GB2243108A

GB2243108A - A component for use in railway track construction

Info

Publication number: GB2243108A
Application number: GB9003328A
Authority: GB
Inventors: Ian Thomas Smith
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-02-14
Filing date: 1990-02-14
Publication date: 1991-10-23
Anticipated expiration: 2010-02-14
Also published as: GB9003328D0; GB2243108B

Abstract

The component (1, 2, 3) comprises a relatively stiff core sheet (1) and an upper (2) and a lower (3) cover layer of a more flexible geotextile material. The core is preferably made from a cuspated plastics material, shaped similarly to an eggbox. In use the component is laid directly onto mechanically flattened ground and covered on its upper geotextile layer (2) by ballast (12) on to which railway track (10) is laid. The component (1, 2, 3) forms a barrier to upward migration of clay and water slurry into said ballast (12). <IMAGE>

Description

RAILWAY TRACKS This invention relates to railway tracks.

When it is desired to lay a railway track on clay or sandstone, or on any ground in poor condition, it is the practice to excavate about 25 to 40cm of such material before building up a foundation for the track and its ballast. This can be done by laying down, successively, a barrier layer, of for example geotextile material or a waterproof polyethylene membrane, such as that sold under the trade mark VISQUEEN followed by about 8cm of sand, a further layer of polyethylene and a further 15 to 25cm of sand.

A barrier is thereby built up which prevents upward migration of a slurry of clay and water which tends to form in the clay foundation beneath the ballast.

Upward migration of this slurry into the ballast is undesirable because it leads to instability of the ballast structure and abrasion of the ballast pieces.

The procedure is however time-consurring, in addition to requiring materials which must be transported to the site. Also, railway wagons are usually needed to transport the sand to the site and to remove excavated material.

The present invention provides a component for use in the construction of a railway track, comprising a relatively stiff core sheet and upper and lower cover layers -of more flexible geotextile material. The core preferably forms an impervious barrier between the cove layers which are advantageously perforate to allow water to pass. The core can have a thickness of from about 4mm up to about 1Omm, each cover layer possible being up to about 4mm thick but preferably being in the thickness range of 1 to 3mm, most preferably in the range 1 to 2mm. The core, which is advantageously of plastics material, is preferably shaped so as to define passageways between its two faces and the respective cover layers. If the core comprises a dentate or cuspated sheet, interconnected labyrinthine passageways will be defined.The core is preferably made of cuspated plastics material, for example of "egg-box" form consisting of staggered arrays of projections extending in respective opposite directions from a median plane.

The geotextile material is conveniently wrapped around opposed edges of the core. The cover layers can accordingly be formed by two sheets of geotextile material which are joined, for example by adhesive, at overlapping joints adjacent the opposed edges. The geotextile layers need be attached to the core only at spaced points or lines, for example by adhesive.

Any suitable geotextile material can be used but the preferred material is a continuous filament felt of synthetic material, for example polypropylene. If perforate, this is conveniently achieved by needle punching.

The component is conveniently formed in a strip of about 3 to 4m in width. Sucha strip can be used to extend below a railway track in a single width.

Narrower strips, for example of about 1m in width, can however be used side-by-side. The core is advantageously sufficiently flexible to allow such strips to be rolled into coils of, for exanple, 25m lengths.

In use, the component can be l-.id di--ectly on clay or sandstone and have the railway track ballast laid directly on the upper geotextile layer. Savings in time, materials and transpprtation can thus be achieved. When it is desired to produce a "fall" to enhance drainage in a particular direction, a layer of sand can be laid between the ground and the component of the invention.

The present invention accordingly also provides a method of constructing a railway track, in which three superposed layers of material are formed directly on existing ground, if desirable after making it "blade" flat (i.e. as can be achieved with a mechanical shovel or an excavator), and the ballast is placed over the uppermost of the three layers, the lowermost and uppermost layers being of more flexible geotextile material and the intermediate layer comprising a relatively stiff core sheet. Other desirable properties of the layers and as described above with reference to the component provided by the present invention.

The three layers are advantageously provided by a component according to the present invention and as described hereinbefore.

The invention further provides a railway track foundation made by the method described in the lastbut-one paragraph.

An embodiment of the invention will now be described by way of example with reference to the drawing, in which: Figure 1 is a transverse sectional view of a constructional component for a railway track and Figure 2 is a perspective view, partly in section, of the component in use.

In Figure 1 the component can be seen to have a core 1 of plastics material which is about 6mm thick and layers 2,3 of geotextile material about 1.5mm thick, one of which is wrapped around the side edges of the core and secured adjacent these edges to the other by overlapping joints and adhesive 5. The core is about 3.5m wide. The layers 2,3 are secured to the core 1 by more adhesive 6. The core 1 is of an "egg box" shape in section, consisting of staggered arrays of peaks 7,8 extending in opposite directions to form an openwork structure. The geotextile material can be, for example, POLYFELT PGM 14 which is a continuous filament polypropylene paving felt and is available from Polyfelt Ges mbH of Linz, Austria. Another suitable material is that sold under the trade mark TERRAM by ICI. In other embodiments the core can be as thin as 4mm or up to 8mm in thickness. Likewise, the geotextile material could range in thickness from lmm to 2mm.

Figure 2 shows a railway track 10 on which a train 11 is running. The track 10 is laid on ballast 12 placed directly on top of the structural component 1,2,3 which is placed directly on a clay foundation without any previous preparation except making blade flat with an excavator or mechanical shovel.

Claims

1. A component for use in the construction of a railway track, comprising a relatively stiff core sheet and an upper and a lower cover layer of a more flexible geotextile material.

2. A component according to claim 1, in which the core sheet forms an impervious barrier between the cover layers.

3. A component according to any preceding claim, in which the core comprises staggered arrays of projections extending in respective opposite directions from a median plane.

4. A component according to any preceding claim, in which the core comprises a dentate or cuspated sheet which defines interconnected labyrinthine passageways between the faces of the core sheet and the cover layers.

5. A component according to any preceding claim, in which the core is of plastics material.

6. A component according to any preceding claim, in which the core is sufficiently flexible for the component to be formed into a coil.

7. A component according to any preceding claim, in which the thickness of the core is in the range of 4 mm to 10 mm.

8. A component according to any preceding claim, in which the geotextile material comprises a continuous filament felt of synthetic material.

9. A component according to claim8, in which the synthetic material is polypropylene.

10. A component according to any preceding claim, in which at least on of the upper cover layer and the lower cover layer is perforate so as to be permeable to water.

11. A component according to claim 10, in which the cover layers are made from needle punched geotextile material.

12. A component according to any preceding claim, in which the upper and the lower cover layers are formed by two sheets of geotextile material connected at overlapping joints adjacent to opposed edges of the core layer.

13. A component according to claim 12, in which the cover layers are joined to each other by means of adhesive at the overlapping joints.

14. A component according to any preceding claim, in which the thickness of the geotextile material is in the range of 1 mm to 3 mm.

15. A component according to any preceding claim, in which the cover layers are attached to the core only at spaced points or lines.

16. A component according to any preceding claim, in which the cover layers are secured to the core layer by adhesive.

17. A component for use in the construction of a railway track, said component being substantially as herein described with reference to the accompanying drawings.