GB2506240A

GB2506240A - Railway track construction with geotextile

Info

Publication number: GB2506240A
Application number: GB201312627A
Authority: GB
Inventors: Ian Thomas Smith
Original assignee: Individual
Current assignee: Individual
Priority date: 2012-07-13
Filing date: 2013-07-15
Publication date: 2014-03-26
Anticipated expiration: 2033-07-15
Also published as: GB201212536D0; GB2503941A; GB201312627D0; GB2506240B

Abstract

The invention relates to the construction of a railway track utilising a geotextile fabric 5 wherein the geotextile fabric is combined with a water absorbent layer therefore may be capable of preventing a pumping phenomenon from a sub grade 4 having high clay content. The railway track comprises a pair of rails 2 with sleepers 1 there between. The railway track is situated on ballast 3, below which is the sub grade. The geotextile may be positioned between the sub grade and the ballast. The geotextile may be formed of a needle punched, non-woven material, impregnated with sodium polyacrylate crystals.

Description

Intellectual Property Office Applicacion Nc,. (lB 1312627.1 RTN'II Dacc: 16 January 2014 The following terms are registered trade marks and should he rcad as such wherever they occur in this document: Tencate Inlelleclual Property Office is an operaling name of the Pateni Office www.ipo.gov.uk

RAILWAY TRACK CONSTRUCTION

The invention relates to geotextiles and their use in the construction of a railway track foundation.

A railway comprises a railway track and an underlying formation. The railway track is usually formed of a pair of rails with sleepers therebetween. Traditionally, a railway track is founded on two distinct layers, the ballast and the subgrade, collectively known as the railway track formation.

The ballast is situated above the subgrade and is often formed from a granular material, such as granite rocks, wherein the granules are of a roughly uniform size. The ballast serves multiple purposes, including facilitating the drainage of water away from the railway track, suppressing vegetation, providing vertical and lateral support to the sleepers and, importantly, allowing for adjustments of the line and level of the railway track when in use.

The formation may include a blanket situated above the subgrade, upon which the required depth of ballast is placed.

The subgrade is the natural ground upon which the railway track is founded and thus, may be formed of various types of soil, for example, soil with a high clay content. The blanket is a layer or several layers of material laid over the subgrade, which gives the formation particular properties. For example, a blanket Zoned of a granular material, such as sand, may enhance the filter properties of the formation. However, a blanket of this nature is often extremely costly and difficult to implement.

A major problem arising in the use of a railway is the failure of the railway track due to a phenomenon known as pumping'.

Pumping' commonly occurs on subgrades with a high clay content that are affected by the presence of water. When a subgrade with a high clay content comes into contact with water, such as rain water or residual ground water, a clay particle/water slurry is formed. The pressure of the passing railway traffic can cause the slurry to be pumped up into the ballast. Over time, this causes deterioration of the railway track, for example, the railway track may lose its line and level. Ultimately, the railway track has to be removed so that its line and level can be restored.

Thus, there is a need for a means of preventing railway track deterioration as a result of the pumping' phenomenon.

According to a first aspect of the invention, there is provided a geotextile combined with a water absorbent material.

The water absorbent material may be impregnated in the geotextile or be present as a layer on the surface of the geotextile, or corrJDned with the geotextile by any other means. Preferably, the water absorbent material is impregnated in the geotextile. The water absorbent material may be impregnated in the geotextile by immersion, for example by passing the geotextile through a bath containing the absorbent material in solution. More preferably, the water absorbent material is evenly distributed throughout the geotextile.

The water absorbent material may comprise an alkali metal salt of a polyacrylate, for example potassium polyacrylate or sodium polyacrylate. Preferably, the water absorbent material comprises sodium polyacrylate. The sodium polyacryJ.ate may be formed ny the polymerisatlon of acrylic acid blended with sodium hydroxide. The sodium polyacrylate may have the general structural formula shown below.

LCH2 CII [ Nat6OJ More preferably, the water absorbent material comprises sodium polyacrylate crystals. Advantageously, the sodium polyacrylate crystals of the invention are capable of absorbing at least about 100 times their own weight of water and preferably from about 100 to about 120 times their own weight of water.

The sodium polyacrylate crystals are capable of absorbing water, subsequently drying out and then reabsorbing water.

This may happen numerous times.

The water absorbent material may be present in an amount of from about 200 g per m2 to about 500 g per m2 of the surface of the geotextile. Preferably, the water absorbent material is present in an amount of from about 300 g per m2 to about 400 g per m2 of the surface of the geotextile.

The geotextile may be woven or non-woven. Preferably, the geotextile is non-woven. More preferably, the geotextile is a needle punched, non-woven geotextile such as TenCate TS8O available from TenCate.

Preferably, the geotextile has a thickness of from about 2 mm to about 8 mm at 2 kPa above atmospheric pressure, and more preferably from about 3 mm to about 4 mm at 2 kPa above atmospheric pressure.

There is also provided the use of the geotextile of the invention in the construction of a railway track formation.

