U.S. patent application number 12/281354 was filed with the patent office on 2009-10-01 for track bed structures.
Invention is credited to Anthony Jay.
Application Number | 20090242654 12/281354 |
Document ID | / |
Family ID | 36218968 |
Filed Date | 2009-10-01 |
United States Patent
Application |
20090242654 |
Kind Code |
A1 |
Jay; Anthony |
October 1, 2009 |
Track Bed Structures
Abstract
A track bed composite structural element issued in railway track
engineering, and has an upper water permeable layer, a lower water
permeable layer and a filter material layer provided between the
upper and lower water permeable layers. The upper and lower layers
may comprise geotextile layers and the filter material may be sand
or glass, for example.
Inventors: |
Jay; Anthony; (Isle of Man,
GB) |
Correspondence
Address: |
GORDON & JACOBSON, P.C.
60 LONG RIDGE ROAD, SUITE 407
STAMFORD
CT
06902
US
|
Family ID: |
36218968 |
Appl. No.: |
12/281354 |
Filed: |
March 2, 2007 |
PCT Filed: |
March 2, 2007 |
PCT NO: |
PCT/GB2007/000749 |
371 Date: |
December 17, 2008 |
Current U.S.
Class: |
238/2 |
Current CPC
Class: |
E01B 2/00 20130101; E01B
1/00 20130101; E01B 2204/05 20130101; E01B 1/008 20130101; E01B
19/00 20130101 |
Class at
Publication: |
238/2 |
International
Class: |
E01B 1/00 20060101
E01B001/00; E01B 19/00 20060101 E01B019/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 2, 2006 |
GB |
0604169.3 |
Aug 17, 2006 |
GB |
0616424.8 |
Claims
1. A track bed composite structural element for use in railway
track engineering, the structural element comprising: an upper
water permeable layer, a lower water permeable layers and a filter
material layer provided between the upper and lower water permeable
layers.
2. A track bed structural element according to claim 1, wherein the
upper and lower water permeable layers comprise geo-textile
materials.
3. A track bed structural element according to claim 1, wherein the
filter layer comprises a filter material encapsulated within the
structural element.
4. A track bed structural element according to claim 1, wherein: i)
the filter material comprises a particulate filter material; and/or
ii) the filter material comprises a sand filter material.
5. (canceled)
6. A track bed structural element according to claim 1, wherein the
filter layer is effective to filter out clay or silt, whilst
permitting liquid water to pass across the element between the
upper and lower water permeable layers.
7. A track bed structural element according to claim 1, wherein the
filter layer inhibits migration of the filter material to spaced
zones of the structural elements.
8. A track bed structural element according to claim 6, wherein the
filter layer includes a dividing structure arranged to inhibit
migration of the filter material to spaced zones of the structural
element.
9. A track bed structural element according to claim 7, wherein: 1)
the dividing structure divides the filter layer into separate zones
or compartments; and/or ii) the dividing structure comprises a
permeable material; and/or iii) the dividing structure comprises an
impermeable material.
10. (canceled)
11. (canceled)
12. A track bed structural element according to claim 7, wherein:
i) the dividing structure comprises a flexible material structure;
and/or ii) the dividing structure comprises a relatively rigid
material structure; and/or iii) the dividing structure divides the
filter layer into a plurality of elongate compartments; and/or iv)
the dividing structure divides the filter layer into a grid array
of cells.
13. (canceled)
14. (canceled)
15. (canceled)
16. A track bed structural element according to claim 1, in the
form of an envelope or panel having opposed major surfaces and a
relatively shallow depth dimension.
17. A track bed structural element according to claim 1, further
comprising an elongate sealing flap extending from an edge of the
structural element.
18. A track bed structural element according to claim 17, wherein:
i) the sealing flap is secured to the lower water permeable layer;
and/or ii) a sealing flap is secured to the upper water permeable
layer; and/or iii) the sealing flap is water impermeable; and/or
iv) the sealing flap extends along substantially an entire edge of
the structural element.
