GEOENGINEERING CONSTRUCTIONS FOR USE IN RAILWAYS

Abstract

There is disclosed a railway geogrid construction suitable for use with high speed trains to mitigate the increased impact of Rayleigh waves generated at high speed and/or over soft subgrades, the construction comprising: a track bed (e.g. having rails for a train) which defines a track located on a track plane; a mass of particulate material (e.g. aggregate) forming a layer located beneath the track plane; and a geogrid located in and/or below the particulate mass in a plane (geogrid plane) substantially parallel to the track plane where the average distance between the track plane and geogrid plane, measured perpendicular to both is greater than 0.65 metres.

Claims

1. A geogrid engineering construction for railways (railway geogrid construction), the construction comprising: a track bed (optionally the track bed comprising rails) which defines a track located on a track plane; a mass of particulate material forming a layer located beneath the track plane; and at least one geogrid located in and/or below the particulate layer, where the at least one geogrid is located in a plane (geogrid plane) substantially parallel to the track plane where the average distance between the track plane and geogrid plane, measured perpendicular to both planes, and denoted herein as Dr, is greater than 0.65 metres.

2. A railway geogrid construction as claimed in claim 1, where the particulate layer is located immediately beneath the track bed.

3. A railway geogrid construction as claimed in claim 1, where the particulate layer has an average thickness less than Dr, preferably less than 0.5 m, more preferably less than 0.4 m, most preferably from 0.1 m to 0.35 m.

4. A railway geogrid construction as claimed in claim 1 in which Dr is greater than or equal to 0.7 metres, more preferably ≥0.8 m, even more preferably ≥0.9 m most preferably ≥1 m.

5. A railway geogrid construction as claimed in claim 1 in which Dr is less than or equal to 5 metres, more usefully ≤4 m, even more usefully ≤3 m most usefully ≤2 m.

6. A railway geogrid construction as claimed in claim 1 in which Dr is from 0.65 to 5 metres, conveniently from 0.7 to 5 metres, more conveniently from 0.8 to 4 m, even more conveniently from 0.9 to 3 m, most conveniently from 1 to 2 m.

7. A railway geogrid construction as claimed in claim 1 where the particulate layer is additionally stabilized by at least one other mechanically stabilized layer and/or chemically stabilized layer.

8. A railway geogrid construction as claimed in claim 1, where the geogrid is in the form of an integral, molecularly oriented, mesh, which comprises polymers which are substantially molecularly oriented in at least one direction.

9. A railway geogrid construction as claimed in claim 1, where the polymers of the geogrid are molecularly oriented in at least two substantially perpendicular directions (biaxial orientation).

10. A railway geogrid construction as claimed in claim 1, where the geogrid comprises interconnecting mesh defining elements including elongate tensile elements.

11. A railway geogrid construction as claimed in claim 1, where the geogrid comprises transverse bars interconnected by substantially straight oriented strands, at least some of the strands extending from one bar to the next at a substantial angle to the direction at right angles to the bars and alternate such angled strands across the width of the geogrid being angled to said direction by equal and opposite angles.

12. A railway geogrid construction as claimed in claim 1, where the geogrid is in the form of an integral, molecularly oriented, plastics mesh structure.

13. A railway geogrid construction as claimed in claim 1, where the geogrid has a thickness of from 0.1 m to 5 mm, preferably from 0.2 to 2 mm.

14. A railway geogrid construction as claimed in claim 1, where the molecular oriented polymers that comprise the polymer geogrid are oriented by the polymer grid (and/or the polymer web from which the grid is formed) having been stretched in at least one direction at stretch ratio of at least 2:1, preferably of at least 2 to 1 to 12 to 1, more preferably of from 2 to 1 to 6 to 1.

15. A railway geogrid construction as claimed in claim 1, where the geogrid has a tensile strength of at least 10 kN/m.

16. A railway geogrid construction as claimed in claim 1, where the geogrid has mesh defining elements that have a width of 2 to 100 mm, the mesh defining elements defining mesh apertures (optionally which apertures may be of identical size and/or shape) having a mean length and/or a mean width of from 5 to 400 mm.

17. A railway geogrid construction as claimed in claim 1 having a Rayleigh wave velocity (Vr) therein of at least 55 ms.sup.−1 (˜125 mph or ˜200 kph), more preferably ≥69 ms.sup.−1 (˜155 mph or ˜250 kph).

