IMPROVEMENTS IN AND RELATING TO CABLE DUCTS AND WALKWAYS

Abstract: A cable duct element (28) connectable to another identical element to form a duct made up of elements disposed end-to-end comprises a trough (29) and a cover (30) for covering the trough (29). Mutual angular displacement of neighbouring elements in the duct is allowed by limited gaps in or between the elements. In preferred embodiments, the trough (29) includes a base (33) and side walls (32) upstanding from the base (33). First interlock means (42) are at one end of the trough (29) and second interlock means (46) are at the opposite end. The interlocks of neighbouring troughs cooperate telescopically, a limited gap between the telescoped interlocks permitting angular displacement between the troughs. A cover (30) for the cable duct element (28) includes flexible means cooperable with the cover (30) of a neighbouring element and allowing angular displacement between the elements.

Description: IMPROVEMENTS IN AND RELATING TO CABLE DUCTS AND WALKWAYS This invention relates to cable ducts and walkways, especially combined cable duct/walkways that are suitable for use beside railway tracks. It is a long-standing and well-known practice to run electrical cables alongside railway tracks. These cables typically convey electrical power and/or signals to serve the railway system but, increasingly, cables are also being laid beside railway tracks for more general power transmission or telecommunications purposes. This better exploits the land occupied by the railway. Cables may be hung above the ground beside a railway track but more commonly they lie in a partially-buried duct extending parallel to the track, for example set into a trench dug in an embankment that carries the track. The duct consists of a series of identical prefabricated elements disposed end-to-end to form a continuous protective channel, the channel possibly being made up of thousands of elements and thus potentially being of great length. Each cable duct element, in turn, comprises a generally U-section open-ended trough and a removable cover that closes the top of the trough to form a generally rectangular box. The shape of this box is often very simple, being made up of plain, essentially flat rectangular walls disposed orthogonally with respect to one another. The cover is a slab held in place over the trough by its own weight. For many years, these simple cable duct elements have been made of precast concrete. Concrete is used because it is a familiar material that is fire-resistant and perceived to be durable, and because simple cable duct elements made from it are easy and inexpensive to cast. However, concrete cable duct elements suffer from numerous problems which the present invention seeks to address. These problems arise from defects of the material - especially the weight and fragility of concrete which outweigh its low manufacturing costs by adding to the difficulty and hence expense of installation and maintenance - and from the crude design of the elements themselves. The weight of concrete poses particular problems in terms of transportation and installation. Installation requires manual labour, and lifting . such heavy and awkward loads presents a risk of injury to workers. There is a corresponding risk that employers will infringe legislation protecting the health and safety of their employees. Inconveniently, installation of cable ducts often takes place in locations that are accessible only via the railway track beside which the duct is being laid. This may require an engineering train to transport workers and materials to where they are needed, resulting in line closures while the engineering train blocks the track to normal rail traffic. Efforts to minimise disruption by carrying out this work when the track is not in use by normal rail traffic (if indeed such traffic ever ceases) inevitably lead to increased labour costs. Turning to fragility, it has been found that concrete is brittle and susceptible to cracking and chipping during storage, transportation and installation of cable ducts. Frost damage is also likely during use. The problem of fragility is worsened by the weight of large concrete components and by the awkwardness of handling them, which means that workers tend carelessly to drop the components into place rather than risk their fingers, often jarring one concrete part against another. Obviously, any damage to a cable duct compromises the protection that it can give to a cable because the cable may become exposed to the weather and susceptible to rodent damage. Damage to the duct may also cause a cover to wobble on its trough if somebody walks on it; this could be enough to cause that person to stumble and fall into the path of a passing train. In terms of their basic design, too, the abovementioned concrete cable duct elements lack sophistication. For example, there is nothing to resist mutual slippage and separation between adjacent elements, and there is a similar lack of any means to anchor the elements with respect to the ground. Instead, reliance is placed upon the great weight of the elements and the fact that they are usually buried in a trench in the ground. There is also no convenient way to cope with variations in line and level without creating gaps between adjacent elements and/or an unstable, uneven line of covers which presents a tripping hazard to railway workers. Cable ducts can never be dead straight for their entire length; there are many practical situations where the line of elements must be curved and, indeed, the line and level may have to vary quite sharply in order to avoid some trackside obstacles. The traditional, labour-intensive practice has been to bevel or mitre the ends of adjacent cable duct elements on site. A final observation is that existing concrete cable duct elements are extremely wasteful of space during