WO2007107742A1

WO2007107742A1 - Underground chambers

Info

Publication number: WO2007107742A1
Application number: PCT/GB2007/000982
Authority: WO
Inventors: Harold Neville Stephen Bell
Original assignee: Radius Systems Ltd; Uponor Innovation AB
Current assignee: Radius Systems Ltd; Uponor Innovation AB
Priority date: 2006-03-20
Filing date: 2007-03-20
Publication date: 2007-09-27
Anticipated expiration: 2008-09-20
Also published as: GB0605567D0; GB2436341B; GB2436341A; EP2002522A1

Abstract

An underground chamber (10) has a wall element (12) defining and lying in a first plane (20) and having inner (16) and outer (18) skins separated by spaced ribs (20) spanning the gap between said skins and joined thereto. A top (22) also joins the skins and lies in a plane substantially perpendicular the skins and ribs. The ribs extend from said top to a level spaced from bottom edges (16b, 18b) of said skins, forming a slot or channel (26). Into this is fitted a stiffener (30) comprising a base (32) and upstanding flanges (34,36). The flanges are of a height, substantially equal to the separation of the bottom of said ribs from said bottom edges. The flanges are supported by stiffening webs (38) connected between said flanges and to said base. An alternative arrangement provides the stiffening under the base. Also, pockets (54) are provided for hanging furniture.

Description

Underground Chambers

The present invention relates to underground chambers used in utility industries, particularly telecommunications. Underground chambers come in many shapes and sizes; they may be complete, or modular. Modular chambers may be ring sections that are stacked on one another, or wall panels that are connected end to end, often with special corner pieces. Chambers may be constructed from concrete or of plastics material, often recycled. Chambers may have a solid construction, or hollow. The present invention is concerned primarily with modular chambers of hollow plastics wall panels connected together.

BACKGROUND

Such chambers are presently sold by the present applicants through Radius Plastics Limited in Northern Ireland under the brand name Radbox®. Somewhat similar ring- shaped chamber sections are also sold by them under the brand name Quadbox®. Both these products have walls that comprise an inner skin, an outer skin, a joining top, and spaced webs or ribs that span the gap between the inner and outer skins and support them. There is an open bottom and the arrangement is such that the elements making up the Radbox® and Quadbox® products can be moulded in two-part moulds that split in a horizontal direction and having a core that forms the space between the skins, as well as the ribs spanning them. By virtue of this construction it is not possible for the skins to be exactly parallel, otherwise there will be no draft provided between the mould halves that enables them to be separated. This method of production produces a component in which the walls lie in a first plane; the inner and outer skins are essentially parallel said first plane, but inclined slightly with respect thereto to provide said necessary draw. Said top is perpendicular to said first plane and said ribs are also substantially perpendicular to said first plane, and also to the top. Thus, at the top, there is three-axis support for the wall provided by the inner and outer skins, the top and the ribs, all supporting one another. Consequently the arrangement at the top of the wall is quite stiff in all directions, including the plane of the top itself. However, at the open end of the wall at its bottom, there is no support for the wall in a plane parallel the plane of the top. Indeed, the ribs are generally stopped short of the bottom of the inner and outer skins because it is often desired to be able to stack walls one on top of the other, with the top of a lower wall being received within the confines of the inner and outer skins of a wall above, which wall is then supported on the top of the wall below entirely on its ribs. This may inevitably be the case, particularly with deep wall sections, by virtue of the draft provided through the inclined skins. Otherwise the room for the top of the wall beneath may be provided by a step in the skins at their bottoms, and in which event the wall above is not just supported on its ribs, but also by the step in its inner and outer skins.

Be that as it may, one effect of stacking walls one upon the other is that the stiffness of top of the wall beneath has the effect of stiffening the bottom of the wall above, at least in the plane perpendicular said first plane and parallel the top. Thus a lack of stiffness in any particular direction is not a particular problem with Quadbox® chambers because any lack of stiffness at the bottom of individual ring sections is compensated by the fact that the rings are stacked one upon the other.

However, with Radbox®-type chambers there is potentially a more pronounced problem. Wall sections are deeper and, quite frequently, backfill around a chamber formed by joined Radbox® wall sections exposes the lack of support in the walls at their bottom (where, incidentally lateral pressures in the plane parallel to the top are at their greatest) and the walls tend to bow inwardly. This can be countered by inserting floor elements that prevent inward bowing, but often it is preferred to insert these last, perhaps after the backfill has already been placed.

