A system and method for erecting a temporary retainer in a trench.

TECHNOLOGICAL FIELD

Embodiments of the present disclosure relate to a system and method for erecting a temporary retainer in a trench. Some relate to a system and method for erecting a temporary retainer in a trench in the construction industry and/or utility industry.

BACKGROUND

Previously ram and waler systems have been used for supporting excavated trenches on construction and utility sites or any activity that involves digging holes or trenches that need safety measures putting in place before a person can access the said hole or trench. A waler, also known as a construction waler, is a structural beam or rail which is pressed against the side of wooden planks, wooden sheets, steel sheets or any other suitable material that the walers can push against the sides of the trench to hold the sides of the excavation in place. The rams are typically hydraulic rams, also known as hydraulic cylinders or linear hydraulic motors, which get their power from a pressurized hydraulic liquid, typically oil, which is used to press out a piston rod. A hand pump or other pumping means is used to increase the pressure of the pressurized hydraulic fluid to cause the piston rod to press out, causing the hydraulic ram to expand in length. The hydraulic ram expands in length until it presses the walers against the sheets and traps the sheets against the sidewalls of the trench, at which point the hydraulic ram can be disconnected from the pumping means and capped off so that it retains the correct pressure to press the walers against sheets to trap the sheets against the sidewalls of the trench.

These systems are one of the most widely used due to their flexibility when digging around existing buried utilities and cost efficiency.

The ram and waler system is currently installed by lowering each separate sheet into the excavation individually and separately lowering in the walers and rams and then placing the walers and rams in a bracing configuration to push the sheets against the side of the trench.

This takes a considerable amount of time due to the need to drive and push down the sheets into the bottom of the trench so that they can stand independently, before the walers and rams are placed in the bracing configuration and push against the sheets. It is usually a three-man job, including the excavator and its’ driver.

Workers also put themselves at risk using this system as typically workers get into the trench whilst the sheets are being lowered, so that they can manually adjust the position of the sheets in the trench, and so that they can help push the sheets down into the trench so that the sheets can stand independently before the rams and walers are installed. This leads to several risks including the risk of the trench collapsing in on the workers. Other risks include the risk of the sheets falling on them or dropping from the lifting equipment that is being used to lower the sheets into the trench. There is also the risk of the rams and walers being dropped onto the workers when they are lowered into the trench.

BRIEF SUMMARY

According to various, but not necessarily all, embodiments there is provided a system for erecting a temporary retainer in a trench comprising: a rigid frame comprising mounting means for mounting rigid sheets for forming the temporary retainer when braced, on opposite edges of the frame so that the sheets extend at least below the frame; hanging means coupled to the frame, for hanging one or more retainer braces below the frame; wherein the one or more retainer braces are configured to be placed in a bracing configuration or a non-bracing configuration, wherein the bracing configuration maintains a determined separation between the rigid sheets when the rigid sheets are braced within a trench; wherein the frame comprises lifting means to enable lifting of the mounted rigid sheets and the one or more retainer braces in the non-bracing configuration together. In some, but not necessarily all examples, the frame comprises a rectangular structure, wherein first and second edges of the rectangular structure are opposite each other and comprise the mounting means, and third and fourth edges of the rectangular structure are opposite each other and are adjustable in length, wherein the first and second edges are perpendicular to the third and fourth edges.

In some, but not necessarily all examples, the system is configured to mount the rigid sheets parallel and opposite each other on the first and second edges of the rectangular structure and perpendicularly to the two sides of the rectangular structure that are adjustable in length to enable the distance between the rigid sheets mounted on opposite edges of the frame to be adjusted.

In some, but not necessarily all examples, the system additionally comprises expanding means for pushing against the first and second edges of the rectangular structure in a direction parallel to the third and fourth edges of the rectangular structure to selectively expand the length of the third and fourth edges.

In some, but not necessarily all examples the expanding means comprise one or more hydraulic rams.

In some, but not necessarily all examples, the one or more retainer braces each comprise a retainer hydraulic ram and two walers, wherein the retainer hydraulic ram is configured to press one waler against one of the rigid sheets and the second waler against another of the rigid sheets in the bracing configuration; wherein the system additionally comprises pumping means for expanding the length of the one or more retainer hydraulic rams and the one or more hydraulic rams, wherein the pumping means is configured to expand the length of the one or more retainer hydraulic rams and the one or more hydraulic rams at the same time.

