FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to excavating equipment and the like, and more particularly, to a vertical trencher employing a vertical helical-shaped cutter body for simultaneously cutting and excavating a trench.

Trench excavation for purposes of installing an underground utility infrastructure is an essential and common activity of any ground development work. The common applications are for various kinds of piping, communications, energy etc. There are different types of digging equipment, and each has its advantages and disadvantages. The common denominator with all equipment manufacturers of mechanical digging equipment is the search for solutions that enable more efficient digging and reduction of the limitations connected with ground hardness.

There are two main types of equipment in use today, excavators and trenchers. Excavators have a jointed arm powered hydraulically, with a digging tool at one end. The advantage of these machines lies in the fact that they are universal and flexible in the type of digging they can achieve. However, they are not efficient as they do not operate continuously, and require three movements, a first movement for digging, a second for removing the soil from the trench and dumping it along the sides ofthe trench, and a third for returning to the trench for digging. Thus, the effective digging time is approximately only 30% of working time.

Additionally, these machines do not move while digging. At the end of a digging cycle, depending on the length of the arm, they must be re-positioned. For this reason, the total effective digging time is reduced below 30% of the working time.

An additional limitation of these machines is the ground cutting speed of the digging tool. The speed is very low and thus the digging tool requires a large force to split the ground, and must be very heavy. For these reasons, these machines have difficulty digging into hard and rocky ground. It is possible to equip excavators with a hydraulic hammer to break the rocks, after which another pass is required to clean the trench. Clearly, these extra operations greatly increase the excavation cost.

Trenchers operate in continuous fashion, thus saving valuable working time. The major disadvantages of these machines are that the digging systems are assembled from a large number of moving parts and chains including a separate soil removal system. Multiplication of systems and moving parts reduce the efficiency and technical reliability, while increasing the price.

Further, since trenchers have a large contact area with the ground, and cut on a diagonal, they require large amounts of power, force and weight for digging operations.

Types of trenchers include those having a large digging wheel with cutting teeth. These machines are limited in their cutting depth which is always less than the wheel radius. This type of trencher also has a large contact area with the ground, and since the wheel is driven from its center, large amounts of power and large moments of force are required for digging operations. An additional soil removal system is required.

Examples of patents disclosing trench excavation equipment include

Japanese Patent No. 60-25-129 to Miwa, in which a drum-shaped cutter is pivotally supported on the front of a traveler with a conveyer to carry excavated soil to the rear.

Russian Patent 457777 to Kudra discloses a trench excavator device having inclined knives attached to a screw conveyor, facing the spiral direction to improve operation.

French Patent 2,566,024 to Corneille discloses a narrow trench digger with vertical rotating auger, with a parallel partition behind, equipped with soil

loosening tools, such as vibrating vertical toothed bars, teeth on the auger spirals, or vertical rotary cutters.

Belgian Patent 902104 to Durieux discloses a trench cutting machine having a rotating tool comprising a pipe on which a flat is spiral wound or threaded with cutting or abrasive pieces. The trench cutting machine propels itself along the ground via a winch. Belgian Patent 1005788 to Durieux discloses a rotary trench cutter with a detachable vertical partition, to produce trenches of different sizes.

Therefore, it would be desirable to provide a trencher for excavating various size trenches, which operates at a high speed with increased capability for use on hard and rocky ground.

SUMMARY OF THE INVENTION

The present invention is of a vertical trencher employing a vertical helical-shaped cutter body for simultaneously cutting and excavating a trench. Accordingly, it is a principal object of the present invention to overcome the disadvantages of prior art excavation systems and provide a vertical trencher having a cutter body with cutting teeth arranged in a helical configuration on its circumference, for excavating various size trenches, which is operable at a high speed and suitable for use on hard and rocky ground. According to the teachings of the present invention there is provided, a vertical trencher attachable to a moving platform carrying a power source for excavating rock and soil to form a trench, the apparatus comprising: (a) a cutter body having: (i) a substantially cylindrical surface having a lower end, an upper end and defined as having a longitudinal central axis, (ii) at least one ridge attached to, and extending outwardly from, the surface in a helical configuration extending continuously along the surface to adjacent to the lower end, the ridge having an upper surface and an outer edge, and (iii) a plurality of cutting elements deployed in fixed relation to the outer edge for cutting rock