The lateral stiffness of the walls can be increased by inclining the ribs. This triangulation increases the stiffness but provides another problem in that hole-drilling through the chamber wall must then be completed in one operation. That is because the drilling is likely to cut a rib and it would be difficult to align adequately holes cut from either side of the wall. With parallel ribs, perpendicular to the skins, this problem does not occur and so cutting the skins from either side is not problematic, even if the alignment between the holes is not perfect. Consequently this arrangement of ribs is preferred, despite it not providing the same degree of stiffness for the wall as inclined ones.

EP-A-787861 discloses ring sections having a wall construction as described above. WO-A-01/73230 describes similar ring sections except here the wall skin spanning the gap between inner and outer skins is not at the top, but intermediate the top and bottom. This means that there is less bias in the stiffness towards the top of the walls. EP-A- 641897 discloses an entire chamber having walls of this construction, wherein the base of the inner skins are connected by a floor that renders the wall at floor level quite stiff. WO-A-98/02617 discloses underground chambers having modular wall panels of the afore-mentioned construction, joined together at their ends to form rings, and wherein the ribs are inclined with respect to one another and the inner and outer skins. US-A- 5181793 discloses a hollow construction of a gutter channel, where a lid, when in place, provides support for the top of the gutter. GB-A-2342676 discloses many features of the Radbox® system described above.

It is therefore an object of the present invention to provide a chamber construction that solves these issues, or at least mitigates their effects.

BRIEF SUMMARY OF THE DISCLOSURE

In accordance with a first aspect of the present invention there is provided an underground chamber comprising a wall element defining and lying in a first plane and having inner and outer skins separated by spaced ribs spanning the gap between said skins and joined thereto, and a top joining said skins and lying in a plane substantially perpendicular said skins and said ribs, said ribs extending from said top to a level of or spaced from bottom edges of said skins, and a stiffener comprising a base, flanges upstanding from said base, and fences separated from one another by an amount to permit a close sliding fit of said fences of the stiffener against said bottom edges when said base is arranged substantially parallel said top, said flanges being supported by stiffening webs connected between said flanges and to said base.

Preferably, in a first variation, said ribs extend from said top to said level spaced from bottom edges of said skins; said flanges and fences are the same components of the stiffener; said close sliding fit of said fences of the stiffener is between said bottom edges; and said flanges are of a height substantially equal to the separation of the bottom of said ribs from said bottom edges.

Preferably, said base has lateral extensions to support said bottom edges.

Preferably, said base has depending lips on its side opposite said flanges, said lips being parallel said flanges and separated from one another by an amount so that said top of another of said wall elements can be a close sliding fit between said lips. Said flanges and bottom edges may have between them catches on one and latches on the other that snap into engagement when the stiffener is inserted between said bottom edges, thereby to retain the stiffener in place, for example during transportation.

Alternatively, in a second variation, said ribs extend from said top to a level with said bottom edges of said skins, said fences extend from said base on the opposite side thereof to said flanges; and said fences are separated by an amount to permit said close sliding fit of the wall element between said fences.

Preferably, said flanges are extended to provide legs, said legs being parallel said flanges and separated from one another by an amount so that said top of another of said wall elements can be a close sliding fit between said legs.

Said fences and bottom edges may have between them catches on one and latches on the other that snap into engagement when the stiffener is inserted around said bottom edges, thereby to retain the stiffener in place, for example during transportation.

Put another way, in accordance with the first variation of a first aspect of the invention there is provided an underground chamber comprising a wall element defining and lying in a first plane and having inner and outer skins separated by spaced ribs spanning the gap between said skins and joined thereto, and a top joining said skins and lying in a plane substantially perpendicular said skins and said ribs, said ribs extending from said top to a level spaced from bottom edges of said skins, and a stiffener comprising a base and upstanding flanges separated by an amount to permit a close sliding fit of said flanges of the stiffener between said bottom edges when said base is arranged substantially parallel said top and said flanges being of a height substantially equal to the separation of the bottom of said ribs from said bottom edges, said flanges being supported by stiffening webs connected between said flanges and to said base.

