TRENCHING APPARATUS AND A METHOD OF TRENCHING

Abstract

A trenching apparatus, includes a body moveable on the ground surface, a ground engagement boom associated with the body, the boom being movable when engaged with the ground to form a trench; a lifting system arranged to control and configure the ground engagement boom so as to enter the ground; in which the ground engaging boom is an endless chain ground-engaging boom, including a main body and a chain tensioner coupled to the main body at or close to the upper end thereof.

Description

The present invention relates to trenching apparatus and a method of trenching.

There are many known trenching machines for digging trenches in soil by use of a prime mover such as a crawler tractor, or a conventional tractor pulling a trailer, in which a cutting device is positioned in the trench on a boom. The main examples are a cutting rotor rotating about an axis transverse to the trench, known as a ripper cutter, or one or more cutting rotors rotating about an axis aligned along the length of the boom, generally known as a milling cutter, or a cutting device having an elongate endless support means carrying a plurality of cutting elements and trained along upper and lower runs on the boom, known as a chain cutter. Where a cutting rotor is used this is mounted on the distal end of a boom projecting forwardly and downwardly from the prime mover, relative to the direction of digging of the trench. Where a chain cutter is used, this is normally mounted on a boom extending downwardly and rearwardly from the prime mover relative to the direction of cutting of the trench.

Examples of such trenching machines are found in, for example, CH-A-239498, WO-A-95/13433, WO-A-03/044286, U.S. Pat. No. 6,467,201, EP-A-080,802, CN-A-2010 50077, CN-A-2517789, GB-A-786,829, WO-A-2007/035,400, JP-H04169696, U.S. Pat. No. 5,540,006, GB-A-972,208, GB-A-848,277, GB-A-735,116, U.S. Pat. No. 6,470,607, GB-A-1,118,907, GB-A-2,088,930, GB-A-155,766, GB-A-2,551,419 and WO-A-2012/123,622.

There are also known types of trenchers that are arranged to utilize a vertical cutting boom. Examples include trenchers provided by Soletanche Bachy. In particular, one example of equipment provided by Soletanche Bachy suitable for deep trenching is known as the TM-80.

One known system for trenching is provided by Hayward Baker Inc and is known as Trench cutting and Remixing Deep (TRD) Soil Mix Walls. The system is described at https://www.haywardbaker.com/uploads/solutions-techniques/trd-soil-mix-walls/Hayward-Baker-TRD-Brochure.pdf. As explained in this reference, the system utilizes a sectional vertical cutter made of cutter post sections that are assembled in situ.

In some situations, improvements in relation to deep trenchers are required.

According to a first aspect of the present invention there is provided a trenching apparatus, comprising: a trencher body moveable on the ground surface, and a ground engagement boom associated with the trencher body;

lifting means arranged to control and configure the ground engagement boom so as to enter the ground in a substantially vertical configuration;

selectively configurable support legs moveable between a first closed position and a second deployed configuration in which the legs are extended in a direction away from the body of the apparatus to provide support to the trenching apparatus when the boom is configured vertically and not engaged with the ground.

In an embodiment, the boom is movable in a substantially vertical plane when engaged with an end surface of the trench. In an embodiment, the trencher body is moveable on the ground surface above the level of the trench.

In contrast to known methods the present invention utilizes support legs to enable a simple vertical angle of attack for a ground engaging boom in a trenching machine. Compared for example to the TRD Soil Mix wall method of Hayward Baker this provides significant advantages. Importantly there is no need for a complex method of modular boom construction so as to enable the base unit that supports and controls the cutter to maintain a low profile. Due to the stability provided by the support legs, it is no longer necessary to ensure that the base unit has a low profile.

In an embodiment, the lifting means is arranged to control and configure the ground engagement boom so as to enter the ground from above.

In an embodiment, the ground engagement boom is a cutting boom for cutting earthen material from the end surface of the trench.

In an embodiment, the cutting boom is an endless chain cutting boom.

In an embodiment, the ground engagement boom is a mixing boom for mixing agent such as (but not limited to) cement or bentonite with earth within the trench.

In an embodiment, the longitudinal length of the ground engagement boom is between 10 and 20 metres.

In an embodiment, the ground engagement boom weighs between 10 and 20 tonnes, and preferably weighs up to 15 tonnes.

In an embodiment, the support legs are pivotally mounted to the body so as to be selectively reconfigurable between the closed and extended configurations.

In an embodiment, the support legs are telescopically mounted so as to be slidably configurable between the first closed and second deployed configuration.

In an embodiment, the legs have a first longitudinal section and a second longitudinal component configured telescopically with respect to the first longitudinal section, and wherein the first longitudinal section is coupled to the body of the prime mover and when extended in the second deployed configuration the second longitudinal component slides out of the first longitudinal component.

In an embodiment, the second longitudinal component has at its distal end a downwardly deployable longitudinal support member.

In an embodiment, each of the downwardly deployable longitudinal support members has a foot removably fixable thereto, for engagement with the ground.

In an embodiment, when in the deployed configuration, the support legs increase the overall envelope of the footprint of the trenching apparatus by at least 150%, and preferably 200%, as compared to when the legs are in the first closed configuration.

In an embodiment, the trenching apparatus comprises tracks for moving the trenching apparatus when the legs are in the first closed configuration.

According to a second aspect of the present invention, there is provided a method of trenching, using trenching apparatus having a trencher body moveable on the ground, and a ground engagement boom associated with the trencher body, the boom being movable in a substantially vertical plane, and lifting means arranged to control and configure the ground engagement boom so as to enter the ground from above in a substantially vertical configuration the method comprising;

extending the legs in a direction away from the body of the apparatus to provide support to the trenching apparatus when the boom is configured vertically and not engaged with the ground.

In an embodiment, the lifting means is arranged to control and configure the ground engagement boom so as to enter the ground from above in a substantially vertical configuration.

According to a third aspect of the present invention there is provided a trenching apparatus, comprising: a body moveable on the ground surface, and a ground engagement boom associated with the body, the boom being movable when engaged with the ground to form a trench; lifting means arranged to control and configure the ground engagement boom so as to enter the ground and to configure the boom to an inclined orientation in which the boom extends at least partially over the body of the apparatus;

a protection chute provided on the body to protect the body from material that falls from the boom, when the boom is in the inclined orientation.

A trenching apparatus is provided that includes a chute positioned to ensure that material that falls from the boom when in an inclined position does not fall onto the apparatus thereby damaging it. Conventionally to perform repairs or cleaning on a ground engaging boom whilst limiting risk of damage to the apparatus, it has been necessary to remove the boom from the apparatus and thereby perform the necessary work at a remote or separate location. In the present trenching apparatus the boom is positioned in an inclined position which can be substantially within the footprint of the apparatus during maintenance and/or cleaning.