and soil adjacent to the outer edge; (b) a housing operatively engaged with the cutter body at the upper end so as to maintain the cutter body with the longitudinal central axis substantially vertical and to allow rotation ofthe cutter body about the longitudinal central axis, the housing having a lateral aperture; (c) a power transmission associated with the cutter body at the upper end for employing power from the power source to generate rotation of the cutter body about the longitudinal central axis; and (d) a back shield securable in fixed relation to the housing so as to present an inner surface extending substantially along and partially circumscribing the cutter body. According to a fiirther feature of the present invention, the ridge is formed such that a rise angle at a point ofthe ridge proximal to the lower end of the upper surface is less than a rise angle at a point of the ridge proximal to the upper end of the upper surface, wherein the rise angle is defined at each point ofthe ridge as the angle between a virtual plane parallel to the upper surface at that point and a virtual plane peφendicular to the longitudinal axis.

According to a further feature of the present invention, the rise angle increases monotonically from the lower end to the upper end ofthe cutter body. In one form of the present invention, the ridge is formed such that the cutting elements lie substantially on a virtual cylinder.. In an alternative form of the present invention, the ridge is formed such that the cutting elements lie substantially on a virtual, truncated, upwardly- diverging cone.

In a still further alternative form ofthe present invention, the cutter body is divided along its length into at least a first part and a second part, and the ridge is formed such that the cutting elements lie substantially on a virtual cylinder along the first part and substantially on a virtual truncated cone along the second part.

Alternatively, according to a further feature of the present invention, a first group ofthe cutting elements lie closer to the lower end ofthe cutter body than a second group of the cutting elements, and the ridge is formed such that a

circle traveled by the first group of cutting elements when the cutter body rotates has a diameter greater than that of a circle traveled by the second group of cutting elements such that the vertical trencher excavates a trench with at least partially undercut sides. In one form of the present invention for excavating trenches with undercut sides, the ridge is formed such that the cutting elements lie substantially on a virtual, truncated, upwardly-converging cone.

In an alternative form of the present invention for excavating trenches with undercut sides, the cutter body has a lower part and an upper part, and the ridge is formed such that the cutting elements lie substantially on a virtual cylinder of a first diameter along the lower part, and substantially on a cylinder of a second diameter along the upper part, the first diameter being greater than the second diameter such that the vertical trencher excavates a trench with a cross-section approximating to an inverted T-shape. According to a further feature of the present invention, there is also provided: (a) a plurality of additional cutting elements mounted in relation to the lower end of the cutter body for cutting downwards; and (b) a vertical drive for raising and lowering at least the cutter body.

According to a further feature of the present invention, there is also provided a deployment mechanism for moving the back shield between the secured position in which it is deployed for excavating a trench and an elevated position in which it is removed from the cutter body to enable the vertical trencher to be used for boring a vertical shaft.

According to a further feature of the present invention, the cutter body provides an ejection surface located within the housing and formed as a continuation of the upper surface of the ridge, the ejection surface being inclined so as to form an outwardly facing surface for ejecting cut rock and soil through the lateral aperture.

According to a further feature of the present invention, the housing provides an upwardly-diverging conical internal surface having an upper edge

adjacent to the lateral aperture, and wherein the ejection surface has a periphery shaped to lie adjacent to the conical internal surface such that rotation of the cutter body causes cut rock and soil to be driven upwards across the conical internal surface and out through the lateral aperture. According to a further feature of the present invention, the inner surface of the back shield is provided with at least one projecting ridge to encourage upward movement of cut rock and soil.

According to a further feature of the present invention, the at least one projecting ridge is implemented as a plurality of parallel inclined strips attached to the inner surface of the back shield, the strips being inclined so as to encourage upward movement of cut rock and soil moving in the direction of rotation ofthe cutter body.

According to a further feature of the present invention, the strips are formed from abrasion-resistant material. According to a further feature of the present invention, the strips are removable, the vertical trencher further comprising an adjustment mechanism for adjusting a clearance between the inner surface of the back shield and the cutter body.

According to a further feature ofthe present invention, the back shield is provided with at least one brush projecting towards the cutter body for reducing angular velocity of cut rock and soil.

According to a further feature of the present invention, there is also provided means for injecting a fluid adjacent to the ridge.

According to a further feature of the present invention, the fluid is directed in a stream against the direction of rotation ofthe cutter body.

According to a further feature of the present invention, the means for injecting a fluid is associated with the back shield.

According to a further feature of the present invention, the means for injecting a fluid is mounted within the cutter body and includes a plurality of perforations for releasing the fluid from the upper surface ofthe ridge.