In some, but not necessarily all examples, the system additionally comprises legs attached to the frame, wherein the legs are configured to enable the system to stand on the ground.

In some, but not necessarily all examples, the legs are long enough to allow the mounted rigid sheets to not touch the ground when the system is stood on the ground. In some, but not necessarily all examples, the legs are adjustable in length.

In some, but not necessarily all examples, the system comprises height adjustment means for adjusting the height of the frame with the legs stood on the ground.

In some, but not necessarily all examples, the height adjustment means changes the vertical position of the frame relative to the legs.

In some, but not necessarily all examples, the system additionally comprises retracting means for reducing the length of the third and fourth edges back to a default length.

In some, but not necessarily all examples, the frame additionally comprises mounting means for mounting rigid sheets on the third and fourth edges of the rectangular structure.

In some, but not necessarily all examples, the first and second edges of the rectangular structure are adjustable in length.

In some, but not necessarily all examples, the mounting means comprises protrusions on edges of the rigid frame.

In some, but not necessarily all examples, the hanging means are flexible.

In some, but not necessarily all examples, the one or more retainer braces can move relative to the rigid sheets in the non-bracing configuration.

According to various, but not necessarily all, embodiments there is provided a method for erecting a temporary retainer, comprising: hanging one or more retainer braces below a frame; mounting a first rigid sheet on one edge of the frame, mounting a second rigid sheet on an opposite edge of the frame, wherein the first and second rigid sheets are mounted so that the rigid sheets extend at least below the frame; lifting the frame to enable lifting of the mounted rigid sheets and the one or more retainer braces in a non-bracing configuration together; placing the frame and the mounted rigid sheets and the one or more retainer braces in a trench; placing the one or more retainer braces in a bracing configuration to maintain a determined separation between the rigid sheets by bracing the rigid sheets within the trench.

In some, but not necessarily all examples, the frame comprises a rectangular structure, wherein first and second edges of the rectangular structure are opposite each other and comprise the mounting means, and third and fourth edges of the rectangular structure are opposite each other and are adjustable in length, wherein the first and second edges are perpendicular to the third and fourth edges; wherein the method additionally comprises expanding the length of one or more hydraulic rams to push against the first and second edges of the frame, causing the third and fourth edges to expand in length, wherein expanding the length of the one or more hydraulic rams is done at the same time as expanding the length of one or more retainer hydraulic rams of the one or more retainer braces to put the one or more retainer braces into the bracing configuration.

In some, but not necessarily all examples, the method additionally comprises removing the frame from the trench after the one or more retainer braces have been placed in the bracing configuration, leaving the rigid sheets and the one or more retainer braces in the trench in the braced configuration.

According to various, but not necessarily all, embodiments there is provided a system for erecting a temporary retainer in a trench comprising: a rigid frame comprising mounting means for mounting rigid sheets for forming the temporary retainer when braced, on opposite edges of the frame so that the sheets extend at least below the frame; hanging means coupled to the rigid sheets, for hanging one or more retainer braces below the frame; wherein the one or more retainer braces are configured to be placed in a bracing configuration or a non-bracing configuration, wherein the bracing configuration maintains a determined separation between the rigid sheets when the rigid sheets are braced within a trench; wherein the frame comprises lifting means to enable lifting of the mounted rigid sheets and the one or more retainer braces in the non-bracing configuration together.

In some, but not necessarily all, examples, the system comprises the rigid sheets.

According to various, but not necessarily all, embodiments there is provided examples as claimed in the appended claims.

BRIEF DESCRIPTION

Some examples will now be described with reference to the accompanying drawings in which:

FIG. 1 shows an example of the subject matter described herein;

FIG. 2 shows another example of the subject matter described herein;

FIG. 3 shows another example of the subject matter described herein;

FIG. 4 shows another example of the subject matter described herein;

FIG. 5 shows another example of the subject matter described herein;

FIG. 6A shows another example of the subject matter described herein;

FIG. 6B shows another example of the subject matter described herein;

FIG. 7 shows another example of the subject matter described herein;

FIG. 8 shows another example of the subject matter described herein;

FIG. 9 shows another example of the subject matter described herein;

FIG. 10 shows another example of the subject matter described herein;

FIG. 11 shows another example of the subject matter described herein;

FIG. 12 shows another example of the subject matter described herein;

FIG. 13 shows another example of the subject matter described herein;

FIG. 14 shows another example of the subject matter described herein.

