GB2042021A - Trench shoring - Google Patents

Abstract

A trenching shield comprises two elongate spaced side walls (10), a blade (12) provided at the front end of each side wall (10), a first transverse member (31) extending between said side walls to connect them together at a location adjacent said blades (12), the mid- point of the height of the first transverse member (31) being not substantially above the mid-point of the height of the shield at the front end thereof, the space between said blades (12) below said first transverse member (31) being unobstructed by any member extending from one side wall to the other and a second transverse member (39) extending between said side walls (10) to connect them together at a location spaced substantially rearwardly of said first transverse member (31). The second transverse member (39) comprises two beams at different heights above the mid point of the height of the shield. <IMAGE>

Description

SPECIFICATION Trenching shield This invention relates to a trenching shield for use in the construction of trenches and more particularly, but not exclusively, in the construction of trenches in which pipework, cables or the like are laid.

An object of the invention is to provide a new and improved trenching shield.

According to the invention we provide a trenching shield comprising two elongate spaced side walls, a blade provided at a front end of each side wall, a first transverse member extending between said side walls to connect them together at a location adjacent said blades, the mid-point of the height of the first transverse member being not substantially above the mid-point of the height of the shield at the front end thereof, the space between said blades below said first transverse member being unobstructed by any member extending from one side wall to the other and a second transverse member extending between said side walls to connect them together at a location spaced substantially rearwardly of said first transverse member.

Said first transverse member may comprise a single beam.

Said second transverse member may comprise a plurality of beams at the same, or substantially the same longitudinal location but spaced at different heights.

The mid-point of the height of at least one of the beams of the second transverse member, may be substantially above the mid-point of the height of the shield at said rearward location.

The second transverse member may comprise two beams one located at or adjacent to the top of the shield at said rearward location and the other located adjacent to but spaced above the mid-point of the height of the shield at said rearward location.

A trenching shield embodying the invention is intended to be used in conjunction with a mechanical excavator of the type having a boom with a dipper arm, carrying an excavating tool, at the end of the boom. In use, an initial trench section is dug by the excavator or other means, the trenching shield is then lowered into the thus formed section and is then dragged forwards by engagement of the excavating tool with the first transverse member of the shield. The blades will thus scrape the sides of the trenches and remove further material as necessary to accommodate the shield between the walls of the initial trench section at a desired depth. This further material is removed subsequently from within the shield by the excavator or other means.

As a result of providing the first transverse member at a location in accordance with the invention, an operator of the excavator has excellent visibility within the shield. Moreover the provision of the first transverse member permits the shield to be advanced by engagement between the first transverse member and the excavating tool of the excavator.

Due to the unobstructed space between the blades and below said first transverse member, an operator of the excavator has an excellent view of the bottom of the trench thus allowing accurate digging to the correct depth ahead of the shield. It also allows the excavator to clean any debris from beneath the first transverse member thereby eliminating the need for manual work.

Further, because of the unobstructed space, the shield may also be used in "lift and drag" operations. That is to say where the stability of the ground to be excavated in front of the shield is poor, then with a shield in accordance with the invention it is possible to advance the shield with the front end thereof inclined upwardly due to the open space at the front of the shield. Thus the ground will not be excavated to the full depth of the trench and the walls of the partially dug trench will be supported. Excavation can be completed within the shield and under the first transverse member and then by exerting pressure downwards on the first transverse member the front of the shield can be pressed into the ground, in one or several stages and debris removed from within the shield, until the trench is of a desired depth.

Blades may also be provided on the bottom edge of the side walls at least adjacent to the front ends of the side walls and facing downwardly, whereby the above operation is facilitated.

The first and second transverse members may be removably connected to the side walls and be of adjustable length or the shield may be provided with a plurality of first and second transverse members of different length which are removably connected to the side walls and are selected as desired to provide a shield of a desired width.

Preferably skid portions are provided along the bottom edges of each side wall adjacent the rear of the shield to restrain the rear end of the shield from sinking into the ground.

These skid portions may comprise planar parts of greater width than the remainder of the bottom edges of the side walls.

The invention will now be described in more detail by way of example with reference to the accompanying drawings wherein: Figure 1 is a side elevation of a trenching shield embodying the invention; Figure 2 is a plan view of the shield of Fig.

1; Figure 3 is a front elevation of the shield of Fig. 1; and Figure 4 is a rear elevation of the shield of Fig. 1.

Referring to the drawings, a shield comprises a pair of parallel spaced vertical side walls 10. At a front end 11 of the shield the side walls 10 each have a forwardly and outwardly inclined part 1 2 which, in use, acts as a blade having a vertical cutting edge 1 3.

In addition, the bottom edge 14 of each of the side walls 10 is inclined downwardly and outwardly over the majority of its length, except for a rearward portion 15, to provide a blade havng an inclined part 1 6 and horizontal cutting edge 1 7.

At the rear end 1 8 of each of the side walls 10 a rearwardly and outwardly inclined surface 19 is provided which acts as a further vertical cutting edge 20. The rearward portion 15 of the bottom edge 14 of each wall 10 has a rearward and upwardly inclined skid part 21.

