the nozzles for ejecting the cutting fluid under pressure to cut into subterranean substrate. At least some of the nozzles are configured to rotate about different axes to one another. Since the nozzles rotate about different axes to one another, the cutting fluid that is ejected from the nozzles traverses over a wider range of areas of the substrate than if the nozzles were all in fixed positions or rotated about the same axis as one another. Particularly in the case of hard subterranean substrates such as rock, the cutting fluid from each nozzle may only cut a very narrow channel in the substrate, and so traversing the nozzles about different axes to one another increases the area of the substrate into which the channels are cut.

Preferably, the different axes of rotation cause the circular channel that the cutting fluid from each nozzle cuts, to cross the circular channel that the cutting fluid from at least one of the other nozzles cuts, helping break down the substrate. This is in contrast to simply cutting concentric circles into the substrate as can occur if all the nozzles are rotated about a single axis. The axis about which each nozzle rotates is preferably remote from a centre of the nozzle, so the nozzle traverses around a circular path about the axis, rather than simply rotating on its own central axis at a single location.

Each nozzle may be configured to eject the cutting fluid at a non-zero angle relative to the axis of rotation about which the nozzle rotates. The cutting fluid ejected from the nozzle then traces around a conical shape as the nozzle rotates, so that the part of the substrate which is struck by the cutting fluid depends on how far away the nozzle is from the substrate. Accordingly, moving the cutting head closer and further from the substrate varies the point at which the cutting fluid from each nozzle impacts the substrate, meaning that a greater area of the substrate can be impacted by the cutting fluid from each nozzle. This is in contrast to nozzles which eject cutting fluid parallel to the axis about which they are rotated, and whose cutting fluid traces out a cylinder as the nozzle rotates, the diameter of the cylinder being constant along its length, so that the same part of the substrate is impacted by the cutting jet almost regardless of how far the nozzle is from the substrate.

The nozzles may be configured to rotate at fixed phases of rotation relative to one another, so that the cutting fluid from each nozzle impacts against the substrate in a predetermined sequence of positions relative to the cutting fluid from the other nozzles. Then, it can be ensured that the points of impact of the cutting fluid against the substrate are evenly distributed over the area of the substrate that is to be cut, rather than some areas of the substrate being impacted much more densely than the other areas.

Each nozzle may be formed in a support member, where each support member has a central axis, and the support member is configured to rotate the nozzle about the central axis. Accordingly, rotation of the support member about its own, central axis, allows the nozzle formed in the support member to traverse about that central axis as the support member is rotated. When these support members are implemented, the formation of the nozzles in different support members to one another, means the nozzles rotate about different axes to one another. Each support member may comprise one or more of the nozzles.

The central axis of at least one of the support members may be non-parallel to the central axis of at least one of the other support members, to further increase the diversity of directions in which the high pressure cutting fluid is directed by the cutting head. The support members may comprise gear teeth that mesh with a toothed ring, the toothed ring configured to drive the rotation of the support member and the nozzle(s) formed in the support member. Each toothed ring comprises teeth extending from an outer peripheral surface of the toothed ring for rotating ones of the support members located just outside the toothed ring, and/or teeth extending from an inner peripheral surface of the toothed ring for rotating ones of the support members located just inside the toothed ring. A plurality of the toothed rings may be arranged concentrically with one another, wherein the gear teeth of each support member mesh with the teeth of two of the toothed rings, the support member located just inside one of the two toothed rings and just outside the other of the two toothed rings. In this manner, the support members can be evenly distributed over a front face of the cutting head, and driving one of the toothed rings to rotate is sufficient to drive all of the toothed rings and support members to rotate, via the teeth.

Each support member may have at least two of the nozzles formed in the support member, and the at least two nozzles may be configured to rotate about the central axis of the support member. The at least two nozzles may be are arranged about the central axis of the support member at regular angular intervals to one another. Providing more than one nozzle per support member spaced at regular angular intervals increases the cutting capacity of the cutting head, and balances the thrust from each of the nozzles about the central axis of the support member, so that the support member can easily rotate about its central axis without excessive vibration. Each support member may be substantially spherical in shape.