Said base may have lateral extensions to support said bottom edges. Said base may have depending lips on its side opposite said flanges, said lips being parallel said flanges and separated from one another by an amount so that said top of the wall element can be a close sliding fit between said lips.

By this measure two wall elements can be stacked on top of one another with several advantages being experienced. In the first case, whether between stacked wall elements or a bottom wall element supported on the ground or some other flat surface, the wall elements are stiffened in a plane parallel said top by the introduction of said stiffening element between said bottom edges of the wall element. In order to bow inwardly, the stiffening element must also bow in a direction resisted by said element, in much the same way as the top of the wall element resists sideways forces. Consequently less bowing takes place. This is despite the potential lack of any other connection between the stiffener and wall element.

Also put another way, in accordance with the second variation of said first aspect of the invention there is provided an underground chamber comprising a wall element defining and lying in a first plane and having inner and outer skins separated by spaced ribs spanning the gap between said skins and joined thereto, and a top joining said skins and lying in a plane substantially perpendicular said skins and said ribs, said ribs extending from said top to a level with bottom edges of said skins, and a stiffener comprising a base and upstanding fences separated by an amount to permit a close sliding fit of the wall element between said fences when said base is arranged substantially parallel said top, and flanges depending from said base being supported by stiffening webs connected between said flanges and to said base.

In either variation, the bottom of the wall element is supported laterally by the stiffener whose stiffness is provided by the flanges, the base and the webs. Whether the stiffener fits inside the slot channel provided at the base of the wall element, or the wall element is seated on the base between the fences, with the flanges and webs being below, is largely immaterial.

For stacking wall elements one upon the other in said second variation, said flanges may be extended to provide legs, said legs being parallel said flanges and separated from one another by an amount so that said top of the wall element can be a close sliding fit between said legs.

Preferably, in either variation, said stiffener is a plastics moulding. Said webs may be arranged so that they lie in planes inclined with respect to said flanges but perpendicular said base. Said chamber is preferably modular, and said wall element is an independent component. It may be an integral part of a ring section. Alternatively, it may be a separate wall panel joined edge to edge to other wall panels to construct a ring section. Multiple ring sections may be stacked one upon the other to construct said chamber. Said ribs are preferably perpendicular said skins.

As mentioned above, such chambers may have a separate floor element that, possibly at a late stage in the construction of the chamber, is inserted. If such floors are not retained in position, and are constructed from plastics material, then a potential problem occurs if the chamber should flood. Then, the floor may float on the flood water, disguising the fact that the chamber is flooded and trapping a hapless engineer into relying on it with inconvenient, if amusing (at least for those observing), results.

In accordance with a second aspect of the present invention there is provided an underground chamber comprising a wall element defining and lying in a first plane and having inner and outer skins separated by spaced ribs spanning the gap between said skins and joined thereto, and a top joining said skins and lying in a plane substantially perpendicular said skins and said ribs, said ribs extending from said top to a level spaced from bottom edges of said skins, a step being provided in said skin between said top and bottom edges to support furniture on said step, an external edge of said step defining the profile of the skin beneath said step until it terminates adjacent the bottom edge of said inner skin to form an undercut above said bottom edge whereby a floor element may be retained under said undercut.

The height of the undercut above said bottom edge is preferably arranged to be of a thickness some what greater than the thickness of said floor element, so that an edge of the floor element can be accommodated under the undercut without lifting the wall element.

It is also desirable that furniture may be supported in the chamber off the floor of the chamber. Such furniture may comprise steps to permit operatives gain access to the chamber, or bearers whereby cabling or the like can be hung.

In accordance with a third aspect of the present invention there is provided an underground chamber comprising a wall element having inner and outer skins separated by spaced ribs spanning the gap between said skins and joined thereto, said inner skin defining and lying in a first plane, said second skin being substantially parallel thereto, and a top joining said skins and lying in a second plane substantially perpendicular said first plane and said ribs, a furniture hook support being provided in the form of a base ledge of the inner skin, said ledge lying parallel said second plane intermediate said top and a bottom edge of said inner skin, a top section of the inner skin above said base ledge being spaced towards said outer skin with respect to a bottom section of the inner skin below said ledge, a base pocket being formed between said base ledge and said top section whereby hooked furniture components may be connected to said wall element by hooking over said base ledge and into said pocket.