18. A railway geogrid construction as claimed in claim 1, which further comprises a railway track having rails, where the rails have a critical track velocity at least 140 ms.sup.−1 (˜310 mph or ˜500 kph), more preferably at least 150 ms.sup.−1 (˜335 mph or ˜540 kph).

19. A railway geogrid construction as claimed in claim 1 that has the one or more, preferably two or more, more preferably three or more, even more preferably four or more, most preferably five or more, for example all six, of any of the following properties selected from (i) to (vi) i) Radial Secant stiffness at 0.5% strain of at least 100 kN/m, preferably of from 200 to 800 kN/m more preferably of from 220 to 700 kN/m, most preferably of from 250 to 600 kN/m with further optionally in each case a tolerance of from minus (−) 60 to minus (−) 100. ii) Radial Secant stiffness at 2% strain (in kN/m of at least 80 kN/m, preferably of from 150 to 600 kN/m more preferably of from 170 to 500 kN/m, most preferably of from 200 to 450 kN/m with further optionally in each case a tolerance of from minus (−) 60 to minus (−) 100. iii) Radial Secant stiffness Ratio (dimensionless) of at least 0.5 preferably of from 0.6 to 0.9, most preferably of from 0.70 to 0.85, most preferably of from 0.75 to 0.80, with further optionally in each case a tolerance of from minus (−) 0.10 to minus (−) 0.20, more optionally minus (−) 0.15. iv) Junction efficiency of at least 90% preferably at least 95%, more preferably of at least 97%, most preferably of at least 99%, for example of 100%, with further optionally in each case a tolerance of at least minus (−) 10. v) Pitch (preferably hexagon pitch) of at least 30 mm, preferably of from 40 to 150 mm, more preferably of from 50 to 140, most preferably of from 65 to 125 mm, with further optionally in each case a tolerance of from minus (−) 60 to minus (−) 100. vi) Product weight of at least 0.100 kg/m.sup.2, preferably of from 0.120 to 0.400 kg/m.sup.2, more preferably of from 0.150 to 0.350 kg/m.sup.2, most preferably of from 0.170 to 0.310 kg/m.sup.2, for example from 0.180 to 0.300 kg/m.sup.2 with further optionally in each case a tolerance of from minus (−) 0.025 to minus (−) 0.040, more optionally of from minus (−) 0.030 to 0.035.

20. A method for constructing a geogrid engineering construction for railways (railway geogrid construction), optionally the railway geogrid construction as claimed in claim, the method comprising the steps of: providing a track bed (optionally the track bed comprising rails) which defines a track located on a track plane; providing a particulate layer lying beneath the track plane with a geogrid located in and/or adjacent to the particulate layer, where the geogrid is located in a plane (geogrid plane) substantially parallel to the track plane where the average distance between the track plane and geogrid plane, measured perpendicular to both, and denoted herein as Dr, is greater than 0.65 metres.

21. A geogrid suitable for use in a railway geoengineering construction as claimed in claim 1, in which the geogrid has one or more, preferably two or more, more preferably three or more, even more preferably four or more, most preferably five or more, for example all six, of any of the following properties selected from (i) to (vi) i) Radial Secant stiffness at 0.5% strain of at least 100 kN/m, preferably of from 200 to 800 kN/m more preferably of from 220 to 700 kN/m, most preferably of from 250 to 600 kN/m with further optionally in each case a tolerance of from minus (−) 60 to minus (−) 100. ii) Radial Secant stiffness at 2% strain (in kN/m) of at least 80 kN/m, preferably of from 150 to 600 kN/m more preferably of from 170 to 500 kN/m, most preferably of from 200 to 450 kN/m with further optionally in each case a tolerance of from minus (−) 60 to minus (−) 100. iii) Radial Secant stiffness Ratio (dimensionless) of at least 0.5 preferably of from 0.6 to 0.9, most preferably of from 0.70 to 0.85, most preferably of from 0.75 to 0.80, with further optionally in each case a tolerance of from minus (−) 0.10 to minus (−) 0.20, more optionally minus (−) 0.15. iv) Junction efficiency of at least 90% preferably at least 95%, more preferably of at least 97%, most preferably of at least 99%, for example of 100%, with further optionally in each case a tolerance of at least minus (−) 10. v) Pitch (preferably hexagon pitch) of at least 30 mm, preferably of from 40 to 150 mm, more preferably of from 50 to 140, most preferably of from 65 to 125 mm, with further optionally in each case a tolerance of from minus (−) 60 to minus (−) 100. vi) Product weight of at least 0.100 kg/m.sup.2, preferably of from 0.120 to 0.400 kg/m.sup.2, more preferably of from 0.150 to 0.350 kg/m.sup.2, most preferably of from 0.170 to 0.310 kg/m.sup.2, for example from 0.180 to 0.300 kg/m.sup.2 with further optionally in each case a tolerance of from minus (−) 0.025 to minus (−) 0.040, more optionally of from minus (−) 0.030 to 0.035.