The cutting head may further comprise a return port connected to a return conduit passing along the length of the cable, wherein the return port and the return conduit are configured to carry the cutting fluid and the cut subterranean substrate back along the cable.

The cable may be rigid, for example if the subterranean excavation machine is intended for drilling a fixed diameter hole such as a tunnel, or the cable may be a bendable cable, for example if the subterranean excavation machine is a mining machine, the cable is a mining cable, and the cutting head is a mining head. Therefore, according to a second aspect of the invention, there is provided a mining machine, comprising a mining cable and a mining head at an end of the mining cable. The mining head comprises a plurality of nozzles which receive cutting fluid from one or more cutting fluid conduits passing along a length of the mining cable, the nozzles for ejecting the cutting fluid under pressure to perform subterranean mining. The mining head further comprises a return port connected to a return conduit passing along the length of the mining cable, the return port and the return conduit for carrying mined material and the cutting fluid back along the mining cable, wherein the mining cable comprises a plurality of rigid length portions and a plurality of actuable bend portions. Each actuable bend portion is connected between two immediately adjacent ones of the rigid length portions so the rigid length portions and the actuable bend portions alternate with one another along the length of the mining cable, wherein each actuable bend portion is actuable to control a bend angle between the two immediately adjacent rigid length portions connected by the actuable bend portion, so the actuable bend portions are actuable to control movement of the mining head relative to another end of the mining cable opposite the mining head. The mining head may or may not be the same type of head as the cutting head of the first aspect of the invention.

The alternate rigid length portions and actuable bend portions mean that the bendable cable can be actuated to move the cutting head to a wide variety of different subterranean locations, even whilst the other end of the cable opposite from the cutting head remains fixed. The bendable cable can enter a subterranean area of interest at a single location on the surface, and the cutting head can be moved beneath the ground to excavate a large volume beneath the ground. This is particularly useful for mining applications where there is a desire to limit the disturbance at the surface of the mined area to avoid environmental damage.

The cutting fluid may be supplied at very high pressure to cut though the subterranean substrate, and the high forces involved limit the maximum cross-sectional area of the one or more cutting fluid conduits, and limit the volume of cutting fluid that can be delivered. Therefore, in some situations, there may be an insufficient or sub-optimum volume of cutting fluid for carrying the excavated subterranean material into the return port and along the return conduit. Accordingly, the cutting head may further comprise a bulk fluid supply port connected to a bulk fluid supply conduit passing along the length of the cable, the bulk fluid supply conduit for supplying additional fluid to collect and sweep the excavated subterranean material into the return port and along the return conduit.

Each actuable bend portion may comprise two rings that are respectively connected to the two immediately adjacent rigid length portions on either side of the actuable bend portion. The rings may be interspaced by at least one linear actuator extending from one ring to the other ring, each linear actuator controlling the distance between the rings at the location of the linear actuator, to control a bend angle between a central axis of one of the two immediately adjacent rigid length portions and a central axis of the other one of the two immediately adjacent rigid length portions. Each linear actuator may be a hydraulic cylinder, so that large loads can be supported by the linear actuator. The hydraulic cylinders may be spaced at regular intervals around an axis extending from a centre of one of the two rings to a centre of the other of the two rings.

Each arrangement of two rings and linear actuators may form a sub-portion of the actuable bend portion, and a plurality of the sub-portions may be stacked on one another to form the actuable bend portion, with their rings abutting one another. Accordingly, the rings of each sub-portion may be connected to the immediately adjacent rigid length portions via the rings and linear actuators of other sub-portions of the actuable bend portion.

Each actuable bend portion may comprise a plurality of stabiliser pistons between the plurality of linear actuators, each stabiliser piston extending from one of the two rings to the other of the two rings and configured to resist rotation of the two rings relative to one another. Then, the position of the cutting head can be controlled more accurately.

Each actuable bend portion may comprise an exterior defined by a flexible skirting pipe that extends from one of the two immediately adjacent rigid length portions to another of the two immediately adjacent rigid length portions. The skirting pipe helps prevent any unwanted earth/rock material from entering between the immediately adjacent rigid length portions and damaging the linear actuators.

