Patent Application
20050252985
This invention relates to a ballast-free track structure suitable for carrying railway rails, and to a rail sleeper for use in such a structure.
Conventional methods for laying a railway track involve placing large wooden, reinforced concrete or steel sleepers on a ballasted track bed, after which rails are fastened to the sleepers. The purpose of the ballast is to provide a free-draining foundation with high shear strength and good elastic (resilient) properties.
However, for over a century there has been very little fundamental improvement in the design and construction of conventional, ballasted railway track. Consequently, some serious and persistent problems have never been completely resolved. In particular, the progressive degradation of the track structure under repeated loading remains problematic. This degradation is manifest in several ways, including loss of geometric stability (the ballast spreads and settles, resulting in loss of vertical and horizontal alignment); loss of resilience (the ballast degrades and becomes contaminated by finer material resulting in increased dynamic damage to track structure (corrugations) as well as to rolling stock); and pumping of sub-grade (caused by dynamic loading, and resulting in ballast fouling and destruction of formation).
The control of these problems is expensive due to heavy ongoing maintenance requirements as well as foreshortened track and rolling stock life spans. In recent years additional environmental requirements to reduce noise and ground-borne vibrations have added impetus to a growing interest in the rail industry to move away from the old ballasted track systems towards more rigid structures, which provide enduring geometric stability and require reduced maintenance.
Several efforts have been made to develop more rigid track structures, most of which have centred on “sleeper-track” or “slab-track” alternatives. One such system is the Japanese “ladder track” system, in terms of which two longitudinal parallel sleepers are joined to each other by transverse steel or concrete sleepers extending between the longitudinal sleepers and which act as gauge ties, the arrangement being such that the finished product looks like a ladder laid on the ground. The concrete sleepers are partially pre-stressed in a factory.
A major disadvantage of this system is that it still relies on a ballasted formation and so remains susceptible to the problems described hereinbefore. A further disadvantage associated with this system is that it is often characterised by poor load dispersal and weak resistance to longitudinal creep movement of the sleepers.
Yet another method of installing a railway track is by in situ casting of the track sleepers. This can be done, for example, by preparing longitudinal trenches for the rails and laying flexible tubes in the trenches. The flexible tubes are filled with concrete so that a rail sleeper is formed that is dimensioned for accepting the rails. Alternatively, the sleepers can be cast on the ground surface by providing lateral restraint to the wet concrete by means of shutters.
One of the disadvantages associated with this method is the relatively extensive time involved for construction, maintenance and reconstruction of the track, because of curing times of the concrete. Other disadvantages include the logistics and complexity of construction, and accompanying difficulties associated with site quality assurance and control.
It is an object of the present invention to provide a rail sleeper suitable for use in erecting a railway track that will overcome or at least minimize some of the problems associated with the prior art and which will facilitate rapid installation and replacement of railway tracks.
It is a further object of the invention to provide a ballast-free track structure and a method for laying the same that will overcome or minimize some of the problems associated with known track structures, or at least will provide a useful alternative to known structures of this nature.
According to the invention there is provided a prefabricated rail sleeper suitable for use in erecting a track structure, the sleeper comprising an elongate body portion for supporting rails, the body portion including a top face, a bottom face and at least two side faces, and terminating at least at one end thereof in a transition joint formation dimensioned matingly to engage a complimentarily dimensioned transition joint formation of an adjacent rail sleeper in use so as to form a substantially continuous track structure.
The rail sleeper may be located on a ballast-free track bed during erection of the track structure.
The body portion may terminate at both ends thereof in a transition joint formation, the arrangement being such that when a series of rail sleepers are arranged in end-to-end orientation on a track bed, they together form a substantially continuous track structure without the need for continuity of reinforcement between adjacent sleepers. The rail sleepers may be orientated in end-to-end orientation on a ballast-free track bed in such a manner that a transition joint space is defined between the transition joint formations of adjacent sleepers for permitting gradual stress transfer between sleepers and preventing lateral displacement between the same.
The rail sleeper also may include at least one block formation dimensioned for supporting a rail. In a preferred form of the invention the rail sleeper may include a number of block formations equally spaced along the length of the sleeper such that the bottom surfaces of the block formations are arranged substantially flush with the bottom face of the body portion. The block formations may be at least partially flared block formations, each block formation including a top surface, a bottom surface and at least two side surfaces. The side surfaces may be characterised therein that they are at least partially outwardly flared from the top surface towards the bottom surface, extending beyond the side faces of the body portion, so as to increase shear interlock of the sleeper with the track bed to reduce longitudinal creep.