The railway track formation may comprise ballast and a subgrade positioned below the ballast. Preferably, the ballast comprises a plurality of granite rocks and the subgrade comprises at least one of clay, soil with a high clay content and mudstone.

The geotextile may be positioned between the ballast and subgrade of the railway track formation. Preferably, no blanket is present in the railway track formation, since the geotextile effectively acts as a blanket. Thus, any existing blanket should be removed from the railway track formation prior to the installation of the geotextile.

The geotextile of the present invention is able to absorb significant quantities of water, such as rain water or residual ground water. Thus, when the geotextile is used in a railway track formation as described above, it is able to maintain a clay or clay-containing subgrade in a substantially dry condition. What is meant by the term substantially dry' in this instance, is that there is not enough water present in the subgrade to generate a clay particle/water slurry and so the pumping' phenomenon is significantly suppressed or prevented.

According to a second aspect of the invention, there is provided a method for the construction of a railway track formation, wherein a geotextile is positioned in the railway track formation and the geotextile is a geotextile which is combined with a water absorbent material.

The geotextile may be combined with the water absorbent material prior to being positioned in the railway track formation or in situ. Preferably the geotextile is combined with the water absorbent material prior to being positioned in the railway track formation.

For the avoidance of any doubt, references to features of the first aspect of the invention discussed above are optionally applicable to the method of the second aspect, as appropriate.

The invention is further described by way of example, with reference to the following schematic figure: Figure 1: shows a railway with a geotextile according to the invention positioned between a subgrade and ballast.

Figure 1 schematically shows a railway construction. The railway is made up of a railway track, ballast and subgrade.

The railway track comprises a pair of rails 2 with sleepers 1 therebetween. The railway track is situated on a ballast 3 to allow for adjustments of the Line and level of the railway track when in use. Below the ballast is a subgrade 4.

The ballast 3 and subgrade 4 constitute the formation. A geotextile 5 is positioned between and in contact with the subgrade 4 and the ballast 3. The geotextile 5 is able to prevent the pumping' phenomenon when used in the way shown.

The geotextile 5 is formed of a needle punched, non-woven material with a thickness of 3.2 mm at 2 kea above atmospheric pressure. The geotextile 5 is impregnated with sodium polyacrylate crystals in an amount of 385 g per using a gel coating machine. Here, the geotextile 5 is passed through a bath containing the sodium polyacrylate crystals in solution, using a series of rollers. The geotextile 5 is then pressed to remove any excess solution and subsequently dried.

Claims

CLAmS: 1. Use.n the construction of a railway track formation of a neotextile combined with a water absorbent material.
2. A use according to claim 1, wherein the railway track formation comprises a ballast and a subgrade.
3. A use according to claim 2, wherein the geotextile is positioned between the ballast and the suhgrade.
4. A use according to any of claims 1 to 3, wherein the subgrade comprises clay and/cr soil with a high clay content.
5. A method for the construction of a railway track formation wherein a geotextile is positioned in the railway track formation and the geotextile is a geotextile which is combined with a Wa er absorbent material
6. A method according* *o claim 5, wherein the geotextile is combined with the water absorbent material prior to being positioned in the railway track formation.
7. A method according to claim 5, wherein the geotextile is combined with the water absorbent material ±n situ.
8. A railway track formation which includes a geotextile combined with a water absorbent material.
9. A railway track formation according to claim 8, comprising a ballast and a subgrade.
10. A railway track formation according to claim 9, wherein the geotextile is positioned between the ballast and the subgrade.
11. A railway track forrntion according to any of claims 8 to 10.wherein the suhgrade comprises clay and/or soil with a high clay content.
12. A use, method or torn*ation according to any of claims 1 to 11, wherein the geotextile is impregnated with the water absorbent material.
13. A use, method or formation according io claim 12, wherein the geotextile is coated with the water absorbent material.
14. A use, method or formation according to claims 12 or 13, wherei nthe water absorbent material is present in an amount of about 300 g per m2 to about 400 g per m2 of the surface of the geotextile.
15. A use, method or formation according to any claims 12 to 14, wherein the water absorbent material comprises sodium polyacrylate -
16. A use, method or formation according to any claims 12 to 15, wherein the water absorbent material comprises sodium polyacrylate crystals.
17. A use, method or formation according to any claims 12 to 16, wherein the geotextile is non-woven.
18. A use, method or formation according to claim 17, wherein the non-woven geotextile is needle punched.
19. A use, method or formation according to any claims 12 to 18, wherein the geotextile has a thickness of from about 2 mm to about 8 nu at 2 kPa above atmospheric pressure.
20. A use, method or formation according to claim 19, wherein the geotextile has a thickness of from about 3 mm to about 4 mm at 2kPa above atmospheric pressure.
21. A use of a geotextile, the use being substantially as hereinbefore described with reference to the drawing.
22. A method for the construction of a railway track, the method being substantially as hereinbefore described with reference to the drawing.
23. A railway track formation substantially as hereinbefore described with reference to the drawing.