GB2500225A

GB2500225A - Low CO2e emission trenching unit

Info

Publication number: GB2500225A
Application number: GB1204484.8A
Authority: GB
Inventors: Danny Albert Crosbie
Original assignee: Individual
Current assignee: Individual
Priority date: 2012-03-14
Filing date: 2012-03-14
Publication date: 2013-09-18
Also published as: GB201204484D0

Abstract

A low CO2e emission trenching unit comprising a soil retention and feeder unit 7, a trenching blade 1 and a tractor unit or backhoe arm. A void formed by the forward movement of blade 1 is maintained in an open configuration for the insertion of drainage pipes or units, or cabling. A void may be created in a range of soils substantially without the soil being mixed. A method of trenching comprising forward movement of trenching blade 1 such that soil retention unit 7 provides a substantially spoil-free void. The method may comprise laying visual alerting tape over cable, pipes, or drains in the soil. The method may comprise laying cable or gas or water piping and warning tape in a single operation. A method of trenching using a self-propelled, towed, winched, or rail-mounted trenching unit comprising a soil retention unit 7 or multiplicity thereof adjustably fitted to one or more base plates 2 to provide one or more substantially vertical voids in the soil by compressing the soil by forward movement of the unit.

Description

Low C02e emission trenching unit

There is general agreement that carbon dioxide (C02) and other greenhouse gases may well be leading to global warming. One effect of global warming 5 will be to accelerate the decomposition of soil organic matter, thereby releasing C02 into the atmosphere, which will in turn exacerbate the warming trend. Such a feedback mechanism could be important because C02 is thought to account for around half of the increase in radiative forcing arising from anthropogenic emission of gases, and there is around twice as much carbon in 10 the top metre of soil as in the atmosphere. It is the top metre of soil that gets disturbed while trenching to lay drains, install cables and pipes, etc. It is clear that more C02 emissions can occur from tilled soil than that which is relatively undisturbed as tillage produces a soil microenvironment that favours accelerated microbial decomposition of plant and animal residues. Tillage 15 breaks down soil aggregates, helps mix soil and organic particles, improves infiltration and water retention capacity and thus increases C02 production. It has been observed that immediately after tillage, C02 fluxes along tilled transects increased by a factor of 2-4 compared to undisturbed soil.

This flush of gas release is caused by the escape of C02 trapped in soil pores 20 as a result of root respiration. The C02 concentration in soil gas found in pores can be up to 10% compared to 0.038% in the atmosphere.

At a time of concerns about global warming, these are clearly factors that responsible trenching operators and their clients need to take into account and the present invention seeks to provide trenching for drainage, etc., while 25 very significantly reducing the energy consumption by trenching plant, C02 emissions from disturbing soil, and the costs associated with trenching. Other

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gases are naturally also released during trenching operations; for example NOx accounts for approximately 19% of vehicle emissions and has a global warming effect that is over seven times more environmentally damaging than 30 C02. There are two major sources of emissions when trenching; one from outgassing of C02 from disturbed soil and emissions from the motorised plant used in trenching operations and hence comparisons are based on C02 equivalents - C02e.

35 When groundsmen of sports fields or golf courses need to lay cables, drainage pipes, etc., below ground, they require the minimum disturbance to their pitches which fits well with minimising C02 emissions. Above all they wish to prevent the bane of sinkage associated with traditional means of trenching, which require repeated remedial works that are expensive in financial terms 40 and costly in terms of emissions, and yellow striping caused by clay being mixed with topsoil during drainage operations. Groundsmen work hard to maintain the good condition of pitches and wish to keep disruption and costs to a minimum. There are many devices in the art for cutting trenches in soil and many machines have been devised. One common feature is that they are 45 expensive to buy, maintain and operate, mainly due to their complexity and the number of vehicular movements involved. In operation, they have the grave disadvantage of tending to mix subsoil and topsoil when retrieving it to the surface. When trenching using excavators, operators tend to dump spoil on the ground adjacent the trench and push it back in after the operation has 50 been completed, often leaving stones on the ground and mixing the returned soil, even if they have endeavoured to separate the grades of soil being extracted. This cannot of course be achieved using chain and rotary