In an embodiment, the ground engagement boom is a cutting boom for cutting earthen material from the end surface of the trench.

In an embodiment, the cutting boom is an endless chain cutting boom.

In an embodiment, the ground engagement boom is a mixing boom for mixing cement mixing agent such as (but not limited to) cement or bentonite with earth within the trench.

In an embodiment, the longitudinal length of the ground engagement boom is between 10 and 20 metres.

In an embodiment, the ground engagement boom weighs between 10 and 20 tonnes, and preferably weighs up to 15 tonnes.

In an embodiment, the chute is sized to receive the entire part of the boom that extends over the body of the trenching apparatus when the ground engagement boom is in the inclined orientation.

In an embodiment, the chute is supported by arms fixed to the body of the trenching apparatus.

In an embodiment, the chute is orientated at an angle to the horizontal plane of the trenching apparatus.

In an embodiment, the angle is between 10 and 45 degrees.

In an embodiment, the trencher comprises at its end, e.g. its rear end a boom engagement cage for controlling the depth in the ground or height relative thereto at which the boom is positioned.

In an embodiment, the boom engagement cage comprises a continuation chute which when the boom is in the inclined orientation forms a continuous channel with the protection chute.

In an embodiment, the trenching apparatus comprises water or fluid outlets such as jets to direct and cause fluid to flow along the protection chute when the boom is arranged therein.

According to a fourth aspect of the present invention, there is provided a method of trenching which could include trench digging or mixing, using a trenching apparatus comprising a body moveable on the ground surface, and a ground engagement boom associated with the body, the boom being movable when engaged with the ground to form a trench; lifting means arranged to control and configure the ground engagement boom so as to enter the ground and to configure the boom to an inclined orientation in which the boom extends at least partially over the body of the apparatus, the method comprising: providing a protection chute on the body to protect the body and/or the apparatus from material that falls from the boom, when the boom is in the inclined orientation.

According to a fifth aspect of the present invention there is provided a trenching apparatus, comprising: a body moveable on the ground surface, a ground engagement boom associated with the body, wherein the ground engagement boom comprises a chain for interacting with earth in use; lifting means arranged to control and configure the ground engagement boom so as to enter the ground and to configure the boom to an inclined orientation in which the boom extends at least partially over the body; a winch provided on the body to engage with the chain of the ground engagement boom when in the inclined orientation.

In an embodiment, the ground engagement boom is movable in a substantially vertical plane.

There is provided a trenching apparatus in which a winch for changing the chain on a chain cutting or mixing boom is provided on the trenching apparatus (or body thereof) itself, and not on the boom itself. Positioning of the winch in the present system on the body of the machine or apparatus itself enables and ensures that a chain can easily be changed on the ground engaging boom irrespective of the size of the ground engaging boom and the associated size and weight of the cutting chain itself.

In an embodiment, the ground engagement boom is a cutting boom for cutting earthen material from the end surface of the trench.

In an embodiment, the ground engagement boom is a mixing boom for mixing an agent such as (but not limited to) cement with earth within the trench.

In an embodiment, the longitudinal length of the ground engagement boom is between 10 and 20 metres.

In an embodiment, the ground engagement boom weighs between 10 and 20 tonnes, and preferably weighs up to 15 tonnes.

In an embodiment, the apparatus comprises a protection chute provided on the body of the trencher to protect the body from material that falls from the boom and to support the boom in the inclined orientation.

In an embodiment, the apparatus comprises a spool with a cable having an end connector for engagement with the end of a replacement chain to be put on the ground engagement boom when in the inclined orientation.

In an embodiment, the cable is routed via a shoulder on the distal end of the ground engagement boom to enable substantially the entire length of the ground engagement boom to be surrounded by the replacement chain.

In an embodiment, the shoulder comprises a pulley.

In an embodiment, the shoulder is slidably mounted on the body of the boom so that it can be moved from the top end to the distal end at which end it can be used to change the chain on the boom.

A shoulder is provided slidably mounted on the boom for housing a pulley or routing point for directing the cable of the winch used when changing the chain on the boom. This means that the shoulder can be selectively repositioned at appropriate times so that it is placed in position for changing the chain only when needed and at other times can be appropriately positioned or stowed so as not to cause any possible obstruction during normal use of the trenching apparatus.

In an embodiment, in the inclined orientation, the ground engagement boom is at an angle of between 10 and 45 degrees to the body of the trencher.

According to a sixth aspect of the present invention, there is provided a method of putting a chain on to the ground engagement boom of a trencher, wherein the trencher comprises a body that is moveable on the ground surface and a ground engagement boom associated with the body, and lifting means arranged to control and configure the ground engagement boom so as to enter the ground from above and to configure the boom to an inclined orientation in which the boom extends at least partially over the body of the trencher, the method comprising, orienting the boom in the inclined orientation; engaging one of the ends of the chain with a cable of a winch provided on the body of the trencher; activating the winch to pull the chain onto the ground engagement boom.

In an embodiment, the ground engagement boom is movable in a substantially vertical plane.

There is provided a trenching method in which a winch for putting a chain onto a boom, or changing the chain on a chain cutting or mixing boom, is provided on the trenching apparatus (or body thereof) itself, and not on the boom itself. Positioning of the winch in the present system on the body of the machine or apparatus itself enables and ensures that a chain can easily be changed on the ground engaging boom irrespective of the size of the ground engaging boom and the associated size and weight of the cutting chain itself.

In an embodiment, the cable is routed via a shoulder on the distal end of the ground engagement boom to enable substantially the entire length of the ground engagement boom to be surrounded by the chain.

The method can include moving e.g. slidably moving a shoulder or pulley mounted on the boom for directing the cable of the winch used when changing the chain on the boom. This means that the shoulder can be selectively repositioned at appropriate times so that it is placed in position for changing the chain only when needed and at other times can be appropriately positioned or stowed so as not to cause any possible obstruction during normal use of the trenching apparatus.

According to a seventh aspect of the present invention there is provided a trenching apparatus, comprising: a body moveable on the ground surface; a ground engagement boom associated with the body, the boom being movable when engaged with the ground to form a trench; lifting means arranged to control and configure the ground engagement boom for engagement with the ground; in which the ground engaging boom is an endless chain ground-engaging boom, comprising a main body and a chain tensioner coupled to the main body at the upper end thereof.

By providing the chain tensioning mechanism on the ground engaging boom and particularly at or close to the top of the ground engaging boom it is possible to ensure that the tensioning mechanism is less likely itself to go below the surface of the ground. Thus it can remain relatively free of material from the ground.