19. (canceled)
20. (canceled)
21. (canceled)
22. (canceled)
23. (canceled)
24. (canceled)
25. (canceled)
26. (canceled)
27. A railway track bed comprising: a sub-grade layer; a track bed
composite structural element including an upper water permeable
layer, a lower water permeable layer, and a filter material layer
provided between the upper and lower water permeable layers; and a
ballast layer above the track bed structural element.
28. A railway track bed according to claim 27, wherein the
structural element is laid on top of the sub-grade layer and the
ballast is laid on top of the structural element.
29. A method of construction of a railway track bed, the method
comprising; laying a track bed composite structural element on a
sub-grade layer and subsequently laying a ballast layer above the
track bed structural element, wherein the track bed composite
structural element includes an upper water permeable layer, a lower
water permeable layer, and a filter material layer disposed between
the upper and lower water permeable layers.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to track bed structures and in
particular to an improved track bed structure for use in railway
track engineering, ameliorating undesirable effects including
sub-grade erosion.
[0003] 2. State of the Art
[0004] Cohesive and fine soils have behaviour characteristics that
are dominated by their fine particulate content, particularly clay
and silt content. Such soils are prone to sub-grade erosion beneath
a railway track bed. Mudstones and shale although appearing
relatively hard compared with soils, also abrade quickly under
ballast comprising the track bed, and are also prone to sub-grade
erosion.
SUMMARY OF THE INVENTION
[0005] The process of sub-grade erosion begins when permeable
ballast allows rainwater to percolate downwards and wet the soil
below. Alternatively water may flow upwards from the soil beneath,
where the sub-grade is lower than the adjacent ground water surface
profile (water table). This typically occurs in cuttings or where
natural springs, or artesian structures occur.
[0006] Silt structures will readily disintegrate in water, as will
clay structures, but more slowly. The vibration from a train on the
track above causes agitation and fluidisation and accelerates this
disintegration process for silts, clay and mudrock structures.
Additionally, under the effect of a passing train, pressure and
deflection can cause the slurry formed by the silt and clay
suspended in water to be forced by hydraulic pressure or `pumped`
up into the ballast. The ballast becomes contaminated with fines
which eventually can result in failure of the track bed. The
undesirable consequences of sub-grade erosion are ground loss from
the sub-grade, loss of vertical alignment of the track and
contamination of ballast leading to a detrimental effect on
functional properties, such as a loss of ability for the ballast
structure to hold its shape and provide the structural stability
required. As a result track maintenance becomes necessary more
frequently which is disruptive to transport schedules and
expensive.
[0007] Previously, sub-grade erosion has been ameliorated by use of
a suitable solution to the problem using blanketing sand in
accordance with a UK Standard RT/CE/S/033. The sand blanket
prevents rainwater from `ponding` directly on the sub-grade soil.
The fine sand component of the blanketing sand acts as a fine soil
filter, inhibiting the passage of silts and clays. Excavation into
blanketing sand has shown that the silt and clay sub-grade soil
penetrates no more than a few millimetres into the blanketing sand
before forming a stable soil filter. A liquid-permeable geo-textile
is laid over the blanketing sand in order to prevent the ballast
above penetrating into the blanketing sand. Geo-textiles are well
known for use in this application and such materials which are
permeable, are usually of plastics material, and commercially
available from a number of manufacturers such as the material
available under the trade name Terram.
[0008] Such a track bed arrangement is disclosed in FIG. 1 in which
101 represents the track bed, 102 the rails and 103 the sleepers.
Standard ballast 104 lies above the geo-textile 105, which is in
turn laid over the blanketing sand 106, which overlays the
sub-grade material 107.
[0009] The solution described works adequately, but has severe
drawbacks in terms of disruption and cost of installation.
[0010] Track renewals and repairs are frequently carried out at
night and the length of track being improved has to be closed to
traffic. This is a major cost. The more quickly that repairs can be
effected, then the less disruption and expense.
[0011] Often, when repairing the railway track bed, the railway
track is the only means of transport of materials to the repair
site. This presents logistical problems.
[0012] Excavating 100 to 150 mm below ballast to make space for
blanketing sand takes time. It also takes resources to have the
waste material taken away. It takes time to bring in the blanketing
sand unload it and spread it in an even layer of 100 mm thickness.
This can be a very slow labour intensive job and, in poor working
conditions at night, perhaps when it is raining or snowing and
under sever time constraints. Good quality control is not always
easy to achieve.
[0013] The availability of suitable grade sand is poor and can
require bringing in from significant distances.
[0014] An improved technique and product have now been devised.
[0015] According to a first aspect, the present invention
provides
a track bed composite structural element for use in railway track
engineering, the structural element comprising an upper water
permeable layer, a lower water permeable layer and a filter
material layer provided between the upper and lower water permeable
layers.
[0016] Typically the element comprises a panel, blanket, envelope,
strip or tile like structure having opposed major faces and which
in use is arranged to lie on one of its major faces. The element
may be rigid, or flexible in which case it may be capable of being
formed into a roll.
[0017] It is preferred that the upper, and/or the lower water
permeable layers comprise geo-textile materials. Such materials are
robust and suited to civil engineering situations.
[0018] Beneficially, the filter layer comprises a filter material
encapsulated within the structural element.
[0019] In certain embodiments, the filter material may beneficially
comprise a particulate filter material, particularly preferred
grade sand filter material, such as in the grading limits specified
in RT/CE/S/033. Additionally or alternatively, in certain
embodiments the particulate filter material may beneficially
comprise ground and/or graded glass material such as glass bead
material.
[0020] It is desirable that the filter material layer is effective
to filter out clay or silt, whilst permitting liquid water to pass
across the element between the upper and lower water permeable
layers.
[0021] It is preferred that means is provided to inhibit migration
of the filter material to spaced zones of the structural element.
In certain embodiments, it is preferred that the filter layer
includes a dividing structure arranged to inhibit migration of the
filter material to spaced zones of the structural element. The
dividing structure beneficially divides the filter layer into
separate zones or compartments. In certain embodiments the dividing
structure may comprise a permeable structure. In certain
embodiments the dividing structure may comprise an impermeable
structure. The dividing structure may comprises a flexible material
structure, or a rigid material structure dependent upon the
embodiment.
[0022] The dividing structure divides the filter layer into a
plurality of elongate compartments, such as for example elongate
side by side compartments or channels.
[0023] Alternatively, the dividing structure may divide the filter
layer into a grid array of cells, such a square or hexagonal
cells.
[0024] Beneficially, the track bed structural element comprises a
an envelope or panel having opposed major surfaces and a relatively
shallow depth dimension.
[0025] In certain embodiments, it is preferred that the structural
element further comprises an elongate sealing flap extending from
an edge of the structural element. Beneficially, the sealing flap
is secured to the lower water permeable layer of the structural
element.
[0026] It certain embodiments it will be desirable that the sealing
flap is water impermeable. In other situations it may be preferable
that the flap is permeable. In this case the function is more
protective against foreign bodies intruding into the joint rather
than being liquid sealing. Preferably, the sealing flap extends
along substantially an entire edge of the structural element. Also,
this protects against loss of filter material from the joint
through pumping or movement.
[0027] A sealing flap may also be secured to the upper water
permeable layer of the structural element. The upper sealing flap
may in some circumstances be permeable, however, an impermeable
sealing flap is generally preferred.
[0028] According to a further aspect, the invention therefore
provides a structural element for use in civil engineering
applications, the structural element comprising an upper surface
and a lower surface, and a filter material layer provided between
the upper and lower surfaces, wherein the structural element has a
sealing flap arrangement comprising an elongate sealing flap
extending from an edge of the structural element.
[0029] Beneficially, the sealing flap arrangement comprises:
transversely extending marginal sealing flap portions provided
along first and second transverse edges of the lower surface,
transversely extending marginal sealing flap portions provided
along first and second transverse edges of the upper surface, which
edges are on opposite sides of the element to the edges of the
flaps of the upper surface of the element.