The subterranean excavation machine may further comprise a rigid cable that is not bendable connected to the bendable cable, wherein the rigid cable is connected to the bendable cable at an end of the bendable cable opposite from the cutting head, the rigid cable being formed of rigid cable length portions that are attachable and removable from the rigid cable to define a length of the rigid cable. Then, in mining applications, the cutting head can first be used to drill vertically downward, with additional rigid cable length portions being added at the surface until the bendable cable and cutting head reach the desired depth where the minerals to be extracted are located.

The subterranean excavation machine may further comprise a cutting fluid pumping station for pressuring the cutting fluid, and a return fluid pumping station for sucking up the excavated substrate material and the cutting fluid via the return conduit.

According to a third aspect of the invention, there is provided a subterranean excavation machine comprising a cable and a cutting head at an end of the cable. The cutting head comprises a plurality of rotatable nozzles which receive cutting fluid from one or more cutting fluid conduits passing along a length of the cable, the rotatable nozzles for ejecting the cutting fluid under pressure to cut into subterranean substrate, wherein each rotatable nozzle comprises a mixing chamber that is configured to mix an abrasive material with the cutting fluid before the cutting fluid exits the rotatable nozzle.

The abrasive material increases the ability of the cutting fluid to cut into the subterranean substrate.

DETAILED DESCRIPTION

Embodiments of the invention will now be described by way of non-limiting example only and with reference to the accompanying drawings, in which:

Fig. 1 shows a schematic diagram of a subterranean excavation machine according to an embodiment of the invention being used to mine subterraneously;

Fig. 2 shows an enlarged schematic diagram of the subterranean excavation machine of Fig. i ;

Fig. 3 shows a schematic diagram of a bendable cable and cutting head of the subterranean excavation machine of Figs. 1 and 2;

Fig. 4 shows a schematic diagram of part of an actuable bend portion of the bendable cable of

Fig. 3;

Fig. 5 shows an enlarged schematic diagram of the cutting head of Fig. 3, intended for cutting through earth or soil substrates;

Fig. 6 shows a schematic diagram of an alternative cutting head, intended for cutting through rock substrates;

Fig. 7 shows a schematic diagram of the cutting head of Fig. 6, where the internal details of how support members including nozzles are rotated can be seen;

Fig. 8 shows a schematic cross-sectional diagram taken along line A- A’ marked on Fig. 7,

Fig. 9 shows an enlarged schematic diagram of internal details of one of the support members in which the nozzles are formed;

Fig. 10 shows a schematic diagram of another subterranean excavation machine according to an embodiment for boring tunnels;

Fig. 11 shows a schematic diagram side diagram of the subterranean excavation machine of Fig. 10; and

Fig. 12 shows a schematic diagram of an alternative cutting head to the cutting head of Fig. 3.

The figures are not to scale, and same or similar reference signs denote same or similar features.

The schematic diagram of Fig. 1 shows a subterranean excavation machine according to an embodiment of the invention, being used to mine gold from an alluvial soil layer 2. The machine comprises a cutting head 10 at an end of a bendable cable 15, and a rigid cable 20 connected at an opposite end of the bendable cable 15 from the cutting head 10. The end of the rigid cable 20 opposite from the end where the bendable cable 15 is connected, is held in place by a support structure 25. The support structure 25 is positioned in place by a vehicle 30.

The cutting head 10 comprises nozzles and at least one return port. The nozzles eject cutting fluid into a hole 5 in the alluvial soil layer 2, cutting through the soil and creating a turbulent slurry of soil and cutting fluid, that is sucked up through the return port. The bendable and rigid cables 15 and 20 define a cutting fluid conduit that delivers cutting fluid from the support structure 25 to the nozzles, and a return conduit that carries the slurry of soil and cutting fluid from the return port up to the support structure 25.

The cutting fluid conduit is connected to a cutting fluid pumping station 7 at the surface, and the cutting fluid pumping station pumps the cutting fluid down to the nozzles at high pressure, via the support structure 25. In this embodiment, the cutting fluid is water, however other cutting liquids could be used in alternate embodiments. The cutting fluid pumping station 7 is held on a vehicle 26 for easy transportation.