Advantageously, the tensioning mechanism is remote from the lower end of the ground engaging boom which will be interacting on a more regular basis with the earth formation being trenched. It is less likely therefore to be damaged by impact on use.

Second, the tensioning mechanism is kept away from the section of the boom that is likely to be most engaged with the mixing agent such as (but not limited to) cement or bentonite mixing agent, such as cement or bentonite, when used as a mixing mechanism. It is known and conventional to provide such tensioning mechanisms at the distal end of a ground engaging boom but it has been recognised that by providing the tensioning mechanism at the top end of the cutting boom the risk from the mixing agent being used setting and thereby possibly rendering the tensioning mechanism ineffective, is significantly reduced.

In an embodiment the lifting means is arranged to configure and control the ground engaging boom so as to enter the ground in a substantially vertical configuration.

In an embodiment, the chain tensioner comprises an arm pivotally coupled to the main body of the ground engagement boom.

In an embodiment, the arm is hydraulically controllable to move between a first closed position in which its distal end is close to the main body and a second deployed position in which its distal end is moved away from the main body to tension a chain arranged on the ground engagement boom.

In an embodiment, the apparatus comprises an endless chain mounted on the main body.

In an embodiment, the chain is a cutting or mixing chain.

In an embodiment, the ground engagement boom weighs between 10 and 20 tonnes, and preferably weighs up to 15 tonnes.

In an embodiment, the arm comprises a pinion at its distal end to gearingly engage with the chain as it is driven around the ground engagement boom.

In an embodiment, the arm is between 1 and 3 metres long.

In an embodiment, the arm has a plurality of hydraulic drive cylinders provided to hydraulically control the position of the arm with respect to the body.

In an embodiment, the chain tensioner is positioned with respect to the main body such that when the ground engaging boom is fully engaged with the ground the chain tensioner is above ground surface.

According to a eighth aspect of the present invention, there is provided an endless chain ground-engaging boom, in which the ground engaging boom, comprises a main body and a chain tensioner coupled to the main body at or close to the upper end thereof.

As above with the trenching apparatus according to the first aspect of the present invention, by providing the chain tensioning mechanism on the ground engaging boom and particularly at or close to the top of the ground engaging boom it is possible to ensure that the tensioning mechanism is less likely itself to go below the surface of the ground. Thus it can remain relatively free of material from the ground. Also the tensioning mechanism is kept away from the section of the boom that is likely to be most engaged with the mixing agent, such as cement or bentonite, mixing agent such as (but not limited to) cement or bentonite when used as a mixing mechanism.

In an embodiment, the chain tensioner comprises an arm pivotally coupled to the main body of the ground engagement boom.

In an embodiment, the arm is hydraulically controllable to move between a first closed position in which its distal end is close to the main body and a second deployed position in which its distal end is moved away from the main body to tension a chain arranged on the ground engagement boom.

In an embodiment, the ground engaging boom comprises an endless chain mounted on the main body.

In an embodiment, the chain is a cutting or mixing chain.

In an embodiment, the ground engagement boom weighs between 10 and 20 tonnes, and preferably weighs up to 15 tonnes.

In an embodiment, the arm comprises a pinion at its distal end to gearingly engage with the chain as it is driven around the ground engagement boom.

In an embodiment, the arm is between 1 and 3 metres long.

In an embodiment, the arm has a plurality of hydraulic drive cylinders provided to hydraulically control the position of the arm with respect to the body.

In an embodiment, the chain tensioner is positioned with respect to the main body such that when the ground engaging boom is fully engaged with the ground the chain tensioner is above ground surface.

According to a ninth aspect of the present invention, there is provided a method of varying tension in the chain of a ground-engaging boom of trenching apparatus, in which the trenching apparatus comprises a body moveable on the ground surface and a ground engagement boom associated with the body, the boom being movable when engaged with the ground to form a trench, the method comprising: controlling the tension of the chain using a chain tensioner coupled to the main body of the ground engaging boom at the upper end thereof.

According to a tenth aspect of the present invention there is provided a trenching apparatus, comprising: a body moveable on the ground surface, and a ground engagement boom associated with the body, the boom being movable when engaged with the ground to form a trench; a main power supply to provide power to the apparatus; lifting means, powered by the main power supply, arranged to control and configure the ground engagement boom so as to enter the ground; an auxiliary power supply arranged to provide power to the lifting means in the event of failure of the main power supply

In an embodiment, the lifting means is arranged to control and configure the ground engagement boom so as to enter the ground from above in a substantially vertical orientation.

There is provided a trenching apparatus including an auxiliary power supply which can be used to provide power to the apparatus in the event of failure of the main power supply of the apparatus. This is important as it enables power to be provided in situations that might be time critical such as when there is a power supply failure during trenching. This is particularly the case when trenching involves the use of some setting material, such as cement or bentonite, to perform soil or ground mixing. In these situations if there is a failure of the main apparatus power supply the ground engaging boom can be left for extended periods of time within the environment of the recently mixed setting material. This can then cause the material to harden and set around the ground engaging boom which can then be impossible, or economically unfeasible, to retrieve in a reusable way from the ground.

The inventors have recognised that use of an auxiliary power supply will solve this technical problem. Forming a trench can of course include the process of actually digging the trench so as to leave a an empty trench in the ground, or indeed the mixing of a material, such as but not limited to, cement with soil in so as to form a trench of mixed soil and material.

In an embodiment, the lifting means is arranged to selectively reconfigure the boom from the substantially vertical orientation to an inclined orientation in which the boom extends at least partially over the body of the apparatus

In an embodiment, the ground engagement boom is a cutting boom for cutting earthen material from the end surface of the trench.

In an embodiment, the ground engaging boom is an endless chain cutting boom.

In an embodiment, the ground engagement boom is a mixing boom for mixing cement with earth within the trench. In an alternative, instead of cement another mixing agent could be used. In other words the boom is a ground engagement boom for mixing an agent in general and not limited to cement.

In an embodiment, the longitudinal length of the ground engagement boom is between 10 and 20 metres.

In an embodiment, the ground engagement boom weighs between 10 and 20 tonnes, and preferably weighs up to 15 tonnes.

In an embodiment, the apparatus comprises a protection chute, to protect the body of the apparatus from material that falls from the boom.

In an embodiment, the chute is sized to receive the entire part of the boom that extends over the body of the trenching apparatus when the ground engagement boom is an inclined orientation.

In an embodiment, the auxiliary power supply is integrated with the body of the apparatus.