22. A geogrid stabilized particulate layer suitable for use in a railway geoengineering construction as claimed in claim.

23. Use of a geogrid and/or component thereof to increase the speed of the Rayleigh wave therein (Vr) and/or increase the critical track velocity along rails of a track laid thereon (Vc) above a maximum allowed train velocity denoted Vt, where Vt is at least 55 ms.sup.−1, preferably ≥69 ms.sup.−1.

24. A geogrid engineering construction for railways (railway geogrid construction), the construction comprising: a track bed (optionally the track bed comprising rails) which defines a track located on a track plane; a particulate layer lying beneath the track plane; and a geogrid located in and/or adjacent to the particulate layer, where the geogrid is located in a plane (geogrid plane) substantially parallel to the track plane such that the geogrid stabilizes the particulate layer such that the properties of the particulate layer satisfy Equation 4A; $\begin{array}{cc}55\ge \left(\frac{A+\mathrm{Bv}}{1+v}\right).Math.\surd \frac{G_0}{\rho }& \mathrm{Equation}.Math..Math.4.Math.A\end{array}$ where υ denotes the Poisson ratio of the particulate layer, which preferably is from 0.1 to 0.5, more preferably from 0.2 to 0.4, most preferably from 0.2 to 0.35; G.sub.0 the small strain stiffness property of the particulate layer; and ρ is density of the particulate layer; and where optionally the average distance between the track plane and geogrid plane, measured perpendicular to both, and denoted herein as Dr, is greater than 0.65 metres.

25. A method for constructing a geogrid engineering construction for railways (railway geogrid construction), the method of construction comprising: defining a track bed plane (optionally the track bed comprising rails) along which the track bed will be located; providing an particulate layer beneath the track plane with a geogrid located in and/or adjacent to the particulate layer, where the geogrid is located in a plane (geogrid plane) substantially parallel to the track plane such that the geogrid stabilizes the particulate layer such that the properties of the particulate layer satisfy Equation 4A; $\begin{array}{cc}55\ge \left(\frac{A+\mathrm{Bv}}{1+v}\right).Math.\surd \frac{G_0}{\rho }& \mathrm{Equation}.Math..Math.4.Math.A\end{array}$ where υ denotes the Poisson ratio of the particulate layer, which preferably is from 0.1 to 0.5, more preferably from 0.2 to 0.4, most preferably from 0.2 to 0.35; G.sub.0 the small strain stiffness property of the particulate layer; and ρ is density of the particulate layer; and where optionally the average distance between the track plane and geogrid plane, measured perpendicular to both, and denoted herein as Dr, is greater than 0.65 metres.

26. Use of a geogrid in a method to construct a geogrid engineering construction for railways (railway geogrid construction comprising: defining a track bed plane (optionally the track bed comprising rails) along which the track bed will be located; defining an particulate layer lying beneath the track plane with a geogrid located in and/or adjacent to the particulate layer, the geogrid being located in a plane (geogrid plane) substantially parallel to the track plane such plane being defined such that the geogrid is calculated to stabilize the particulate layer such that the properties of the particulate layer satisfy Equation 4A; $\begin{array}{cc}55\ge \left(\frac{A+\mathrm{Bv}}{1+v}\right).Math.\surd \frac{G_0}{\rho }& \mathrm{Equation}.Math..Math.4.Math.A\end{array}$ where υ denotes the Poisson ratio of the particulate layer which preferably is from 0.1 to 0.5, more preferably from 0.2 to 0.4, most preferably from 0.2 to 0.35 G.sub.0 the small strain stiffness property of the particulate layer; and ρ is density of the particulate layer; and where optionally the average distance between the track plane and geogrid plane, measured perpendicular to both, and denoted herein as Dr, is greater than 0.65 metres more preferably Dr has and/or is in any of the values and/or the ranges as described herein as desired and/or suitable for the present invention.