The side walls 10 are made by welding together box section beams 22. At the front end 11 of the shield the ends of the beams 22 extend within a front blade part 23 as indicated at 22a in Figs. 1 and 2. The blade part 23 comprises an outer plate 24, an inner plate 25 and an inclined front plate 26 which provides the part 12, the plates 24, 25 and 26 being welded together and to the end parts 22a of the beams 22. At the rear end 18 of the shield the ends of the beams 22 are cut off at an angle and a plate 27 welded thereto to provide the surface 1 9. The bottom blade surface 16 is afforded by a plate 28 welded across a bottom angle section 22b whilst the upwardly and rearwardly inclined surface 2t is provided by a plate 29 welded to an appropriately cut end part of the bottom angle section 22b.Lifting lugs 30 are welded to a top beam section 22c.

Adjacent the front end 11 of the shield the side walls 10 are connected together by a first transversely extending member 31 which is in the form of an I-section girder having reinforcing plates 31 b welded across the flanges thereto to provide a reinforced box section beam. The box section beam is bolted as shown at 32 to three brackets 33a, 33b, 33c welded to the inner plates 25. The bracket 33a extends vertically and is intended to withstand forward thrust whilst brackets 33b and 33c are intended to withstand upward and downward thrust respectively. Gussets 33d protect the bolt heads whilst the nuts are protected inside the beam. Apertures, not shown, are provided in the rear plate 31 b to permit of access to the nuts.

The first transversly extending member 31 is provided with a bar 31 a over part of its width to increase its height to the total vertical dimensions of the brackets 33a and 33b. This bar protects the brackets 33b from downward pressure exerted by an excavator bucket for example, during lift and drag operation.

The first transverse member 31 is located so that the mid-point M1 of its height is not substantially above the mid-point M2 of the height of the shield at the front end 11 and is preferably below the mid-point M2. The member 31 is of such dimensions as to be capable of rigidly holding the side walls 10 together at the front end and to permit the shield to be moved forwardly in use as hereinbefore described without any further transverse member at or adjacent the front 11 of the shield.

Adjacent the rear end 18 the shield has reinforcing members 35 welded thereto, the reinforcing members 35 being of basically box configuration and having inwardly directed brackets 36 extending therefrom having flanges 37 on which are bolted end flanges 38 of a pair of beams 39 of box section which together comprise a second transverse member. One of the beams 39 of the second transverse member is located at the top of the shield and the other at a location spaced above the mid-point M3 of the height of the shield.

If desired the second transverse member may comprise a single beam of appropriate dimensions or may comprise more than two beams.

The first 31 and second 39 transverse members may be of any desired length and in practice a plurality of such members are provided each of different lengths so that transverse members of a selected length may be used to permit of adjustment of the width of the shield. For example, the shield can have a maximum width of 1550 mm. and a minimum width of 650 mm. In the latter case the flanges 37 of the brackets 36 would be bolted directly together so that the brackets 36 constitute the whole of the beams of the second transverse members. Alternatively, the transverse member may be of adjustable length to permit adjustment of the width of the shield.

The shield described herein before with reference to Figs. 1 to 4 is used as and has the advantage apertaining to shield embodying the invention described hereinbefore.

Claims (11)

1. A trenching shield comprising two elongate spaced side walls, a blade provided at a front end of each side wall, a first transverse member extending between said side walls to connect them together at a location adjacent said blades, the mid-point of the height of the first transverse member being not substantially above the mid-point of the height of the shield at the front end thereof, the space between said blades below said first transverse member being unobstructed by any member extending from one side wall to the other and a second transverse member extending between said side walls to connect them together at a location spaced substantially rearwardly of said first transverse member.

2. A trenching shield according to claim 1 wherein said first transverse member comprises a single beam.

3. A trenching shield according to claim 1 or claim 2 wherein said second transverse member comprises a plurality of beams at the same, or substantially the same longitudinal location but spaced at different heights.

4. A trenching shield according to claim 3 wherein the mid-point of the height of at least one of the beams of the second transverse member, is substantially above the mid-point of the height of the shield at said rearward location.

5. A trenching shield according to claim 3 or claim 4 wherein the second transverse member comprises two beams, one located adjacent to the top of the shield at said rearward location and the other located adjacent to but spaced above the mid-point of the height of the shield at said rearward location.

6. A trenching shield according to any one of the preceding claims wherein blades are provided on the bottom edges of the side walls at least adjacent to the front ends of the side walls and facing downwardly.

7. A trenching shield according to any one of the preceding claims wherein the first and second transverse members are removably connected to the side walls.

8. A trenching shield according to any one of the preceding claims wherein the first and second transverse members are of adjustable length to provide a shield of a desired width.

9. A trenching shield according to any one of claims 1 to 6 wherein a plurality of first and second transverse members of different length are provided which may be selected as desired to provide a shield of a desired width and removably connected to the side walls.

10. A trenching shield according to any one of the preceding claims wherein skid portions are provided on the underside of each side wall adjacent the rear of the shield to restrain the rear end of the shield from sinking into the ground.

11. A trenching shield according to claim 10 wherein the skid portions comprise planar parts of greater width than the remainder of the bottom edges of the side walls.

1 2. A trenching shield substantially as herein before described with reference to and as shown in the accompanying drawings.