DETAILED DESCRIPTION

FIG. 1 illustrates an example system for erecting a temporary retainer in a trench. The system 100 comprises a rigid frame 110 comprising mounting means 120 for mounting rigid sheets. The rigid sheets are mounted on opposite edges of the frame 110. In the example of FIG. 1 mounting means 120 are shown along one edge of the frame 110, however the mounting means 120 on the opposite edge are present but not visible in the figure. The rigid sheets form the temporary retainer when braced against the walls of the trench. The rigid sheets are mounted on the mounting means 120 near the top of the sheets so that the sheets extend at least below the frame 110 as will be shown in later figures.

The system 100 also comprises hanging means 130, for hanging the one or more retainer braces below the frame 110. The hanging means 130 are coupled to the frame 110, and in this example the hanging means 130 are chains.

As will be described later, the one or more retainer braces are configured to be placed in a bracing configuration or a non-bracing configuration. The bracing configuration maintains a determined separation between the rigid sheets when the rigid sheets are braced within a trench.

The frame comprises lifting means 111 to enable lifting of the mounted rigid sheets and the one or more retainer braces in the non-bracing configuration together. In the example of FIG. 1 the lifting means 111 are the edges of the frame 110 itself, however in other examples anchor points are provided on the frame 110 which can be used as the lifting means 111.

The system 100 enables the rigid sheets and the one or more retainer braces to be lifted together in the position that they would at least approximately be when in the bracing configuration in the trench. They are lifted in the non-bracing configuration as the bracing configuration can only occur when the one or more retainer braces can push the sheets against the sidewalls of the trench. The ability to lift the rigid sheets and the one or more retainer braces together is more efficient than lifting and lowering the sheets and one or more retainer braces separately into the trench.

The mounting means 120 in the example of FIG. 1 are protrusions which can fit through holes which are stamped through the rigid sheets, and the protrusions can have holes through them to allow a clip to be placed through. Securing the clip to the protrusions after a sheet has been placed on the protrusions allows for a secure fastening of the rigid sheet to the frame 110. This allows the rigid sheets to be lifted in a vertical position suitable for positioning in the trench in a safe manner. FIG. 2 illustrates another example system 100 for erecting a temporary retainer in a trench. In the example of FIG. 2 the frame 110 comprises a rectangular structure. First and second edges 160, 170 of the rectangular structure are opposite each other and comprise the mounting means 120 (note that in FIG. 2 the mounting means 120 are on the first edge 160 are not visible but are present). Third and fourth edges, 140, 150 of the rectangular structure are opposite each other and are adjustable in length. In the example of FIG. 2 the third and fourth edges 140, 150 are each telescopic nested tubes which allow for the adjustment in length. The first and second edges 160, 170 are perpendicular to the third and fourth edges 140, 150. The ability for the third and fourth edges 140, 150 to be adjusted in length enables the distance between rigid sheets mounted on the opposite first and second edges 160, 170 to be adjusted. This allows for the system 100 to be used for different sized trenches and also allows the frame 100 to be used in the process of bracing the sheets against the sidewalls of the trench as described below.

In the example of FIG. 2 the system 100 also comprises expanding means 180. The expanding means 180 are mounted to the frame 100 against the first and second edges 160, 170. When the expanding means 180 expand, this pushes against the first and second edges 160, 170. When the expanding means 180 expand in length and push against the first and second edges 160, 170 this causes the third and fourth edges 140, 150 to expand in length due to their adjustable length. In the example of FIG. 2 the expanding means 180 are two hydraulic rams.