Said furniture hook support preferably further comprises an intermediate ledge between said base ledge and said top section and between said base ledge and said top, an intermediate pocket being provided between said intermediate ledge and said top section, said base ledge and intermediate ledge forming connection sites whereby hooked furniture components may be connected to said wall element by hooking into said connection sites, said furniture thereby being prevented from rotating about either of its connection sites to said inner skin.

The or each pocket may be open so that there is at least one passage through said inner skin. Said base pocket is preferably at a bottom end of a channel in said inner skin extending parallel said ribs from a top end of said channel at said top, whereby said top section lies in a plane between said first plane and said outer skin.

Said intermediate ledge is preferably formed by a web across said channel intermediate the plane of said top section and said first plane.

Said base ledge is preferably at the top of an inward fold of said inner skin, whereby said bottom section lies in a plane on the side of said first plane remote from said outer skin. Said top section may lie in said first plane.

One of said ledges may lie in said first plane, the other ledge being offset with respect thereto in a direction parallel said top. The other ledge may be within a channel formed in said wall element and extending from said top. Alternatively, the other ledge may be on a fold of the inner skin in a direction away from said outer skin. Said bottom section may be on the side of said first plane remote from the outer skin and be formed by an inward fold of said inner skin, said bottom section terminating adjacent the bottom edge of said inner skin to form an undercut above said bottom edge whereby a floor element may be retained under said undercut. In this sense, "inward" means away from the outer skin and generally inwardly of the chamber being formed.

The height of the undercut above said bottom edge is arranged to be of a thickness somewhat greater than the thickness of said floor element, so that an edge of the floor element can be accommodated under the undercut without lifting the wall element.

Put another way, these two variations of the third aspect of the present invention provide, on the one hand, an underground chamber comprising a wall element defining and lying in a first plane and having inner and outer skins separated by spaced ribs spanning the gap between said skins and joined thereto, and a top joining said skins and lying in a plane substantially perpendicular said skins and said ribs, an inset being provided in said top defining a channel lying in said inner skin parallel said ribs and terminating in a base ledge of said inner skin, a base aperture being provided between said base ledge and the bottom of said channel whereby hooked furniture components may be connected to said wall element.

Preferably, between said base ledge and said top, an intermediate ledge is disposed defining the floor of the channel between said intermediate ledge and said base ledge, an intermediate aperture being provided between said intermediate ledge and the base of said channel extending to said top, whereby hooked furniture components may be connected to said wall element by hooking into both said intermediate and base apertures, said furniture thereby being prevented from rotating about either of its connection sites to said inner skin.

Said channel may have no depth, in which event, said ledge or ledges are protruding from the side of the inner skin, which is thereby folded.

On the other hand, this aspect also provides an underground chamber comprising a wall element defining and lying in a first plane and having inner and outer skins separated by spaced ribs spanning the gap between said skins and joined thereto, and a top joining said skins and lying in a plane substantially perpendicular said skins and said ribs, a composite pocket being provided in said inner skin between said top and bottom edges comprising a first, upper ledge and a second, lower ledge of said inner skin, each ledge having an upstanding lip, whereby furniture having first and second hooks can engage and hang from the upstanding lips of each step.

Preferably, at least one of said ledges is flush with said inner skin. In that event, the other ledge will be within a channel formed in said wall element and extending from said top, or on a fold of the inner skin in a direction away from said outer skin.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are further described hereinafter, by way of example only, with reference to the accompanying drawings, in which

Figures 1a, b and c are respectively a side section through a wall element and stiffener in accordance with a first variation of the first aspect of the invention, a perspective view of the stiffener, and a side section through a different application of the arrangement shown in Figure 1a;

Figure 2 is a perspective view into a comer of a chamber in accordance with the second aspect of the present invention;

Figures 3a and b are respectively a perspective view of part of a chamber in accordance with the third aspect of the present invention, and a side section of the mould arrangements to mould the parts shown in Figure 3a;

Figure 4 is a perspective, partly cut-away view of a modified arrangement in accordance with both the second and third aspects of the present invention;

Figure 5a, b and c are respectively a side section, perspective view and modified side section, of part of an underground chamber wall element in accordance with the fourth aspect of the present invention;

Figure 6 is a perspective view of a refinement of the arrangements shown in Figures 4 and 5b; and

Figure 7a, b and c show views corresponding with Figures 1a to c of a second variation of the arrangements illustrated in Figures 1 to c.

