GB2386919A

GB2386919A - Component for use in railway track construction

Info

Publication number: GB2386919A
Application number: GB0307094A
Authority: GB
Inventors: Ian Thomas Smith
Original assignee: AQUA GEOCOMPOSITES Ltd
Current assignee: AQUA GEOCOMPOSITES Ltd
Priority date: 2002-03-28
Filing date: 2003-03-27
Publication date: 2003-10-01
Also published as: GB0307094D0

Abstract

The component comprises a core including a layer 10' of plastics material sandwiched between first and second layers 12', 14' of geotextile material wrapped around the core layer to form outer layers which are preferably joined at an overlapped joint. The core layer 10' is apertured 18' at intervals. In use, the component is laid directly on mechanically flattened ground and covered directly by ballast on which the railway track is laid. The core layer can be a layer of "egg box" section (Fig 4, not shown), and/or is supplemented by an additional layer of geotextile material 24. The outer geotextile layer may be formed from two sheets with overlapped ends.

Description

1 2386919

COMPONENTS FOR USE IN RAILWAY TRACK CONSTRUCTION

This invention relates to components for use in the construction of railway tracks.

5 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 anything from about 15 to about 50 cm, but usually no more than 30 cm, of ground material before building up a foundation for the track and its ballast. This 10 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 7 or 8 cm of sand, a further layer of polyethylene and a further layer of sand, usually from 12 to 15 25 cm deep but sometimes as deep as 30 cm. 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 20 ballast structure and abrasion of the ballast pieces.

The procedure is however time-consuming, 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.

25 GB-A-2243108 describes a component which comprises a relatively stiff core sheet and upper and lower cover layers of more flexible geotextile material.

GB-A-2367319 describes a component which comprises two relatively stiff inner layers, a geotextile layer inbetween 30 and outer cover layers of geotextile material.

Whilst such components are effective in overcoming the disadvantages of the procedure mentioned above, they nevertheless are subject to disadvantages.

The present invention provides a component for use in the 35 construction of a railway track, comprising a core layer of

impermeable plastics material and first and second outer layers of geotextile material, the outer layers extending over respective major surfaces of the core layer which is apertured at intervals to provide for flow of liquid therethrough.

5 Preferably, the core layer has on its respective major surfaces formations which define interconnected labyrinthine passageways between the core layer and the adjacent surfaces of the outer layers.

More preferably, the core layer comprises a dentate or 10 cuspated sheet defining said labyrinthine passageways.

The thickness of the core layer preferably exceeds that of each outer layer by a factor of at least three.

The invention also provides a component for use in the construction of a railway track, comprising a core, the core 15 comprising a layer of impermeable plastics material and a layer of geotextile material, and first and second outer layers of geotextile material, the first outer layer extending over a major surface of the layer of impermeable plastics material, the second outer layer extending over a major 20 surface of the core layer of geotextile material and the layer of impermeable plastics material being apertured at intervals to provide for flow of liquid therethrough.

Preferably, the layer of impermeable plastics material has on its respective major surfaces formations which define 25 interconnected labyrinthine passages between the core layer and the respective adjacent surfaces of the first outer layer and the core layer of geotextile material.

More preferably, the layer of impermeable plastics material comprises a dentate or cuspated sheet defining said 30 labyrinthine passageways.

The impermeable plastics material is preferably high density polyethylene.

The apertures may comprise circular holes of 1 to 25 mm in diameter, preferably 5 to 15 mm in diameter.

35 The layer of impermeable plastics material is preferably

from lmm to 10 mm in thickness.

The thickness of the outer layers is preferably from O.5 mm to 2.5 mm.

The present invention further provides a component for 5 use in the construction of a railway track, comprising a core, the core comprising a layer of impermeable plastics material and a layer of geotextile material, and first and second outer layers of geotextile material, the first outer layer extending over a major surface of the layer of impermeable plastics 10 material of the core and the second outer layer extending over a major surface of the layer of geotextile material of the core. Preferably, the layer of impermeable plastics material has on its respective major surfaces formations which define 15 a first set of interconnected labyrinthine passages between the layer of impermeable plastics material of the core and the first outer layer of geotextile material and a second set of interconnected labyrinthine passages between the layer of impermeable plastics material of the core and an adjacent 20 layer of the component.

More preferably, the adjacent layer is the layer of geotextile material of the core.