storage and transportation. In one sense, the present invention seeks to overcome these and other defects of known cable duct elements. However, a related facet of the invention relates to walkways; so, a summary of the art of walkways now follows. The safety of railway workers demands that walkways are provided beside railway tracks. In the United Kingdom rail industry, such a walkway is a legal requirement and is called a "cess safety path"; however, the term "walkway" will be used hereafter for simplicity. A railway walkway is usually formed from compacted fill retained by kerbs of, for example, timber, concrete or concrete/steel. The kerbs may be retained by concrete benching or steel pins that anchor the kerbs with respect to the ground. A handrail and/or a retaining wall may also be needed in some situations. A handrail may, for example, be needed on the side of a walkway away from the track if there is a drop on that side of the walkway, or on the side adjacent the track if collision with passing trains is a risk. A retaining wall may be required to hold back a bank of earth where the track and walkway lies in a cutting. Again, these handrails and retaining walls require expensive building operations such as preparation of foundations. It will be clear that constructing a walkway beside miles of railway track is a laborious and expensive process which shares many of the drawbacks of cable duct construction discussed above. It is common for the walkway to lie beside a partially-buried cable duct element, with the surface of the walkway being on the same level as the exposed top surface of the cable duct cover so that the cable duct cover becomes an extension of the walkway and can be stepped upon. Such an arrangement is shown in Figure 1 of the drawings, which will be described in more detail later. In the United Kingdom railway industry, regulations specify that a walkway must be a certain minimum distance away from a track. This distance can be difficult to achieve where there is little suitable ground beside the track because of an obstruction or a slope such as an embankment. The minimum distance is all the more difficult to achieve in these circumstances if a cable duct beside the walkway consumes some of the available ground. Practitioners in the art have made several proposals to address the problems suffered by conventional concrete cable ducts, although few if any of these proposals have ever been adopted. An early effort was GB 476316, which discloses concrete cable duct elements having mutually interlocking formations at their ends. Interlocking the elements in this way helps to prevent slippage of one element with respect to another. However, it will be noted that these formations do not prevent the creation of gaps between successive elements if the elements are angularly displaced with respect to one another, for example to follow a curve or an undulation. The concrete cable duct elements of GB 476316 define parallel longitudinal channels separated by partitions which help to support the lid or cover against downward loads. A thinner-section partitioned cable duct employing a similar principle is disclosed in GB 1214938; the duct therein is a collection of plastics extrusions, namely a U-section channel, a closure and a separating wall extending along the channel that supports and/or secures the closure. However, GB 1214938 is concerned with undemanding low-load applications such as domestic cabling. GB 1412648 is a heavier-duty evolution in which a shallow cable duct for fitting flush with a walkway is made of PVC plastics material. Again, partitions divide the interior of the duct and support a flat lid. Noting the readiness with which PVC expands with temperature, gaps are left between successive lengths of ducting and separate joint elements are provided for bridging the gaps while permitting thermal expansion and contraction. The trend toward plastics materials has, of course, continued to the present day. A modern proposal disclosed in WO94/01907 is a plastics cable duct element designed to be interchangeable with existing concrete cable duct elements. By taking a concrete element as its starting point - thus basically attempting to reproduce a concrete element in plastics - this proposal suffers in comparison with a design from first principles. For example, there remains a need for a separate walkway even though it is acknowledged that workers may tread on top of the duct and so need a non-slip surface thereon. Moreover, interlocking means are again provided for connecting one element to another in series but these means do not permit any angular displacement between successive elements and so introduce problems of their own. Similar problems are suffered by the interlocking cable duct elements of GB 2181206 and GB 2257490. Finally and most recently, WO94/21018 discloses a buriable plastics cable duct element that is also usable as a walkway. A lid or cover wide enough to walk upon is attached to a trough by interlocking means, the lid simply fitting between vertical formations at the upper edges of the trough. These interlocking means may be supplemented by hinges and locks connecting the lid to the trough. At first sight, WO94/21018 is the most complete prior art proposal in terms of addressing the problems of traditional concrete cable ducts and separate walkways. Certainly, the combination of walkway and cable duct would save space and installation costs. However, the main emphasis of WO94/21018 is upon drainage of water that may enter the trough in use, and other aspects of the design are inferior in many respects to the traditional concrete duct. For example, as in so many of the prior art documents, interlocking means connect one element to another in series but these means do not permit sufficient angular displacement between successive elements to cope with anything other