According to a further feature ofthe present invention, the fluid is water.

According to a further feature of the present invention, the fluid is compressed air.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic side cross-sectional view of a vertical trencher, constructed and operative according to the teachings ofthe present invention, in use attached to a vehicle; FIG. 2A is a side view ofthe vertical trencher of Figure 1 ;

FIG. 2B is a front view ofthe vertical trencher of Figure 1; FIG. 2C is a top view ofthe vertical trencher of Figure 1; FIG. 3 is a schematic side cross-sectional view ofthe vertical trencher of Figure 1 showing a back shield lifted to enable vertical boring; FIG. 4A is a partially cross-sectional front view of a vertical trencher, constructed and operative according to the teachings of the present invention, showing a preferred embodiment of an ejection geometry;

FIG. 4B is a horizontal cross-section along the line A-A of Figure 4A; FIG. 5 is a perspective view of a preferred embodiment of a back shield for use in the vertical trencher of Figure 1 ;

FIG. 6A is a partial perspective view of a vertical trencher, constructed and operative according to the teachings of the present invention, showing an additional brush assembly;

FIG. 6B is a horizontal cross-sectional view through the vertical trencher of Figure 6A;

FIG. 7 A is a perspective view of a back shield of a vertical trencher, constructed and operative according to the teachings of the present invention, showing a first additional fluid injection system;

FIG. 7B is a front view ofthe back shield of Figure 7A;

FIG. 7C is a horizontal cross-sectional view through the back shield of Figure 7A;

FIG. 8 A is a partial perspective view of a cutter body of a vertical trencher, constmcted and operative according to the teachings of the present invention, showing a second additional fluid injection system;

FIG. 8B is a detailed front view ofthe cutter body of Figure 8A;

FIGS. 9A-9D are schematic cross-sectional views of trenches being cut by vertical trenchers constmcted and operative according to the teachings ofthe present invention, showing examples of altemative cutter bodies for excavating trenches of different shapes; and

FIG. 10 is a schematic side view of a vertical trenching vehicle, constmcted and operative according to the teachings of the present invention, which advances within the trench as it is cut.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is of a vertical trencher employing a vertical helical-shaped cutter body for simultaneously cutting and excavating a trench.

The principles and operation of vertical trenchers according to the present invention may be better understood with reference to the drawings and the accompanying description.

Referring now to the drawings, Figures 1 and 2 show a vertical trencher, generally designated 10, constmcted and operative according to the teachings of the present invention. Generally speaking, vertical trencher 10 includes a cutter body 12 having at least one helical ridge 14 attached to, and extending outwardly from, a generally cylindrical surface 16. Helical ridge 14 extends along cylindrical surface 16 to adjacent to the lower end 18 of cutter body 12. A set of cutting elements 20 are deployed in fixed relation to the outer edge of helical ridge 14 for cutting rock and soil adjacent to the cutter body 12. Vertical

trencher 10 also includes a housing 22 which surrounds cutter body 12 at its upper end so as to maintain cutter body 12 with its longitudinal central axis substantially vertical while allowing it to rotate. Housing 22 features a lateral aperture 24 for ejection of excavated material. A power transmission 26 is provided for employing power from some suitable power source to generate rotation of cutter body 12 within a bearing assembly 27 about its longitudinal central axis. A back shield 28, securable in fixed relation to housing 22, presents an inner surface 30 which extends substantially along and partially circumscribing cutter body 12. In accordance with a preferred embodiment of the present invention, helical ridge 14 is formed such that a rise angle at a point near the lower end of its upper surface is less than a rise angle at a point near the upper end of its upper surface. For the purpose of the description and claims, the rise angle is defined at each point of helical ridge 14 as the angle between a virtual plane parallel to the upper surface at that point and a virtual plane perpendicular to the longitudinal axis of cutter body 12. Preferably, the rise angle increases monotonically from the lower end to the upper end of cutter body 12, although it is not critical that the increase be either constant or uniform. The increasing rise angle maximizes the effectiveness of the cutter body since the accumulated soil from its lower regions rises at an increasing axial speed without slowing rotation. The graduated rise angle also provides increasing inter-ridge volume for the accumulating quantity of excavated material as it moves up the cutter body.