[0030] It is preferred that the structural elements are in use laid
in side by side arrangement, preferably in a in raster type order
or tile pattern in which;
a first structural element is laid, a second structural element is
laid to the side of the first element and on top of the side flap
extending from the lower layer of the first structural element; a
third structural element is laid forward of the first structural
element and on top of a forward flap extending from the lower layer
of the first structural element.
[0031] This is believed to be novel and inventive per se and
accordingly provides a further aspect of the invention.
[0032] The laying up procedure continues in this fashion. The top
flaps, where present, neatly overlay the joins along the opposed
edges to the lower flaps.
[0033] It is preferred that where sealing flaps are provided on the
upper layer of the structural element, that an overlaying anchor is
provided upon which the ballast can be laid. The overlaying anchor
can be a permeable geo-textile and/or a geo-grid layer to weight
down the flaps and prevent them `lifting` when the ballast is
applied on top. A geo-grid adds additional strength to the
arrangement.
[0034] Sealing flaps can be provided to suit particular
applications and conditions in various possible permutations,
specifically the element may be provided with or without the top
flap arrangement, and/or with or without the bottom flap
arrangement. Also the flaps may be bonded or sealed to the adjacent
structural elements or not (remaining simply freely overlaying or
underlaying). [0035] Additionally the joints may be filled with
filter material during the laying process in order to provide
filtering in the region of the joints. This is however frequently
not necessary.
[0036] According to a further aspect, the invention provides a
railway track bed comprising:
a sub-grade layer; a track bed composite structural element, as
herein defined; and, a ballast layer above the track bed structural
element.
[0037] According to a further aspect, the invention provides a
method of construction of a railway track bed, the method
comprising laying a track bed composite structural element, as
herein defined, on a sub-grade layer and subsequently laying a
ballast layer above the track bed structural element.
[0038] The invention will flow be further described, by way of
example only, with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] FIG. 1 is a schematic sectional view of a known track
bed;
[0040] FIG. 2 is a schematic perspective view of a track bed in
accordance with the invention;
[0041] FIG. 3A is a schematic perspective view of a track bed
structural element in accordance with the invention;
[0042] FIG. 3B is a more detailed perspective view of the
structural element of FIG. 3A;
[0043] FIG. 3C is a schematic detailed sectional view of the
structural element of FIGS. 3A and 3B;
[0044] FIG. 4 is a schematic perspective view of an alternative
embodiment of structural element according to the invention;
[0045] FIG. 5 is a schematic perspective view of an alternative
embodiment of structural element according to the invention;
[0046] FIG. 6 is a side view of a jointed structural element
arrangement according to the invention;
[0047] FIG. 7 is a detailed view of the jointed structural element
arrangement of FIG. 6;
[0048] FIGS. 8A to 8C are plan and perpendicular section views
respectively of an alternative embodiment of structural element
according to the invention;
[0049] FIG. 9 is a schematic view of a system for laying the
structural elements of FIG. 8.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0050] Referring to the drawings and in particular FIG. 2, there is
shown a track bed similar to that shown in FIG. 1, but in which a
structural element 5 of the present invention is positioned below
the ballast 4 but above the sub-grade fine soil or mudrock layer
7.
[0051] As shown in FIGS. 3A to 3C, the track bed structural element
5 comprises a an elongate structural envelope 5 having an upper
liquid permeable surface 9 of geo-textile material, a lower liquid
permeable surface 10, which may be identical to the upper surface
or different in terms of material, thickness, permeability or other
physical properties. The longitudinally opposed ends 11,12 of the
structural envelope 5 are closed by end panels, which may be
permeable and of geo-textile material. Longitudinally running edges
14, 15 of the structural envelope are also closed, but shown open
in FIGS. 3A to 3C for explanatory purposes. A bulk filler filter
material 15 is contained or encapsulated internally of the
structural envelope 5. In a preferred embodiment the bulk filter
material may be appropriate particulate sized filter sand.