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excavators. The alternative is to use for example a dumper truck to remove spoil as it is excavated which means more vehicular movements and more 55 damage to the pitch or ground. Either way, conventional trenching operations for drainage and cable laying are expensive and above all tend to boost C02e release from disturbing the soil and from the engines of contractors' plant. In a report commissioned by the inventor in January 2011 from the Centre for Sports Surface Technology, School of Applied Sciences, Cranfield University, it 60 was found in a comparison with the most efficient alternative, a driven wheel excavator, that whilst there was a comparative advantage of as much as 7% in favour of the present invention for C02e outgassing from soil disturbance, the overall advantage from machinery and outgassing emissions was of the order of 57%. Accordingly, trenching using the present invention in the report 65 gave savings approaching 60%, or considerably more compared to excavator operations. At the same time, since there is less soil structure modification while operating the present invention, there should be less oxidation of organic soil matter which should in turn lead to lower downstream emissions.

70 The smallest practicable excavator bucket in general use is a 9" (23cm) bucket, or 4" cup in the case of chain excavators. This means that very considerable volumes of soil are being extracted - and energy used to do so -to lay a cable that may only be 10 mm or less in diameter. Another disadvantage of chain and wheel excavators is that they are very noisy to 75 operate, unlike trenching with the present invention which has an overall extremely low acoustic signature and the tractor unit operates at low engine speeds. Further, there is no need for the large number of support vehicles associated with conventional trenching.

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It is now a general legal requirement for coloured plastic warning tape to be 80 used when laying gas and water pipes and electric cables. Excavating trenches using even a narrow bucket on a backhoe needs a lot of force to be applied because of the friction of the soil. It is often very difficult for machinery operators to see or feel if they are about to hit a cable or pipe. It can also be difficult to determine the depth that a bucket has reached.

85

Moling ploughs, either self-propelled or attached to a tractor unit, can be used to drag a cable underground. They may leave little spoil on the surface but their tendency to cause cables to stretch and piping to rupture and the inability of the operator to be able to inspect pipes, cabling, etc., before laying 90 warning tape, make moling unsuitable for cable-laying in most situations and soil conditions. Doing so would also generally invalidate warranty conditions for most commonly used cables. Moling does not allow the insertion of drainage panels or for example clay pipes and it is also not possible to lay plastic warning tape above any cabling. Agricultural subsoilers perform a good 95 job of loosening compacted soil but are practically always used with a tractor unit and are solely intended to improve soil structure, break up panning and to prevent ponding.

Pipes and cables can also be laid below ground using a pneumatic driver but it 100 is almost impossible to control the unit which can be deflected by a stone and go off course. It is also not possible to comply with the requirement for laying warning plastic tape at the same time. Again, pulling cables through the soil is bad practice as it tends to rupture delicate cables such as optical fibre cables.

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105 In addition to satisfactorily addressing the above problems, as noted above the present invention also seeks to deal with the acute problem of reducing C02e emissions while preventing ground sinkage on playing fields and elsewhere associated with drain and cable laying works, and the problem of working in restricted spaces.