In the example of FIG. 2 the system 100 also comprises legs 190 attached to the frame 110. The legs may be adjustable in length and are configured to enable the system to stand on the ground without assistance. In some examples the legs are therefore beneficial in allowing one or more workers to mount the sheets on the frame and hang the one or more retainer braces below the frame without any assistance from any lifting equipment. Suspending the frame 110 in the air by the legs 190 allows the sheets to hang below the frame 110 and the legs may be sized so that the sheets do no touch the ground when mounted on the mounting means 120. The legs also allow the one or more retainer braces to be suspended by the hanging means in the approximate location they need to be for putting into the bracing configuration to push the sheets against the sides of the trench. The system 100 illustrated in FIG. 2 also comprises retracting means 185, which are biased to return the edges 140, 150 to their default length after having been expanded by the expanding means 180. For example, when the outward pressure from the expanding means 180 is released the biasing of the retracting means 185 pulls the edges 140, 150 back together to shorten the length of the edges 140, 150 so that they return to their default length. The retracting means 185 may be a spring or a bungy or alternatively the hydraulic rams 180 may be configured so that when the outward pressure is released, they naturally return to the default length. In other examples the retracting means 185 are not provided and the edges 140, 150 are placed back in their default length manually.

FIG. 3 illustrates an example retainer brace 300. The retainer brace 300 comprises at least one retainer hydraulic ram 310 and two walers 320, 330. The one or more retainer hydraulic rams 310 are configured to press one waler 320 against one of the rigid sheets and the second waler 330 against another of the rigid sheets in the bracing configuration.

FIG. 4 illustrates an example system 100 where the retainer brace 300 of FIG. 3 is hung by the hanging means 130 of the system 100. As illustrated in FIG. 4 the retainer brace 300 is suspended in mid-air due it being hung below the frame which is held off the ground by the legs 190. Alternatively, in other examples where the system 100 doesn’t have legs 190 then the frame 110 could be suspended in mid-air by the lifting means and the retainer brace 300 would still be hung below the frame and suspended in mid-air.

FIG. 5 illustrates an example system 100 with rigid sheets 500, 510 mounted on the mounting means 120 and a retainer brace 300 hanging on the hanging means 130. Although not illustrated in FIG. 5, clips may be fastened over the mounting means 120 to secure the sheets 500, 510 onto the frame 110. FIG. 5 illustrates the retainer brace 300 and the rigid sheets 500, 510 in the non-bracing configuration.

FIG. 5 illustrates a system 100 with legs 190. In other examples without legs 190, the system 100 can be suspended by the lifting means 111, so that the rigid sheets 500, 510 and the one or more retainer braces 300 can be suspended in mid-air in the approximate relative positions they need to be when placed in the bracing configuration within the trench.

FIG. 6A illustrates the system 100 with the sheets 500, 510 and the retainer brace 300 as illustrated in FIG. 5 and additionally hydraulic pipes 600 connected to the hydraulic rams 180 and the retainer hydraulic rams 310. The hydraulic pipes 600 are typically attached to the hydraulic rams 180 and retainer hydraulic rams 310 after the sheets 500, 510 and the retainer brace 300 have been mounted on the system 100. FIG. 6B illustrates the hydraulic pipes 600 with attachment points 601 , 602, 603, 604 for attaching to the hydraulic rams 180 and the retainer hydraulic rams 310. FIG. 6B also illustrates attachment point 610 which attaches to pumping means as described later.

FIG. 7 illustrates an example system 100 with sheets 500, 510 mounted on the frame 110 and a retainer brace 300 hanging from the frame 110. In the example of FIG. 7 the system 100 with the rigid sheets and the retainer brace 300 have been lifted by the lifting means and lowered into the trench 700. The sheets 500, 510 are lined up next to the walls of the trench 720, 730.

FIG. 8 illustrates the system 100 of FIG. 7 with the sheets and retainer brace in the trench 700 and additionally illustrates the hydraulic pipes 600 connected to the hydraulic rams 180 and the retainer hydraulic rams 310. Pumping means 800 are attached to the hydraulic pipes 600 via connection 610 illustrated in FIG. 6B. FIG. 8 illustrates the system 100 and retainer brace 300 after they have already been expanded in length by the pumping means 800 and the hydraulic rams 180 and hydraulic retainer rams 310. In this example, whilst the system 100 and retainer brace 300 are expanded in length, lifting means suspends the system 100 slightly off the floor 710 of the trench 700 so that the legs 190 of the system 100 are not touching the floor 710, which would prevent/resist the expansion of the system 100 due to friction between the legs 190 and the floor 710 of the trench.