This embodiment provides the advantage that no separate components are required whilst still providing the effective redundancy of power supply which is useful in some specific situations as described above. The auxiliary power supply will be a separate power circuit and pump but can be built into or permanently coupled to the housing of the trenching apparatus. The auxiliary power supply may be a hydraulic pump having an inlet conduit and an outlet conduit with connectors for connecting the inlet and outlet conduits to hydraulic power lines of the apparatus that during power supply from the main power supply are connected to hydraulic conduits of the main power supply.

In an embodiment, the auxiliary power supply is an independent separate unit connectable to the apparatus in the event of failure of the main power supply. This is advantageous as it can be supplied or provided (or replaced) separately from the trenching apparatus itself. Again, as with the integrated auxiliary power supply, the separate auxiliary power supply may be a hydraulic pump having an inlet conduit and an outlet conduit with connectors for connecting the inlet and outlet conduits to hydraulic power lines of the apparatus that during power supply from the main power supply are connected to hydraulic conduits of the main power supply.

In an embodiment, the main power supply is a hydraulic pump arranged to pump hydraulic fluid along hydraulic power lines to operate the lifting means.

In an embodiment, the auxiliary power supply is a hydraulic pump arranged to pump hydraulic fluid along the hydraulic power lines when there is a failure of the main power supply to the boom.

In an embodiment, the hydraulic pump of the auxiliary power supply has an inlet conduit and an outlet conduit with connectors for connecting the inlet and outlet conduits to the hydraulic power lines.

According to a eleventh aspect of the present invention, there is provided a method of operating a trenching apparatus, wherein the apparatus comprises a body moveable on the ground surface above the level of a trench, and a ground engagement boom associated with the body, the boom being movable when engaged with the trench, a main power supply to provide power to the apparatus and lifting means, powered by the main power supply to control the ground engagement boom so as to enter the ground, and an auxiliary power supply, the method comprising: in the event of failure of the main power supply providing power to the lifting means from the auxiliary power supply.

In an embodiment, the lifting means is arranged to control and configure the ground engagement boom so as to enter the ground from above in a substantially vertical orientation.

There is provided a trenching method including an auxiliary power supply which can be used to provide power to the apparatus in the event of failure of the main power supply of the apparatus. This is important as it enables power to be provided in situations that might be time critical such as when there is a power supply failure during trenching. This is particularly the case when trenching involves the use of some setting material, such as cement or bentonite, to perform soil or ground mixing. In these situations if there is a failure of the main apparatus power supply the ground engaging boom can be left for extended periods of time within the environment of the recently mixed setting material. This can then cause the material to harden and set around the ground engaging boom which can then be impossible, or economically unfeasible, to retrieve in a reusable way from the ground.

The inventors have recognised that a method of using an auxiliary power supply will solve this technical problem.

In an embodiment, the main and auxiliary power supplies comprise hydraulic power supplies and the method comprises, in the in the event of failure of the main power supply, disconnecting the main hydraulic power supply from the apparatus and connecting hydraulic fluid conduits of the auxiliary power supply to the apparatus to thereby power the apparatus.

In an embodiment, the auxiliary power supply is integrated with the body of the apparatus.

In an embodiment, the auxiliary power supply is an independent separate unit connectable to the apparatus in the event of failure of the main power supply.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

FIGS. 1 and 2 are a schematic views of a known trenching apparatus;

FIG. 3 is a schematic view of component parts of a vertical chain cutting trencher;

FIG. 4 is a schematic view of the trencher FIG. 3, assembled prior to engagement of the ground engaging boom with the ground;

FIG. 5 is a schematic view of the trencher in FIG. 4 with the ground engaging boom at full depth in the ground;

FIG. 6 is a schematic view of the trencher machine on a trailer arriving at a trenching site;

FIG. 7 is a schematic view of the machine of FIG. 6 with support legs extended;

FIG. 8 is a schematic view of the machine of FIG. 7 with support legs extended and feet lowered;

FIG. 9 is a schematic view of the machine of FIG. 8 with tracks provided on the machine;

FIG. 9a is a schematic view of the machine of FIG. 9, with the trailer removed;

FIG. 10 is a schematic view of the machine of FIG. 9A with the legs in a closed position;

FIG. 11 is a schematic view of the machine of FIG. 10 with hydraulic reels provided thereon;

FIG. 12 is a view of the machine of FIG. 11 with a protective chute provided thereon;

FIG. 13 is a view of the machine of FIG. 12, assembled with the ground engaging boom prior to engagement of the ground engaging boom with the ground and prior to connection of the boom to hydraulic lines;

FIG. 14 is a view of the machine of FIG. 13 with the ground engaging boom lowered for connection of chain drive services such as hydraulic lines;

FIG. 14A is a view of the machine of FIG. 14 with the ground engaging boom partly submerged, i.e. at an intermediate trenching depth;

FIG. 15 is a view of the machine of FIG. 14A with the ground engaging boom at full trenching depth;

FIG. 16 is a detailed view of the machine including the ground engaging boom cradle;

FIG. 17 is a schematic view of the machine showing the boom cradle open;

FIG. 18 is a schematic view of the machine with the boom cradle open without a cutting boom assembled therein including a chute extension;

FIG. 19 is a representation of the machine with a ground engaging boom in position but no cutting chain installed;

FIG. 20 is a view of a close-up of the top of the ground engaging boom.

FIG. 21 is a schematic view of a machine including an auxiliary power supply; and

FIG. 22 is a view of a trenching machine including an auxiliary power supply unit.

FIGS. 1 and 2 show schematic views of a known trenching apparatus. It is a trench cutting apparatus as described in EP-A-0080802, for cutting a trench in rock.

Two crawler chassis 3 and 5 are coupled together by tie bars 7, the rear crawler 3 having a cutting boom 2 pivotally mounted at 6. The forward end of the boom 2 has a cutting boom 2 pivotally mounted at 6. The forward end of the boom 2 has a cutting rotor 7 driven in rotation about an axis transverse to the trench to be cut. The distal end of the boom 2 is coupled to the forward crawler 5 by a telescopic control arm 8 comprising a hydraulic ram and telescopically extending sleeves coupled to the boom 2 by a coupling 9. In operation the machine is positioned to straddle the line of the trench and the boom 2 is lowered into contact with the ground. The cutting head 7 is rotated while applying force by way of the hydraulic ram 8 to move the cutting head 7 on an arcuate path downwardly and to remove rock from the forward end of the trench. An endless chain conveyor 4 is positioned behind the cutting rotor 7 and the spoil is carried away. The boom 2 is then raised and the machine moved forward and the process is repeated.