than the gentlest curves. Even if the interlocking means could cope with sharp curves and undulations, gaps and irregularities would be created between adjoining covers at those points, possibly presenting a tripping hazard and admitting rodents to the cable duct channel. It is also notable that none of the abovementioned prior art documents address the common need for handrails or retaining walls. So, to add a handrail or retaining wall to the cable duct/walkway defined by WO94/21018, one would have to perform substantial building works; this tends to negate the cost savings allowed by the combination of cable duct and walkway. In summary, therefore, there is a long-standing history of efforts to replace traditional concrete cable duct elements with more sophisticated and lightweight designs. However, the newer designs have failed to gain commercial acceptance; this is probably because they are less flexible and adaptable than traditional elements, whose extreme simplicity has benefits of its own. Against this background, the present invention resides in a cable duct element connectable to another identical element to form a duct made up of such elements disposed end-to-end, the duct comprising a trough and a cover for covering the trough, wherein mutual angular displacement of neighbouring elements in the duct is allowed by limited gaps in or between the elements. Allowing gaps to appear in or between adjacent elements permits sufficient angular displacement to cope with shaφ changes in line or level whilst limiting the gaps helps to exclude rodents from the cable path. In a preferred embodiment, a trough for the cable duct element includes a base; side walls upstanding from the base; first interlock means at one end of the trough; second interlock means at an end of the trough opposed to the first interlock means; the first and second interlock means being complementary such that each interlock means is capable of interlocking with the complementary interlock means of an identical neighbouring trough in a duct made up of elements disposed end-to-end; wherein the interlocks of neighbouring troughs cooperate telescopically and a gap between the telescoped interlocks permits angular displacement between the troughs. The first interlock means can be a male telescopic section and the second interlock means can be a female telescopic section capable of receiving the male telescopic section. The gap between the elements is limited by the difference in diameters of the male and female telescopic sections and preferably also by an outwardly-protruding stop on the male telescopic section and/or an inwardly-protruding stop on the female telescopic section which prevents the elements coming apart longitudinally. Conveniently, the outwardly-protruding stop is a flange at the end of the male telescopic section and the inwardly-protruding stop is a flange at the end of the female telescopic section. Gaps between the telescopic sections are limited along the whole length of the flanges. To permit changes in line, each side wall preferably includes a telescopic section and, to permit changes in level, the base preferably also includes a telescopic section. An arrangement permitting angular displacement in both line and level extends the telescopic sections around the base and side walls in a continuous band. To support the cover, the trough preferably includes a central wall upstanding from the base and extending longitudinally along the trough between the side walls. The trough preferably also includes means such as a latch or, to deter vandalism, a key lock for attaching the cover to the trough. The attachment means may be substantially offset towards one end of the trough so that cover of one cable duct element holds down an end of the cover of a neighbouring cable duct element situated at the end adjacent the attachment means. For compactness in storage and transportation, it is preferred that a trough is nestable within an identical trough so that a plurality of troughs can form a nested stack. The invention also resides in a trough for a cable duct element, the trough including fixing means for fixing an elongate member extending upwardly to support a handrail or a retaining wall and/or downwardly into the ground to anchor the trough. The elongate member can be a handrail post and/or an anchor pin. The fixing means preferably includes a collar that receives the elongate member. The provision of fixing means allows a handrail or retaining wall to be constructed with mimmal labour and materials. Similarly, an anchor pin provides a low-cost method of locating the trough and its foundations against slippage. The invention extends to a cover for a cable duct element, the cover including flexible means cooperable with a neighbouring element and capable of accommodating displacement between the elements. Such displacement between the elements can be angular or linear, or a combination of these. In a particularly elegant arrangement, the flexible means is a concertina or bellows-type arrangement in which relatively rigid transverse members are connected to each other and/or to a rigid portion of the cover by flexible joints. An end of the cover suitably terminates in a tab to fit under and be held down by an end of a cover of a neighbouring element. Where flexible means are employed, the tab is preferably at an end of the cover defined by the flexible means. Where the trough has a central longitudinal wall, a central longitudinal portion of the cover conveniently rests upon an upper bearing surface of the central longitudinal wall. Similarly, where relatively rigid transverse members extend laterally across the trough, free ends of the members may conveniently rest upon upper bearing surfaces of the side walls. Another aspect of the invention resides in a method of constructing a cable duct by progressively adding cable duct