DETAILED DESCRIPTION

The inset to Figure 1a shows an underground chamber 10 comprising wall elements 12 joined together by corner units 14. At one end, corner parts are integrated into elements 12a, but these matters form no part of the present invention and are within the present knowledge or skill of those familiar with the present field.

The main part of Figure 1a shows wall element 12 in greater detail in side section. The element 12 has an inner skin 16 and an outer skin 18 separated, but joined, by ribs 20. The tops 16a, 18a are joined by a top skin 22 which is also connected to the ribs 20. The wall 12 lies in a first plane 24, with the skins 16, 18 being essentially parallel thereto. The top skin 22 is perpendicular thereto, although there is no particular reason why it must be flat, or indeed absolutely perpendicular to the plane 24. The ribs 20 are also perpendicular to the plane 24, but in the orthogonal direction with respect to the skins 16,18. The skins 16,18 are not, of course, exactly parallel, because the wall elements 12 are plastics moulded components formed by two-part moulds (not shown) that split in a plane parallel the top 22. A first mould part has a core that extends up between the skins 16,18 forming the space between them, as well as the ribs 20. Thus the skins 16,18 are inclined towards one another in the direction of the top 22 so that draft is formed facilitating separation of the mould halves after injection and solidification of the plastics material. Nevertheless, for most purposes, the skins 16,18 may be regarded as parallel and, indeed, if it is necessary from a functional point of view that they are parallel, this can be arranged, albeit not in the simplest or least costly way.

Thus, at the top 22, the wall element 12 is relatively stiff in all directions, particularly in the direction parallel the top 22. At the bottom, however, the situation is not so stiff. The bottom edges 16b, 18b of the skins 16,18 extend below the bottom of the ribs 18. This provides a slot 26, which could be sized (although is not shown as such here) to fit the top 22 of another wall element 12 so that one wall element can be stacked on another. Indeed, to enable this as shown, the bottoms 16b, 18b can one or both be stepped to fit the top 22 better, if need be, although the draft mentioned above inevitably results in some extra space between the bottom edges 16b, 18b, depending on the depth of the wall element 12 and the amount of draft provided.

Consequently, not only is the bottom of the wall element 12 unsupported laterally by an element corresponding with the top 22, but even the ribs 20 to not extend to the bottom.

However, the invention provides a stiffener 30 (see also Figure 1b), comprising a base 32 and upstanding flanges 34,36, the outside separation of which is arranged to be slightly less than the inside separation of the bottoms 16b, 18b. The flanges 34,36 are supported by webs 38 that extend between them at inclined angles. The triangulation so produced, together with the mutual support provided by the flanges 34,36 and base 32, means that the stiffener 30 is very stiff in the lateral direction - that is to say, in a plane parallel the base 32. Bottoms 16b, 18b are provided with numerous windows 40, forming catches. Flanges 34,36 are formed with latches 42 that can displace inwardly when the stiffener 30 is inserted in the slot 26. The latches 42 are positioned to fit the catches 40 and snap into engagement when the stiffener is fully engaged in the slot 26. However, there is no other connection required between the stiffener and wall element 12, since, in order to bow the wall element 12, it is necessary to bend the stiffener 30 laterally and this it is designed to avoid doing. Consequently it provides similar support to the bottom 16b, 18b that the top 22 does to the tops 16a, 18a of the wall element 12.

Furthermore, where the wall element 12 is to be seated on the ground 46, the stiffener provides a much broader foot than the plain edges 16b, 18b. This is particularly useful on uneven ground that might tend to splay the bottom edges 16b,18b. Indeed, the broader foot supports the chamber better on poor ground. It is to be noted that there is even engagement between the ribs 20 and webs 38, which latter have top edges 38a shaped to fit the slot 26, whose profile is determined by the bottom edges 20b of the ribs 20. Since the webs 38 are inclined, they will intercept the ribs 20 once each. The base 32 has lateral extensions 33 that support the bottom edges 16b, 18b.