Starting from the position shown in FIG. 7 the pumping means 800 pump the hydraulic rams 180 and the retainer hydraulic rams 310 at the same time. This expands the edges 140, 150 of the frame 100 at the same time as the retainer hydraulic rams 310 expand in length. This causes the top of the rigid sheets 500, 510 to be moved apart at the same time as the middle of the sheets 500, 510 are moved apart by the walers 320, 330 pushing against the sheets due to the expansion of the retainer hydraulic rams 310. This causes an evenly distributed pushing of the sheets against the walls of the trench 720, 730 so that the sheets do not bend due to being pushed unevenly in the middle and the top of the sheets. Each of the hydraulic rams 180 and retainer hydraulic rams 310 can also be controlled individually by controlling the pressure entering the rams 180, 310 via attachment points 601 , 602, 603, 604. For example if one ram is expanding too quickly compared to the others, its’ associated attachment point can be controlled to reduce the pressure entering that ram compared to the other rams.

In other examples, multiple retainer braces 300 are provided. For example, a brace 300 can be lined up near the middle of the rigid sheets and another brace 300 can be lined up near the bottom of the rigid sheets. Therefore, when the hydraulic rams 310 on each retainer brace 300 and the hydraulic rams 180 are expanded in length, this causes an even pushing of the sheets against the walls of the trench 720 at the top, middle and bottom of the sheets. Any number of retainer braces 300 can be provided and in any combination of suitable positions relative to the sheets. In some examples the system 100 comprises additional hanging means 130 for the additional retainer brace. For example, another set of hanging means, which can be provided as four more chains, may be provided as additional hanging means 130, with lengths longer than the hanging means 130 illustrated in the Figures so that the additional retainer brace 300 hangs below the retainer brace 300 illustrated in the Figures. There may a set of hanging means (four chains) for each retainer brace hung by the system 100. In other examples, one set of hanging means 130 is used for multiple retainer braces. For example a first retainer brace 300 may be attached part way along the hanging means 130 and a second retainer brace 300 may attached to the end of the hanging means 130.

FIG. 8 illustrates the system 100, the retainer brace 300 and sheets 500, 510 after the hydraulic rams 180 and the retainer hydraulic rams 310 have expanded in length and have pushed the walers 320, 330 against the rigid sheets 500, 510 to trap the sheets 500, 510 against the walls 720, 730 of the trench. When the retainer hydraulic rams 310 are in the correct position to be trapping the sheets 500, 510 against the walls of the trench so that the retainer brace 300 is in the bracing configuration, the pumping means 800 and the hydraulic pipes 600 can be removed. The retainer hydraulic rams 310 can be capped off to maintain their pressure to retain the sheets against the walls of the trench. The system can then be removed from the trench by detaching the retainer braces 300 from hanging means 130, and the sheets can be detached from the mounting means 120, for example by removing the clips of the mounting means 120. The pressure can be released in the hydraulic rams 180, and in some examples the hydraulic rams 180 are configured to reduce in length back to the default length after the pressure is released. As the edges 160, 170 are connected to the hydraulic rams 180, this causes the frame 110 to reduce back to its default length as well. In other examples where the hydraulic rams do not automatically decrease in length, retracting means 185 restore the frame 110 back to its default length. This then allows for easy removal of the system from the trench.

FIG. 9 illustrates the temporary retainer 900 comprising the rigid sheets 500, 510 and the retainer brace 300 within the trench, in the bracing configuration and after the system 100 has been removed from the trench. The temporary retainer 900 supports the excavated trench so that the necessary work within the trench can be carried out. The use of the system 100 is safer and more efficient than the previous method of installing a temporary retainer as the sheets 500, 510 and the retainer 300 are inserted into the trench at the same time in at least the approximate position that they need to be relative to one another to provide the temporary retainer in the bracing configuration. As the hydraulic rams can be put into the bracing configuration within the trench with the sheets straight away whilst the rigid sheets are supported by the frame there is no need to support the sheets in the ground by first driving them into the ground as has been the case previously, which means that workers to do not have to get in the trench and manually handle the sheets as they are being driven into the ground of the trench. This makes the system 100 safer than previous systems.