Although the trenching apparatus described above works well, there is a need for a trenching apparatus that is able to cut a deeper trench. This has application in fields such as the building of trenches in riverbanks for example. Such trenches may be built for the purpose of the creation of water-impermeable barriers or for strengthening the structure of the ground, for example, by mixing earth from the trench region with cement, thereby forming a hardened vertical wall within the ground where the trench is formed. As used herein, the term trenching includes the use of ground engaging members both for cutting trenches in the ground and also for mixing of the earth or material within a trench as might be done for example where cement or some other material is mixed with soil to control various physical properties of the ground.

Accordingly as used herein, the term “ground engaging member” or “ground engaging boom” is to be understood as relating to a member that generally engages with the ground which could include either cutting or forming a trench within the ground or mixing cement or other mixing material such as bentonite, within a trench with the soil in the trench. Indeed considering these two specific examples, either could be referred to as “trenching” and in both cases a trench is formed.

FIG. 3 shows a disassembled schematic view of a trenching apparatus for such purpose.

The apparatus includes a trenching machine 10 arranged to receive a ground engaging boom 12 which may be a cutting boom and importantly which can be inserted into the ground in a vertical orientation. Such a vertical cutting boom trenching machine has particular advantage in that the ground engaging boom can be inserted into the ground effectively within the footprint of the machine itself, i.e. without requiring space outside of the footprint for a cutting arc.

Vertical insertion typically means that the movement of the ground engaging boom is translationally downwards rather than, say pivoted but it need not require that the boom extends and enters the ground at precisely 90 degrees to the ground surface. Typically an angle of attack of the ground engaging boom, i.e. the angle that the longitudinal axis of the ground engaging boom makes to the surface of the ground, will be ±10% to the vertical. More preferably the angle of attack is ±5 degrees to the vertical and most preferably it is vertical.

In the examples shown, the ground engaging boom 12 includes a cutting chain 14 which has the function both of cutting a trench and, in this example, also due to the features and elements 16 on the chain providing a mixing function, for mixing an agent such as (but not limited to) cement that may be provided in the trench with the surrounding earth. As explained above such a process has the advantage in that a barrier of reduced porosity or water permeability can be created which in areas such as those close to river or canal banks is desired.

The trenching apparatus 10 includes tracks 18 and jack legs 20, which provide a significant technical function to this specific type of trenching machine in accordance with a disclosed embodiment, and as will be described in greater detail below.

A protective chute 22 is provided arranged, in use, and as will be described in greater detail below, to couple with a chute section 24 provided as part of a boom cradle 26. The protection chute 22 may also be used for other functions such as washing the ground engaging boom when it is not engaged with the ground.

An engine and control module 28 is provided in which a driver or operator may sit to control the apparatus 10 in use.

Hydraulic reels 30 are provided which are arranged on the main body 34 of the machine 10, arranged to be driven by a main hydraulic power supply (not shown) within the main body 34. The main hydraulic power supply is also arranged to provide power to drive the movement of the ground engaging boom 12 by powering a pinion 40 (see FIG. 18), to be described below. The main hydraulic power supply may typically be a hydraulic pump having an inlet and an outlet and being arranged and configured to pump hydraulic fluid to provide power as required. Any suitable type of hydraulic pump can be used, as will be known to the skilled person.

The hydraulic reels 30 are provided, arranged to receive hydraulic fluid from the main hydraulic power supply and thereby to drive the cutting chain 14. When the machine is assembled and operating in trenching mode, the hydraulic lines 30 are coupled to an upper end 36 of the ground engaging boom 12, as will be descried in greater detail below. The ground engaging boom 12 is provided with an integrated rack 38 arranged in use to interact and be driven by the pinion 40 (see FIG. 18). The pinion 40 is driven, in most cases by the main hydraulic power supply too and thereby controls the vertical position of the ground engaging boom 12 with respect to the cradle 26, and hence to the ground too.

FIG. 4 shows a schematic view of the trenching machine 10 arranged in position ready for operation. In the example of FIG. 4, the ground engaging boom 12 is ready for engagement with the earth, but has not yet been driven into an engaged position. Hydraulic power is provided which drives the ground engaging boom down into the ground. As can be seen, the elements 14 (teeth in this case) at the lower end of the cutting boom 12 are close to the ground, but have not yet broken the surface. The angle of attack of the ground engaging boom 12 is almost exactly 90 degrees in the example shown. In addition due to the manner in which the rack and pinion mechanism forming part of the cradle 26 operates, the driving force will be in line with the boom and thus vertically downwards.

The height of the boom 12 can be as required for the particular job, which could involve cutting and/or mixing a material in a trench, but preferably is at least 10 metres long and more preferably between 15 and 20 metres long. In particular, trenching operations, it is desired that the boom is at least 15 metres long. In such cases, the mass of the boom, including the cutting chain, in use, could be up to 30,000 KG. A plurality of stabilising legs 20 are provided which function to stabilise the machine itself while, or during, the lowering of the cutting or mixing boom 12 into the surface of the soil takes place.

It has been recognised that in the example of vertical or near vertical impact trenching machines such as that shown in FIGS. 3 and 4, a stability providing mechanism flexibly or selectively reconfigurably connected to the housing 34 of the machine 10 provides a convenient and advantageous mechanism for ensuring stability of the machine during the lowering of the trenching/mixing boom 12 into the surface of the soil. It has been recognised that although the centre of mass of the machine will still be positioned above the footprint of the machine the height of the boom itself can generate a lack of stability, particularly if, say the environment is one in which high winds can be present.

Although in known systems there is no suggestion or reason why stability providing legs should be included (indeed it has previously been thought that the boom itself when engaged with the ground is a source of stability), it has now been recognised that they can provide a significant advantage in terms of accounting for atmospheric conditions and their effect on the machine's stability.

Referring to FIGS. 7 to 9 and 9A, the stability legs 20 comprise a proximal end 42 coupled to the machine and a distal end 44 from which a vertically downwardly depending longitudinal support member 46 is arranged to extend. The legs 20 are selectively reconfigurable such that they can be folded (or telescopically collapsed) into close alignment with the machine 10 as shown in, say, FIG. 11 or 12, or provided in an extended configuration as shown in any of, say, FIGS. 7 to 9 and 9A. In such a configuration they are not in close alignment with the body or can be said to extend away from a central longitudinal axis of the machine thereby increasing its stability. In extending away from a central longitudinal axis of the machine the legs could be directionally square on to the axis or at some other angle whilst still extending away from it and thereby extending the width. In one embodiment, the legs are normal to the axis or at an angle of less than ±45 degrees to the normal to the longitudinal axis. The length of the legs when deployed can be variable and selected to provide the required stability.