The return conduit is connected to a return fluid pumping station 8 at the surface, which pumps the slurry of soil and cutting fluid up to the surface from the cutting head, through sluices 9a on a vehicle 27 to extract the gold from the slurry. The slurry is then passed into a gravitational separator 9b on a vehicle 28, which separates out the largest solid particles 4b from the slurry, so they can be transferred into a previously mined hole 4. The remaining liquids and smaller particles are passed to a water purifier 9c on a vehicle 29 that extracts the water from the slurry so that it can be sent to the cutting fluid pumping station 7 and re-used as cutting fluid.

The schematic diagram of Fig. 2 shows an enlarged schematic diagram of the subterranean excavation machine. As shown, the bendable cable 15 comprises a plurality of rigid length portions 16 that alternate with actuable bend portions 17. Each rigid length portion is formed of a rigid material such as metal or carbon fibre, and is substantially unbendable. Typically, each rigid length portion may be lm to l .5m long. Each actuable bend portion 17 is connected between two adjacent rigid length portions 16, and controls a bend angle between the two adjacent rigid length portions 16. The actuable bend portions are controlled by a controller at the support structure 25, to move the cutting head 10 within the hole 5 to target different areas of the alluvial layer 2. The rigid cable 20 is joined to the bendable cable 15 at a joint 19.

During installation, the support structure 25 is moved into position by the vehicle 30, and then the cutting head 10 is used to cut a hole vertically downwardly through the top soil layer 1 and into the alluvial layer 2 where the gold is located. Once the bendable cable is in the ground, successive length portions of rigid cable 20 are added to the end of the cable until the cutting head 10 reaches the required depth. A casing pipe 21 is inserted into the ground around the cable to hold back the surrounding soil from collapsing in around the cable, and preferably a collar 22 seals around the casing pipe at ground level.

Mining commences using the cutting head 10, and the hole 5 begins to form around the cutting head. The hole 5 is expanded to excavate more and more areas of the alluvial layer 2 by controlling the position of the cutting head 10 using the actuable bend portions 17. An air inlet pipe 23 connects to the cavity between the cable and the outer casing 21, and pumping air into the cavity via the air inlet pipe raises the pressure inside the hole 5, and aids extraction of the alluvial layer up the bendable cable. The seal created by the collar 22 prevents the air that is pumped into the cavity from escaping at ground level.

The schematic diagram of Fig. 3 shows the bendable cable 15 and cutting head 10 in more detail. Each actuable bend portion 17 comprises two ends 40 and 50 for connecting between the two adjacent rigid length portions 16, the bend portion being actuable to adjust a bend angle l7b that is created between a central axis l7c of the end 40 of the rigid length portion l6a, and a central axis l7d of the end 50 of the rigid length portion l6b. The exterior of each actuable bend portion is formed by an expandable rubber skirt 18, which can flex to accommodate the changes in the bend angle, and which houses the cutting fluid conduit and the return conduit.

As seen in Fig. 3, the cutting head 10 comprises a rotatable collar 76 surrounding a fixed front ring 70, and a return port 62 that is positioned centrally of the fixed front ring 70. The cutting head 10 has nozzles 60 within the fixed front ring 70, for delivering the high-pressure cutting fluid to the alluvial soil deposit. Subterranean material that is dislodged by the cutting fluid from the nozzles 60 can be easily sucked up into the return port 62, and along the return conduit to the return fluid pumping station 8. In addition to the return port 62, further return ports connected to the return conduit may be positioned at the sides of the cutting head 10, to suck up further subterranean material and cutting fluid.

In this embodiment, a series of bulk fluid supply ports 74 is arranged interspaced between the nozzles 60. The bulk fluid supply ports 74 are connected to a bulk fluid supply conduit passing along the lengths of the bendable and rigid cables. In use, the bulk fluid supply ports 74 supply a much larger volume of bulk fluid than the volume of the cutting fluid supplied by the nozzles 60, and the bulk fluid helps to sweep the subterranean material into the return port 62. The bulk fluid may for example be water, but other liquids could alternatively be used. The bulk fluid is pumped to the bulk fluid supply ports 74 from a pumping station (not shown in Figs) on the vehicle 26.