Figure 1c shows a variation of the stiffener 30' fitted in a first wall element 12a. Here, the stiffener 30' has depending lips 48 from under the base 32 and opposite the flanges 34,36. The lips 48 are sized to fit over the top 22 of a further wall element 12b on which the first, 12a, is stacked. In Figure 1c, the bottoms 16b, 18b are shown to have a similar width to the top 22, which thereby necessitates the use of this stiffener 30'. However, this is unlikely to be truly representative if the depth of the wall element 12 is large. Indeed, lips 48 could be positioned under bottom edges 16b, 18b, or even inside them. In any event, the stiffener 30' here is providing the role of an adaptor and load spreader, more than a stiffener, since the top 22 provides a degree of stiffness which is satisfactory in most respects. The load spreading role is similar to that mentioned above, although it is quite possibly more significant if the top 22 would otherwise fit inside the slot 26 so that the top wall element 12a is carried by the lower one entirely on its ribs 20. The stiffener could also serve as an adaptor to allow existing chambers, or parts of them, to be used in conjunction with this new chamber even if their sizes are not identical. For example, an existing Quadbox® ring could be used as a base element and, to increase the height of this chamber when additional depth is required, such as with road crossings, the adaptor of the present invention could be added.

In fact, with the stiffener 30 and adaptor 30', the draft between the skins can be minimised as much as is desired for convenient manufacturing so that, in the normal course of events, wall elements 12 could not stack one upon the other, at least, not with interlocking engagement between them. Then, adaptors 30' enable such interlocking and stiffener 30 supports the bottom layer of wall elements.

Turning now to Figure 2, an internal corner 50 of a chamber 10 is shown. Here, wall elements 12a, c have integral corner parts 52, provided with a channel 54 having a furniture ledge 56. This might be to receive a hooked step 60 (see inset drawing), for example, which has a hook 62 to latch behind the ledge 56 and a triangular plate 64 whose sides 66 are adapted to rest on steps 68 formed in the wall elements 12a,c.

The skins 16c beneath the step 68 have the same profile as the outside edge 70 of the steps 68, for the simple reason of permitting moulding and mould separation, as described above. However, the step provides an opportunity to enable a floor panel 80, when inserted into the chamber 10, to be latched under undercuts 82 formed by stopping skins 16c under the step 68 before they reach the level of bottom edge 16b.

Turning to Figures 3a and b, a base ledge 56a is formed in a side 16 of a wail element 12d. A channel 54a is formed in top 22a of element 12d and this is terminated by ledge 56a. Channel 54a then continues internally of the element 12d until its termination 55 (not actually visible in Figure 3a, but shown nevertheless) a distance below ledge 56a. This provides extra support for the ledge 56a, which like the ledge 56 of Figure 2, is adapted to receive furniture of one description or another (eg cable bearers). Figure 3b shows one arrangement of mould parts to form the pocket 54a and ledge 56a and termination 55. Here a core 72 meets a shell 74, contacting at 76 to complete the through-passage or aperture 54x shown in Figure 3a. The space between the core 72 and shell 74 form the skins 16,18, base ledge 56a, channel 54a and top 22a.

Turning to Figure 4, here ledge 56a¹ is not at the front of a channel and flush with the inner skin 16. Instead, it is formed as an extension or fold 80 in the skin 16. Again, skin 16 extends down behind ledge 56a' in order to provide support, terminating at 55'. The lower part of Figure 5 shows the fold 80 in section, and also stopping short of the bottom edge 16b of the inner skin 16 so that an undercut 82' is formed for trapping floor components (not shown).

Figures 5a and b show a modified form of the pocket arrangement of Figure 3a. Here is a composite pocket in accordance with the fourth aspect of the present invention.

Between base ledge 56a and top.22, an intermediate ledge 56b is provided at the top of plate 54b which is arranged between the base of channel 54a front skin 16. The two ledges 56a,b in a single channel 54 mean that an article 75 provided with two hooks 77,79 is stably retained. That is to say, it cannot swing in any direction and therefore provides a fixed location for objects. Between the plate 54b and channel base 54a is provided aperture 54x, as described above with reference to Figure 3b. However, it is equally possible to close the aperture, as shown at 54y between plate 54b and inner skin 16 (see Figure 5c). Closing the aperture provides even more support for the overall arrangement, but it does also provide a rain catcher which may be undesirable. On the other hand, a small aperture could be provided as a drain.

This double ledge arrangement is also provided in the variation shown in Figure 6, which is the variation corresponding with Figure 4. Like in Figure 4, the ledges 56b', 56a' are not provided by a channel formed in the skin 16, but by a fold 80', in this case a double fold. Nevertheless, the same security of fixture for cable bearers is provided, as well as the instep undercut 82" to trap a floor element (not shown).