elements to a duct assembled from such elements, the method comprising transporting elements along the assembled portion of the duct. This aspect of the invention contemplates a trolley or other vehicle adapted to travel along the duct and to carry a plurality of cable duct elements. The invention encompasses a cable duct comprising a plurality of cable duct elements, troughs and/or covers as defined above or made by the method as defined above. The cable duct of the invention preferably doubles as a walkway and such an arrangement will be described hereinafter. In order that this invention may be more readily understood, reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 is a schematic partial sectional view through a typical trackside installation consisting of a cable duct and a walkway side-by-side; Figure 2 is an exploded perspective view of a cable duct element in accordance with the invention; Figure 3 is a selection of schematic plan, elevation and sectional views of a trough forming part of the element shown schematically in Figure 2 but without full detail of its interlocking parts; Figures 4(a) and 4(b) are enlarged perspective views from above and below respectively, showing the interlocking parts of juxtaposed troughs in detail; Figure 5 is an enlarged perspective view showing the troughs of Figures 4(a) and 4(b) interlocked; Figure 6 is an enlarged perspective view corresponding to Figure 5 but showing a cover attached to one trough and engaged with the other trough; Figure 7 is an enlarged perspective view from underneath of the cover shown in Figure 2; Figure 8 is an enlarged perspective view corresponding generally to Figure 6 but taken from a different angle and showing an element fitted with a post to support a handrail and an anchor pin or stake extending into the ground; Figure 9 is a partial schematic sectional view through a trackside installation showing the cable duct of the present invention on level ground; Figure 10 is a partial schematic sectional view through a trackside installation showing the cable duct of the present invention against a gently rising embankment; Figure 11 is a partial schematic sectional view through a trackside installation showing the cable duct of the present invention alongside an obstruction; Figure 12 is a partial schematic sectional view through a trackside installation showing the cable duct of the present invention against a steep embankment and supporting a low retaining wall; Figure 13 is a partial schematic sectional view through a trackside installation showing the cable duct of the present invention upon an embankment and supporting an external handrail; and Figure 14 is a partial schematic sectional view through a trackside installation showing the cable duct of the present invention upon an embankment and supporting an internal handrail. Referring firstly to Figure 1, an existing trackside installation of the type outlined previously comprises a walkway 20 situated beside and extending parallel to a partially- buried cable duct 21. The walkway 20 and the duct 21 are separated by a substantial distance from a track 22, in accordance with safety regulations. The cable duct 21 consists of a series of elements of rectangular box section. Each element is of precast concrete and consists of a U-section trough 23 capped by a cover 24. The cover 24 is held on top of the trough 23 only by its weight. The walkway 20 is of compacted fill retained on one side by a concrete kerb 25 between the walkway 20 and the duct 21 and on the other side by a concrete and steel kerb 26 supported by concrete benching or steel pins 27 that extend into the ground. It can be seen in Figure 1 how the surface of the walkway 20 is substantially level with the exposed top surface of the cover 24 of the cable duct 21. Referring to Figures 2 to 8, a combined cable duct and walkway element 28 according to this invention comprises a body or trough 29, a lid or cover 30 removably attachable to the trough, and latches 31 for attaching the cover 30 to the trough 29. The trough 29 is generally oblong in plan, open-ended and generally U-shaped in cross section in that side walls 32 extend upwardly from a base 33. The central longitudinal channel thus defined can accommodate cables when the trough 29 is in use, disposed end-to-end with the troughs of other identical elements to create a cable duct/walkway. To this extent, the trough 29 is largely conventional but there are many unconventional features which will now be discussed. Firstly, the trough 29 is an integral moulding of plastics material such as polypropylene, although any suitable plastics may be used, treated as necessary with fire retardants and so on. A toughened, glass-reinforced polypropylene co-polymer is currently preferred. It is envisaged that with careful fireproofing design, for example by avoiding edges where possible as these can burn readily, a trough of this material would maintain adequate structural integrity if exposed to flame. Nevertheless, measures may be taken to avoid or at least to confine the horizontal spread of fire along the duct, for example by glass filling and flame-retardant additives. In general, plastics material confers robustness and lightness and it is envisaged that all components of the invention can easily be handled by one man. For example, the weight of each trough in the preferred embodiment is approximately 12 kg. The proportions of the trough 29 are also unconventional, being unusually shallow and wide: the trough 29 is approximately 1 m long, 0.7 m wide and 0.27 m deep or high. These proportions sacrifice nothing in cable-carrying capacity - the cross-sectional area of the central channel is no smaller than that of a typical cable duct element which may be deeper but is correspondingly narrower - and have advantages of their own. The principal advantage is that the width of the