27. A particulate material stiffened and/or strengthened by the method of claim 20.

28. A railway geoengineering construction comprising a mass of particulate material strengthened by embedding therein a geogrid as claimed claim 21.

29. A geogrid suitable for use in a method for constructing a geoengineering construction for railways as claimed in claim 20, in which the geogrid has one or more, preferably two or more, more preferably three or more, even more preferably four or more, most preferably five or more, for example all six, of any of the following properties selected from (i) to (vi) i) Radial Secant stiffness at 0.5% strain of at least 100 kN/m, preferably of from 200 to 800 kN/m more preferably of from 220 to 700 kN/m, most preferably of from 250 to 600 kN/m with further optionally in each case a tolerance of from minus (−) 60 to minus (−) 100. ii) Radial Secant stiffness at 2% strain (in kN/m) of at least 80 kN/m, preferably of from 150 to 600 kN/m more preferably of from 170 to 500 kN/m, most preferably of from 200 to 450 kN/m with further optionally in each case a tolerance of from minus (−) 60 to minus (−) 100. iii) Radial Secant stiffness Ratio (dimensionless) of at least 0.5 preferably of from 0.6 to 0.9, most preferably of from 0.70 to 0.85, most preferably of from 0.75 to 0.80, with further optionally in each case a tolerance of from minus (−) 0.10 to minus (−) 0.20, more optionally minus (−) 0.15. iv) Junction efficiency of at least 90% preferably at least 95%, more preferably of at least 97%, most preferably of at least 99%, for example of 100%, with further optionally in each case a tolerance of at least minus (−) 10. v) Pitch (preferably hexagon pitch) of at least 30 mm, preferably of from 40 to 150 mm, more preferably of from 50 to 140, most preferably of from 65 to 125 mm, with further optionally in each case a tolerance of from minus (−) 60 to minus (−) 100. vi) Product weight of at least 0.100 kg/m.sup.2, preferably of from 0.120 to 0.400 kg/m.sup.2, more preferably of from 0.150 to 0.350 kg/m.sup.2, most preferably of from 0.170 to 0.310 kg/m.sup.2, for example from 0.180 to 0.300 kg/m.sup.2 with further optionally in each case a tolerance of from minus (−) 0.025 to minus (−) 0.040, more optionally of from minus (−) 0.030 to 0.035.

30. A geogrid stabilized particulate layer suitable for use in a method for constructing a geoengineering construction for railways as claimed in claim 20.

31. A geogrid stabilized particulate layer suitable for use in a railway geoengineering construction which is obtained and/or obtainable by use of a geogrid as claimed in claim 21.

32. A particulate material stiffened and/or strengthened by the method of claim 25.

Description

FIGURES

[0151] The invention is illustrated by the following non-limiting FIGS. 1 to 5 where:

[0152] FIG. 1 shows a railway track construction over untreated ground (denoted Comp A);

[0153] FIG. 2 shows a railway track construction that uses a granular replacement of underlying material to 5 m depth (denoted Comp B) which is a currently proposed method of constructing high speed train lines;

[0154] FIG. 3 shows a railway track construction using layering and with a geogrid mechanically stabilized layer (MSL) with granular fill (as used in Test Examples 1 to 4 described herein). The construction shown in FIG. 3 was used in a 3D numerical model to calculate speed of shear wave through the ground for a given stiffness and depth of construction given in FIGS. 4 and 5;

[0155] FIG. 4 shows Shear velocity at 0.002% Strain for longitudinal (parallel with embankment length) CSW testing (suffix 2 indicates testing in the Second Test); and

[0156] FIG. 5 shows Shear velocity at 0.002% Strain for lateral (perpendicular to embankment length) CSW testing (suffix 2 indicates testing in the Second Test).

[0157] It should be noted that embodiments and features described in the context of one of the aspects or embodiments of the present invention also apply to the other aspects of the invention whether or not such features are stated as preferred or similar terminology. Although embodiments have been disclosed in the description with reference to specific examples, it will be recognized that the invention is not limited to those embodiments. All intermediate generalizations between the broadest scope of the invention described herein and each of the embodiments and/or examples described herein are thus envisaged as comprising the present invention. Combinations and/or mixtures of any features described in one embodiment of the invention may be applied to any other embodiments of the invention whether by analogy or otherwise and are envisaged as comprising the present invention. Various modifications may become apparent to those of ordinary skill in the art and may be acquired from practice of the invention and such variations are contemplated within the broad scope of protection for the present invention as allowed under applicable local law even if the variant may be outside the literal meaning of the claims. It will be understood that the materials used and the details may be slightly different or modified from the descriptions without departing from the methods and compositions disclosed and taught by the present invention.