110

One major problem when laying cabling or drainage pipes for example, is the need to be able to operate in all kinds of weather and ground conditions. It has been found that in times of drought and clay-rich soil, moling ploughs simply do not work due to resistance of the soil preventing the mole plough 115 from moving through the soil irrespective of the power applied, bearing in mind the potential disruption to the surface from wheel-spin, etc. The present invention uses an optional PTO-driven cutter bar located just ahead of the expander blade, reciprocating in the same plane as the motion of the expander blade, said reciprocating motion designed to run at 8 120 oscillations/sec. The length of the blade is such that it substantially matches the working depth of the retention/feeder box. Tests have shown that this enables the invention to be operated even in hard-baked clay or stony soil, thus obviating the need for the use of alternative, costly systems such as rotary wheel or backhoe trenching. The invention provides a soil 125 retention/feeder box unit rearwardly displaced from the blade but in close conjunction therewith. Whilst superficially resembling a moling arrangement, the blade and expander unit are designed to achieve a different purpose. Whereas in moling, the blade is thin to minimise the slit cut in soil and to use a mole shoe to provide an expanded channel for drainage, the blade and 130 expander used in the present invention are used to expand the soil sufficiently

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to leave space for the rearwardly displaced soil retention box and feeder unit. As the blade passes through the soil, the latter is abruptly displaced and compressed sideways, driving out air and gases in the top layer of soil and leaving a void. The retention box holds open the void to prevent spoil 135 dropping back into the void to allow for drainage pipe or panels/granulate, cabling, etc., to be fed into the void, and warning tape laid thereabove. So whereas typical moling is done with a very narrow blade and a shoe at the bottom of the moling blade, the blade in the present embodiment of the device serves a very different purpose. The box is usually made of mild steel 140 and is adjustable for width to accommodate different sized drainage piping and blade dimensions. Obviously, the narrower the blade and width of the retention unit, the lower the friction and energy required to lay cabling and drainage, etc. The present invention includes an adjustable depth trenching blade usually of high tensile steel for convenient attachment to the universal 145 (Category 1-3) implement attachment points on a tractor or the bucket attaching points of a standard backhoe excavator. The blade unit typically has a width of 75 -100 mm since this balances low energy consumption and exquisite operator control while allowing for most cabling and piping to be laid easily, but the width may also be varied to suit special applications, either by 150 replacing the blade with a broader unit or by adding suitably dimensioned removable sabots to the blade unit.

The invention thus provides a low C02e emission method for trenching using a blade for attachment to a suitable tractor unit or backhoe arm and uses the 155 hydraulics thereof to deploy a blade and characterised in that a void formed by forward movement of the blade is maintained in a open configuration for

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the insertion of drainage pipe or units or cabling and the like and for other operations in the void so formed and rapid post operational trench closure, while reducing C02 outgassing emissions from soil and comparative C02e 160 emissions from machinery. It does so whilst very significantly reducing machinery and noise emissions compared to other widely employed trenching equipment.

In use, in some soils it has been found that greater draught stability can be obtained by fitting a suitably angled shoe or footpiece to the blade or angled 165 fins.

The retention box/feeder unit rearwardly displaced from the blade consists of two parallel steel plates, the leading edges of which may be angled inwards just aft of the blade unit to help keep soil from falling into the trench caused 170 by forward motion of the unit. This box unit is usually of steel and adjustable for width and in use the sides are normally adjusted to be slightly less than the draught of the expander blade so as to reduce wear and loading on the side plates. In a preferred embodiment of the invention, the bottom edges of the side plates are adjusted to be 40 mm higher than the bottom edge of the 175 blade. Tests have shown that this makes for greater stability. The effect of this is to leave a clear void aft of the expander blade irrespective of the soil type, including running sand, into which drainage panels or pipes may be dropped or cable, tape, wire or flexible piping fed.

180 There may further be provided a ramming unit in which a shoe holds drainage panels until sufficient trench has been cut and it is then used by an operative

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to release and ram drainage panel units laid in the trench so formed into intimate conjunction to assist drainage capillary action.