The top surfaces of the block formations may be dimensioned for receiving rail fasteners. In particular, the top surfaces of the block formations may be raised relative to the top face of the body portion such that, in use, a gap exists between a rail foot and the top face of the body portion for permitting rail foot drainage, especially when sleepers are backfilled, thus limiting rail-sleeper abrasion and rail-to-rail signaling shorts. The gap also allows free access for welding of rail joints and the passage of under-rail services.
The rail sleeper optionally may include at least one bore arranged proximate the block formation and extending between the top and bottom faces of the body portion, the bore being dimensioned for receiving grout or the like therein for underpinning the block formation and a rail foot. The bore may be lined with a corrugated polymeric sheath to provide non-brittle shear interlock.
The rail sleeper further may include at least on drainage duct for facilitating drainage of liquid, such as rainwater, away from the rail sleeper. The drainage duct may be a transverse duct extending underneath the rail sleeper and defined by a box-out recess in the bottom face of the body portion, the arrangement being such that liquid can drain between different side faces of the body portion by running through the bottom transverse duct. In a preferred form of the invention, the rail sleeper may include a series of transverse ducts that are longitudinally spaced along the length of the sleeper.
The rail sleeper also may include at least one longitudinal service duct located in and extending along the length of the body portion for accommodating, for example, electrical and/or optic fibre cabling.
The rail sleeper further may include resilient pads of high performance polymers arranged on the top surface of each block formation and dimensioned for receiving a rail foot thereon such that the resilient pads at least partially protect the rail sleepers from dynamic and impact loads exerted on the sleepers, which could result in brittle or fatigue failure modes.
The rail sleeper may be pre-cast from pre-stressed, post-tensioned or conventionally reinforced concrete. The rail sleepers may be characterised therein that they are pre-cast in an upside down manner to ensure that the top face of the sleeper, to which the rails are attached, consists of the densest concrete.
The concrete may be cured by using steam, water or chemical curing compounds. The properties of the wet concrete may be modified using additives such as plasticisers, accelerators or retarders, while the properties of set concrete may be modified by epoxy or polymeric impregnation to increase abrasion resistance and enhance chemical durability.
The reinforcement may be augmented or completely replaced by fibres (fibre reinforced concrete (FRC)) to enhance toughness under repeated loading. The fibres may consist of polymeric, natural or steel fibres (galvanised or epoxy coated steel for aggressive conditions) to provide increased abrasion resistance, increased ductility and crack resistance, and resistance to impact and dynamic loading.
The concrete in the sleepers may be characterised therein that it incorporates a proportion of sand-sized rubber particles such that the rubber particles reduce the Young's Modulus of the concrete while not compromising strength, rendering the concrete less brittle and thus more resistant to dynamic or impact forces.
The rail sleepers may be formed in several lengths so as to accommodate curves of different radii.
According to another aspect of the invention there is provided a prefabricated rail sleeper suitable for use in erecting a track structure, the sleeper comprising an elongate body portion for supporting rails, the body portion including a top face, a bottom face and at least two side faces; and at least on drainage duct for facilitating drainage of liquid, such as rainwater, away from the rail sleeper.
The drainage duct may by a transverse duct extending underneath the rail sleeper and defined by a box-out recess in the bottom face of the body portion, the arrangement being such that liquid can drain between different side faces of the body portion by running through the bottom transverse duct. In a preferred form of the invention, the rail sleeper may include a series of transverse ducts that are longitudinally spaced along the length of the sleeper.
According to yet another aspect of the invention there is provided a prefabricated rail sleeper suitable for use in erecting a track structure, the sleeper comprising an elongate body portion for supporting rails, the body portion including a top face, a bottom face and at least two side faces; and at least one block formation dimensioned for at least partially accommodating a rail, the block formation being characterised therein that it is at least partially flared.
Preferably, the rail sleeper includes a number of block formations equally spaced along the length of the sleeper such that the bottom surfaces of the block formations are arranged substantially flush with the bottom face of the body portion.
Each block formation may include a top surface, a bottom surface and at least two side surfaces. The side surfaces may be characterised therein that they are at least partially outwardly flared from the top surface towards the bottom surface such that the block formations extend beyond the side faces of the body portion so as to increase shear interlock of the sleeper with the track bed.
The top surfaces of the block formations may be dimensioned for receiving rail fasteners. In particular, the top surfaces of the block formations may be raised relative to the top face of the body portion such that, in use, a gap exists between a rail foot and the top face of the body portion for permitting rail foot drainage when sleepers are backfilled, thus limiting rail-sleeper abrasion and rail-to-rail signaling shorts. The gap also allows free access for welding of rail joints and the passage of under-rail services.