[0158] Further aspects of the invention and preferred features thereof are given in the claims herein.

Examples 1 (TX150), 2 (TX130S), 3 (TX170) and 4 (TX190L) and Comps A to C

[0159] The present invention will now be described in detail with reference to the following non limiting examples which are by way of illustration only.

[0160] Without wishing to be bound by any theory the applicant believes that the velocity of the waves generated in a track sub layer may be related to stiffness of the underlying material beneath the track (i.e. ground, typically soil), with the depth of wave penetration increasing with reducing frequency and increasing wavelength (A). Waves of high frequency travel only in shallow layers. Waves of lower frequency travel both in shallow and deep layers. Wave velocity through the ground will therefore vary with frequency and depth a phenomenon commonly known as geometrical dispersion. It is believed that the contribution of the P-wave component to the inherent Raleigh wave velocity (Vr) is small compared to the contribution from the S-wave component. The S-wave velocity (Vs) may thus be used to determine ground stiffness, especially where the ground exhibits substantially elastic behaviour. In one embodiment of the invention the applicant has found Vr may be derived from Vs for example using Equation 1A to a first approximation:

[00007]$\begin{array}{cc}{V}_r\cong \left(\frac{0.874+1.117.Math.v}{1+v}\right).Math.V_s,& \mathrm{Equation}.Math..Math.1.Math.A\end{array}$

where [0161] Vr is the Rayleigh Wave velocity through the ground; [0162] Vs is the velocity of S-waves through the ground; and [0163] υ is the Poisson ratio (the signed ratio of transverse strain to axial strain).

[0164] The velocity profile of the S-waves may be converted to a small strain shear modulus (G.sub.0) using the simple relationship with ground density defined in Equation 2. Given the nature of the relationship with, and limited variance of, ground density (e.g. if soil), the derivation of G.sub.0 is relatively insensitive to assumed ground density if not known.

G.sub.0=ρ(V.sub.s).sup.2  Equation 2, where [0165] G.sub.0 the small strain stiffness property; and [0166] ρ is density of the ground.

[0167] The stiffness represents an approximate average stiffness for a given depth of ground. If the ground is soil, then as soil density typically varies between 1.6 Mg/m.sup.3 and 2.1 Mg/m.sup.3 for most ground conditions (24% variation), derivation of Go is therefore relatively insensitive to assumed soil density (if not known), and the conservative (i.e. lower bound) of soil density is assumed.

[0168] Go may be converted to Young's Modulus (E) using the relationship E=G.(2.(1+υ)). Unlike shear stiffness, E is affected by the stiffness of the soil pore water with Poisson's Ratio, varying between 0.2 (fully drained) and 0.5 (for undrained saturated soils). Selection of an appropriate Poisson's Ratio value is therefore important in determining a representative E value for the prevailing drainage conditions. For drained conditions Poisson's Ratio is generally in the range 0.2-0.35 which results in a 32% range of calculated E values. If Poisson's Ratio is not known, then the conservative (low) values may be selected, generating lower values of stiffness. A default typical lower-bound soil density of 1.80 Mg/m.sup.3 and typical drained Poisson's Ratio of 0.26 may be used where no site specific information is provided. These values may be adjusted where site specific values have been determined or to reflect undrained drainage conditions in saturated soils.

[0169] Stiffness values obtained by testing in the examples described herein are small-strain stiffness values relevant to strain levels below approximately 0.002%. In the examples site testing was carried out using the following Seismic sources and array geophones. Standard Shaker—GSS Standard 80 kg Shaker−10 to 91 Hz; and EM Shaker—GSS Electromagnetic Shaker −50 to 400 Hz. The tests were carried out on a trial embankment 2.0 m high and 40 m long. The embankment used as the fill material granular limestone that complied with UK Specification for Highway works (SHW) 6F1 taken from a quarry stockpile. The embankment was divided into 5 zones each 6 m wide and 2 m deep as shown in Table 1 below.