185 The invention is robustly dimensioned and short coupled. At around 800 kg, the weight of the entire unit is sufficient to allow the blade and retention unit to penetrate to working depth easily even when used with a relatively low power tractor unit. The unit operates very satisfactorily with tractors of 80 HP. The close coupling allows the unit to be operated close to boundaries and 190 structures; the robustness allows for high powered tractor or crawler tractor units to be employed. The unit has been satisfactorily tested using tractor units in the power range of 45 - 400 HP without causing damage to the unit. It has been found that using hydraulic top coupling linkage allows the unit to be deployed to operating depth more rapidly. Clearly with such a short 195 coupled device, the length of the blade when deployed in the ground does require the tractor unit to be able to lift the blade clear of the ground for manoeuvring, and the attachment points are required to be suitably designed to take this into consideration. This feature also means that less soil is disturbed while getting the trenching unit to operating depth which thus 200 reduces C02e emissions. Sports fields generally have some kind of a headland for their rollers, line painters and mowers to manoeuvre, but sports ground designers wishing to keep action close to fans tend to reduce these to a minimum. The present invention is designed to operate in closely confined spaces. Many of the more traditional trenching systems have long trains, 205 often meaning they are unable to operate close to fences and that for example a mini-digger has to be brought in to deal with these areas.

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The invention is herein described as being fitted to a tractor or backhoe but any suitable tractor means could also be employed, including self-propelled 210 units. Similarly, the unit could be wheeled and drawn by a tractor unit without use of its hydraulics.

In tests, it has been found that an adjustable blade depth of 1000 mm is sufficiently deep for most trenching operations. This is of course the zone of 215 soil that generally contains the most CO2 that can be outgassed. In use, the operator merely drives the blade and soil retention box into the soil using the hydraulics and weight of the unit to the depth required and uses the tractor unit or the excavator's hydraulics to pull it through the soil. The passage of the blade shocks the soil, driving out air and causing it to compress to form a 220 void held apart by the steel sides of the retention unit into which cable, piping or drainage panels, etc., may be laid, or indeed gravel/sand backfilled for drainage purposes. No soil is ejected onto the surface and there is minimal soil mixing. When trenching in a sports field, for example, deployment of a turf cutter helps form a neat slit in the turf. Forward of the blade, the present 225 equipment deploys a roller and turf cutter and an oscillating cutter bar driven by the PTO for use in very hard baked clay soils. In use, this has been found to minimise build-up of soil and to lead to a finely cut trench. Even so, as the top soil and turf are parted, they tend to hinge about a point some five to ten centimetres on either side of the slit formed by the cutter and are retained in 230 this position by the soil retention/feeder box unit. After the cable or drain laying operation, passage of a roller or steerable vibrating roller for example over the slit closes the turf neatly together, thus minimising the need for returfing or additional backfilling. Indeed, subsequently running a wheel of a

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tractor, for example, either side of the slit causes it to close. The more rapidly 235 this can be done, the lower the level of C02e emissions and when used on especially sensitive sites such as cricket pitches or heavily tilled areas, a vibrating or other roller may as noted above usually be employed to close the slit. In normal operations with the invention, the slit stays open less than ten seconds before closure, thus reducing the tendency of C02 to escape. 240 Practically no stones or subsoil are left on the surface. In tractor unit operations, the process is continuous. In tests, corrugated agricultural drainage piping was laid as a comfortable speed of 7 seconds/metre. With backhoe operations, the operator is required to move the backhoe and to repeat the trenching process. Although the device is primarily intended for 245 sports grounds with well-defined subsoil structure, the system works equally well in general agricultural and site construction applications.

One benefit in agricultural use is that since operation of the whole unit is so quiet and the whole trenching operation can be completed so rapidly, stock 250 can be left in the field without the risk for example of lambs falling into open trenches or being spooked by noisy operations and multiple vehicle movements.

When operating in an area where there may be previously laid cables and 255 pipes, the degree of control available to the operator makes the present invention the device of choice. Many tractor units are fitted with laser equipment to allow for proper falls to be maintained for drainage purposes and the present invention is so exquisitely adjustable for draught as to make it perfectly suited for such operations. Although many piped drainage systems

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260 do require falls to be properly observed, drainage that relies on for example drainage panels or granulate that operate by means of capillary action are not so susceptible to variations in draught for their effect.