Feet 48 are provided as separate and connectable components which are provided with an engagement region 50 for connection to the distal end of the downwardly depending longitudinal support member 46. In this examples, the downwardly depending longitudinal support members 46 are arranged to extend telescopically from an upper region 49. As will be explained below, the legs 20 are used during the process of erection of the ground engaging boom 12 and lowering of the boom into the surface of the ground. Once the boom 12 has been lowered to a desired depth, the requirement for the extension of the legs 20 into the extended configuration as shown in FIG. 7 is reduced. The boom 12 inserted into the ground, itself provides a stabilising function and therefore the legs 20 can be collapsed or retracted or removed.

As explained above, in one configuration, the legs may be pivotably connected to the machine 10 at the proximal end 42. In an alternative embodiment, they may be removably and fixedly connected. In the example of FIG. 7, the shaping of the legs 20 can be seen. In particular, as will be appreciated, there is an overlap region along the central longitudinal axis of the machine 10, wherein the legs in each of the front and rear pairs overlap with each other. Looking again at FIG. 9, at the rear of the machine 10 there is a first pair of legs 52 and at the front of the machine there is a forward pair of legs 54.

Each of the legs has a length that extends across the width of the body of the machine such that looking at the first pair of legs 52 it can be seen that the longitudinal body of the leg 56 extends under the machine and to the other transverse side. Still looking at the rear pair of legs 52, the end 58 of the second leg of the pair (the foot of which cannot be seen in FIG. 9) can be seen extending towards the opposite transverse side of the machine 10. Thus, there is overlap of the pair of legs in the region of the body of the machine 10 as indicated by the arrow A. This ensures that the legs, when extended and engaged with the ground, through their interaction with the centre of mass of the body of the machine 10, provides significant stability to it.

In one example and in the specific example of FIGS. 7 to 9 and 9A, due to the extension of the legs across the entire width of the body, the legs may be formed of two telescopic sections such that there is an outer telescopic section 60 and an inner telescopic section 62 which, when in a closed configuration, will be positioned substantially within the length of the first telescopic section 60.

The use of such telescopically extending legs 20 ensures that stability can be provided to the machine as a whole during insertion or lowering of the boom 12 into a trench for cutting or mixing. Typically whenever the ground engaging boom 12 is not engaged with the ground, i.e. not submerged below ground surface, the legs will be extended so as to provide stability to the trenching apparatus.

Referring again to FIG. 3, the protective chute 22 will now be described. The machine 10 includes an integrated protective chute 22 which has a generally U-shaped cross-section. The position and configuration of the chute on the machine is so as to be able to prevent fouling of the machine body 34 during the forward folding and transporting of the ground engaging boom or cutting mechanism. Referring to, say, FIGS. 14 and 16, the chute 22 can be seen coupled to the body 34 of the machine 10. Coupling arms 66 are provided to support the chute 22 along its longitudinal extension.

As can be seen, the cradle 26 is included with a chute extension 24 which, when the cradle 26 is in the upwards (folded) position as shown in FIG. 14 for transporting of the ground engaging boom 12, forms a continuous channel with the fixed chute 22. The dimensions of the chute 22 and the chute section 24 forming part of or associated with the cradle 26, are such that the end 68 of the chute 22 will fit within the dimensions of the end 70 of the chute section 24. Typically, the general dimensions will be substantially the same, but the end 70 of the chute section 24 may have a slightly enlarged width so as to accommodate the cross-section of the end 68 of the chute 22.

Looking again at FIG. 14, it can be seen that the chute and chute section 24 when assembled, form a continuous channel within which at least some of the cutting elements 14 of the chain are positioned. This assembly is particularly advantageous since it means that the chain 14 and its cutting elements 16 can be easily washed by water or other washing fluid introduced to flow down the chute 22 under the force of gravity and/or from pressurised fluid flow from an associated pump. The configuration of the assembled chute 22 and chute section 24 ensures that washed or dropped cutting material from the chain 14 is directed away from the machine and to a suitable place. Typically, the water and the washings from the chain 14 may be directed into the trench that has just been cut or indeed onto the ground in a region where a trench will shortly be cut. In either case, the positioning of the washings is advantageous in that it is away from the machine 10 itself and importantly the cuttings or droppings from the chain do not fall onto the machine.

In a preferred example, it could be that the chain is actually driven when in the configuration as shown in FIG. 16 at the same time as a pressurised flow or jet of water is directed down the down the chute and chute extension 24 such as to ensure that all cutting elements on the chain 14 of the boom 12 are washed. This means for washing the chain of a chain cutter is advantageous as it is conveniently performed by the machine 10 itself and at least partially within the footprint of the machine itself.

Referring again to FIG. 3, a winch 80 is shown mounted on the machine 10. The winch 80 is configured to function as a source of force to pull a chain onto the ground engaging boom when required. In known systems, such a winch may typically be provided on the ground engaging boom itself. It has been recognised that this may be disadvantageous given the weight of the ground engaging boom. The positioning of the winch in the present system is on the machine 10 itself. As will be described below, this ensures that a chain can easily be changed on the ground engaging boom irrespective of the size of the ground engaging boom and the associated size and weight of the cutting chain itself.

Operation and functioning of the cradle 26 will now be described. Looking at FIGS. 3, 5, 14 and 16 to 18, it can be seen that a plurality of hydraulic drive cylinders 82 are provided. The configuration of the hydraulic drive cylinders 82 can be seen clearly in FIG. 5 which shows the hydraulic drive cylinders 82 having a pivoted connection 84 to a rear wall 86 of the cradle 26. The cradle also has a central pivoted coupling 88 to a fixed section of the machine 10. The cradle 26 is usually, during mixing/ground engagement, arranged with the hydraulic drive cylinders 82 extended such that the back surface 86 is generally vertical. This is a configuration shown in, say, FIG. 3.

To change the cutting chain on the ground engaging boom, the ground engaging boom is first lifted out of the ground and the hydraulic drive cylinders 82 are contracted. This causes the back surface 86 of the cradle to pivot about pivot point 88 such that the ground engaging boom will then be rested within the chute 22, as described above. In this configuration, the winch 80 can be activated as described with reference to FIG. 19. The winch 80 is coupled to a longitudinal coupling member such as a rope or wire cable 90.

As can be seen in FIG. 19, the cable 90 extends back and forth around a shoulder 92 including a pulley wheel 94 around which the cable 90 is arranged to go. The cable 90 then extends backwards to the top of the cutting boom 36 and then forwards again to its end 96. The end 96 of the rope or cable 90 may then be coupled to a replacement chain, the first link 98 of which is visible in FIG. 19. Replacing the cutting chain on the boom is then simply achieved by activating the winch 80 to wind up the rope 90 and thereby pull the chain 98 along the length of the ground engaging boom so as to entirely surround the both longitudinal sides of the boom and enable the chain to be fixed to it.

