The present invention relates to a strut for use in shoring trenches or tunnels.

When a trench or tunnel is excavated, the unsupported side walls of the trench or the roof of the tunnel are susceptible to sudden collapse thereby posing a significant safety risk to personnel who may be working in the trench or tunnel and, in the case of a trench, personnel who may be in close proximity to the edges of the trench. It has been previously proposed to line the opposite side walls of a trench with wooden panels, commonly referred to as soldiers, following the excavation of a section of a trench, and then to insert a number of timber props between opposed panels to thereby keep the panels apart to prevent the walls from collapsing. However, in order to install these timber props it has been necessary for the operator to descend into the unsupported trench to position and mount the props. Further, the operator usually finds it necessary to trim the timber props to a more suitable length so that the soldiers can be better positioned in relation to the walls to match the specific shape of the trench. This method of shoring is inherently unsafe, inefficient and wasteful as the timber props are often discarded after the soldiers have been removed from the trench.

It has also been previously proposed, in an attempt to reduce the risk of in ury to personnel working in or near the trench, to construct an assembly, comprising a pair of opposed panels, a number of length adjustable props which are linked to the panels and a threaded rod which engages each of the props. The assembly is lowered into a trench as a single unit and the props are then extended from above the trench by an operator who rotates

a hand wheel which is fixed to an outer end of the threaded rod. However, such an assembly is very expensive to manufacture and extremely cumbersome and difficult to use. Further, -each strut is not individually length adjustable so that the soldiers cannot be adjusted separately to more closely match the shape of the particular trench after the props have been extended by the operator.

The present invention seeks to provide a strut which is simple in structure, inexpensive to manufacture and lightweight so that it can be installed speedily and efficiently by a single operator. The present invention also seeks to provide a strut which can be collapsed for mounting on a soldier set and which can then be extended, either from inside or outside a trench.

The present invention further seeks to provide a strut which may be used as a component of a shoring assembly which may be preassembled above ground for subsequent installation in a trench and which can be extended from outside the trench.

According to the present invention there is provided a strut for use in shoring trenches or tunnels comprising a pair of elongate members which are linked at adjacent inner ends for relative pivotal movement from an extended condition to a collapsed condition, wherein when the ^_ members are in their extended condition the members lie substantially in the same plane and a free end portion of each member abuts against a respective shoring means whereby to brace the shoring means, and when the members are in their collapsed condition the free end portions of the members are relatively closer together to permit release of the strut from the shoring means, and wherein locking means is carried on the members for releasably

locking the members, one member relative to the other member, when the strut is substantially in its extended condition.

The members may be pivotable about a common pivot axis for movement from the extended condition to the collapsed condition and the locking means may comprise a latching means which is carried on one of the members and a receiving means which is carried on the other one of the members whereby the latching means can engage the receiving means to lock the members, one relative to the other, when the members are in their extended condition.

It is preferable that at least one of the members is length adjustable. The adjustable member or members may comprise two elongate arms which are slidable lengthwise relative to each other, for example the arms may be of substantially telescopic form, and each arm may have one or more bores therethrough which are capable of being aligned to receive a fixing element, for example a bolt, to thereby fix the length of the or each adjustable member.

Conveniently, one or both of the members may have an actuating lever which extends from the inner end of the or each member to provide leverage for extending the members.

It is envisaged that the strut of the present invention may be adapted for use in other orientations, for example, in the case of an extremely wide trench it may be deε__rable to shore a wall against the floor, rather than against an opposed wall. Here, the strut would be mounted between the floor and a soldier at an angle.

It is also envisaged that the strut of the present invention may find application in the shoring of tunnels in which case the strut would be oriented substantially vertically between the roof and the floor of the tunnel to act as a support for the roof of the tunnel.

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

Figure 1 shows a side view of an embodiment of a strut in its collapsed condition;

Figure 2 shows one panel of a soldier set for use with the strut of Figure 1;

Figure 3 shows the strut of Figure 1 in use;

Figure 4 shows a soldier set and two of the struts of Figure 1 which have been preassembled for lowering into a trench as a single unit; and

Figure 5 shows a detail of Figure 4.