Each block formation optionally may include at least one bore extending at least partially between the top and bottom surfaces of the block formation and dimensioned for receiving grout or the like therein for underpinning the block formation and a rail foot. The bore may be lined with a corrugated polymeric sheath to provide non-brittle shear interlock. A rock dowel or micro pile may be installed through the bore for underpinning the sleeper in poor ground conditions and for fixing sleeper location on steep grades, sharp curves or the like, the rock dowel or micro pile comprising of an elongate bore extending vertically through the rail sleeper and into the ground underneath, the elongate bore being filled with concrete, grout, crushed rock particles or the like.
According to another aspect of the invention there is provided a ballast-free track structure suitable for carrying rails of a railway track, the track structure comprising a series of rail sleepers according to the invention wherein the sleepers are located in end-to-end orientation on a ballast-free track bed such that the transition joint formation of one sleeper matingly engages the transition joint formation of an adjacent sleeper, the arrangement being such that they form a substantially continuous track structure without the necessity for continuity of reinforcement between adjacent sleepers.
The transition joint formations may be dimensioned for limiting lateral movement of the sleepers so as at least partially to limit independent deflection of the sleepers and for reducing bending and shear stresses in a rail. The transition joint between adjacent rail sleepers may be secured by underpinning the joint using in-situ polymeric concrete, installing a jockey slab underneath the joint, or by means of bolted connections for accommodating longitudinal expansion and contraction of adjacent sleepers.
According to another aspect of the invention there is provided a ballast-free track structure suitable for carrying rails of a railway track wherein the track structure comprises at least two rail sleepers according to the invention located in spaced parallel orientation on a ballast-free track bed so as to define a centre drain between the sleepers; and a mesh located between the sleepers for reinforcing the centre drain.
The mesh may be fixed to the body portion of at least one rail sleeper and may extend from a side face thereof. In one form of the invention, the mesh may be fixed to both of the rail sleepers so that the sleepers and mesh-reinforced centre drain form a track slab. The mesh may be weld mesh. Once the rail sleepers are laid on the track bed, successive weld meshes may be laced together for effecting structural continuity of the track slab.
The rail sleepers may be connected to each other by means of at least one cross tie extending between adjacent parallel sleepers. In a preferred form of the invention, the rail sleepers are connected to each other through a series of steel cross ties extending between adjacent parallel sleepers spaced along the length of the track structure.
The track structure also may include one or more resilient mats arranged intermediate the bottom face of the body portion and the track bed. The resilient mats may comprise of relatively soft polymers adapted at least partially to absorb dynamic or impact loading between the rail sleepers and hard sub-strata such as tunnel floors, concrete bridges and the like, and to attenuate structure-borne or ground-borne noise and vibration.
The track structure also may comprise at least one rock dowel or micro pile located underneath the rail sleeper and proximate a block formation for underpinning the sleeper in poor ground conditions and for fixing sleeper location on steep grades, sharp curves or the like, the rock dowel or micro pile comprising of an elongate bore extending vertically through the rail sleeper and into the ground, the elongate bore being filled with concrete, grout, crushed rock particles or the like.
The track structure may be adapted to accommodate slow and high-speed installations, and may range from light axle load applications, such as mine tracks (in the order of 10 tonne axle load), to heavy haul applications in surface track (in excess of 35 tonne axle load).
According to yet a further aspect of the invention there is provided a method of laying a ballast-free track structure which is suitable for carrying rails of a railway track, the method comprising the steps of constructing a base formation (earthworks) layer works to a specified strength and dimensional tolerances; fixing rail sleepers according to the invention in spaced parallel orientation to form track panels; laying the fixed track panels in end-to-end orientation on the pre-prepared ballast-free formation layer works; placing and fastening rails into position on the rail sleepers; and mechanically adjusting vertical and horizontal alignment of the rail sleepers.
Vertical alignment may be achieved by lifting (jacking) and wedging the track panels to the correct height and packing dry-mix concrete or crusher run underneath the sleepers. Alternatively, where setting times allow, vertical alignment may be achieved by appropriate grout injections or by inserting grout packs. Horizontal alignment may be achieved by dragging the sleeper laterally. Re-alignment of previously installed track may be achieved by exposing the base of the sleeper and tamping in additional dry mix or other material.
The sleepers may be pre-cast upside down in specially designed steel shutters to ensure that the top face of the sleeper, to which the rails are attached, consists of the densest concrete. The concrete is placed into steel shutters and vibrated to ensure maximum density.
Without limiting the scope thereof, two embodiments of the invention will now be described by way of example only and with reference to the accompanying drawing wherein—
A rail sleeper according to the invention there is generally designated by reference numeral 10. The rail sleeper 10 comprises an elongate body portion 12 for supporting rails 14. The body portion 12 includes a top face 12.1, a bottom face 12.2 and at least two side faces 12.3.