FIG.10 illustrates an example auxiliary mounting means 1000 which can be mounted onto any of the edges 140, 150, 160, 170 so that mounting means 120 can be provided on all sides of the frame 110. This allows for rigid sheets to be mounted on all four sides of the frame 100, and can be mounted on the frame at the same time. The system 100 can therefore have one, two, three or four edges of the frame mounted with sheets. The auxiliary mounting means 1000 comprises a frame mounting portion 1010 which fits over the edges of the frame 110 and also comprises a protrusion 1020 and a hole 1030. The rigid sheets are placed over the protrusion 1020 with holes in the rigid sheets and a clip can be inserted through the hole 1030 to secure the rigid sheet onto the auxiliary mounting means 1000 and therefore the frame 110.

FIG. 11 illustrates an example method 1100 for erecting a temporary retainer. The method 1100 comprises as a first step 1110, hanging one or more retainer braces below a frame and as second and third steps 1120, 1130 mounting a first rigid sheet on one edge of the frame and mounting a second rigid sheet on an opposite edge of the frame. As described previously, this enables placing the different components of the temporary retainer in the approximate position they need to be in the trench so that they can be placed in the bracing configuration. The next step 1140 of the method comprises lifting the frame so that the mounted rigid sheets and the one or more retainer braces are lifted together in a non-bracing configuration and the method comprises as a next step 1150 placing the frame and the mounted rigid sheets and the one or more retainer braces in a trench. The next step of method 1160 comprises placing the one or more retainer braces in a bracing configuration as described herein.

Optionally the method additionally comprises the step 1170 as illustrated by the dashed box around step 1170. This step of the method may be used if the system 100 for erecting the temporary retainer comprises expansion means 180. This optional step in the method 1170 comprises expanding the length of the one or more expansion means 180 (in this example hydraulic rams) of the frame 110 to push against the first and second edges of the frame causing third and fourth edges of the frame to expand in length. This step 1170 may be performed at the same time as the step 1160, to ensure that an even pressing force is applied to the top, middle and/or bottom of the rigid sheets.

Optionally the method also comprises step 1180 which comprises removing the frame from the trench, leaving the rigid sheets and the one or more retainer braces in the trench in the bracing configuration. The system 100 and the frame 110 can be left in the trench, however it is more often the case that the system 100 will be removed leaving the temporary retainer in the trench in the brace configuration by itself.

FIG. 12 illustrates another example system 100 for erecting a temporary retainer in a trench 700. FIG. 13 illustrates the example system of FIG. 12 after the sheets 500, 510 and the at least one retainer brace 300 (in this example comprising a hydraulic ram 310 and walers 320, 330) have been lowered into the trench 700 in the non-bracing configuration.

FIG. 14 illustrates the example system 100 of FIG. 12 and FIG. 13 in plan view.

In this example system 100 of FIG. 12, FIG.13 and FIG. 14, the system 10 comprises height adjustment means 1200 for adjusting the height of the frame 110, with the legs 190 stood on the ground. The height of the frame 110 is therefore adjustable relative to the trench 700. In this example the height adjustment means 1200 comprise leg receiving means for allowing the legs 190 to pass through, which changes the vertical position of the frame 110 relative to the legs 190. The leg receiving means can comprise locking pins or other locking means to lock the frame 110 at a particular position on the legs 190.

As illustrated in FIG. 14, the mounting means 120 are provided on the inside of the edges 160, 170. This enables the sheets 500, 510 to be lowered into the trench 700 whilst keeping the legs 190 on the ground outside of the trench 700. This provides a stable platform while the sheets 500, 510 are lowered into the trench. The hanging means 130 are provided in any suitable location to enable the at least one retainer hydraulic ram 310 and the two walers 320, 330 to be lowered in the trench between the sheets 500, 510. For example, the hanging means can be provided on the edges 140, 150 as illustrated in FIG. 12, FIG. 13. In other alternate examples the hanging means may be attached to the sheets 500, 510.