Alternative envisaged suitable materials may be other particulate
bulk materials such as glass granules or beads, lightweight fibre
or filter amorphous agglomerations, or mesh, net or other
reticulated materials. The important physical characteristics of
the bulk filler filter material 15 is that it is capable of
filtering out clay silt or other sub-grade materials, especially in
this particular field of use, in particle size distribution
specified in accordance with, for example BS5930, whilst permitting
liquid water to pass through the structural element envelope 5. The
structural envelope element 5 should overall have good supporting
properties in situ and preferably settle to a packed compressed
configuration when in situ in the railway track bed.
[0052] In order to prevent loose particulates comprising the bulk
filler filter material 15 from migrating (during transportation or
laying down) from one location within the envelope 5 to another,
and resulting in an unacceptably uneven distribution of the
material within the envelope, the arrangement is provided with
means for holding the bulk filler material together and preventing
such migration to other parts of the structure. In one realisation,
this is achieved by the interior of the envelope being divided into
a plurality of compartments by one or more dividing structures. In
the embodiment described in FIG. 3, the dividing structure
comprises an internal water permeable geo-textile 18 formed
serpentine to define the relevant compartments 22. In the
embodiment shown, the dividing structure geo-textile 18 is a
flexible geo-textile material which is bonded by means of gluing,
heat bonding, pressure bonding, welding or other suitable bonding
technique to the respective upper surface 9 and lower surface 10 of
the envelope structure 5 along seam lines 23 running transversely
to the longitudinal direction of the envelope structure 5. The
dividing structure geo-textile permits liquid water to egress along
or across the envelope structure without permitting the bulk filler
filter material to move from compartment 22 to compartment 22. The
portions of the dividing structure membrane extending between the
surfaces 9 and 10 act to `tie` the envelope inhibiting bulging of
the structure.
[0053] The envelope structure 5 may be flexible enabling it to be
stored in roll up format. Alternatively the envelope structure may
be rigid, and in panel form. In panel form, like structural
elements may be laid up in side by side relationship as one would
lay tiles. Exemplary envisaged dimensions for a composite
structural element such as that shown is depth 15 mm, 1.95 m Width
(dimension X in FIG. 3A), and 0.75 m long (dimension Y in FIG. 3A).
Rigid panels or roll up envelopes of such dimensions with
appropriate grade sand as filler filter material should be capable
of manual handling and placement. Larger structural elements 5 may
require the use of mechanical handling techniques. The structural
elements are laid long side 14 adjacent next panel long side 14
with the track direction being in the width direction (width Y in
FIG. 3A).
[0054] FIG. 4 shows a structural element 5 generally similar in
construction to the structural element of FIG. 3A (and with like
structural integers denoted by like reference numerals). In the
arrangement of FIG. 4, the serpentine dividing structure
geo-textile 18 of FIG. 3 is replaced with a series of web elements
28 bonded to the opposed surfaces 9, 10 at margins 29. This again
defines divided compartments 22.
[0055] FIG. 5 shows a structural element 5 which comprises a
plastics injection moulded grid 48 having perpendicular sidewalls
41, 42 defining a series of compartment cells 44 open at their top
and bottoms. The perimeter of the grid 48 is closed by a perimeter
wall 49 formed integrally as part of the moulded structure of the
grid. A water permeable geo-textile 59 is bonded to the upper
surface of the grid 48, and a water permeable geo-textile 60 is
bonded to the underside surface of the grid 48. Bulk filler filter
material (such as appropriate grade sand) is present inside the
compartment cells 44 and prevented from passing out of the open
ends of the cells by means of the bonded geo-textile membranes. The
cell walls dividing structure grid 44 permits liquid water to
egress across the envelope structure 5 (bottom to top or vice
versa) without permitting the bulk filler filter material to move
from cell compartment 44 to cell compartment 44. The composite
structural element embodiment of FIG. 4 provides a relatively rigid
structural panel, but having sufficient flexibility to conform to
the shape of an uneven underlaying ground surface.
[0056] Referring now to FIGS. 6 and 7, structural elements 5 and 5A
are shown in side by side relationship in accordance with the
invention laid on the sub-grade material 57 beneath ballast 54.