The operation of vertical trencher 10 is easily understood with reference to Figure 1 in which vertical trencher 10 is shown mounted on a vehicle 32 which is moving from left to right at velocity V (arrow) to cut a trench 34. Cutter body 12 rotates as the vertical trencher moves along, causing cutting elements 20 to grind against the adjacent soil and rock. Material cut by cutting elements 20 falls on to the upper surface of helical ridge 14, then being transported upwards at an increasing axial speed by the rotation of cutter body

12. The material is then ejected through lateral aperture 24 at speed, falling to the sides ofthe cut trench. Back shield 28 prevents fall-out of cut material from helical ridge 14 back into the cut trench so that a one-step continuous trenching operation results in a cleanly excavated trench. It will immediately be appreciated that the stmcture of the present invention provides a number of major advantages over the prior art systems. Specifically, many advantages of the present invention result from its use of cutter body 12 as the sole moving part. This simplifies the constmction and operation of the apparatus, thereby reducing cost. The cutter body has low contact area with the soil because of its vertical orientation. This also reduces the rotational power required.

The power supply itself for vertical trencher 10 is also structurally simple, reliable and cost effective. Vehicle 32, which may be a conventional tractor or the like, or purpose built, typically supplies rotational power to cutter body 12 through power transmission 28, for example, a hydraulic engine mounted on housing 22. The horizontal driving force for vertical trencher 10 is provided directly by vehicle 32. The platform of vehicle 32 to which vertical trencher 10 is attached preferably also features a vertical drive 36 for raising and lowering vertical trencher 10 for convenience of operation. Vertical trencher 10 is also highly effective at trenching continuously in all types of ground, including rock and frozen soil. Cutting elements 20 may be of any appropriate type including, but not limited to, grinding bits, teeth, blades and digging cups.

Cutter body 12 may feature a single helical ridge 14 as shown, or two, three or more similar ridges arranged as a multiple helix. The choice of number and pitch of helical ridges 14 depends primarily upon the size of trench to be excavated, as well as on the capabilities ofthe vehicle support platform and the expected ground conditions. The principles of the invention apply equally to a wide range of applications, from small scale trenching with widths and depths of a fraction of a meter, up to large scale infrastmcture projects.

Turning now additionally to Figure 3A, it should be noted that vertical trencher 10 preferably also includes a plurality of additional cutting elements 38, mounted at the lower end of cutter body 12 for cutting downwards. Typically, additional cutting elements 38 are distributed in a pattem over the lower surface and sides of a horizontal boring plate 40, attached to the lower end of cutter body 12. The distribution of cutting elements 20 on helical ridge 14 and additional cutting elements 38 on boring plate 40 is arranged such that, when cutter body 12 rotates, the entire length of cutter body 12 from housing 22 downwards presents an uninterrupted front of cutting elements. This allows vertical trencher 10 to advance horizontally, cutting the entire cross section of a trench as it advances.

Figure 3 illustrates a secondary use of vertical trencher 10 for boring vertical shafts. For this purpose, back shield 28 is hingedly attached to housing 22 at a hinge 42, and a deployment mechanism 44, typically including a hydraulic piston, is provided. Deployment mechanism 44 is effective to move back shield 28 between its normal position in which it is securely deployed for excavating a trench (Figure 1) and an elevated position in which it is removed from the cutter body (Figure 3). The raised position shown in Figure 3 enables rotating cutter body 12 to be lowered vertically by vertical drive 36 so as to bore a vertical shaft.

In this context, it should be appreciated that the mechanism for raising back shield 28 is optional, and is only required for vertical boring applications. For normal trenching operation, a relatively small vertical clearance of back shield 28 above the bottom of cutter body 12 allows vertical trencher 10 to be lowered by vertical drive 36 at an attack angle of about 45° while vehicle 32 is advancing until it reaches its intended trenching depth.

With reference now to Figures 4A and 4B, a preferred geometry of housing 22 and the contained portion of cutter body 12 for efficient ejection of excavated material will be described. It should be appreciated that the design of vertical trencher 10 inherently generates a highly advantageous distribution of

excavated material in the form of even piles along the sides of, and somewhat distanced from, the excavated trench. This distribution results, to a great extent, from the motion of cutter body 12. Firstly, the rapid rotation of cutter body 12 provides a high angular velocity of the cut material which, when released through lateral aperture 24, translates to a high tangential horizontal velocity. And secondly, the graduated rise angle of helical ridge 14 induces an increasing axial upwards velocity. These two factors alone ensure that, when the cut material is released, it is ejected upwards and outwards at sufficient velocity to clear the immediate vicinity of vertical trencher 10, to land to the side of the trench. However, this effect may be further enhanced by appropriate choice of the ejection geometry, as will now be described.