Referring now to Figure 1, an embodiment of a strut of the present invention, generally indicated by the numeral 1, comprises a pair of elongate arms 2, 4 which are linked for pivotal movement about a common pivot axis 6 so that the arms 2, 4 can be moved from a collapsed condition, as shown in Figure 1, to an extended condition as shown in Figure 3. When the arms 2, 4 are extended so that they are substantially in the same plane, the arms 2, 4 can be locked, one arm relative to the other arm, by means of a locking arrangement 8 which is mounted on the arms 2, 4. A pivotal foot 10, 12 is mounted at a respective free end portion 14, 16 of each arm 2, 4 for

pivotal movement relative to its respective arm 2, 4 about an axis 17, and each foot 10, 12 is shaped to enable the strut 1 to detachably engage a soldier set 18, as will be described hereinbelow.

A soldier set 18 comprises a pair of substantially rectangular wooden ply panels 22, or soldiers, one of which is shown in Figure 2, each panel 22 usually being taller than it is wide. An elongate U-channel 24 which is fabricated from steel, or other suitable material, is mounted on one face 26 of the panel 22 and extends along the longest dimension of the panel 22 in a central region of the panel 22. The channel 24 has a longitudinal opening 28 which extends outwardly from the panel 22 and a number of steel cleats 30 are mounted, for example by welding or by means of bolts and nuts, at intervals along a web 31 of the channel 24 to receive the feet 10, 12 of the strut 1. The cleats 30 being generally L-shaped to thereby provide a recess for receiving a lower end portion 10a, 12a of the pivotal foot 10, 12 of the strut 1.

In use, for example in the shoring of a trench 32, after a section of the trench 32 has been excavated by shovelling or by operation of a back hoe, an operator measures the width and depth of the trench 32 to be shored and selects an appropriate soldier set 18 and lowers the soldier set 18 into the trench 32 until the bottom end 34 of the U-channel 24 of each panel 22 contacts the floor 36 of the trench 32. The operator, when selecting the soldier set 18 ensures that the soldier set 18 is sufficiently tall that a top end portion 36 of the U-channel 24 will extend upwardly out of the trench 32 in accordance with standard practice. A wooden face 38 of each panel 22 is abutted against the mutually opposed earthen side walls 40, 42 of the trench

32 so that the openings 28 of the respective panels 22 face each other and a collapsed strut 1 is then lowered into the trench 32 and the feet 10, 12 of the strut 1 are inserted into the openings 28 of the U-channels 24 of the soldier set 18 and the collapsed strut 1 is permitted to slide downwardly until each foot 10, 12 comes to rest on a cleat 30. It is most preferable that the pair of cleats 30 on which the feet 10, 12 of the strut 1 are to be mounted are substantially in the same horizontal plane so that when the arms 2, 4 of the strut 1 are ultimately moved to extend the strut 1, the extended strut 1 is then substantially horizontal. This ensures that the support strength of the strut 1 and soldier set 18 combination is maximised.

When the strut 1 has been mounted on the soldier set 18, the operator pushes downwardly on the arms 2, 4 to move the strut 1 into its extended condition, as shown in Figure 3. When the arms 2, 4 are sufficiently extended so that they are substantially in the same plane, the operator slides a lock bolt 44 of the locking arrangement 8 into a corresponding recess 46 which is welded onto the top face 48 of the arm 2. In the process of extending each strut 1 the earthen side walls 40, 42 will be slightly compacted. Therefore, to facilitate the movement of one arm relative to the other arm to extend the strut 1, one arm 4 has an extension 50 which is welded onto the top face 51 of the arm 4 to give the operator sufficient leverage to extend the strut 1 against the reactive force of the trench walls 40, 42.

The operator usually fits more than one strut 1 to each soldier set 18, the number of struts 1 depending on the depth of the trench 32, generally the deeper the trench 32 the more struts 1 that are required. It is preferable, as a matter of safe working practice, to

mount the first strut 1 near the top 52 of the trench 32 and then work downwardly into the trench 32 to mount the remainder of the struts 1. After the operator has mounted the first strut 1, a ladder (not shown) may be lowered into the trench 32 and, after the ladder has been secured, the operator can descend into the trench and mount the remaining struts 1 on the soldier set 18.

It is also preferable, as an additional safety feature, that the members 2, 4 are unable to collapse completely so that if the walls of the trench 40, 42 were to suddenly give way, the soldier set 18 would still be kept apart, even if the distance between them is somewhat reduced. This may be achieved by restricting the pivotal movement of one member 2, 4 relative to the other member, for example, by welding an abutment (not shown) on one member 2, 4 which prevents further pivotal movement of the other member 2, 4 relative to it.