element 28 is in itself sufficient to define a safe walkway on top of the duct; there is no need to add a walkway beside the duct, which allows a dramatic saving on installation costs and also saves space, thus making it easier to achieve the minimum safe distance between the walkway and a railway track in confined surroundings. By way of illustration, it is envisaged that the width of the combined cable duct/walkway would be at least 280 mm less than the combined width of the traditional adjacent cable duct and walkway used to date. Another advantage is that the shallow profile of the element 28 requires a shallower trough 29 to achieve a desired level, again saving installation costs by reducing the depth of the trench that must be dug. It will be seen in Figure 2 that the channel is divided by a line of pillars 34A, 34B and 34C that together define an interrupted centre wall 34 that rises from the base 33 and extends longitudinally along the channel. The trough moulding has thin walls (ideally approximately 3 mm thick) to save material and reduce weight; adequate strength is assured by a liberal reinforcement of transverse ridges 35 in the base and side walls, combined with ribs 36 in the hollow underside. It will also be apparent that the side 32 and centre 34 walls taper inwardly moving away from the base 33; this provides a moulding draft and also facilitates nesting and stacking of multiple troughs during storage and transportation, thus saving space. Similarly, the pillars 34A, 34B, 34C are hollow, being open-bottomed at the underside of the base 33. When the cover 30 is attached to the trough 29 in use, the pillars 34A, 34B and 34C defining the centre wall support the central portion of the cover 30 against sagging under load and also allow for cables within the channel to be separated if necessary. For example, power cables could go on one side of the centre wall and telecommunications cables could go on the other to reduce the possibility of interference from the power cables. More generally, the divided longitudinal channel makes recabling much simpler and gives space beside the cabling route for cable joints. The gaps which divide the centre wall 34 into pillars 34A, 34B and 34C provide a cable crossover path allowing cables to cross from one side of the centre wall 34 to the other when required; the ends of the pillars 34A, 34B and 34C on respective sides of the gaps are radiused for this purpose. In the embodiment illustrated, the gaps or crossover points are spaced apart by approximately 0.3 m. An upright hollow post 37 aligned with the pillars 34A, 34B, 34C rises from the base 33 of the trough 29 at its end adjacent pillar 34A and opposite pillar 34C. The post is of circular cross-section and tapers upwardly like the pillars 34A, 34B and 34C. As will be detailed below, interlocking means are provided whereby juxtaposed troughs 29 in a row can be interlocked. The post 37 is positioned and dimensioned to fit loosely within the hollow pillar 34C of a juxtaposed interlocked trough 29 when the troughs 29 are interlocked in this way. When positioned within the pillar 34C of an interlocked trough 29, the post 37 acts as a pivot point permitting pivotal movement of one trough 29 with respect to another about the pivot. This movement provides for angular misalignment of one trough 29 in relation to the other by pivoting about a vertical pivot axis, thereby allowing for changes in line while preventing separation of the troughs 29. Additionally, the loose fit of the post 37 within the pillar 34C permits angular misalignment about a horizontal transverse pivot axis, thereby allowing for changes in level, and about a horizontal longitudinal pivot axis, thereby allowing for longitudinal twisting of the line of troughs 29. Finally, the elongate pillar 34C accommodates relative longitudinal displacement of interlocked troughs 29. It will be noted that a through-hole 38 is provided at the top of the post 37, penetrating into the interior of the post 37. A corresponding through-hole 39 is provided in the pillar 34C, penetrating into the interior of the pillar 34C. When the holes 38 and 39 are aligned, juxtaposed troughs 29 can optionally be linked together by an elongate link such as a bolt (not shown) extending through both of the aligned holes 38, 39. The link can be loose enough to permit relative movement between the juxtaposed troughs 29, while preventing separation of one trough 29 from another. A pair of tubular sockets 40 and a pair of collars 41 are moulded integrally on the outside of the side walls 32, one socket 40 and one collar 41 on each side wall 32. The longitudinal axes of the sockets 40 and collars 41 extend parallel to one another and orthogonally to the plane of the base 33. The pair of collars 41 are located substantially centrally, albeit slightly offset, with respect to the respective side walls 32 whereas the pair of sockets 40 are markedly offset, being situated close to one end of the trough 29. The collars 41 extend slightly above the upper edge of the side walls 32 whereas the sockets 40 terminate flush with the side walls 32. As will be explained in more detail later, the sockets 40 locate the latches 31 and the collars 41 can accept upwardly-extending posts for handrails or retaining walls and/or downwardly-extending anchor pins or stakes to be driven into the ground. The open ends of the trough 29 are provided with mutually complementary interlock formations enabling a series of identical troughs 29 to be laid together end-to-end while being linked together without excessive gaps. A female interlock formation 42 at an end of the trough 29 has an inwardly-protruding flange 43 behind which there is a recess 44 that receives a complementary outwardly-protruding flange 45 of a male interlock formation 46 at an end of an adjacent trough 29. The detail view of the assembled interlock