Specifically, housing 22 preferably features an upwardly-diverging conical intemal surface 48 having an upper edge adjacent to lateral aperture 24. The upper end of cutter body 12 forms a complementary-shaped ejection surface 46 within housing 22 which has an outer periphery shaped to lie adjacent to conical intemal surface 48. Ejection surface 46 is formed as a continuation of the upper surface of helical ridge 14, but is inclined so as to form an outwardly facing surface for ejecting cut rock and soil through lateral aperture 24. As a result of this stmcture, rotation of cutter body 12 causes cut rock and soil to be driven upwards across conical intemal surface 48 and out through lateral aperture 24, thereby imparting to it an additional radial velocity component. Furthermore, the increased diameter of cutter body 12 within housing 22 also increases the tangential velocity component of the ejected material. It should be noted that the word "lateral" in this context is used to denote sideways-facing relative to the direction of advance of vertical trencher 10. As a result, the position of lateral aperture 24 ensures that the cut material is directed away from the excavated trench to form tidy piles on the ground along the sides ofthe trench.

In a preferred embodiment, housing 22 features two opposite lateral apertures 24, each provided with a latchable cover (not shown). Selective closure of one or other cover allows cut material to be distributed exclusively to a selected side of the trench. In normal operation, both covers are opened to allow even distribution of cut material to each side ofthe trench.

Turning to Figures 5-8, a number of additional features of vertical trencher 10 will now be described. These features relate generally to enhancements for optimizing the vertical conveyor effect of helical ridge 14. This enables larger amounts of soil to be removed, thereby improving efficiency. It should be noted that these features are generally independent in implementation, while being complementary in effect, so that vertical trencher 10 may be constmcted with any combination of the features described herein. Furthermore, these features are generally modular in nature such that they may be installed or removed as required, depending upon the operating conditions and type of ground to be excavated.

Referring now to Figure 5, this shows a preferred design of back shield 24 in which the inner surface is provided with projecting ridges 50 to encourage upward movement of cut rock and soil. Projecting ridges 50 are typically implemented as a set of parallel strips attached to the inner surface of back shield 24, inclined so as to encourage upward movement of cut rock and soil moving in the direction of rotation of cutter body 12. The strips are made from abrasion-resistant material and serve additionally to protect back shield 24 from abrasion caused by the cut material.

The strips may be attached by welding. Preferably, the strips are attached by recessed bolts or the like so as to be readily replaceable when worn. Optionally, vertical trencher 10 may be adapted to operate with the strips in place or removed. This may be advantageous when vertical trencher 10 is to be used on various different types of ground. In this case, vertical trencher 10 includes an adjustment mechanism for adjusting the clearance between back

shield 24 and cutter body 12 as appropriate for the presence or absence of the strips.

Referring now to Figures 6A and 6B, these illustrate an additional optional feature in which back shield 24 is provided with at least one brush 52 projecting towards cutter body 12. Brush 52 serves to reduce the angular velocity of cut rock and soil, thereby improving the vertical conveyor effect of rotating helical ridge 14. Bmsh 52 additionally functions to clear cutting elements 20 of any debris which may have become lodged on them and which might otherwise impede the subsequent cutting action. Bmsh 52 is typically made out of tough polymer materials and is removable attached to either the inner or side surface of back shield 24. Optionally, a number of additional brushes (not shown) may be spaced around the inner surface of back shield 24. In some cases, it may even be preferable to line substantially the entire inner surface of back shield 24 with multiple bmshes or a single continuous brush- like element.

Figures 7 and 8 relate to two arrangements, to be used together or separately, for injection of a fluid adjacent to helical ridge 14. The injection of fluid, typically water or compressed air, may serve a number of different purposes. Firstly, if the fluid is directed in a stream against the direction of rotation of cutter body 12, it serves to reduce the angular velocity of the cut material in a manner similar to, or complementing, the action of bmsh 52 described above. Secondly, if injected between the cut material and the upper surface of helical ridge 14, the fluid forms a buffer to reduce friction between the cut material and helical ridge 14, thereby improving its vertical conveyor effect. Thirdly, if injected in an upward direction, the fluid may directly impart additional vertical momentum to the cut material. Fourthly, the fluid, especially in the case that water is used, may serve to cool cutter body 12 during operation. Fifthly, water injection serves to reduce dust generation during excavation, particularly important in built-up areas. Finally, depending on the composition of the ground to be excavated, adjustment of the proportion of

injected water can be used to adjust the consistency of cut soil to optimize the excavation process.