The schematic diagram of Fig. 4 shows a sub-portion of one of the actuable bend portions 17 in more detail. Each actuable bend portion 17 comprises three sub-portions l7a (see Fig. 3) that are stacked on one another, to increase the angle that each actuable bend portion can bend through. Each sub-portion l7a comprises first and second rings 41 and 51, each ring being connectable to a ring of an adjacent sub-portion l7a, or to an end 40 or 50 of one of the rigid length portions 16. In this embodiment, the rings are made of metal, and are bolted to the rings of adjacent sub-portions or to the ends of the rigid length portions 16, but other materials and other methods of connecting the rings are possible in alternate embodiments. The expandable rubber skirt 18 and the various conduits running along the bendable cable are not shown in Fig. 5, for the sake of clarity.

The rings 41 and 51 are connected to one another by linear actuators in the form of hydraulic cylinders 45. Each hydraulic cylinder 45 extends from an annular face of the ring 41, to an annular face of the ring 51, to control the distance between the annular faces of the rings at the points where the hydraulic cylinder is connected to the rings. The annular faces of the rings face towards one another. The hydraulic cylinders are spaced evenly around the annular faces of the rings, and controlling the extension of each hydraulic cylinder controls the bend angle between the central axis of the ring 41 and the central axis of the ring 51, and therefore the bend angle l7b between the rigid length portions 16 that are connected to the acutable bend portion 17. The hydraulic cylinders are controlled via hydraulic pipes 48 that extend along the bendable 15 and rigid cables 20, up to a controller at the support structure 25. In this embodiment, there are 12 hydraulic cylinders spaced at equal angular intervals around the rings, but the numbers of cylinders may vary in alternate embodiments.

To help resist relative rotation of the rigid length portions 16 about the axes of the rings 41 and 51, each sub-portion l7a also has stabiliser pistons 53 that in this embodiment are spaced at equal angular intervals around the rings, in between the hydraulic cylinders. Each stabiliser piston 53 extends from the annular face of the ring 41, to the annular face of the ring 51, to prevent relative rotation between the rings.

Each stabiliser piston comprises a base plate 54 connected to a piston sheath 55, and a piston shaft 56 connected to a top plate 57. The base plate 54 is bolted to the annular face of the ring 51, and the top plate 54 is bolted to the annular face of the ring 41.

The piston shaft 56 is movable in directions in and out of the piston sheath 55, and the piston shaft 56 has a restraining pin 58 which extends through a slot 59 in the piston sheath 55, the slot 59 extending longitudinally along the piston sheath 55. The restraining pin 58 in the slot 59 prevents rotational movement of the piston shaft 56 relative to the piston sheath 55. The piston shaft 56 is free to move in and out of the piston sheath 55, under the influence of the hydraulic cylinders 45.

The hydraulic cylinders and stabiliser pistons are capable of flexing along their length as some of the hydraulic cylinders are extended and some of the hydraulic cylinders are retracted, to create the bend angle, and stacking three of the sub-portions together allows a larger bend angle to be created by the overall bend portion 17. Each one of the three sub-portions l7a bends through 1/3 of the angle l7b shown in Fig. 3, to together produce the angle l7b.

In use, the controller at the support structure is used to control which direction the mining head 10 points in, by controlling the actuable bend portions 17 via the hydraulic pipes 48. It will be appreciated that other types of actuable bend portion could be used in alternate embodiments.

The schematic diagram of Fig. 5 shows an enlarged perspective diagram of the cutting head 10 of Fig. 3, which is intended for cutting through earth or soil substrates. The cutting head 10 comprises a fixed front ring 70, which is connected to the end-most rigid length portion 16, and is stationary with respect to that rigid length portion. The fixed front ring 70 has an aperture through its centre, the aperture defining the return port 62, through which the excavated material and cutting fluid is sucked up and along the return conduit to the return fluid pumping station 8.