in Figure 5 shows that the outwardly- protruding flange 45 has considerable freedom of movement within the recess 44 of the female interlock formation 42 without leaving any substantial gaps between the troughs 29. A substantial gap may be regarded as a gap large enough to admit a rodent into the assembled cable duct, say a gap greater than 10 mm to 15 mm. Indeed, the interlock is flexible enough to accommodate angular variations in line and level of at least 4° to 5° 5 from one element 28 to the next. Nevertheless, a trough 29 can transfer load to its neighbour via the interlock, and the flanges 43, 45 limit separation of the interlocked troughs 29 to ensure that covers 30 can always be fitted to the troughs 29 with no gap, or at least a minimum gap, between them. Each latch 31 has a shank 47 and a cam-shaped head 48 offset with respect to the shank 10 47. The shank 47 is received in a socket 40 by a snap fit, screw thread or other suitable connection that holds the shank 47 within the socket 40 whilst allowing the head 48 to turn to the extent necessary to lock or release the cover 30. In any event, it is preferred that the latches 31 are attached to the trough 29 permanently so that the latches 31 cannot fall out of the sockets 40 and be lost. The head 48 is provided with a transverse 15 slot 49 for engagement by a suitable latch operating tool (not shown). The cover 30 is an integral plastics moulding which, in the currently preferred embodiment, is of toughened PBT (polybutylene terephthalate) which is naturally flame retardant, UV resistant and flexible. UV resistance is a particular issue but even if a row of covers suffers UV degradation over long periods in use, it is easy to replace the 0 covers without disturbing the troughs underneath. The cover 30 is generally oblong so as to correspond to and close off the top of the trough 29. Preferably, as illustrated, the cover 30 is wide enough to shade the buried trough 29 from the potentially damaging effects of ultraviolet light in use. This enables material to be selected for the trough 29 without undue reliance upon its UV resistance; 5 this is an important factor if a row of troughs 29 is to remain in place while new covers 30 have to be fitted due to UV degradation of the covers 30. A pair of shallow part-circular cut-outs 50 provided in the long sides of the cover 30 and situated approximately midway along the cover 30 accommodate the parts of the collars 41 that extend above the upper edge of the side walls 32 of the trough 29; this helps to locate the cover 30 longitudinally with respect to the trough 29. A pair of latch cut-outs 51 in the long sides of the cover 30 are situated close to one end of the cover 30 in positions corresponding to the sockets 40. Each of these cut-outs 51 accommodates the head 48 of a latch 31 and is large enough to allow the head 48 to pass through the cover 30 when the head 48 is in a release position, as shown at 48A in Figure 8. When the head 48 is turned by a quarter turn into a lock position as shown at 48B in Figure 8, however, the head 48 engages in a recess 52 adjacent to the cut-out 51 to lock the cover 30 to the trough 29. The slot 49 in the head 48 facilitates this movement; more generally, all components of the present invention are designed so that necessary operations can be made in wet, muddy and cold conditions with gloved hands. Being of plastics material, the cover 30 is too light to remain in place under its own weight but, once locked in place on top of the trough 29, the cover 30 is held firmly against lifting or misplacement due to wind or knocks. Individual covers 30 and indeed individual troughs 29 can be lifted with minimal or no disturbance to neighbouring covers 30 and troughs 29. The upper surface of the cover 30 has an array of transverse recesses 53 moulded in to provide a slip-resistant walkway. Also, as best shown in Figure 7, the recesses 53 define transverse beams when viewed from underneath the cover 30; these beams impart extra stiffness to the cover 30. A major portion of the cover 30, including the cut-outs 50 and the latch cut-outs 51, is a generally planar solid panel. However, the remaining minor portion of the cover at the end opposed to the latch cut-outs 51 is an articulated portion defined by two transverse grooves 54 extending from one long side of the cover 30 to the other in a bellows or concertina arrangement. The grooves 54 define two relatively rigid transverse members 55 separated from each other and from the major portion of the cover by thin relatively flexible integral webs 56 of plastics material. Flexibility is imparted to the webs 56 by their thinness and by their U-shaped folded cross-section as best shown in Figure 7 which allows the transverse members 55 to move to a limited extent with respect to each other and with respect to the major portion of the cover 30. In this way, the cover 30 can shorten or lengthen either generally, in the sense of overall length, or locally, in the sense of one side lengthening and the other shortening. This latter possibility can be visualised as the transverse members 55 pivoting about a vertical axis orthogonal to the general plane of the major portion, thereby to accept changes in line in a row of covers 30 disposed end- to-end. Also by virtue of the flexible webs 56, the transverse members 55 can tilt above or below the general plane of the major portion of the cover 30. This is to accept changes in level in a row of covers 30 disposed end-to-end. Again, this tilting can be a general movement, in the sense that all parts of the transverse members 55 lie above or below the general plane, or a local movement, in the sense of twisting such that one end of a transverse member 55 is above the general plane and the other end is below the general plane. In other words, this twisting movement is about a longitudinal horizontal axis parallel to the general plane. It is of course possible for the lengthening, shortening, pivoting, twisting and/or tilting movements to be combined in a general warping or flexing movement. The end of the cover 30 defined by the articulated portion terminates in a rectangular tab 57 which, on assembly of a cable duct, fits under the latch end of the abutting cover 30 of an adjacent element 28. Referring to the view from underneath of Figure 7, it will be noted that the tab 57 is a heavily-ribbed open-bottomed box section that depends from the transverse member 55 at the end of the cover 30 in downwardly stepped relation. The purpose of the tab 57 is best explained with reference to Figure 6 from which it will be seen that the tab 57 fits snugly within the recess 44 of an adjacent interlocked trough 29 in a series of cable duct elements laid end-to-end. When a further cover 30 (not shown) is latched to that adjacent trough 29, its abutting end will lie over and hold down the tab 57 received in the recess 44. In this way, each cover 30 is connected to two troughs 29: at one end portion to one trough 29 and at the other end portion to a juxtaposed interlocked trough 29. As each cover 30 is connected to two troughs 29, relative movement between the troughs 29 will cause the articulated portion of the cover 30 to move too, by lengthening, shortening, pivoting, twisting and/or tilting. This ensures that the line of covers 30 in a row of elements 28 conforms to the lie of the underlying troughs but without introducing a tripping hazard - because each cover runs smoothly into the next - or admitting water or rodents to the interior of the cable duct. The central longitudinal portion of the cover 30 is supported against downward loads by the centre wall 34 of the trough 29 on which lie the central portions of the beams defined by the recesses 53. The side longitudinal portions of the cover 30 are similarly supported by the upper edge of the side walls 32 of the trough 29, on which lie the outer ends of the beams defined by the recesses 53. The transverse members 55 are, however, free to slide upon the centre 34 and side 32 walls of the trough 29 while being supported thereby; they can therefore move as necessary to accommodate the variations in line from each element 28 to the next. Moving on to Figure 8, a row of posts 58 (only one shown) is inserted into the collars 41 on one side of the duct, forming a support for a handrail or a retaining wall (not shown). The posts 58 can be of any suitable material, such as galvanised steel tubing. The collars 41 on the other side of the duct carry anchor pins or stakes 59 (again, only one shown) of similar diameter to the posts 58; these pins 59 extend downwardly into the ground to hold the cable duct elements securely in place despite their light weight. Where posts 58 and anchor pins 59 are both required on the same side of the duct, it is entirely feasible for the posts 58 to continue downwardly through the collar 41 and into the ground, the posts 58 thus also serving as the anchor pins 59. Indeed, this arrangement is preferred in any event because it strengthens the foundations of the posts 58, which may have to resist substantial side loads in use. Figures 9 to 14 are partial sectional views through various trackside installations including a cable duct/ walkway of the present invention in typical situations. Figure 9 is on level ground and Figure 10 shows the cable duct/walkway 28 next to a gentle embankment 60. A more demanding situation is shown in Figure 11 in which the cable duct/walkway 28 is close to a wall 61. A safe distance to the track 22 has been maintained in this instance, but it will be clear how difficult that would be to achieve with the traditionally separate walkway 20 and cable duct 21 of Figure 1. Where the cable duct/walkway 28 of the present invention is up against a steep embankment 62 as shown in Figure 12, posts 63 passing through the collars 41 can support a low retaining wall 64. The posts 63 also continue down into the ground to serve as anchor pins. Finally, Figures 13 and 14 show the cable duct/walkway 28 of the present invention upon an embankment 65 with posts 63 serving as anchor pins on both sides of the duct and supporting a two-rail handrail 66 on one side; the handrail 66 is internal in Figure 13 and external in Figure 14. The components of the present invention are lightweight thanks to their design and material and are compact due to the facility for nesting. This lends the invention to a novel delivery method in which components are simply delivered to the workplace along sections of cable duct/walkway that have already been laid. This reduces reliance upon engineering trains and so minimises disruption to rail traffic during installation. A development of this concept involves a trolley or other vehicle adapted to travel along the cable duct/walkway of the invention. Many variations are possible without departing from the inventive concept. For example, cable entry/exit ports may be provided in each side wall of a trough to allow cables to be fed into and out of the cable duct at various points along the cabling route. These ports may be covered by removable plugs until required, or they may be defined by cutout or knock-out panels moulded integrally with the trough. A grommet may be employed to seal around a cable passing through such a port. The inventive concept may also be realised by T-section cable duct elements which allow cable runs to be branched, and the latches may be upgraded to locks for resistance to vandalism. In general, the present invention may be embodied in other specific forms without departing from its essential attributes. Accordingly, reference should be made to the appended claims and other general statements herein rather than to the foregoing specific description as indicating the scope of the invention.