Turning now to Figures 7A-7C, these show an array of nozzles 54 mounted within back shield 24 for injecting a fluid. Nozzles 54 each communicate with a vertical main supply line 56 and are directed horizontally in a stream against the direction of rotation of cutter body 12. This geometry serves to reduce the angular velocity of the cut material. Additionally, because of the angle of helical ridge 14, the fluid tends to form a buffer to reduce friction between the cut material and helical ridge 14, and is largely deflected into an upward stream. Thus, by appropriate choice of operating fluid and supply pressure, this arrangement may be used to perform all ofthe above listed functions.

Figures 8A and 8B show a second arrangement in which arrays of nozzles or perforations 58 are provided for releasing a fluid from the upper surface of helical ridge 14. Nozzles 58 are supplied by an axial main supply line 60 within cutter body 12 which connects to a number of radial supply lines 62 within helical ridge 14. This arrangement directly provides a friction- reducing fluid cushion along the upper surface of helical ridge 14 and imparts additional vertical upward momentum to the cut material. This arrangement is also highly effective for direct cooling of cutter body 12.

Turning to Figures 9A-9C, it should be understood that the present invention readily allows excavation of trenches with a wide range of cross- sectional profiles which have proved difficult or impossible to produce by prior art techniques. Any cross-sectional profile required can be produced simply by designing an appropriate cutter body 12 with a helical ridge 14 having the corresponding extemal shape. The rate of change of the rise angle of helical ridge 14 may also be adjusted according to the proportions of soil accumulated along the height of cutter body 12.

By way of example only, Figures 9A-9D show four variant forms of the helical ridge of cutter body 12 for specific applications. It will be clear that

other shapes can easily be designed for any particular shape of trench required. Where one vertical trencher is to be used for multiple applications, all or part of cutter body 12 is made interchangeable. Preferably, only the lower part of the cutter body from below housing 22 is exchanged. Figure 9A shows vertical trencher 10 with cutter body 12 shaped to form a trench with outwardly-sloped sides. In this case, cutter body 12 features a helical ridge 63 formed such that cutting elements 20 lie substantially on a virtual, tmncated, upwardly-diverging cone.

Figure 9B shows vertical trencher 10 with cutter body 12 shaped to form a trench which is partially parallel-sided and partially outward-sloping. In this case, cutter body 12 features a helical ridge 64 formed such that cutting elements 20 lie substantially on a virtual cylinder along a first part of cutter body 12 and substantially on a virtual tmncated cone along a second part of cutter body 12. A further possibility enabled by vertical trencher 10 is excavation of an undercut trench. This is of particular value for providing large cross- sectional area with minimum dismption to features of the existing ground surface. An undercut trench can be simply achieved by constmcting cutter body 12 with a helical ridge formed such that a circle traveled by a group of cutting elements closer to the lower end of cutter body 12 when it rotates has a diameter greater than that of a circle traveled by a group of cutting elements further from the lower end. In the case of an undercut trench, a larger initial channel is formed as vertical trencher 10 is lowered until it reaches its intended trenching depth.

A first example of an undercut trench is shown in Figure 9C in which cutter body 12 is provided with a helical ridge 66 formed such that cutting elements 20 lie substantially on a virtual, tmncated, upwardly-converging cone. This design produces a trench with inwardly sloping sides.

A second example is shown in Figure 9D in which cutter body 12 is provided with a helical ridge 68 formed such that cutting elements 20 lie substantially on a virtual cylinder of a first diameter along a lower part 70, and

substantially on a cylinder of a smaller second diameter along an upper part 72.

Vertical trencher 10 equipped with this design excavates a trench with a cross- section approximating to an inverted T-shape.

Finally, with reference to Figure 10, a vertical trenching vehicle, generally designated 74 will now be described. Vertical trenching vehicle 74 is designed to advance under remote control within a trench as it is cut, and is therefore particularly valuable for use in hostile environments or in warfare.

Vertical trenching vehicle 74 features a front-mounted vertical trencher 76 similar to vertical trencher 10 described above, but with an additional guide element 78 for following the ground surface in front of vertical trencher 76. Vertical trencher 76 is attached to vehicle 74 through a vertical drive 80. Vehicle 76 is itself a narrow tracked vehicle which is remotely controllable by means of a remote control panel 82.

It will be appreciated that the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the spirit and the scope ofthe present invention.