Advantageously, the layer of impermeable plastics material comprises a dentate or cuspated sheet defining said 25 labyrinthine passageways.

The layer of impermeable plastics material is preferably from 1 mm to 10 mm in thickness.

The thickness of the outer layers is preferably from 0.5 mm to 2.5 mm in thickness.

30 Advantageously, the layer of geotextile material of the core is thicker than the first and second outer layers, preferably at least twice the thickness.

In all aspects of the invention, the impermeable plastics material is preferably high density polyethylene.

35 In all aspects of the invention, the geotextile material

is preferably a continuous filament synthetic felt material, for example of polypropylene.

The adjacent layers of the component may be secured together at intervals, for example by adhesive.

5 In all aspects of the invention, the component can be made in a width, for example about 3.5 m, suitable for use in a single piece beneath a single railway track. Further, the component can be made in continuous lengths but, if insufficiently flexible to be rolled for storage and 10 transportation, the component can be made in panels of relatively short length.

In all aspects, the outer layers of geotextile material may be formed from a single sheet of material which extends around opposite edges of the core layer, marginal edge 15 portions of the sheet being overlapped and secured to each other. This kind of construction is preferred when the width of the component is about 2 m or less. For wider widths, another kind of embodiment is preferred in which the first and second outer layers are formed from respective first and 20 second sheets of material. Preferably one sheet extends around opposite edges of the core and is secured at its longitudinal edges to the other sheet.

Embodiments of the invention will now be described by way of example with reference to the drawings of this 25 specification, in which:

Figure 1 is a partial transverse sectional view of a first embodiment of a component for use in railway track construction; Figure 2 is a partial plan view of the component shown 30 in figure 1, the successive layers of the component being shown cut-away) Figure 3 is a view corresponding to figure 1 of a second embodiment; Figure 4 is a view corresponding to figure 1 of a third 35 embodiment;

Figure 5 is a partial somewhat schematic plan view of a fourth embodiment, the successive layers of the component being shown cut-away; Figure 6 is an interrupted somewhat schematic sectional 5 view on the line VI-VI on Figure 5; and Figure 7 corresponds to Figure 6 but shows a modified component which is a fifth embodiment.

The component shown in Figures 1 and 2 of the drawings is about 3.5 m or 4 m wide and is formed in lengths of about 10 25 m. The component has an impermeable middle layer 10 which is formed by a sheet of high density polyethylene of suitable thickness to allow the component to be rolled longitudinally.

A sheet of geotextile material which is about 1.5 mm thick is wrapped around the middle layer 10 so that it is in 15 face-to-face contact with the major surfaces of the middle layer 10. The sheet thus forms respective outer layers 12, 14 of the component. The edges of the sheet forming the outer layers 12,14 are overlapped to form a joint, which is secured by two parallel lines of adhesive 20,22 extending 20 longitudinally of the component.

The middle layer 10 is perforated at regular intervals with circular holes 18 which are about 10 mm in diameter. The holes 18 are positioned at approximately 100 mm centres in rows spaced by approximately 100 mm and extending across the 25 layer, the holes of each row being offset about 50 mm from those of the adjacent rows. The purpose of the holes 18 is to allow flow of water through the otherwise impermeable middle layer 10.

The geotextile material from which the outer layers 12, 30 14 are made can be, for example, that sold under the trade mark AQUABLACK 1000 which is a continuous-filament polypropylene felt and is available from Aqua Geocomposites Limited of Skelmersdale, UK. Another suitable material available from Aqua Geocomposites Limited is one sold under 35 the trade mark TERRATEX.

In the second embodiment of figure 3, parts corresponding to the embodiment of Figures 1 and 2 are indicated by the same reference numerals primed. The difference between the first and second embodiments is that the second embodiment includes 5 a further layer 24 of geotextile material located between the impermeable layer 10' and one of the outer layers 14'. The geotextile material of the further layer can be, for example, one of the materials mentioned above, or another suitable material. The further layer 24 can be from about 1.5 mm to 10 about 7 mm thick, preferably 3 mm to 6 mm.

In this second embodiment, the layers 10,24 together form a core layer of the component. This modification can lead to improved performance under certain ground conditions.

