GB2159192A - A trenching method and apparatus - Google Patents

Abstract

A trench, particularly a drainage trench for grassed sports fields and the like, is formed by a two stage method in which the upper half of the trench is excavated by removing soil with a rotary cutting tool 4, and the lower half of the trench is ploughed to its finished depth without removing soil. Immediately behind the plough there is a delivery chute 17 extending the full depth and width of the trench and has an inclined exit aperture,which delivers material to fill the trench from above-ground hoppers. The chute may be partitioned to form separate upper and lower exit apertures connected with separate hoppers to deliver, for example, gravel to the lower part of the trench and sand above it. <IMAGE>

Description

SPECIFICATION Atrenching method and apparatus The invention relates to a trenching method and apparatusforforming slit-like drainage trenches in sports fields and the like.

Grassed playing surfaces have to be drained of surface water as rapidly as possible in order to minimise the damage that would inevittably result from their use in a saturated or waterlogged state.

Although pitches, fields and parks may be provided with underground drainage systems, because these have to be buried at some depth below the ground surface, there is an inherent time delay before appreciable quantities of surface water are completely drained away.

In order to speed-up drainage it is known to provide, at intervals in the playing surface, slit trenches filled with sand and other aggregates which can conduct water towards to the drainage system more quickly. Clearly, these slit trenches must not introduce any uneveness or irregularity into the playing surface, so that the top of the trench in-fill material has to be flush with the normal surface. But if the trenches are excavated by the removal of soil the filling material tends to compact leaving a surface hollow requiring frequent top-dressing, and if the trenches are ploughed there is so much ground heave along the margins of the trench that considerable heavy rolling is needed to level the ground.

The present invention seeks to overcome these disadvantages by providing a method of forming the trenches which does not cause excessive heave along the trench margins and in which subsequent subsidence of the trench filling material does not occur. The invention also provides apparatus for carrying out the method.

According to the invention there is provided a method of forming a trench comprising the steps of partially excavating the trench by the removal of material to part only of the final depth and ploughing the trench for the remainder of its full depth.

Preferrably the step of partial excavation is carried out by means of a rotating cutting tool and is followed by ploughing the trench to its final depth.

The invention also provides trenching apparatus for performing the method of forming a trench, mentioned above, comprising a carriage having mounted thereon first means for partially excavating a trench to part only of its final depth and second means for ploughing the trench to the remainder of its final depth.

Preferrably the trenching apparatus further comprises a rotating cutting tool or excavator, for carrying out the step of partial excavation, and also comprises means for delivering granular material to fill the trench, which means may comprise a delivery chute having a partition to provide upper and lower delivery apertures which communicate respectively with individual hoppers containing the in-fill material. In use these hoppers may contain different sized granular material, e.g. coarse aggregate in one and sand in the other, which can thereby be delivered to different levels in the trench in one operation.

The invention will now be described in greater detail, by way of example only, with reference to an embodiment of the trenching apparatus illustrated in the accompanying drawing.

Referring now to the drawing the trenching apparatus comprises a carriage or rigid supporting frame 1 which is adapted to be towed behind a tractor vehicle (not shown). Mounted in a vertical supporting sleeve in the carriage lisa plough 2 which is rigidly secured to the frame 1 by means of mounting bolts 3.

A rotating cutting tool 4 is carried ahead of the plough 2. This rotary tool 4 comprises a rotatable discS around the periphery of which are mounted a plurality of cutting teeth or heads, such as 6. The disc 5 is rotatably mounted in a sub-frame 7 vertically adjustable relative to the carriage by substantially axial movement of a tie rod 8 connected to an operating lever on the tractor, a well known arrangement. The tool 4 may thus be raised and lowered to cuttingly engage the ground by movementof the lever, the depth of excavation may be varied to suit ground conditions and the tool 4 may be raised completely if an underground obstruction is encountered and damages to the cutting head is to be avoided.

The carriage 1 is also provided with a similar vertically adjustable arrangement, generally indicated at 9, which may be operated by a second tie rod 10 so that the carriage 1 may be raised and lowered with respect to the tractor vehicle to set the depth of the plough 2.

Attached to the rear of the carriage 1 is an hopper arrangement, generally indicated at 11 comprising one or more hopper compartments. The hopper or hoppers have vertical end walls and flat sides which taper inwardly towards the bottom to meet a rectangular exit orifice feeding directly into a delivery chute 12.

A delivery chute 12 comprises two parallel sides, and extending vertically at their forward edge to the full depth of the plough 2. The forward vertical side of the chute is closed by a member 15, which may be L shaped or joined to a short horizontal member at the bottom to form a partially closed bottom face 16 between the parallel sides. The remaining length of the lower edges of the sides of the chute 13, 14 are inclined upwardly towards the rear of the hopper 11 to form a rectangular lower delivery aperture 16 through which material contained in the hopper is delivered. In use, the carriage 1 is generally lowered so that the delivery chute extends to the full depth of the trench and substantially fills the width of the trench, then as the apparatus moves forward material flows from the chute to fill the whole of the trench.Lower forward regions 18 of the sides 13 and 14 may be reinforced by ribs to mitigate against excessive wear of the chute side plates as the chute is pulled through the trench.

The hopper 11, as illustrated, comprises a single hopper having a vertical partition 19 which divides the hopper 11 into two compartments roughly equal in volume and which extends downwardly into the delivery chute 12, towards the lower edge thereof also dividing the delivery aperture 17 into upper and lower delivery apertures 17A and 17B respectively.

The hopper 11 may be mounted on the carriage 1 by means of a support 20 attached to the carriage 1 through a vibratable mounting 21. The vibrator contained within the mounting 21 is operative to vibrate the hopper 11 transversely, that is from side to side with respect to the direction of travel of the apparatus. Thus, in use, the hopper 11 may be vibrated in order to promote smooth flow of material from the hopper through the delivery chute 12 into the trench. The effect ofthe vibrator 21 is also to transversely vibrate the plough 2 with respect to the direction in which the slit trench is being formed.

In the embodiment described all power for the trenching apparatus is provided from the tractor vehicle, which is a normal agricultural tractor. The vibrator mechanism is driven by a conventional power drive from the tractor, for exampie, by a shaft coupling (not shown). The rotary cutting tool is driven by a hydraulic motor, mounted on the trenching apparatus but powered by hydraulic fluid pressure from an hydraulic pump on the tractor.

In operation of the trenching apparatus the carriage 1 is mounted behind a tractor vehicle (not shown) and towed in the direction of formation of a drainage slit trench. The rotary cutting tool 4 is lowered to engage the ground to the required depth and when rotated is effective to excavate, by removal of soil, the upper part of a trench to the width of the cutting heads. The plough 2 is set to the full depth of the trench, that is it is set to plough to a depth substantially greater than excavated by the rotary tool 4. The delivery chute 12, immediately behind the plough 2, extends to substantially the full depth of the slit trench with its delivery aperture 17 facing rearwardly so that material contained in the hoppers is delivered to fill-in the trench as the trenching apparatus is moved forward by the tractor vehicle.

It is preferred in use to fill the forward section of the partitioned hopper 11 with a coarse aggregate material such as gravel, and to fill the rearward portion with sand. Therefore as the apparatus moves forward the ploughed lower part of a trench is filled with the coarse material and the excavated upper part with sand.

According to the method of using the apparatus described above a trench is formed in two stages the first being to excavate the upper part of a trench by the removal of material with a rotary cutter, and in the second part to plough the trench to its full depth, preferably the filling material of the trench is deposited immediately after the trench is cut. A typical drainage trench has a full depth of approximately 12 inches, or 30 cms and approximately 2 inches or 6 cms in width. As previously mentioned the delivery aperture 17 of the chute is divided into two approximately equal upper and lower apertures 17A and 17B so that the lower half of the trench is filled with coarse material and the upper half is filled with sand to ground level.

It is found in practice that by removing material from approximately the top half of a trench and ploughing only the lower half of the trench that ground heave along the margins of the trench is minimised and normal ground level can be readily restored with only light rolling. Also, it is found that by ploughing the lower half of the trench and immediately filling with coarse material and sand that subsequent settling of the trench filling material is virtually eliminated so that little or no top dressing is later required. Grass is able to grow through the top layer of the sand without difficulty so that within a relatively short period the normal surface is fully restored.

Claims (15)

1. A method of forming a trench comprising the steps of partially excavating the trench by the removal of material to part only of the final depth and ploughing the trench for the remainder of its full depth.

2. A method according to Claim 1 wherein the step of partial excavation is carried out using a rotating cutting tool.

3. A method according either Claim 1 or Claim 2 wherein the step of ploughing is carried out following the step of partial excavation.

4. Trenching apparatus for performing the method of any one of Claims 1 to 3 comprising a carriage having mounted thereon first means for partially excavating a trench to part only of its final depth and second means for ploughing the trench to the remainder of its final depth.

5. Trenching apparatus according to Claim 4 wherein the first means comprises a rotating cutting tool or excavator.

6. Trenching apparatus according to either Claim 4 or Claim 5 wherein the second means comprises a plough.

7. Trenching apparatus according to any of Claims 4 to 6 further comprising means for delivering granular material to fill the trench.

8. Trenching apparatus according to Claim 7 wherein said means for delivering granular material includes a chute extending into the trench and having an open lower end for delivery of the material.

9. Trenching apparatus according to Claim 8 wherein the open lower end of the chute has a delivery aperture facing rearwardly and inclined upwardly towards the rear.

10. Trenching apparatus according to Claim 9 wherein the delivery chute is partitioned to provide upper and lower delivery apertures.

11. Trenching apparatus according to any one of Claims 4 to 10 further including vibrator means, which in use is effective to laterally vibrate at least the delivery chute.

12. Trenching apparatus according to any one of Claims 4to 11 wherein the carriage is adapted to be trailed by a powered tractor vehicle.

13. Trenching apparatus according to Claim 12 wherein the carriage is further adapted to receive a power drive from the tractor vehicle to drive, in use, at least the excavating means.

14. A method of forming a drainage trench substantially as hereinbefore described.

15. Trenching apparatus substantially as hereinbefore described with reference to the accompanying drawing.