In a preferred embodiment of the present invention, a vibrating or static hopper is fitted with a feed into the feeder box with an adjustable scraper 265 blade so that granulate of suitable material to allow for drainage by capillary action can be fed into the trench formed by forward movement of the blade and feeder box, the top level of which can be finely adjusted in keeping with precise drainage requirements. Such granulate may be used in conjunction with precast drainage panels.

270

In areas of contaminated soil where it is a requirement that the contaminated subsoil should not be disturbed, trenching to lay cables or pipes to collect outgassing for example in accordance with the invention means that contaminated subsoil is not disturbed and that contaminants are not brought 275 to the surface as they would be with other excavating devices. The minimal disturbance caused by the unit also tends to reduce the release of contaminant gases and indeed C02held in the soil.

There is a legislative requirement for warning tape to be laid above water, gas 280 and power cables. An attachment to the present invention situated aft of the retention/feeder box has cutter blades outwardly displaced from a detachable unit that cuts soil and forces it onto the top of the cable, or pipe, etc, and then feeds warning tape on top of this. Doing so in a single pass means that no separate operation is required to lay tape and the trench can then be

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285 immediately closed. This saves an operation and thus reduces machinery emissions.

The present invention will now be described for illustration purposes only with reference to the attached annotated drawings wherein Figure 1 gives a side 290 view of the blade and expander unit (1) and turf cutter/roller unit (6) attached to the base plate (2), and the soil retention/feeder unit (7), the optional draught control shoe (9) fitted to the base of the blade (1), and soil retention/feeder unit in place, together with the warning tape reel (13) and feeder pipe (12), and warning tape attachment (10) and outwardly displaced 295 soil cutters (11). The shaft from the PTO is shown (15) goes through a drive means (not shown) to the reciprocating blade (5). Figure 2 shows the soil retention/feeder unit (7) with the optional hopper (14) attached. Figure 3 shows the soil retention/ feeder unit (7) and ramming shoe attachment (4). This incorporates a backfill levelling device that enables the operator to set 300 the level of the backfill in a trench to the most appropriate level, thus saving on backfill and associated backfill transport operations, and hence C02e emissions. There are two embodiments of the turf cutter/roller unit (6) for different applications. First a simple disc cutter manually adjustable for depth intended for general agricultural applications and secondly a disc cutter and 305 roller unit intended for football pitches etc where fine finish is more important. In the present invention, a preferably high tensile steel blade and expander unit (1) is adjustably positioned within a slot in a reinforced base plate (2), usually of steel, designed to be attachable to the universal implement attachment fittings of a tractor or the bucket fittings of a standard backhoe 310 excavator arm (3). In a preferred version of the present invention, the

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expander unit (1) is substantially at right angles to the base plate (2). The leading edge of the expander unit (1) consists of a blade of preferably hardened or hard-faced steel or other suitably dense material. The blade and expander unit may be adapted to accept detachable sabots (16) to provide 315 additional expansion.

A turf cutter/roller unit (6) is positioned in front of an optional PTO-powered reciprocating cutter (5) which is usually adjusted to oscillate 8 times/sec substantially to the depth of the retention/feeder box (7). This assists in neatly parting turf and preventing a build up of spoil ahead of the blade unit 320 (1) while allowing for subsequent rapid neat closure of the turf to limit C02e emissions from disturbed soil. It also facilitates the continuous operation round bends. Rearwardly displaced from the blade/expander unit is a soil retention box/feeder unit (7) comprising two steel plates, usually of 10 mm mild steel, designed to hold apart the soil compressed by the blade unit and to 325 prevent spoil from dropping into the trench so formed. The retention/feeder unit (7) allows drainage panels, cabling or piping and backfill to be dropped into the void to the pre-selected depth. The bottom edge of the retention unit is preferably positioned so as to be upwardly displaced by for example 40 mm above the lower edge of the blade and expander unit so as to provide greater 330 stability.