In this example the mounting means 120 can also be provided on the edges 140, 150 to mount sheets in a direction parallel to the edges 140, 150. The example system 100 can also comprise expansion means 180 as in other examples. The edges 140, 150 can be adjustable in length as in other examples. The expansion means 180 can be provided in any suitable location, for example the expansion means 180 may be provided close to the edges 140, 150 so that it does not interrupt the space provided for the sheets 500, 510. In other examples the expansion means 180 may be provided within or as part of the edges 140, 150 of the frame 110. The height adjustment means 1200 can in some examples be provided by the legs 190 having telescopic nested portions.

When putting the at least one retainer brace into the bracing configuration, the system 100 may be lifted slightly so that the sheets 500, 510 and the legs 190 do not resist the movement required to put the at least one retainer brace into the bracing configuration due to friction on the ground.

In the example of FIG. 1 , no expansion means 180 are provided. The system 100 of FIG. 1 may therefore be used in trenches which have a known width which is very close to the width of the system with the sheets and retainer braces mounted on the system, so that little or no expansion of the retainer braces is required. The example system of FIG. 1 may also be used in trenches of different widths, and the sheets may not be securely fastened on the mounting means 120 so that as the retainer braces expand in width the sheets can disengage from the mounting means 120.

In examples where the system includes expansion means 180, the expansion means 180 are shown as being fixed to the frame 110. In other examples, the expansion means 180 are detachable from the frame 110, and may be temporarily attached to the frame 110 when required by fastening the expansion means 180 between two edges of the frame 110.

In the examples illustrated in the figures the sheets 500, 510 and the one or more retainer braces 300 do not form part of the system 100. In other examples, the sheets 500, 510 and the retainer braces 300 do form part of the system 100. In other examples, the temporary retainer 900 forms part of the system 100.

In the examples illustrated in the figures, one sheet is mounted on the mounting means 120 of each edge of the frame 110. In other examples, multiple sheets may be mounted on the same edge of the frame 110 using the mounting means 120 of the edge.

In the examples illustrated in the figures, the mounting means 120 comprise protrusions which can have detachable clips for securing the sheets onto the mounting means 120. In other examples, the mounting means 120 can have incorporated selectable securing means for selectively securing the sheets to the frame. This avoids the need for using detachable clips which may easily be lost.

In the examples illustrated in the figures, only one retainer brace 300 is illustrated. However multiple retainer braces may be provided. If there are multiple retainer braces they may be hung on the same hanging means 130 at different heights below the frame or alternatively separate hanging means 130 are provided for the different retainer braces 300. In this particular example the hanging means 130 for the different braces will be of different lengths.

In some examples, all edges 140, 150, 160, 170 of the frame 110 are adjustable in length.

In the examples illustrated the rigid sheets may be of any suitable material including metals, wood, plastic.

In the examples illustrated the system 100 including the frame 110 and the legs 190 may be made of any suitable material including metals, wood and hard plastic.

The hanging means 130 can be flexible. For example, they can be chains or ropes.

In the examples, the one or more retainer braces can move relative to the rigid sheets in the non-bracing configuration. This is because the one or more retainer braces 300 are not fixed to the rigid sheets 500, 510.

The term ‘comprise’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use ‘comprise’ with an exclusive meaning then it will be made clear in the context by referring to “comprising only one..” or by using “consisting”.

In this description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term ‘example’ or ‘for example’ or ‘can’ or ‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus ‘example’, ‘for example’, ‘can’ or ‘may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all of the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example as part of a working combination but does not necessarily have to be used in that other example.

Although examples have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the claims.

Features described in the preceding description may be used in combinations other than the combinations explicitly described above.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain examples, those features may also be present in other examples whether described or not.

The term ‘a’ or ‘the’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a/the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use ‘a’ or ‘the’ with an exclusive meaning then it will be made clear in the context. In some circumstances the use of ‘at least one’ or ‘one or more’ may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer any exclusive meaning.

The presence of a feature (or combination of features) in a claim is a reference to that feature or (combination of features) itself and also to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result. In this description, reference has been made to various examples using adjectives or adjectival phrases to describe characteristics of the examples. Such a description of a characteristic in relation to an example indicates that the characteristic is present in some examples exactly as described and is present in other examples substantially as described.

Whilst endeavoring in the foregoing specification to draw attention to those features believed to be of importance it should be understood that the Applicant may seek protection via the claims in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not emphasis has been placed thereon.

I/we claim: