Note: Descriptions are shown in the official language in which they were submitted.
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RAIL SLEEPER AND BALLAST-FREE TRACK STRUCTURE
Technical field
This invention relates to a ballast-free track structure suitable for carrying
railway rails,
s and to a rail sleeper for use in such a structure.
Background art
Conventional methods for laying a railway track involve placing large wooden,
reinforced concrete or steel sleepers on a ballasted track bed, after which
rails are
io fastened to the sleepers. The purpose of the ballast is to provide a free-
draining
foundation with high shear strength and good elastic (resilient) properties.
However, for over a century there has been very little fundamental improvement
in the
design and construction of conventional, ballasted railway track.
Consequently, some
is serious and persistent problems have never been completely resolved. In
particular,
the progressive degradation of the track structure under repeated loading
remains
problematic. This degradation is manifest in several ways, including loss of
geometric
stability (the ballast spreads and settles, resulting in loss of vertical and
horizontal
alignment); loss of resilience (the ballast degrades and becomes contaminated
by finer
2o material resulting in increased dynamic damage to track structure
(corrugations) as well
as to rolling stock); and pumping of sub-grade (caused by dynamic loading, and
resulting in ballast fouling and destruction of formation).
The control of these problems is expensive due to heavy ongoing maintenance
2s requirements as well as foreshortened track and rolling stock life spans.
In recent years
additional environmental requirements to reduce noise and ground-borne
vibrations
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have added impetus to a growing interest in the rail industry to move away
from the old
ballasted track systems towards more rigid structures, which provide enduring
geometric stability and require reduced maintenance.
s Several efforts have been made to develop more rigid track structures, most
of which
have centred on "sleeper-track" or "slab-track" alternatives. One such system
is the
Japanese "ladder track" system, in terms of which two longitudinal parallel
sleepers are
joined to each other by transverse steel or concrete sleepers extending
between the
longitudinal sleepers and which act as gauge ties, the arrangement being such
that the
io finished product looks like a ladder laid on the ground. The concrete
sleepers are
partially pre-stressed in a factory.
A major disadvantage of this system is that it still relies on a ballasted
formation and so
remains susceptible to the problems described hereinbefore. A further
disadvantage
Is associated with this system is that it is often characterised by poor load
dispersal and
weak resistance to longitudinal creep movement of the sleepers.
Yet another method of installing a railway track is by in situ casting of the
track sleepers.
This can be done, for example, by preparing longitudinal trenches for the
rails and
20 laying flexible tubes in the trenches. The flexible tubes are filled with
concrete so that a
rail sleeper is formed that is dimensioned for accepting the rails.
Alternatively, the
sleepers can be cast on the ground surface by providing lateral restraint to
the wet
concrete by means of shutters.
2s One of the disadvantages associated with this method is the relatively
extensive time
involved for construction, maintenance and reconstruction of the track,
because of
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curing times of the concrete. Other disadvantages include the logistics and
complexity
of construction, and accompanying difficulties associated with site quality
assurance
and control.
s Obiect of the invention
It is an object of the present invention to provide a rail sleeper suitable
for use in
erecting a railway track that will overcome or at least minimize some of the
problems
associated with the prior art and which will facilitate rapid installation and
replacement of
railway tracks.
to
It is a further object of the invention to provide a ballast-free track
structure and a
method for laying the same that will overcome or minimize some of the problems
associated with known track structures, or at least will provide a useful
alternative to
known structures of this nature.
is
Disclosure of invention
According to the invention there is provided a prefabricated rail sleeper
suitable for use
in erecting a track structure, the sleeper comprising an elongate body portion
for
supporting rails, the body portion including a top face, a bottom face and at
least two
zo side faces, and terminating at least at one end thereof in a transition
joint formation
dimensioned matingly to engage a complimentarily dimensioned transition joint
formation of an adjacent rail sleeper in use so as to form a substantially
continuous
track structure.
2s The rail sleeper may be located on a ballast-free track bed during erection
of the track
structure.
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The body portion may terminate at both ends thereof in a transition joint
formation, the
arrangement being such that when a series of rail sleepers are arranged in end-
to-end
orientation on a track bed, they together form a substantially continuous
track structure
s without the need for continuity of reinforcement between adjacent sleepers.
The rail
sleepers may be orientated in end-to-end orientation on a ballast-free track
bed in such
a manner that a transition joint space is defined between the transition joint
formations
of adjacent sleepers for permitting gradual stress transfer between sleepers
and
preventing lateral displacement between the same.
io
The rail sleeper also may include at least one block formation dimensioned for
supporting a rail. In a preferred form of the invention the rail sleeper may
include a
number of block formations equally spaced along the length of the sleeper such
that the
bottom surfaces of the block formations are arranged substantially flush with
the bottom
is face of the body portion. The block formations may be at least partially
flared block
formations, each block formation including a top surface, a bottom surface and
at least
two side surfaces. The side surfaces may be characterised therein that they
are at least
partially outwardly flared from the top surface towards the bottom surface,
extending
beyond the side faces of the body portion, so as to increase shear interlock
of the
2o sleeper with the track bed to reduce longitudinal creep.
The top surfaces of the block formations may be dimensioned for receiving rail
fasteners. In particular, the top surfaces of the block formations may be
raised relative
to the top face of the body portion such that, in use, a gap exists between a
rail foot and
2s the top face of the body portion for permitting rail foot drainage,
especially when
sleepers are backfilled, thus limiting rail-sleeper abrasion and rail-to-rail
signaling
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shorts. The gap also allows free access for welding of rail joints and the
passage of
under-rail services.
The rail sleeper optionally may include at least one bore arranged proximate
the block
s formation and extending between the top and bottom faces of the body
portion, the bore
being dimensioned for receiving grout or the like therein for underpinning the
block
formation and a rail foot. The bore may be lined with a corrugated polymeric
sheath to
provide non-brittle shear interlock.
io The rail sleeper further may include at least on drainage duct for
facilitating drainage of
liquid, such as rainwater, away from the rail sleeper. The drainage duct may
be a
transverse duct extending underneath the rail sleeper and defined by a box-out
recess
in the bottom face of the body portion, the arrangement being such that liquid
can drain
between different side faces of the body portion by running through the bottom
is transverse duct. In a preferred form of the invention, the rail sleeper may
include a
series of transverse ducts that are longitudinally spaced along the length of
the sleeper.
The rail sleeper also may include at least one longitudinal service duct
located in and
extending along the length of the body portion for accommodating, for example,
2o electrical and/or optic fibre cabling.
The rail sleeper further may include ,resilient pads of high performance
polymers
arranged on the top surface of each block formation and dimensioned for
receiving a rail
foot thereon such that the resilient pads at least partially protect the rail
sleepers from
2s dynamic and impact loads exerted on the sleepers, which could result in
brittle or
fatigue failure modes.
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The rail sleeper may be pre-cast from pre-stressed, post-tensioned or
conventionally
reinforced concrete. The rail sleepers may be characterised therein that they
are pre-
cast in an upside down manner to ensure that the top face of the sleeper, to
which the
rails are attached, consists of the densest concrete.
The concrete may be cured by using steam, water or chemical curing compounds.
The
properties of the wet concrete may be modified using additives such as
plasticisers,
accelerators or retarders, while the properties of set concrete may be
modified by epoxy
or polymeric impregnation to increase abrasion resistance and enhance chemical
io durability.
The reinforcement may be augmented or completely replaced by fibres (fibre
reinforced
concrete (FRC)) to enhance toughness under repeated loading. The fibres may
consist
of polymeric, natural or steel fibres (galvanised or epoxy coated steel for
aggressive
is conditions) to provide increased abrasion resistance, increased ductility
and crack
resistance, and resistance to impact and dynamic loading.
The concrete in the sleepers may be characterised therein that it incorporates
a
proportion of sand-sized rubber particles such that the rubber particles
reduce the
2o Young's Modulus of the concrete while not compromising strength, rendering
the
concrete less brittle and thus more resistant to dynamic or impact forces.
The rail sleepers may be formed in several lengths so as to accommodate curves
of
different radii.
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According to another aspect of the invention there is provided a prefabricated
rail
sleeper suitable for use in erecting a track structure, the sleeper comprising
an elongate
body portion for supporting rails, the body portion including a top face, a
bottom face
and at least two side faces; and at least on drainage duct for facilitating
drainage of
s liquid, such as rainwater, away from the rail sleeper.
The drainage duct may by a transverse duct extending underneath the rail
sleeper and
defined by a box-out recess in the bottom face of the body portion, the
arrangement
being such that liquid can drain between different side faces of the body
portion by
io running through the bottom transverse duct. In a preferred form of the
invention, the rail
sleeper may include a series of transverse ducts that are longitudinally
spaced along
the length of the sleeper.
According to yet another aspect of the invention there is provided a
prefabricated rail
is sleeper suitable for use in erecting a track structure, the sleeper
comprising an elongate
body portion for supporting rails, the body portion including a top face, a
bottom face
and at least two side faces; and at least one block formation dimensioned for
at least
partially accommodating a rail, the block formation being characterised
therein that it is
at least partially flared.
Preferably, the rail sleeper includes a number of block formations equally
spaced along
the length of the sleeper such that the bottom surfaces of the block
formations are
arranged substantially flush with the bottom face of the body portion.
2s Each block formation may include a top surface, a bottom surface and at
least two side
surfaces. The side surfaces may be characterised therein that they are at
least partially
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outwardly flared from the top surface towards the bottom surface such that the
block
formations extend beyond the side faces of the body portion so as to increase
shear
interlock of the sleeper with the track bed.
s The top surfaces of the block formations may be dimensioned for receiving
rail
fasteners. In particular, the top surfaces of the block formations may be
raised relative
to the top face of the body portion such that, in use, a gap exists between a
rail foot and
the top face of the body portion for permitting rail foot drainage when
sleepers are
backfilled, thus limiting rail-sleeper abrasion and rail-to-rail signaling
shorts. The gap
to also allows free access for welding of rail joints and the passage of under-
rail services.
Each block formation optionally may include at least one bore extending at
least
partially between the top and bottom surfaces of the block formation and
dimensioned
for receiving grout or the like therein for underpinning the block formation
and a rail foot.
is The bore may be lined with a corrugated polymeric sheath to provide non-
brittle shear
interlock. A rock dowel or micro pile may be installed through the bore for
underpinning
the sleeper in poor ground conditions and for fixing sleeper location on steep
grades,
sharp curves or the like, the rock dowel or micro pile comprising of an
elongate bore
extending vertically through the rail sleeper and into the ground underneath,
the
2o elongate bore being filled with concrete, grout, crushed rock particles or
the like.
According to another aspect of the invention there is provided a ballast-free
track
structure suitable for carrying rails of a railway track, the track structure
comprising a
series of rail sleepers according to the invention wherein the sleepers are
located in
zs end-to-end orientation on a ballast-free track bed such that the transition
joint formation
of one sleeper matingly engages the transition joint formation of an adjacent
sleeper,
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the arrangement being such that they form a substantially continuous track
structure
without the necessity for continuity of reinforcement between adjacent
sleepers.
The transition joint formations may be dimensioned for limiting lateral
movement of the
s sleepers so as at least partially to limit independent deflection of the
sleepers and for
reducing bending and shear stresses in a rail. The transition joint between
adjacent rail
sleepers may be secured by underpinning the joint using in-situ polymeric
concrete,
installing a jockey slab underneath the joint, or by means of bolted
connections for
accommodating longitudinal expansion and contraction of adjacent sleepers.
io
According to another aspect of the invention there is provided a ballast-free
track
structure suitable for carrying rails of a railway track wherein the track
structure
a
comprises at least two rail sleepers according to the invention located in
spaced parallel
orientation on a ballast-free track bed so as to define a centre drain between
the
is sleepers; and a mesh located between the sleepers for reinforcing the
centre drain.
The mesh may be fixed to the body portion of at least one rail sleeper and may
extend
from a side face thereof. In one form of the invention, the mesh may be fixed
to both of
the rail sleepers so that the sleepers and mesh-reinforced centre drain form a
track
Zo slab. The mesh may be weld mesh. Once the rail sleepers are laid on the
track bed,
successive weld meshes may be laced together for effecting structural
continuity of the
track slab.
The rail sleepers may be connected to each other by means of at least one
cross tie
2s extending between adjacent parallel sleepers. In a preferred form of the
invention, the
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rail sleepers are connected to each other through a series of steel cross ties
extending
between adjacent parallel sleepers spaced along the length of the track
structure.
The track structure also may include one or more resilient mats arranged
intermediate
s the bottom face of the body portion and the track bed. The resilient mats
may comprise
of relatively soft polymers adapted at least partially to absorb dynamic or
impact loading
between the rail sleepers and hard sub-strata such as tunnel floors, concrete
bridges
and the like, and to attenuate structure-borne or ground-borne noise and
vibration.
io The track structure also may comprise at least one rock dowel or micro pile
located
underneath the rail sleeper and proximate a block formation for underpinning
the
sleeper in poor ground conditions and for fixing sleeper location on steep
grades, sharp
curves or the like, the rock dowel or micro pile comprising of an elongate
bore extending
vertically through the rail sleeper and into the ground, the elongate bore
being filled with
is concrete, grout, crushed rock particles or the like.
The track structure, may be adapted to accommodate slow and high-speed
installations,
and may range from light axle load applications, such as mine tracks (in the
order of 10
tonne axle load), to heavy haul applications in surface track (in excess of 35
tonne axle
load).
According to yet a further aspect of the invention there is provided a method
of laying a
ballast-free track structure which is suitable for carrying rails of a railway
track, the
method comprising the steps of constructing a base formation (earthworks)
layer works
zs to a specified strength and dimensional tolerances; fixing rail sleepers
according to the
invention in spaced parallel orientation to form track panels; laying the
fixed track panels
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in end-to-end orientation on the pre-prepared ballast-free formation layer
works;
placing and fastening rails into position on the rail sleepers; and
mechanically adjusting
vertical and horizontal alignment of the rail sleepers.
s Vertical alignment may be achieved by lifting (jacking) and wedging the
track panels to
the correct height and packing dry-mix concrete or crusher run underneath the
sleepers.
Alternatively, where setting times allow, vertical alignment may be achieved
by
appropriate grout injections or by inserting grout packs. Horizontal alignment
may be
achieved by dragging the sleeper laterally. Re-alignment of previously
installed track
io may be achieved by exposing the base of the sleeper and tamping in
additional dry mix
or other material.
The sleepers may be pre-cast upside down in specially designed steel shutters
to
ensure that the top face of the sleeper, to which the rails are attached,
consists of the
is densest concrete. The concrete is placed into steel shutters and vibrated
to ensure
maximum density.
Specific embodiment of the invention
Without limiting the scope thereof, two embodiments of the invention will now
be
2o described by way of example only and with reference to the accompanying
drawing
wherein -
Figure 1 is an isometric view of a rail sleeper according to one embodiment of
the
invention, wherein the rail sleeper is designed for light axle load
2s applications such as underground mining;
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Figure 2 is an isometric view of a rail sleeper according to another
embodiment of
the invention, wherein the rail sleeper is designed for heavier axle loads
such as main line applications;
Figure 3 is an isometric view of a track structure according to one embodiment
of
s the invention;
Figure 4 is an isometric view of a track structure according to another
embodiment
of the invention, including a wire mesh extending between the sleepers;
Figure 5 is a transverse cross-sectional view of the track structure of Figure
4;
Figure 6 is a transverse cross-sectional view of a track structure according
to the
io invention illustrating a possible configuration of a centre drain and
underpinning of the rail sleeper;
Figure 7 is a plan view of the track structure of Figure 4.
A rail sleeper according to the invention there is generally designated by
reference
is numeral 10. The rail sleeper 10 comprises an elongate body portion 12 for
supporting
rails 14. The body portion 12 includes a top face 12.1, a bottom face 12.2 and
at least
two side faces 12.3.
The body portion 12 terminates at least at one end thereof in a transition
joint formation
20 16 that is dimensioned for matingly engaging a complimentarily dimensioned
transition
joint formation 16 of an adjacent rail sleeper 10 in use. The arrangement is
such that
the connection between the sleepers 10 forms a substantially continuous track
structure
30.