TABLE-US-00001 TABLE 1 Control Zone Zone 2 Zone 3 Zone 4 (Comp C) (Ex 1) (Ex 2) (Ex 3) (Ex 4) Geogrid None TX150 TX130S TX170 TX190L (non-stabilized)

[0170] Comp A and Comp B are shown in respective FIGS. 1 and 2 and represent prior art railway geoengineering constructions without (Comp A) and with (Comp B) a geogrid. The Examples 1 to 4 and Comp C from Table 1 used in these tests were constructed as shown in FIG. 3 with the geogrid located in a horizontal plane immediately below the layer labelled MSL and above that marked granular fill. The geogrids used were those respective geogrid products available commercially from Tensar International Limited under the registered trade mark TriAx® together with the trade designations given in Table 1 except for Comp C where the same construction without any geogrid was used.

[0171] To verify that a similar degree of compaction was achieved in the embankment test sections, Nuclear Density Meter (NDM) tests (calibrated for the specific fill used) were carried out on the embankment together with a calibration test for the fill material. The NDM tests were carried out in the top 200 mm of the test embankment only and in-situ density and the moisture content obtained from these tests is summarised in Table 2

TABLE-US-00002 TABLE 2 Bulk Density (Mg/m.sup.3) Moisture Content %.sup.(b) Ex Average.sup.(a) Range Average.sup.(a) Range Comp C 2.27 2.23 to 2.28 6.3 6.0 to 6.5 Ex 1 2.29 2.24 to 2.34 6.3 6.0 to 6.7 Ex 2 2.25 2.18 to 2.29 6.4 6.0 to 6.9 Ex 3 2.26 2.17 to 2.31 6.4 5.9 to 6.7 Ex 4 2.25 2.23 to 2.27 6.4 5.8 to 6.8 .sup.(a)Average of 6 tests carried out per zone. .sup.(b)Moisture content undertaken in the laboratory on collected bulk samples

[0172] It was observed that the ground beneath the test embankment contained quarry waste having particulate material of various sizes (fine grained soil to boulder size grains) and thus was loosely compacted. The tests were performed twice on the same test embankment at different times a few months apart. The first test was performed in rainy and damp conditions and the second test in dry and bright conditions with a strong wind. The soil below the control zone (Comp C) and the zone of Ex 1 was observed to be particularly wet in comparison to the rest of the embankment during the first test. The measurements in each test zone were taken in both a longitudinal direction (see FIG. 4) and laterally across the embankment (see FIG. 5) with reverse-direction measurements also being taken.

[0173] Dispersion curves were plotted in FIGS. 4 to 5 showing the shear wave velocity (Vs) along the longitudinal axis of the embankment (FIG. 4) and also Vs along its width (FIG. 5). These curves were calculated using Equation 1A above from the trial data, assuming Poisson ratio (u) of 0.26 for the embankment material. The range of the combined frequencies of the two seismic sources used in these tests was from 10 Hz to 400 Hz. The penetration depth was directly dependent on characteristics of the source frequency and predominantly on velocity of the S-waves (Vs) in the embankment medium. For example, where the average velocity of the S-waves generated in a test embankment is about 200 m/s, then a 10 Hz component of a corresponding Rayleigh wave generated in the embankment would penetrate to a depth of from about 7 to about 10 m below ground level and a 400 Hz component of the corresponding Rayleigh wave would penetrate the embankment to a depth of from about 0.2 to about 0.3 m below ground level.

[0174] Corresponding Rayleigh wave denotes a Rayleigh wave that when generated in the embankment (e.g. by movement of a train along the track) would comprise a S-wave component equivalent to the S waves induced in the embankment in these tests by the seismic sources (and recorded by the array geophones) as previously described. For completeness, profiles of Vs were calculated using test data in the models described herein to a depth of 15 m below ground level. However as the depth of the test embankment was only 2.0 m below ground level the Vs values presented in FIGS. 4 and 5 are those calculated for the top 2 m only.

[0175] Results

[0176] The results obtained from second test show reduced shear velocity (Vs) near the surface (to about 0.4 to 0.5 m) compared to those of the first test. This is believed to be due to weathering leading to strain-softening in the near two-month interval between the two tests, whereas in practise this particulate material would be covered by some 600 mm of construction in use and would not be exposed in such a way. The longitudinal stiffness (from FIG. 4) for both the control and the test embankments was greater than the lateral stiffness (from FIG. 5) by about 25%. This is believed to be due to the test embankment being less restrained across its width compared to its length. Both these effects are artefacts of the trial and would be unlikely to be encountered in real world railway tracks constructed for practical use and so these differences are not considered especially relevant.