The body portion 12 terminates at least at one end thereof in a transition joint formation 16 that is dimensioned for matingly engaging a complimentarily dimensioned transition joint formation 16 of an adjacent rail sleeper 10 in use. The arrangement is such that the connection between the sleepers 10 forms a substantially continuous track structure 30.
In a preferred form of the invention, the body portion 12 terminates at both ends thereof in a transition joint formation 16, the arrangement being such that when a series of rail sleepers 10 are arranged in end-to-end orientation on the track bed, they together form a substantially continuous track structure 30 without the need for continuity of reinforcement between adjacent sleepers 10. The rail sleepers 10 are orientated in end-to-end orientation on a ballast-free track bed in such a manner that a transition joint space 18 (
The rail sleeper 10 also includes at least two spaced block formations 20 for supporting the rails 14. Each block formation 20 includes a top surface 20.1, a bottom surface 20.2 and at least two side surfaces 20.3. The block formations 20 are at least partially flared block formations 20. More particularly, the side surfaces 20.3 are characterised therein that they are at least partially outwardly flared from the top surface 20.1 towards the bottom surface 20.2, extending beyond the side faces 12.3 of the body portion 12, so as to increase shear interlock of the sleeper 10 with the track bed. The rail sleeper 10 preferably includes a number of block formations 20 that are substantially equally spaced along the length of the sleeper 10 such that the bottom surfaces 20.2 of the block formations 20 are arranged substantially flush with the bottom face 12.2 of the body portion 12.
The top surfaces 20.1 of the block formations 20 are dimensioned for receiving rail fasteners 37 for the rails 14. In particular, the top surfaces 20.1 of the block formations 20 are raised relative to the top face 12.1 of the body portion 12 such that, in use, a gap exists between a rail foot and the top face 12.1 of the body portion 12 for permitting rail foot drainage when the sleepers 10 are backfilled, such as in surface track applications, thus limiting rail-sleeper abrasion and rail-to-rail signaling shorts.
A block formation 20 optionally also includes at least one bore 22 (
The rail sleeper 10 further includes at least on drainage duct 26 for facilitating drainage of liquid, such as rainwater, away from the rail sleeper 10. The drainage duct is a transverse duct 26 extending underneath the rail sleeper 10 and defined by a box-out recess in the bottom face 12.2 of the body portion 12, the arrangement being such that liquid can drain between different side faces 12.3 of the body portion 12 by running through the bottom transverse duct 26. In a preferred form of the invention, the rail sleeper 10 includes a series of transverse ducts 26 that are longitudinally spaced along the length of the sleeper 10.
The rail sleeper 10 also includes at least one longitudinal service duct 24 located in and extending along the length of the body portion 12 for accommodating, for example, electrical and/or optic fibre cabling.
The rail sleeper 10 also includes resilient pads 36 (
The rail sleeper 10 is generally pre-cast from pre-stressed, post-tensioned or conventionally reinforced concrete.
The invention also provides for a ballast-free track structure 30 suitable for carrying rails 14 of a railway track. The track structure 30 comprises a series of rail sleepers 10 according to the invention wherein the sleepers 10 are located in end-to-end orientation on a ballast-free track bed such that the transition joint formation 16 of one sleeper 10 matingly engages the transition joint formation 16 of an adjacent sleeper 10. The arrangement is such that they form a substantially continuous track structure 30 without continuity of reinforcement between adjacent sleepers 10.
The transition joint formations 16 are dimensioned for limiting lateral movement of the sleepers 10 so as at least partially to limit independent deflection of the sleepers 10 and for reducing bending and shear stresses in a rail 14. The transition joint between adjacent track sleepers 10 are secured by underpinning the joint using in situ polymeric concrete, installing a jockey slab underneath the joint, or by means of bolted connections for accommodating longitudinal expansion and contraction of adjacent sleepers.
The track structure 30 further includes a second row of track sleepers 10 that are located in spaced parallel orientation from the first row of track sleepers 10 on a ballast-free track bed. The rail sleepers 10 are held at the correct spacing by means of steel or concrete cross ties 60 fixed to or cast into a rail sleeper 10 on either side.
An optional feature is to place in-situ concrete 42 (
The track structure 30 also includes one or more resilient mats 38 (
The track structure 30 also comprises at least one rock dowel or micro pile 40 (
The track structure 30 is adapted to accommodate slow and high-speed installations, and range from light axle load applications, such as mine tracks (in the order of 10 tonne axle load in), to heavy haul applications in surface track (in excess of 35 tonne axle load).
It will be appreciated that various other embodiments of the invention may be possible without departing from the spirit or scope of the invention as defined in the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2002/1735 | Mar 2002 | ZA | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/ZA03/00010 | 1/21/2003 | WO | 6/10/2005 |
