Geoengineering constructions for use in railways

Abstract

A railway geogrid construction is 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 includes a track bed which defines a track located on a track plane, a mass of particulate material such as an aggregate forming a layer located beneath the track plane, and a geogrid located in and/or below the particulate mass in a 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, the construction comprising: a track bed 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 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; $\begin{array}{cc}55\left(\frac{A+\mathrm{Bv}}{1+v}\right)\frac{G_0}{}& \mathrm{Equation}4A\end{array}$ where A is a dimensionless constant; B is a dimensionless constant; denotes the Poisson ratio of the particulate layer; G.sub.0 is the small strain stiffness property of the particulate layer; and is density of the particulate layer.

2. The geogrid engineering construction for railways of claim 1, wherein the track bed comprises rails.

3. The geogrid engineering construction for railways of claim 1, wherein is from 0.1 to 0.5.

4. The geogrid engineering construction for railways of claim 1, wherein is from 0.2 to 0.4.

5. The geogrid engineering construction for railways of claim 1, wherein is from 0.2 to 0.35.

6. The geogrid engineering construction for railways of claim 1, wherein 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.

7. A method for constructing a geogrid engineering construction for railways, the method of construction comprising: defining a track plane 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 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; $\begin{array}{cc}55\left(\frac{A+\mathrm{Bv}}{1+v}\right)\frac{G_0}{}& \mathrm{Equation}4A\end{array}$ where A is a dimensionless constant; B is a dimensionless constant; denotes the Poisson ratio of the particulate layer; G.sub.0 is the small strain stiffness property of the particulate layer; and is density of the particulate layer.

8. The method of claim 7, wherein the track bed comprises rails.

9. The method of claim 7, wherein is from 0.1 to 0.5.

10. The method of claim 7, wherein is from 0.2 to 0.4.

11. The method of claim 7, wherein is from 0.2 to 0.35.

12. The method of claim 7, wherein 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.

13. A particulate material stiffened and/or strengthened by the method of claim 7.

14. Use of a geogrid in a method to construct a geogrid engineering construction for railways comprising: defining a track plane along which the track bed will be located; defining a 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 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; $\begin{array}{cc}55\left(\frac{A+\mathrm{Bv}}{1+v}\right)\frac{G_0}{}& \mathrm{Equation}4A\end{array}$ where A is a dimensionless constant; B is a dimensionless constant; denotes the Poisson ratio of the particulate layer; G.sub.0 is the small strain stiffness property of the particulate layer; and is density of the particulate layer.

15. The use of claim 14, wherein the track bed comprises rails.

16. The use of claim 14, wherein is from 0.1 to 0.5.

17. The use of claim 14, wherein is from 0.2 to 0.4.

18. The use of claim 14, wherein is from 0.2 to 0.35.

19. The use of claim 14, wherein 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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is illustrated by the following non-limiting FIGS. 1 to 5 where:

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

(3) 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;

(4) 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;

(5) 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

(6) 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).

(7) FIG. 6 provides an exploded view of the various structural elements of the geogrid engineering construction according to one embodiment of the invention, including the location of the geogrid element within the construction.

(8) FIG. 7 provides an enlarged view of the various structural elements of the geogrid element shown in FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(9) Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

(10) 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.

(11) 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

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

(13) FIG. 6 provides an exploded view of the various structural elements of the geogrid engineering construction according to one embodiment of the invention, including the location of the geogrid element 70 within the construction. For example, the geogrid engineering construction can include, according one embodiment, a railway track bed 50, a granular fill 60, a geogrid 70, and a subgrade 80.

(14) 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 (). 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:

(15) $\begin{array}{cc}{V}_r\left(\frac{0.874+1.117v}{1+v}\right)V_s,& \mathrm{Equation}1A\end{array}$
where Vr is the Rayleigh Wave velocity through the ground; Vs is the velocity of S-waves through the ground; and is the Poisson ratio (the signed ratio of transverse strain to axial strain).

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

(17) 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.

(18) Go may be converted to Young's Modulus (E) using the relationship E=G.Math.(2.Math.(1+)). 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.

(19) 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 ShakerGSS Standard 80 kg Shaker10 to 91 Hz; and EM ShakerGSS Electromagnetic Shaker50 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.

(20) 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)

(21) 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 70 located in a horizontal plane immediately below the layer labelled MSL and above that marked granular fill. The geogrids 70 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. See, for example, such a geogrid 70 as depicted in application FIG. 7, according to one embodiment of the instant invention. FIG. 7 provides an enlarged view of the various structural elements of the geogrid 70.

(22) 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

(23) 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

(24) 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.

(25) 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 () 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.

(26) 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.

(27) Results

(28) 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.

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

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

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

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

(33) 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.

(34) Required certification for stabilization function is ETA 12/0530

(35) 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

(36) 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

(37) 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
Notes for Tables 3a, 3b and 4 (Ex 1 to 5)
(1) Measured in accordance with EOTA Technical report TR41 B.1.
(2) Measured in accordance with EOTA Technical report TR41 B.2.
(3) Measured in accordance with EOTA Technical report TR41 B.4.
(4) Measured in accordance with EOTA Technical report TR41 B.3.
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.
(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.
(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.

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

(39) The invention being thus described, it will be apparent that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be recognized by one skilled in the art are intended to be included within the scope of the following claims.