Although the channel 54a is shown in the drawings as terminating (at 55' in Figures 4, 5b and 5c) beneath the level of the ledge 56'a or 56b (Figure 5b and c), or terminating in pocket bottom 54y, there is no reason, other than the difficulties associated with the moulding process, why the channel 54a cannot continue all the way to the bottom edge 16b. This will certainly increase stiffness. Indeed, the ledges 56a, b could simply be formed on bars or webs that, albeit offset from one another, simply span the channel 54a, intermediate its base and the plane of the inner skin 16, in the case of the intermediate web, and flush with the skin in the case of base ledge 56a.

Finally, referring to Figures 7a to c, a variation of the arrangements of Figure 1 is illustrated where the ribs 20' of the wall element 12' extend all the way to the bottom edges 16b', 18b', lying roughly flush therewith. The stiffener 30a now has downwardly depending flanges 34', 36' from the base 32', and between which flanges are formed diagonal (and in this case overlapping or X-shaped) webs 38'. Upstanding fences are arranged on the base 32', with a separation between them providing a close sliding fit of the bottom end 16b',18b' of the wall element between them. Although the arrangement shown in Figure 7a means that the chamber is sitting on the grid formed by the flanges 34', 36', and webs 38', this may be advantageous if they can be bedded into the base, which may be wet concrete.

Adaptor 30a', shown in Figure 7a, differs from stiffener 30a of Figure 7a, by virtue of depending legs 48'. There is no reason why these legs should depend directly from the flanges 34',36': there could be a step in them like the step between flanges 34,36 and the lips 48 of the Figure 1c arrangement. However, equally, there is no difficulty in arranging the flanges 34'36 to have the appropriate separation so that a step is avoided. In any event, upper wall element 12a' is supported on the top 22 of lower wall element 12b' through the adaptor 30a'. Catches 42' may be provided on the fences 49 to locate and lock in latches 40' formed on bottom edges 16b', 18b'.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. An underground chamber comprising a wall element defining and lying in a first plane and having inner and outer skins separated by spaced ribs spanning the gap between said skins and joined thereto, and a top joining said skins and lying in a plane substantially perpendicular said skins and said ribs, said ribs extending from said top to a level of or spaced from bottom edges of said skins, and a stiffener comprising a base, flanges upstanding from said base, and fences separated from one another by an amount to permit a close sliding fit of said fences of the stiffener against said bottom edges when said base is arranged substantially parallel said top, said flanges being supported by stiffening webs connected between said flanges and to said base.

2. A chamber as claimed in claim 1 , in which: said ribs extend from said top to said level spaced from bottom edges of said skins; said flanges and fences are the same components of the stiffener; said close sliding fit of said fences of the stiffener is between said bottom edges; and said flanges are of a height substantially equal to the separation of the bottom of said ribs from said bottom edges.

3. A chamber as claimed in claim 2, in which said base has lateral extensions to support said bottom edges.

4. A chamber as claimed in claim 2 or 3, in which said base has depending lips on its side opposite said flanges, said lips being parallel said flanges and separated from one another by an amount so that said top of another of said wall elements can be a close sliding fit between said lips.

5. A chamber as claimed in claim 2, 3 or 4, in which said flanges and bottom edges have between them catches on one and latches on the other that snap into engagement when the stiffener is inserted between said bottom edges, thereby to retain the stiffener in place, for example during transportation.

6. A chamber as claimed in claim 1 , in which said ribs extend from said top to a level with said bottom edges of said skins, said fences extend from said base on the opposite side thereof to said flanges; and said fences are separated by an amount to permit said close sliding fit of the wall element between said fences.

7. A chamber as claimed in claim 6, in which said flanges are extended to provide legs, said legs being parallel said flanges and separated from one another by an amount so that said top of another of said wall elements can be a close sliding fit between said legs.

8. A chamber as claimed in claim 6 or 7, in which said fences and bottom edges have between them catches on one and latches on the other that snap into engagement when the stiffener is inserted around said bottom edges, thereby to retain the stiffener in place, for example during transportation.