[0177] Example 1 (TX150) provided an acceptable, though lower, increase in stiffness of the embankment for both tests.

[0178] Example 2 (TX130S) had a similar effect to Ex 3 (TX170) at the top of the layer.

[0179] Example 3 (TX170) increased the longitudinal stiffness of the embankment by between 20% and 60%.

[0180] Example 4 (TX190L) which used the stiffest of the geogrids used showed the most improvement in longitudinal stiffness of between 30% and 70%.

[0181] Example 5 (TX150L), which is a slightly thicker version of Example 1, also provides an acceptable increase in stiffness of the embankment, generating similar results to those given herein for Examples 1 to 4 in the tests describe herein.

[0182] Required certification for stabilization function is ETA 12/0530

TABLE-US-00003 TABLE 3a Performance related physical properties of the products Product Characteristic Unit Ex (product) Declared Value Tolerance Radial Secant (1) kN/m 1 (TX150) 360 −65 Stiffness at 0.5% strain 2 (TX130S) 275 −75 3 (TX170) 480 −90 4 (TX190L) 540 −90 5 (TX150L) 365 −90 Radial Secant Stiffness — 1 (TX150) 0.80 −0.15 Ratio (1) 2 (TX130S) 0.75 −0.15 3 (TX170) 0.80 −0.15 4 (TX190L) 0.75 −0.15 5 (TX150L) 0.75 −0.15

TABLE-US-00004 TABLE 3b Performance related physical properties of the products (continued) Product Characteristic Unit Ex (product) Declared Value Tolerance Junction Efficiency (2) % 1 (TX150) 100 −10 2 (TX130S) 100 −10 3 (TX170) 100 −10 4 (TX190L) 100 −10 5 (TX150L) 100 −10 Hexagon Pitch (3) mm 1 (TX150) 80 ±4 2 (TX130S) 66 ±4 3 (TX170) 80 ±4 4 (TX190L) 120 ±6 5 (TX150L) 120 ±6

TABLE-US-00005 TABLE 4 Properties for identification of the products Product Ex Declared Characteristic Unit (Product) Value Tolerance Radial Secant kN/m 1 (TX150) 250 −65 Stiffness (1) 2 (TX130S) 205 −65 at 2% strain 3 (TX170) 360 −65 4 (TX190L) 400 −100 5 (TX150L) 290 −100 Hexagon mm 1 (TX150) 80 ±4 Pitch (3) 2 (TX130S) 66 ±4 3 (TX170) 80 ±4 4 (TX190L) 120 ±6 4 (TX150L) 120 ±6 Weight of the kg/m.sup.2 1 (TX150) 0.205 −0.035 product (4) 2 (TX130S) 0.180 −0.030 3 (TX170) 0.270 −0.035 4 (TX190L) 0.300 −0.035 5 (TX150L) 0.240 −0.035

[0183] Notes for Tables 3a, 3b and 4 (Ex 1 to 5)

[0184] (1) Measured in accordance with EOTA Technical report TR41 B.1.

[0185] (2) Measured in accordance with EOTA Technical report TR41 B.2.

[0186] (3) Measured in accordance with EOTA Technical report TR41 B.4.

[0187] (4) Measured in accordance with EOTA Technical report TR41 B.3.

[0188] Durability Statement (5,6 &7) The minimum working life of the geogrid in natural soils with a pH value between 4 and 9 is assumed to be 100 years in soil temperatures less than 15° C. and expected to be 50 years in soil temperatures less than 25° C., when covered within 30 days.

[0189] (5) Resistance to weathering of geogrid assessed in accordance with EN 12224. The retained strength is greater than 80% giving a maximum time for exposure after installation of 1 month.

[0190] (6) Resistance to Oxidation is determined in accordance with EN ISO 13438. For the assumed working life of 50 years, the principle of Method A2 of EN ISO 12438 is followed, with the deviation that the exposure temperature is 120° C. and the exposure time 28 days. Justification for this is provided in ETA Certificate 12/0530.

[0191] (7) Resistance to acid and alkali liquids is determined in accordance with EN 14030.