In the third embodiment of figure 4, parts corresponding 15 to the embodiment of figures 1 and 2 are indicated by the same reference numerals double-primed. The difference between the first and third embodiments is that the third embodiment has a middle layer 26 which is formed from a dentate or cuspated sheet of plastics material of "egg box" shape in section, the 20 sheet consisting of staggered arrays of peaks 27, 28 extending in opposite directions from a median plane in order to form interconnected labyrinthine passageways between the median planes and the respective adjacent geotextile layers 12", 14".

The overall, peak-to-peak, thickness of the layer is about 6 25 mm. A suitable material is one made from high density polyethylene and is available from Wavin of Sully-sur-Loire, France. The layer 26 has circular apertures 18" of the same size and spacing as the apertures 18 in the first embodiment.

The component of the third embodiment may be modified as 30 the first embodiment by inclusion of a further layer of geotextile material corresponding to the layer 24 of the second embodiment.

The component shown in figures 5 and 6 of the drawings may be from about 2 m to 5 m wide, conveniently about 4 m, and 35 is formed in lengths of about 25 m. The component has a core

which consists of a layer 41 of geotextile material and a layer 42 of high density polyethylene. The layer 41 is about 5 mm thick. A suitable material is that sold under the trade mark TERRATEX which is a continuousfilament polypropylene 5 felt and is available from Aqua Geocomposites Limited of Skelmersdale, UK. The layer 42 is formed from a dentate or cuspated sheet of plastics material of "egg box" shape in section, the sheet consisting of staggered arrays of peaks 49, 50 extending in opposite directions from a median plane. The 10 peaks 49 form interconnected labyrinthine passageways between the median plane and the geotextile layer 41. The overall, peak-to-peak, thickness of the layer 42 is about 6 mm. A suitable high density polyethylene material is available from Wavin of Sully-sur-Loire, France.

15 A sheet of geotextile material 44 which is about 1.5 mm thick is wrapped around the core so that it is in face-to-face contact with the major surface of the geotextile layer 41 which is distant from the eggbox layer 42 and in face-to-face contact with the surface of the egg-box layer 42 which is 20 distant from the geotextile layer 41. A suitable material is that sold under the trade mark AQUABLACK 1000 which is a continuous-filament polypropylene felt which is also available from Aqua Geocomposites Limited of Skelmersdale, UK.

The peaks 50 of the egg-box layer 42 extending in the 25 opposite direction to the peaks 49 form interconnected labyrinthine passageways between the median plane and the adjacent layer of geotextile material 44. The sheet 44 thus forms respective outer layers of the component. The lateral edges of the sheet 44 are overlapped to form a joint, which 30 is secured by two parallel lines of adhesive 46, 47 extending longitudinally of the component. The geotextile material from which the sheet 44 is formed can be the same as, or different from, the material mentioned above from which the layer 41 is formed. 35 If desired, the layers of geotextile and egg-box material

41, 42, 44 may be secured together by adhesive at spaced intervals. In the modification shown in figure 7 (where like features are indicated by primed reference numerals), the 5 outer layers of the component are formed from first and second sheets 44', 44" of the same material as the sheet 44 in figure 5. The first sheet 44' extends over one face of the egg-box layer 42' and around the longitudinal edges of the egg-box layer 42' and the geotextile layer 41'. The second sheet 44" 10 extends over the face of the geotextile layer 41' distant from the egg-box layer and extends almost to the longitudinal edges of the geotextile layer 41' to which it is attached by lines of adhesive 46", 47". Edge portions of the first sheet 44' overlie edge portions of the second sheet 44" and are secured 15 thereto by lines of adhesive 46',47'.

In a further modification, the second sheet 44" extends over the opposite surfaces of the edge portions of the first sheet 44' and is secured thereto, the edge portions being in turn secured to the geotextile layer 41'.

20 In use in the construction of a railway track, any of the components described is laid directly on a clay foundation which has not undergone any previous preparation except being made blade flat with an excavator or mechanical shovel. The railway track is then laid on ballast which is placed directly 25 upon the component embodying the invention.

The components described with reference with figures 1 to 4 may be used either way up but there described with reference to figures 5 to 7 and preferably used such that their geotextile layers 41, 41' and below the respective egg-box 30 layers 42, 42'.

Claims

1. A component for use in the construction of a railway track, comprising a core layer of impermeable plastics material and first and second outer layers of geotextile 5 material, the outer layers extending over respective major surfaces of the core layer which is apertured at intervals to provide for flow of liquid therethrough.