Each of the structural elements 5, 5A has a water impermeable
membrane flap 71 bonded to a leading longitudinal edge 14a at the
underside of the structural element 5, 5A. Bonding material bead 72
can be seen in the figure. The trailing longitudinal edge 14b of
each structural element 5 5A is provided with a preferably water
impermeable membrane flap 75 bonded to the up-side of the
structural element. The trailing edge 14b of element 5 is placed
adjacent the leading edge 14a of element 5A, resting on the flap
71, and may be bonded thereto, for enhanced security of sealing,
using a suitable sealant. The sealing bead 77 is shown in the
figure. The top flap of 75 at the trailing edge of element 5 flaps
down on the leading edge of element 5A. The flap 75 may be lifted
permitting the gap between the trailing edge of element 5 and the
leading edge of element 5A to be filled with sand or other suitable
filler filter material, to filter out clay silt or other sub-grade
materials, whilst permitting liquid water to pass. The flap 75 may
be sealed down onto the leading edge of element 58 following
positioning and filling of the joint (if this is desired).
[0057] Elements 5 and 5A form a close location joint. Rainwater
percolating down through the ballast and entering the joint will
not be able to directly enter the sub-grade soil below, because of
the impermeable flap 71. the rainwater will thus be forced to enter
the structural element 5 or 5A via the permeable geo-textile outer
perimeter. Similarly upward flow of groundwater is forced to avoid
flowing directly into the joint and must pass, at least initially
into the elements 5 or 5A. The weight of the ballast and settlement
caused by train passage should enhance sealing of the joint. In
order to enhance sealing further the structural elements bay be
overlaid initially with an anchoring structure such as a permeable
geo-textile and/or other reinforcing grid, membrane or layer,
before loading on of the ballast. This would aid in preventing the
flaps lifting (as might otherwise occur) and ballast entering the
joints, which would be undesirable. Indeed it is envisaged that in
certain instances the top flaps would not be needed and for example
the joints could be sand filled and a covering geo-textile or
membrane overlaid.
[0058] In the embodiment of FIG. 8, the structural element 80 has a
sand filled perimeter marked by the lines 81, 82, 83, 84. The
underside permeable geo-textile layer overlaps the sand filled
perimeter to provide an L shaped bottom marginal flap 85 (having
limbs 85a, 85b) along the 2 perpendicular edges 81 and 84. The
upper side permeable geo-textile layer overlaps the sand filled
area to provide an L shaped top marginal flap 87 (having limbs 87a,
87b) along the 2 perpendicular edges 82 and 83.
[0059] When laying the structural elements 80 in side by side
relationship a specific sequential pattern is followed. The
structural elements are in use laid in side by side arrangement,
preferably in a in raster type order or tile pattern (as
exemplified in FIG. 9) in which a first structural element (1) is
laid in the orientation as shown in FIG. 8 having the flap 85
extending to the left and forward. A second structural element (2)
is laid to the side of the first element and on top of the side
flap 85b. A third element can be laid to the left of the second
element (and so on, in order to build Up the required width) or, as
in the sequence shown in FIG. 9, the third structural element (3)
is laid forward of the first structural element (1) and on top of
the forward flap 85a of element (1). The top flaps 87 of the second
and third elements overlay the firs element (1). This arrangement
and laying up pattern enables the a good jointing system to be
effected simply by laying up the panels in the required
configuration and order. The laying up procedure continues in this
fashion. The top flaps, where present, neatly overlay the joins
along the opposed edges to the lower flaps.
[0060] An overlaying anchor is provided upon which the ballast can
be laid. The overlaying anchor can be a permeable geo-textile or a
geo-grid layer to weight down the flaps and prevent them `lifting`
when the ballast is applied on top.
[0061] Scaling flaps can be provided to suit particular
applications and conditions in various possible permutations,
specifically the element may be provided with or without the top
flap arrangement, and/or with or without the bottom flap
arrangement. Also the flaps may be bonded or sealed to the adjacent
structural elements or not (remaining simply freely overlaying or
underlaying).
[0062] Additionally the joints may be filled with sand during the
laying process in order to provide filtering in the region of the
joints. This is however frequently not necessary.
* * * * *