Claims: CLAIMS 1. A cable duct element connectable to another identical element to form a duct made up of such elements disposed end-to-end, the duct comprising a trough and a cover for covering the trough, wherein mutual angular displacement of neighbouring elements in the duct is allowed by limited gaps in or between the elements. 2. A trough for the cable duct element of claim 1 , the trough including a base; side walls upstanding from the base; first interlock means at one end of the trough; second interlock means at an end of the trough opposed to the first interlock means; the first and second interlock means being complementary such that each interlock means is capable of interlocking with the complementary interlock means of an identical neighbouring trough in a duct made up of elements disposed end-to-end; wherein the interlocks of neighbouring troughs cooperate telescopically and a gap between the telescoped interlocks permits angular displacement between the troughs. 3. A trough according to claim 2, wherein the first interlock means is a male telescopic section and the second interlock means is a female telescopic section capable of receiving the male telescopic section. 4. A trough according to claim 3 and including an outwardly -protruding stop on the male telescopic section and/or an inwardly-protruding stop on the female telescopic section. 5. A trough according to claim 4, wherein the outwardly-protruding stop is a flange at the end of the male telescopic section and the inwardly-protruding stop is a flange at the end of the female telescopic section. 6. A trough according to any of claims 2 to 5, wherein each side wall includes a telescopic section. 7. A trough according to any of claims 2 to 6, wherein the base includes a telescopic section. 8. A trough according to any of claims 2 to 7, wherein angular displacement is possible in both line and level. 9. A trough according to claim 8, wherein the telescopic sections extend around the base and side walls in a continuous band. 10. A trough according to any of claims 2 to 9 and further including pivot means associated with the interlock means. 11. A trough according to claim 10, wherein the pivot means includes a first pivot part and a second pivot part, a respective one of said pivot parts being associated with each of said first and second interlock means such that when the interlocks of neighbouring troughs cooperate telescopically, the first and second pivot parts of the neighbouring troughs come together to form the pivot means. 12. A trough according to claim 11, wherein the pivot parts fit loosely to one another. 13. A trough according to claim 12, wherein the first pivot part and the second pivot part are movable relative to one another in a telescoping direction. 14. A trough according to any of claims 10 to 13, wherein the pivot means is integral with the base. 15. A trough for a cable duct element according to claim 1 or as defined in any of claims 2 to 14, the trough including fixing means for fixing an elongate member extending upwardly to support a handrail or retaining means and/or downwardly into the ground. 16. A trough according to claim 15, wherein the elongate member is a handrail post, a support for a retaining wall and/or an anchor pin. 17. A trough according to claim 15 or claim 16, wherein the fixing means includes a collar that receives the elongate member. 18. A trough according to any of claims 2 to 14, the trough including a central wall upstanding from the base and extending longitudinally along the trough between the side walls. 19. A trough for a cable duct element according to claim 1, the trough including means for attachment of the cover. 20. A trough according to claim 19, wherein the attachment means is offset towards one end of the trough. 21. A trough according to claim 19 or claim 20 and further including means for engaging a cover of a neighbouring trough. 22. A trough according to any of claims 2 to 21 and being nestable within an identical trough. 23. A cover for a cable duct element according to claim 1 , the cover including movable means cooperable with a neighbouring element and capable of accommodating displacement between the elements. 24. A cover according to claim 23, wherein the movable means is a flexible means. 25. A cover according to claim 24, wherein the flexible means is a concertina or bellows-type arrangement. 26. A cover according to claim 25, wherein the flexible means comprises relatively rigid transverse members connected to each other and/or to a rigid portion of the cover by flexible joints. 27. A cover according to any of claims 23 to 26 and adapted to cooperate with the cover and/or trough of a neighbouring element. 28. A cover according to claim 27, and including engaging means adapted to fit under and be held down by a cover of the neighbouring element. 29. A cover according to claim 28, wherein the engaging means is adapted to engage the trough of the neighbouring element. 30. A cable duct element according to claim 1 and including a trough according to claim 18 and a cover according to claim 23, wherein the cover rests upon an upper bearing surface of the central longitudinal wall. 31. A cable duct element according to claim 30, wherein the cover rests upon upper bearing surfaces of the side walls. 32. A cable duct comprising a plurality of cable duct elements as defined in any of claims 1, 30 or 31, a plurality of troughs as defined in any of claims 2 to 22, and/or a plurality of covers as defined in any of claims 23 to 29. 33. A cable duct, a cable duct element or a trough for a cable duct element, substantially as hereinbefore described with reference to any of Figures 2 to 14 of the accompanying drawings. 34. A trough for a cable duct element, substantially as hereinbefore described with reference to or as illustrated in any of Figures 2 to 6 and 8 to 14. 35. A cover for a cable duct element, substantially as hereinbefore described with reference to or as illustrated in any of Figures 2 or 6 to 14.

Inventors: MCKEAGUE SEAN THOMAS, WHITLEY DARREN JOSEPH, MCKEAGUE, SEAN, THOMAS, WHITLEY, DARREN, JOSEPH
Applicants: MCKEAGUE SEAN THOMAS, SERVIRAIL CONSTRUCTION LTD, WHITLEY DARREN JOSEPH, MCKEAGUE, SEAN, THOMAS, SERVIRAIL CONSTRUCTION LIMITED, WHITLEY, DARREN, JOSEPH
Application year: 1998
Main classification: H02G9
IPC codes: H02G9