2. A component according to claim 1, wherein the core layer has on its respective major surfaces formations which 10 define interconnected labyrinthine passageways between the core layer and the adjacent surfaces of the outer layers.

3. A component according to claim 2, wherein the core layer comprises a dentate or cuspated sheet defining said labyrinthine passageways.

15 4. A component according to any preceding claim, wherein the thickness of the core layer exceeds that of each outer layer by a factor of at least three.

5. A component for use in the construction of a railway track, comprising a core, the core comprising a layer of 20 impermeable plastics material and a layer of geotextile material, and first and second outer layers of geotextile material, the first outer layer extending over a major surface of the layer of impermeable plastics material, the second outer layer extending over a major surface of the core layer 25 of geotextile material and the layer of impermeable plastics material being apertured at intervals to provide for flow of liquid therethrough.

6. A component according to claim 5, wherein the layer of impermeable plastics material has on its respective major 30 surfaces formations which define interconnected labyrinthine passages between the core layer and the respective adjacent surfaces of the first outer layer and the core layer of geotextile material.

7. A component according to claim 6, wherein the layer 35 of impermeable plastics material comprises a dentate or

cuspated sheet defining said labyrinthine passageways.

8. A component according to any of claims 5 to 7, wherein the core layer of geotextile material is from 1.5 mm to 7 mm in thickness.

5 9. A component according to any preceding claim, wherein the liquidflow apertures are circular holes of 1 to 25 mm in diameter.

10. A component according to claim 9, wherein the holes are from 5 to 15 mm in diameter.

10 11. A component for use in the construction of a railway track, comprising a core, the core comprising a layer of impermeable plastics material and a layer of geotextile material, and first and second outer layers of geotextile material, the first outer layer extending over a major surface 15 of the layer of impermeable plastics material of the core and the second outer layer extending over a major surface of the layer of geotextile material of the core.

12. A component according to claim 11, wherein the layer of impermeable plastics material has on its respective major 20 surfaces formations which define a first set of interconnected labyrinthine passages between the layer of impermeable plastics material of the core and the first outer layer of geotextile material and a second set of interconnected labyrinthine passages between the layer of impermeable 25 plastics material of the core and an adjacent layer of the component. 13. A component according to claim 12, wherein the layer of impermeable plastics material comprises a dentate or cuspated sheet defining the labyrinthine passageways.

30 14. A component according to claim 13, in which the adjacent layer is the layer of geotextile material of the core. 15. A component according to any of claims 11 to 14, in which the layer of geotextile material of the core is thicker 35 than the first and second outer layers.

16. A component according to claim 15, in which the layer of geotextile material of the core is at least twice as thick as the first and second outer layers.

17. A component according to any of claims 11 to 14, in 5 which the layer of geotextile material of the core is from 1.5 mm to 7 mm in thickness.

18. A component according to any preceding claim, in which the first and second outer layers are formed from a single sheet of material which extends around opposite edges 10 of the core, edge portions of the sheet being overlapped and secured to each other.

19. A component according to any preceding claim, in which the first and second outer layers are formed from respective first and second sheets of material.

15 20. A component according to claim 19, in which one of the sheets extends around opposite edges of the core and is secured at its opposite edges to the other sheet.

21. A component according to any preceding claim, in which the layer of impermeable plastics material is from 1 mm 20 to 10 mm in thickness.

22. A component according to any preceding claim, in which the outer layers are each from 0.5 mm to 2.5 mm in thickness. 23. A component according to any preceding claim, in 25 which the geotextile material comprises a continuous-filament felt of synthetic material.

24. A component according to claim 23, in which the synthetic material is polypropylene.

25. A component according to any preceding claim, in 30 which the adjacent layers are secured together at spaced points or along spaced lines only.

26. A component according to claim 25, in which the layers are secured together by adhesive.

27. A component for use in the construction of a railway 35 track, the component being substantially as herein described

with reference to figures 1 and 2, figure 3, figure 4, figures 5 and 6 or figure 7 of the accompanying drawings.

28. A method of constructing a railway track, in which a component according to any preceding claim is laid on 5 existing ground in a single width to underlie the track to be constructed, ballast is placed over the upper cover layer of the component, and the track is laid on the ballast.

29. A method according to claim 28, in which the ground is made blade flat before the component is laid.

10 30. A railway track constructed according to the method of claim 28 or 29..