The fixed front ring 70 has a plurality of holes at its exterior, in which nozzle support members 72 are located. The nozzles 60 are formed in the support members 72. In this embodiment, each support member 72 is a spherical ball, which is rotatable within the corresponding hole in the fixed front ring 70. There are two nozzles 60 formed in each spherical ball, the nozzles pointing away from the spherical ball in directions that are different from one another and different from the axis of rotation of the spherical ball. Each spherical ball 72 has gear teeth around its periphery, just behind the fixed front ring 70, as described further below with reference to Fig. 8. These gear teeth are driven by a toothed ring to make all the balls of the fixed front ring rotate. Alternatively, the balls 72 may be configured to rotate under thrust generated by the nozzles 60 as they eject the cutting fluid.

The cutting head 10 is substantially cylindrical, and the spherical balls 72 with the nozzles 60 are arranged in a ring shape around the fixed front ring 70, at a front end of the cutting head 10. There are two rings of spherical balls 72 arranged in the fixed front ring 70; the outermost ring has spherical balls that each rotate about an axis parallel to the rigid length portion 16, and the innermost ring has spherical balls that each rotate about an axis that is not parallel to the axis of the rigid length portion 16. The return port 62 is positioned inside of the rings formed by the spherical balls 72.

The fixed front ring 70 also has the plurality of bulk fluid supply ports 74, which eject bulk fluid from a bulk fluid conduit passing along the bendable and rigid cables and up to the vehicle 26 having the cutting fluid pumping station 7. A bulk fluid pumping station of the vehicle 26 pumps the bulk fluid to the bulk fluid supply ports. In this embodiment, the bulk fluid is water, and the water helps sweep the excavated subterranean substrate up into the return port 62, along with the cutting fluid.

The rotatable collar 76 surrounds the fixed front ring 70, and is configured to rotate relative to the fixed front ring 70 and the end-most rigid length portion that the cutting head 10 is connected to. The rotatable collar 76 also has holes in its exterior which form nozzles 60a, the nozzles 60a for ejecting cutting fluid at high pressure to aid cutting of the soil.

During operation, the cutting fluid is squirted out of the nozzles 60 and 60a at very high pressure, and dislodges subterranean substrate material, so that it is swept up by the bulk fluid from ports 74 into the return port 62. Since the spherical balls 72 all rotate about different axes to one another, and since the nozzles 60 of each spherical ball eject fluid in directions different from the axis of rotation, the cutting fluid from each spherical ball spreads out in a cone shape. Those cone shapes of adjacent spherical balls overlap with one another, so that the full area of the subterranean substrate in front of the cutting head can be struck with cutting fluid by moving the cutting head closer and further away from the subterranean substrate.

The schematic diagram of Fig. 6 shows an alternative cutting head lOa, which has many more of the spherical balls 72, to assist in cutting through harder subterranean substrates such as rock. This alternative cutting head lOa is similar to the cutting head 10, but instead of the return port 62 being at the front centre of the cutting head, multiple return ports 62a are provided around the end of the end- most rigid length portion, as shown. Then, the front centre of the cutting head is used for additional balls 72. The return ports 62s are arranged in a ring shape that surrounds the ring shape defined by the outermost ring of spherical balls 72 at the front of the cutting head.

As shown in the schematic diagram of Fig. 7, the balls 72 of the cutting head lOa can be rotated by a plurality of toothed rings 80, 81, and 82 that are arranged concentrically with one another. The toothed rings each have teeth 83 running around their internal and external

circumferences, which mesh with teeth 75 of the balls 72. The outermost toothed ring 80 is driven to rotate by a hydraulic or electric motor 78, and the rotation of the toothed ring 80 drives the rotation of the spherical balls and the other toothed rings. Some of the balls 72, such as 72a, may only have one nozzle 60 if desired.

A cross-sectional diagram of two of the spherical balls is shown in Fig. 8, taken along line A- A’ marked on Fig. 7. As shown, each ball 72 is mounted on a swivel 85, allowing the ball 72 to rotate about the central axis 72c of the ball. Each ball 72 has the two nozzles 60 directed at approximately 90 degrees to one another, both nozzles 60 directed at approximately 45 degrees to the axis of rotation 72c of the spherical ball 72. To improve the efficiency of cutting, an abrasive material may be supplied to the nozzle of each ball, and mixed with the cutting fluid in a mixing chamber 88 of each nozzle 60. The abrasive material in this embodiment is a suspension of fine metal particles, however other types of abrasive material could alternatively be used, for example stone or ceramic.