Once the link 98 reaches the position of the wheel 94 and shoulder 92, the rope 90 can be disconnected form the new chain 98 and the chain closed in known ways. This for example could involve pulling round the then distal (free) end of the chain that has not yet been pulled onto the boom and connected to the end of the chain that has been pulled by the rope or cable 90.

Looking still at FIG. 19, a tensioning mechanism is provided at the top end 36 of the boom 12. The tensioning mechanism 100 can be seen more clearly in FIG. 20. The tensioning mechanism includes a pivot arm 102 pivotally connected to the top end of the cutting boom via a pivot 104. A pinion 106 is provided for engagement with the chain 14. In use, the chain will pass between the pinion 106 and bracket 108 which acts as a restraining or containing mechanism for the chain on the tensioning system 100. The arm 102 is driven via a hydraulic drive system including cylinders 110 which is pivotally mounted to a fixed pivot 112 on the top end of the boom and a fixed pivot 114 at the distal end of the arm 102 of the tensioning mechanism 100. It will be appreciated that by extension of the hydraulic system 110, the arm 102 will be pivoted about pivot 104 relative to the boom, thereby tensioning the chain 14 around the cutting boom 12.

The positioning of the chain adjustment mechanism on the ground engaging boom itself and importantly at the upper end of the boom, provides a number of significant advantages. First, the tensioning mechanism is remote from the lower end of the ground engaging boom 12 which will be interacting on a more regular basis with the earth formation being trenched. Secondly, this will ensure that the tensioning mechanism is kept away from the section of the boom that is likely to be most engaged with the mixing agent, such as cement, when used as a mixing mechanism. It is known and conventional to provide such tensioning mechanisms at the distal end of a ground engaging boom but it has been recognised that by providing the tensioning mechanism at the top end of the cutting boom the risk from the mixing agent being used setting and thereby possibly rendering the tensioning mechanism ineffective, is significantly reduced. The chain tensioning mechanism can be provided at the end or within 1-2 metres of the upper end of the boom. In some examples it is positioned at a distance that is no more than 5% (or 10 or 15%) of the way along the length of the boom from the upper end thereof.

Finally, referring to the cradle 26, reference is made to FIG. 17. The cradle 26 has a number of sections and the cradle can be opened or closed to enable replacement and/or orientation of the ground engaging boom 12. The cradle in the example of FIG. 17 includes a pivoted door section 41 hingedly mounted via hinges 43 to a rear section 45. A pinion 40 is provided which in use is arranged to mesh with rack 38 formed of a plurality of teeth on the ground engaging boom 12. The pinion 40 is preferably driven by hydraulic power from main trencher body 34 that may be derived from hydraulic power lines 15 (seen in FIG. 4, but not shown in FIG. 17). Thus by the interaction of the pinion 40 and rack 38 it can be simply and reliably ensured that the direction of drive of the ground engaging boom is always aligned with the longitudinal axis of the ground engaging boom 12.

FIG. 18 shows the cradle 26 open and with the ground engaging boom 12 removed. Thus the chute section 24 can be seen with flared ends 70 and 71. The chute section is preferably provided as a fixed or integrated part of the cradle and ensures that a continuous channel can be formed with the chute 22 when the cradle is in a raised (folded), such as that shown in FIG. 14.

The process of use of the machine described above will now be described. Initially, as shown in FIG. 6, the machine 10 may be provided on a trailer 120 for moving to an area where trenching is to be performed. The legs 20 are stowed so as not to generate unnecessary width of the machine during transport. Next, referring to FIG. 7, the legs 20 are extended and feet 48 arranged in position to receive and engage with the legs. Any suitable form of fixing can be used to lock the feet 48 temporarily to the legs 20. With the machine still on the trailer, the legs 20 are jacked down such as to engage with the feet 48 as shown in FIG. 8. With the machine still on the trailer, tracks are coupled to the machine as shown in FIG. 9. With the legs and feet coupled as shown in FIG. 9A, the trailer can be removed leaving the machine 10 supported by the legs and feet 48.

The machine is then lowered onto the ground as seen in FIG. 10 and the legs 20 may be pulled back into the body of the machine as described above. FIG. 10 shows clearly the tracks now supporting the machine on the ground with the feet 48 lifted such that they are no longer in contact with the ground.

Looking at FIG. 11, the hydraulic reels 30 are positioned on the machine 10 and the cradle 26 is coupled to the rear of the machine. Next, as shown in FIG. 12, the chute 22 is fitted to the machine 10. The chute section 24 is already fixed to the cradle 26.

Next, the mixing boom 12 is engaged with the cradle 26 as shown in FIG. 13. A crane may be used to initially lift the ground engaging boom 12 into position for engagement with the cradle 26. It is noted that the legs 20 are extended at this stage, thereby providing stability to the machine during the assembly of the machine with the boom 12 and prior to the boom actually engaging the ground and thereby providing stability of its own.

The machine or rather the ground engaging boom is then lowered as shown in FIG. 14 by tilting back of the cradle 26. This is achieved as described above by operation of the hydraulic controls via hydraulic cylinders 82 and the various pivot configurations provided on the back wall of the cradle. In this lowered position, connection of the chain drive services, via tubes (hoses) from the hydraulic reels 30 is possible.

As shown in FIG. 3, at this stage, the legs 20 are extended in preparation for the fitting of the ground engaging boom 12, because this is the point in the process at which the centre of gravity of the machine 10 is highest due to the vertical extent of the ground engaging boom 12 once there has been initial engagement in the cradle 26 (as shown in FIG. 13).

Once this process is achieved the ground engaging boom 12 is now ready for folding down, (i.e. tilting backwards into the configuration shown in FIG. 14) for connection of the hydraulic supply lines 30. The hydraulic supply lines 30 are coupled to the top of the boom for driving the cutting and mixing chain on the ground engaging boom. When the boom is then rotated back to the vertical configuration, as shown in FIG. 4, the ground engaging boom 12 is now ready for engagement with the ground. The legs 20 provide stability in this configuration.

As shown in FIG. 14A, the trenching operation has commenced with the boom driven down by use of the rack and pinion described above provided within the cradle 26 and on the boom itself. In the configuration of FIG. 14A the ground engaging boom is partially submerged within the ground. The boom is submerged to a desired depth which will produce a desired depth of trench. The legs 20 are raised and brought into the body of the machine 10 as described above since they are not needed at this stage for stability. With the chain operated by the chain drive services the tracks of the machine can be controlled to control the formation of and the direction of the trench.

As shown in FIG. 15, the machine trenching is now at full depth with the boom deep underground and thereby providing an anchor and stability to the machine 10 in operation.