9. A chamber as claimed in any preceding claim, in which said stiffener is a plastics moulding.

10. A chamber as claimed in any preceding claim, in which said webs are arranged so that they lie in planes inclined with respect to said flanges but perpendicular said base.

11. A chamber as claimed in any preceding claim, in which said chamber is modular, and said wall element is an independent component.

12. A chamber as claimed in claim 11 , in which said wall element is an integral part of a ring section.

13. A chamber as claimed in claim 11, in which said wall element is a separate wall panel joined edge to edge to other wall panels to construct a ring section.

14. A chamber as claimed in claim 12 or 13, in which multiple ring sections are stacked one upon the other to construct said chamber.

15. A chamber as claimed in any preceding claim, in which said ribs are perpendicular said skins.

16. An underground chamber comprising a wall element defining and lying in a first plane and having inner and outer skins separated by spaced ribs spanning the gap between said skins and joined thereto, and a top joining said skins and lying in a plane substantially perpendicular said skins and said ribs, said ribs extending from said top to the level of or spaced above bottom edges of said skins, a step being provided in said skin between said top and bottom edges to support furniture on said step, an external edge of said step defining the profile of the skin beneath said step until it terminates adjacent the bottom edge of said inner skin to form an undercut above said bottom edge whereby a floor element may be retained under said undercut.

17. A chamber as claimed in claim 16, in which the height of the undercut above said bottom edge is arranged to be of a thickness somewhat greater than the thickness of said floor element, so that an edge of the floor element can be accommodated under the undercut without lifting the wall element.

18. An underground chamber comprising a wall element having inner and outer skins separated by spaced ribs spanning the gap between said skins and joined thereto, said inner skin defining and lying in a first plane, said second skin being substantially parallel thereto, and a top joining said skins and lying in a second plane substantially perpendicular said first plane and said ribs, a furniture hook support being provided in the form of a base ledge of the inner skin, said ledge lying parallel said second plane intermediate said top and a bottom edge of said inner skin, a top section of the inner skin above said base ledge being spaced towards said outer skin with respect to a bottom section of the inner skin below said ledge, a base pocket being formed between said base ledge and said top section whereby hooked furniture components may be connected to said wall element by hooking over said base ledge and into said pocket.

19. A chamber as claimed in claim 18, in which said furniture hook support further comprises an intermediate ledge between said base ledge and said top section and between said base ledge and said top, an intermediate pocket being provided between said intermediate ledge and said top section, said base ledge and intermediate ledge forming connection sites whereby hooked furniture components may be connected to said wall element by hooking into said connection sites, said furniture thereby being prevented from rotating about either of its connection sites to said inner skin.

20. A chamber as claimed in claim 18 or 19, in which the or each pocket is open so that there is at least one passage through said inner skin.

21. A chamber as claimed in claim 18, 19 or 20, in which said base pocket is at a bottom end of a channel in said inner skin extending parallel said ribs from a top end of said channel at said top, whereby said top section lies in a plane between said first plane and said outer skin.

22. A chamber as claimed in claim 21 when dependent on claim 19, wherein said intermediate ledge is formed by a web across said channel intermediate the plane of said top section and said first plane.

23. A chamber as claimed in claim 18, 19 or 20, in which said base ledge is at the top of an inward fold of said inner skin, whereby said bottom section lies in a plane on the side of said first plane remote from said outer skin.

24. A chamber as claimed in claim 23 in which said top section lies in said first plane.

25. A chamber as claimed in claim 23, in which one of said ledges lies in said first plane, the other ledge being offset with respect thereto in a direction parallel said top.

26. A chamber as claimed in claim 25, in which the other ledge is within a channel formed in said wall element and extending from said top.

27. A chamber as claimed in claim 25, in which the other ledge is on a fold of the inner skin in a direction away from said outer skin.

28. A chamber as claimed in any of claims 18 to 27, in which said bottom section is on the side of said first plane remote from the outer skin and is formed by an inward fold of said inner skin, said bottom section terminating adjacent the bottom edge of said inner skin to form an undercut above said bottom edge whereby a floor element may be retained under said undercut.

29. A chamber as claimed in claim 28, in which the height of the undercut above said bottom edge is arranged to be of a thickness somewhat greater than the thickness of said floor element, so that an edge of the floor element can be accommodated under the undercut without lifting the wall element.

30. An underground chamber, substantially as hereinbefore described with reference to the accompanying drawings.