In a preferred embodiment of the device, there is provided a manually or optionally automatically operated unit (4) to ram drainage panels to provide intimate location of adjoining panels to assist in drainage capillary action. In use in some types of soil such as humus-rich topsoil, some spoil would 335 inevitably drop back into the trench but the sides of the retention unit (7)

preclude this, thus very significantly speeding operations and hence reducing

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C02e emissions. In clay-rich soils, the sides of the trench are generally immaculate with no spoil drop-back. It has been found in tests that deployment of the turf cutter/roller (6) is critical for ensuring a neat post-340 operational appearance of turf and also that spoil does not build up ahead of the expander unit (1), which could then otherwise drop into the trench. In a preferred embodiment of the unit, there is further provided a ready-use magazine (8) which may have the capacity to store some 50 m of drainage panels or pipes, said magazine being recharged by the operative as trenching 345 progresses. If cable is being laid, a reel unit (9) may also be attached with a further reel unit (13) for warning tape. Warning tape may be laid as required by regulations above pipes and cabling using tape from the reel (13) which feeds through a feeder tube (12) and into a detachable soil cutter and tape laying unit (10) with outwardly displaced blades (11) to cut and feed soil onto 350 the pipes/cables and above the tape then laid thereon, to hold it in place before the trench is closed.

For continuous drainage pipes operations, the piping is carried on the detachable reel (9) and fed into the soil retention unit (7) through a shoe (not shown), and then if required, backfill can be poured into the trench using the 355 hopper and adjustable backfill depth levelling unit (14).

If trenches are being cut for granular capillary drainage material, a hopper (14) may be positioned above the feeder/retention unit (7). An optionally vibrating hopper helps ensure even feed of granulate or shingle.

360 When being used to lay heavy armoured power cable for example, this is flaked out on the ground alongside the trench to be cut. The device is deployed and one end of the cable fed through the retention/feeder box (7).

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As the tractor unit progresses, the cable is merely fed into the feeder box and the trench by an operative. Warning tape can be fed on top of the cable 365 thereafter from a reel on the device (13) through the tape laying soil cutter device (10). Again, in normal operations, the trench stays open for less than 10 seconds before closure.

The unit may be fitted with a rearwardly positioned trailer attachment point to attach a vibrating roller or to facilitate use of a trailer to transport drainage 370 panels etc, and the unit may optionally be fitted with one or a plurality of wheels for safe road transport or operational purposes (not shown).

The base plate (2) is provided with reinforcing about the slot through which the expander unit (1) passes. For some applications requiring uniform 375 configuration of the unit, it may be deemed more appropriate to weld or fix the expander unit in position, although full adjustability has been found to be most convenient in general operations. The present invention further provides very considerable savings in fuel and time/labour, the two major cost constraints for contractors, while also, as noted above, very considerably 380 reducing C02e emissions compared to other commonly used trenching devices.

In comparative tests at a football pitch, a tractor and driver equipped with the unit in accordance with the present invention and a single operative were able to lay 100 m of capillary action drainage panels and make good the site with a 385 powered roller in less than 12 minutes. According to the Cranfield report, C02e emissions in so doing would have been 3.23 kg, 57% less than the powered cutter wheel system with a crew of four. Conventional excavator trenching would take a crew of eight and it would take some three hours to

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excavate and make good 100 m of trench. There would have been very 390 considerably more site damage when using conventional equipment and this would not include having to revisit the site for sinkage rectification, which typically requires around 40 tons of sand per acre. Reseeding with grass would also not be required. Accordingly, using the present device offers very substantial savings indeed of the order of 10:1 in fuel and time and more on 395 savings on site damage and very significant reductions in C02e outgassing and machinery emissions.

There are or course many different types of excellent plant available in the art for backfilling gravel and sand into narrow trenches which cause very limited 400 damage to grass surfaces, but deploying additional machinery adds to total emissions and cost.

One additional benefit in laying drainage using the present invention is that grass subsequently grows more lushly over the drains, due probably to 405 aeration, making it possible to easily identify where the drain runs have gone after works have finished for subsequent mapping operations where GPS mapping has not been used. It has been found in tests that when soil is compressed in using the present invention and drainage panels or piping or cable are laid and the trench closed by for example running a roller over the 410 trench or running a vehicle wheel adjacent the trench, the compressed soil decompresses gradually and there is no tendency for humps to form. Use of a vibrating roller does however speed the regenerative process.

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On a sports ground, drainage is typically laid at 1 or 2 m centres. Obviously 415 the magnitude of emissions in providing drainage for a whole football pitch depends on the lateral spacing of drains. At 1 m centres, the Cranfield report estimated that use of the present invention would lead to emissions of around 260 kg C02. In order to achieve equivalent emissions, the spacing of drain runs would have to be increased to 2 m for the driven wheel excavator, and 420 indeed more for backhoe excavator trenching. The present invention is designed to be operated as a single unit or a dual unit with two blades adjustably positioned a metre apart. This obviously increases the power requirement but a single tractor unit can easily form twin trenches. Another feature of the present invention is that the driver of the tractor unit has all the 425 workings of the invention in full sight. He can immediately see if there are problems for example with the warning tape or drainage pipe feeds as these are in full view, unlike many conventional trenching units which require ancillary staff to monitor proceedings. The speed and ease of operation makes this approach highly suitable for laying optical fibre and telephone cabling. 430 The sensitivity of operation and depth control make it possible for example retroactively to lay optical fibre cable breakage systems above backbone fibre cabling. Although the unit is in full view of the driver, clearly the bottom of the trench is not in view and in an embodiment of the device, robust cameras are fitted aft of the base plate for in-cabin monitoring of the trench. Since the 435 trench provided by the device in operation is so clear-cut and defined,

cameras can be deployed for the operator to visually monitor progress and to detect any warning tape or signs of previous trenching or digging operations. Even if no cameras are fitted, once the unit has been inserted into the ground, it is also possible for an assistant to observe progress from close quarters

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440 without danger since the movement of the blade unit is generally in one direction only. Said operative can then observe for plastic warning tape. In trials, skilled operatives have stated that they can easily detect previous drainage operations and warning tape, thus helping preclude damage to previously laid drains, pipes and cables.

445

There may be circumstances in which it is desired to cut a trench at an angle to the vertical, such as when wishing to lay a cable or drain underneath another cable of drain or obstacle. Clearly this can be easily accommodated by angling the blade accordingly or by employing a different configuration of the 450 blade unit with a lower portion of the blade inclined at say 45 degrees to provide a dogleg trenching action, with a channel being formed laterally at the bottom of the trench. Although calling for more operator skill, tests have shown it to be entirely feasible. The soil compression afforded by use of the present invention helps keep the trench so made intact for cabling operations, 455 etc., while not disturbing other pipes, etc., lying above.

The device works efficiently in all soil types, including sandy soils, since the soil retention unit prevents sandy soil for example from running into the trench while cable or drainage pipe/panel operations, etc., are proceeding.

460

One particular area of application for the unit is in areas where sinkage is absolutely precluded due to safety or cost constraints, such as roads and runways and aircraft manoeuvring areas. Although the tarmac or concrete needs to be removed using traditional methods, use of the present invention 465 to cut a trench for cable laying for example compresses the soil. After laying

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the cable and adding backfill, the decompressing soil exerts sufficient pressure on the backfill to prevent sinkage. The upper layer of tarmac or concrete can then be reapplied without concerns of expensive subsequent repair works.

470 Apart from the PTO-driven reciprocating cutter blade which may be deployed when trenching for example in very severe drought conditions, the unit has no driven parts, unlike many other driven wheel and cup trenching systems, and since the normal forward service speed is 5 kph, there is little risk to the health and safety of operatives. Further, the maintenance requirement is 475 extremely simple and low, further reducing C02e emissions compared to the high maintenance requirement of conventional trenching systems.

Tree-planting is a laborious and costly process when done manually. The present invention can be easily adapted for tree planting purposes since the 480 soil retention/feeder box is open at the rearward end and is adjustable for width and allows for quite sizeable saplings and trees to be planted and support stakes to be positioned contemporaneously. This obviates the need for lengthy operations using augurs whilst also making it possible to lay water/nutrient lines at the same time. The trench can then, as noted above, 485 be readily closed by running a vehicle wheel or roller along it to complete the planting operation while not damaging the trees. The quicker this is done, the lower the C02 outgassing. If no lengthy trenches are required, the unit may be used to just cut short trenches. Traditionally, many operators have used plough arrangements to cut trenches but the soil then has to be spread back 490 once planting is done and the presence of vulnerable saplings makes this

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labour intensive. The present invention obviates this, thus cutting costs while limiting the time soil is exposed to outgassing.

In normal trenching operations when laying drainage panels or perforated 495 pipe, the forward speed is limited by the ability of the operative actually laying the panels or refilling the hopper with gravel to keep up without getting fatigued. The normal service speed in use is normally around 5 kph. However, when laying cable and warning tape off a drum which require little assistant operator input, much higher speeds are possible, typically 10 kph or more. 500 Deployment of a towed rolling unit then closes the trench typically within a further 3 seconds, thus very considerably cutting the time available for degassing. In tests on pasture, reels of 100 m lengths of 25 mm water pipe and warning tape were laid at a depth of 750 mm in six minutes in a single operation using a single driver operative.

505

Whereas the scenarios hereinbefore set forth typically refer to a wheeled tractor, a crawler tractor unit would reduce the ground pressure signature in operation, which would extend the suitability of using this method and equipment, for example in inclement weather which would preclude excavator 510 and driven excavator wheel operations, whilst not causing site damage of soil compaction. Again, whilst usage would normally be for a wheeled or belt driven tractor unit, there is nothing to prevent towed or winched operations using a suitably modified configuration of the present invention for subsea or river crossing operations, or indeed rail-mounted operations, although the 515 emissions signatures would then be rather different.

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Claims

1. A soil retention and feeder unit deployed in conjunction with a trenching blade and a suitable tractor unit or backhoe arm characterised in that a void

520 formed by forward movement of the blade is maintained in a open configuration for the insertion of drainage pipe or units or cabling and the like and for other operations in the void so formed and rapid post operational trench closure, while reducing C02 outgassing emissions from soil and comparative C02e emissions from machinery.

525

2. A soil retention and feeder unit in accordance with Claim 1 characterised in that a trench formed in accordance with Claim 1 creates a void in a range of soils in said trench substantially without soil being mixed.

530

3. A method of trenching using forward movement of a blade, characterised in that a soil retention unit provides a substantially spoil-free void into which drainage material, cables or pipes may be fed and the trench rapidly closed to leave minimal sign of operations.

535

4. A method of trenching in accordance with any preceding claim to lay visual alerting tape over cables, pipes or drains in soil.

5. A method of trenching in accordance with any preceding claim characterised in that use of the present invention in trenching works

540 minimises outgassing and ground sinkage.

6. A method of laying cable or gas or water piping and warning tape in a single operation in a trench formed and closed accordance with any preceding claim.

545

7. A method of low C02e trenching using a self-propelled, towed, winched or rail-mounted trenching unit characterised in that it deploys a soil retention unit or a multiplicity of these adjustably fitted to one or more base plates to provide one or more substantially vertical voids in soil by compressing same

550 by forward movement of the unit(s).

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8. A method of laying drainage panels or drainage granulate in a void formed by forward movement of a soil retention unit adjustably fitted to a base plate.

9. A method of tree planting utilising a trench formed in accordance with any preceding claim.

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