In the embodiment of the strut 1 shown in Figure 1, both of the arms 2, 4 are of telescopic form to allow the length of each arm 2, 4 to be varied. Each arm 2, 4 comprising an outer arm 2a, 4a and an inner arm 2b, 4b, the inner arms 2b, 4b being partially disposed within its respective outer arm 2a, 4a to allow lengthwise movement of the inner arms 2b, 4b relative to the outer arms 2a, 4a. Further, the arms 2a, 2b and 4a, 4b each have a series of transverse holes 54a, 54b bored therethrough which can be aligned, after the arm 2, 4 has been adjusted to a suitable length, to enable the operator to insert a pin 56 to temporarily fix the length of the arms 2, 4. After all of the struts 1 for a particular soldier set 18 have been mounted, and each strut 1 has been extended, the operator may then safely work within the trench 32 to re-adjust, or fine tune, the length of each strut 1, one at a time, to adjust the panels 22 to more

- 8 - closely match the specific shape of the side walls 40, 42 of the trench 32. It may be determined, prior to mounting the struts on the soldier set 18, that a particular strut 1 is either too long, or not long enough, to safely span a freshly excavated trench 32. In such a situation, the operator can simply remove one or both of the telescopic arms 2b, 4b and substitute therefor another arm or arms 2b, 4b which are of a" ^{^} suitable length.

Alternatively, a shoring assembly 58 which comprises the soldier set 18 and the required number of struts 1, - can be preassembled as a single unit at ground level for subsequent installation in the trench 32. This preassembly operation comprises, first of all, laying the soldier set 18 on the ground, so that each panel 22 rests on its longitudinal edge with each panel 22 having the longitudinal opening 28 of its U-channel 24 facing the corresponding opening 28 of the other panel 22 of the soldier set 18. Each strut 1 is then adjusted for length to suit the previously measured width of the trench 32 and all of the struts 1 are then mounted, in their collapsed condition, on the soldier set 18 in corresponding cleats 30. A lifting chain 60 is then connected to the top end portion 36 of each soldier 18 and the shoring assembly 58 is then lifted from the ground and lowered into the trench 32, as shown in Figure 4, by a back hoe, for example.

As the struts 1 are likely to extend under their own weight when the shoring assembly 58 is being lowered into the trench 32, respective lower end portions 61 of the face 26 of each panel 22 are linked by a chain 62 to prevent the struts 1 from extending. This being achieved by way of the chain 62 being shorter-_than an extended strut 1. As shown in Figure 5, the chain 62 is shackled

at one end 64 to the lower end portion 61 of the face 26 of one of the panels 22 and is detachably connected at its other end 66 to a corresponding lower end portion 6L of the corresponding panel 22 of the soldier set 18. The other end 66 of the chain 62 is connected to the panel 22 by means of a connecting arrangement 68 which comprises a slide bolt 70 which extends downwardly from the top of the soldier through a pair of spaced apart keepers ^{^} 72, 74 which have a bore (not shown) to slidably receive the slide bolt 70. When preassembling the shoring assembly 58, prior to installing it into the trench 32, the slide bolt 70 is retracted from the connecting arrangement 68 and a link 76 of the chain 62 is inserted between the keepers 72, 74, the slide bolt 70 is then moved downwardly through the link 76 to thereby retain the chain 62. After the shoring assembly 58 has been lowered into the trench 32, the slide bolt 70 is again retracted to release the link 76 of the chain 62. The struts 1 can then be extended by the operator from outside the trench 32 by using a suitable probe (not shown) to press downwardly on the extension 50 of the arm 4 of each strut 1.

The operator may then safely enter the trench 32 and engage the locking arrangement 8 for each strut 1 and, if required, fit a padlock (not shown) to each strut 1.

When it is subsequently required to remove the shoring assembly 58 from the trench 32, the operator lowers a ladder (not shown) into the trench 32 and, after the ladder has been secured, the operator then enters the trench 32 and disengages each locking arrangement 8. The operator then climbs out of the trench 32 and, while standing on a pair of planks (not shown) which span the trench 32, uses an elongate probe (not shown) which has a hook at one end to engage the extension 50 of the arm 4.

- 10 -

By pulling upwardly on the hooked probe, each strut 1 is collapsed in succession, preferably commencing with the bottom-most strut 1 and working upwardly towards the top 46 of the trench 32. The shoring assembly 58 is then removed from the trench by connecting the lifting chain 60 to the back hoe, as before, and the shoring assembly 58 is lifted out of the trench 32 for subsequent dismantling.

The invention has been described by way of example only and modifications are possible within the scope of the invention.