Thus, the machine is able to operate with an extended boom whilst not risking any lack of stability which could be catastrophic. This is particularly the case in high-wind situations, which may be encountered in some operating environments of trenching machines of this nature. In particular, when the machines are used in a river bank location, and winds occur, which is likely, the risk of damage to the ground engaging boom and even the machine 10 itself is significant.

FIGS. 21 and 22 are, views of a machine 75 including an auxiliary power supply 74. FIG. 21 is a simplified schematic view. In some situations, it is possible that the main hydraulic power supply provided as part of the machine 75 fails. This could occur for a number of reasons such as, for example, the supply runs out of fuel or one of the supply hoses becomes damaged in use or breaks off from the machine. In this situation, which may generally be thought of as failure of the main hydraulic power supply, there is a risk to the machine and in particular the ground engaging boom 12 which will typically be engaged with the ground if the main hydraulic power supply is in operation providing power to drive the pinion as described above. In such a situation, when the ground engaging boom is being used for, for example, mixing of a mixing fluid with soil, the mixing fluid in the case of a mixing agent such as (but not limited to) cement could set thereby fixing the ground engaging boom in the trench that has been cut and filled with said mixing agent/cement.

Typically, in the event of such a main power supply failure, it might be up to three days until a replacement can be obtained or indeed engineers can be provided to fix the power failure on the machine 75. In accordance with one aspect of the present system, an auxiliary power supply 74 is provided which can be used as a “hot stab” unit, i.e. which is then able to immediately replace the main hydraulic power supply of the machine and provide the required power to remove the ground engaging boom 12 from its engaged position. The boom can then be extracted using the existing rack and pinion mechanism, described above, which is powered by the auxiliary power unit 74.

By ensuring that the ground engaging boom 12 can be quickly and reliably removed from the ground in the event of main power supply failure, this ensures that the ground engaging boom will not become set in the ground due to the delay that would otherwise be encountered.

The auxiliary power supply unit 74 may be referred to as a hot stab unit since it will typically include a pair of hydraulic supply lines 76 which are connected to hydraulic inputs in a power circuit of the machine to thereby drive the pinion and extract the ground engaging boom from its engaged position.

Looking at FIG. 21, which shows schematically, the arrangement of an auxiliary power supply unit, it can be seen that a lift motor 79 arranged in normal use to receive power from supply lines 30 is provided with sockets 81 to which the connectors 83 of the auxiliary supply unit can be connected. Valves 85 on the supply lines 30 are closed and the lift motor 79 is instead powered by the hydraulic pump and supply unit via inputs 81. The lift motor may be the motor that in use powers the pinion 40.

Looking at FIG. 22, the auxiliary power supply unit 74 is preferably provided as a separate unit. It may be provided entirely independently, but preferably is arranged coupled to the machine 75. The machine 75 includes input sockets 81 arranged in normal use to be provided with power from the existing hydraulic supply lines of the machine but, in the event of main power supply failure, connectors 83 provided at the distal ends of the supply line 76 maybe coupled to the inputs 81 to power the pinion and thereby, via interaction with the rack on the ground engaging boom 12, cause the boom to be lifted out of the ground.

Embodiments of the present invention have been described with particular reference to the examples illustrated. However, it will be appreciated that variations and modifications may be made to the examples described within the scope of the present invention.

Claims

1-44. (canceled)

45. A trenching apparatus, comprising: a body moveable on the ground surface,a ground engagement boom associated with the body, the boom being movable when engaged with the ground to form a trench;lifting means arranged to control and configure the ground engagement boom so as to enter the ground;in which the ground engaging boom is an endless chain ground-engaging boom, comprising a main body and a chain tensioner coupled to the main body at or close to the upper end thereof.

46. Apparatus according to claim 45, in which the chain tensioner comprises an arm pivotally coupled to the main body of the ground engagement boom.

47. Apparatus according to claim 46, in which the arm is hydraulically controllable to move between a first closed position in which its distal end is close to the main body and a second deployed position in which its distal end is moved away from the main body to tension a chain arranged on the ground engagement boom.

48. Apparatus according to any of claim 47, comprising an endless chain mounted on the main body, in which the chain is a cutting or mixing chain.

49. (canceled)

50. Apparatus according to claim 45, in which the ground engagement boom weighs between 10 and 20 tonnes.

51. Apparatus according to claim 46, in which the arm comprises a pinion at its distal end to gearingly engage with the chain as it is driven around the ground engagement boom.

52. Apparatus according to claim 46, in which the arm is between 1 and 3 metres long.

53. Apparatus according to claim 47, in which the arm has a plurality of hydraulic drive cylinders provided to hydraulically control the position of the arm with respect to the body.

54. Apparatus according to claim 45, in which the chain tensioner is positioned with respect to the main body such that when the ground engaging boom is fully engaged with the ground the chain tensioner is above ground surface.

55. A ground engaging boom for use with a trenching apparatus, wherein the ground engaging boom is an endless chain ground engaging boom, in which the ground engaging, comprises a main body and a chain tensioner coupled to the main body at or close to the upper end thereof.

56. A ground engaging boom according to claim 55, in which the chain tensioner comprises an arm pivotally coupled to the main body of the ground engagement boom.

57. A ground engaging boom according to claim 56, in which the arm is hydraulically controllable to move between a first closed position in which its distal end is close to the main body and a second deployed position in which its distal end is moved away from the main body to tension a chain arranged on the ground engagement boom

58. A ground engaging boom according to claim 57, comprising an endless chain mounted on the main body.

59. A ground engaging boom according to claim 58, in which the chain is a cutting or mixing chain.

60. A ground engaging boom according to claim 55, in which the ground engagement boom weighs between 10 and 20 tonnes.

61. A ground engaging boom according to claim 56, in which the arm comprises a pinion at its distal end to gearingly engage with the chain as it is driven around the ground engagement boom.

62. A ground engaging boom according to claim 5611, in which the arm is between 1 and 3 metres long.

63. A ground engaging boom according to claim 57, in which the arm has a plurality of hydraulic drive cylinders provided to hydraulically control the position of the arm with respect to the body.

64. A ground engaging boom according to claim 55, in which the chain tensioner is positioned with respect to the main body such that when the ground engaging boom is fully engaged with the ground the chain tensioner is above ground surface.

65. A method of varying tension in the chain of a ground-engaging boom of trenching apparatus, in which the trenching apparatus comprises a body moveable on the ground surface and a ground engagement boom associated with the body, the boom being movable when engaged with the ground to form a trench, the method comprising: controlling the tension of the chain using a chain tensioner coupled to the main body of the ground engaging boom at or close to the upper end thereof.

66-83. (canceled)