The high-pressure cutting fluid is supplied to each ball 72 via a cutting fluid pipe 85a that passes through the swivel joint 85, and abrasive material is supplied via pipes 88a and 88b. The pipes 88a are fixed in position external to the balls 72, and the pipes 88b are internal to the balls 72, and so the pipes 88b rotate relative to the pipes 88a. The pipes 88a communicate with the pipes 88b via slots 88c. This is more easily appreciated from the schematic diagram of Fig. 9, which shows the internal details of the spherical ball 72a when looking towards the ball in the direction 89 marked on Fig. 8.

The slots 88c are formed as a series of arcs around the axis of rotation of the ball 72, and each slot 88c is connected to a corresponding pipe 88b that leads to the mixing chamber 88. As the ball 72 rotates, different ones of the slots 88c come into alignment with the pipes 88a, and the abrasive material is carried to the mixing chamber 88, where it becomes mixed with the high pressure cutting fluid, and ejected from the nozzle 60. The schematic diagram of Fig. 10 shows a cutting head 90 of a subterranean excavation machine according to another embodiment, for use in boring tunnels. A view of the cutting head 90 in use is shown in Fig. 11, where the cutting head 90 is mounted to a front of a truck 100, at an end of cables 105 that supply and receive the various fluids to and from the cutting head 90. The cutting head 90 is being used to bore a tunnel 110 into a rock substrate 120.

The cutting head 90 comprises an outer housing 92 with a front plate 94. An array of the spherical balls 72 is arranged in the front plate 94. The spherical balls 72 each rotate, and eject cutting fluid in the same manner as described hereinabove to cut into the rock substrate 120. Around the periphery of the front plate 94, there are a plurality of bulk fluid supply ports 74a, for supplying bulk fluid to help gather the material cut from the rock substrate 120. The outer housing 92 may be considered to define a short length of rigid cable, with the spherical balls at the end of the rigid cable.

The front plate 94 also comprises a plurality of return ports 62b, into which the slurry of cutting fluid, bulk fluid, and cut rock material is sucked.

The schematic diagram of Fig. 12 shows an alternative cutting head lOf which is intended for cutting through earth or soil substrates, and which could be fitted to the bendable cable 15 of Fig. 3, in place of the cutting head 10. The cutting head lOf comprises a ring of nozzles 60f that are spaced around a front circular face of the cutting head lOf, and a return port 62f that is positioned centrally of the front circular face of the cutting head lOf. Therefore, subterranean material that is dislodged by the cutting fluid from the nozzles 60f can be easily sucked up into the return port 62f, and along the return conduit to the return fluid pumping station 8. In addition to the return port 62f, further return ports connected to the return conduit may be positioned at the sides of the cutting head lOf, to suck up further subterranean material and cutting fluid.

In this embodiment, a ring of bulk fluid supply ports 65f is arranged inside the ring of nozzles 60f. The bulk fluid supply ports 65f are connected to a bulk fluid supply conduit passing along the lengths of the bendable and rigid cables. In use, the bulk fluid supply ports 65f supply a much larger volume of bulk fluid than the volume of the cutting fluid supplied by the nozzles 60f, and the bulk fluid helps to sweep the subterranean material into the return port 62f. The bulk fluid may for example be water, but other liquids could alternatively be used. The bulk fluid is pumped to the bulk fluid supply ports 65f from a pumping station (not shown in Figs) on the vehicle 26.

The cutting head lOf comprises a fixed front ring 70f, which is connected to the end-most rigid length portion 16, and is stationary with respect to that rigid length portion. The fixed front ring 70f has an aperture through its centre, the aperture defining the return port 62f, through which the excavated material and cutting fluid is sucked up and along the return conduit to the return fluid pumping station 8.

The fixed front ring 70f has a plurality of holes at its exterior, in which the nozzles 60f are located.

Many other variations of the described embodiments falling within the scope of the invention will be apparent to those skilled in the art.