Zs In a preferred form of the invention, the body portion 12 terminates at
both ends thereof
in a transition joint formation 16, the arrangement being such that when a
series of rail
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sleepers 10 are arranged in end-to-end orientation on the track bed, they
together form
a substantially continuous track structure 30 without the need for continuity
of
reinforcement between adjacent sleepers 10. The rail sleepers 10 are
orientated in
end-to-end orientation on a ballast-free track bed in such a manner that a
transition joint
s space 18 (Figure 7) is defined between the transition joint formations 16 of
adjacent
sleepers 10 in a manner permitting gradual stress transfer between the
sleepers 10 and
limiting independent movement of the sleepers 10 so as at least partially to
limit
independent deflection of the rail sleepers 10 and for reducing bending and
shear
stresses in a rail 14.
io
The rail sleeper 10 also includes at least two spaced block formations 20 for
supporting
the rails 14. Each block formation 20 includes a top surface 20.1, a bottom
surface 20.2
and at least two side surfaces 20.3. The block formations 20 are at least
partially flared
block formations 20. More particularly, the side surfaces 20.3 are
characterised therein
is that they are at least partially outwardly flared from the top surface 20.1
towards the
bottom surface 20.2, extending beyond the side faces 12.3 of the body portion
12, so as
to increase shear interlock of the sleeper 10 with the track bed. The rail
sleeper 10
preferably includes a number of block formations 20 that are substantially
equally
spaced along the length of the sleeper 10 such that the bottom surfaces 20.2
of the
2o block formations 20 are arranged substantially flush with the bottom face
12.2 of the
body portion 12.
The top surfaces 20.1 of the block formations 20 are dimensioned for receiving
rail
fasteners 37 for the rails 14. In particular, the top surfaces 20.1 of the
block formations
zs 20 are raised relative to the top face 12.1 of the body portion 12 such
that, in use, a gap
exists between a rail foot and the top face 12.1 of the body portion 12 for
permitting rail
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foot drainage when the sleepers 10 are backfilled, such as in surface track
applications, thus limiting rail-sleeper abrasion and rail-to-rail signaling
shorts.
A block formation 20 optionally also includes at least one bore 22 (Figures 6
and 7)
s extending at least partially between the top and bottom. surfaces 20.1, 20.2
of the block
formation 20. The bore 22 is lined with a corrugated polymeric sheath (not
shown) to
provide non-brittle shear interlock. The bore 22 is dimensioned for receiving
grout or
the like therein for underpinning the rail sleeper 10.
io The rail sleeper 10 further includes at least on drainage duct 26 for
facilitating drainage
of liquid, such as rainwater, away from the rail sleeper 10. The drainage duct
is a
transverse duct 26 extending underneath the rail sleeper 10 and defined by a
box-out
recess in the bottom face 12.2 of the body portion 12, the arrangement being
such that
liquid can drain between different side faces 12.3 of the body portion 12 by
running
is through the bottom transverse duct 26. In a preferred form of the
invention, the rail
sleeper 10 includes a series of transverse ducts 26 that are longitudinally
spaced along
the length of the sleeper 10.
The rail sleeper 10 also includes at least one longitudinal service duct 24
located in and
zo extending along the length of the body portion 12 for accommodating, for
example,
electrical and/or optic fibre cabling.
The rail sleeper 10 also includes resilient pads 36 (Figure 5) of high
performance
polymers arranged on the top surtace 20.1 of each block formation 20 and
dimensioned
Zs for receiving a rail foot thereon such that the resilient pads 36 at least
partially protect
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the rail sleepers 10 from dynamic and impact loads exerted on the sleepers 10,
which
could result in brittle or fatigue failure modes.
The rail sleeper 10 is generally pre-cast from pre-stressed, post-tensioned or
s conventionally reinforced concrete.
The invention also provides for a ballast-free track structure 30 suitable for
carrying rails
14 of a railway track. The track structure 30 comprises a series of rail
sleepers 10
according to the invention wherein the sleepers 10 are located in end-to-end
orientation
to on a ballast-free track bed such that the transition joint formation 16 of
one sleeper 10
matingly engages the transition joint formation 16 of an adjacent sleeper 10.
The
arrangement is such that they form a substantially continuous track structure
30 without
continuity of reinforcement between adjacent sleepers 10.
is The transition joint formations 16 are dimensioned for limiting lateral
movement of the
sleepers 10 so as at least partially to limit independent deflection of the
sleepers 10 and
for reducing bending and shear stresses in a rail 14. The transition joint
between
adjacent track sleepers 10 are secured by underpinning the joint using in situ
polymeric
concrete, installing a jockey slab underneath the joint, or by means of bolted
2o connections for accommodating longitudinal expansion and contraction of
adjacent
sleepers.
The track structure 30 further includes a second row of track sleepers 10 that
are
located in spaced parallel orientation from the first row of track sleepers 10
on a ballast-
2s free track bed. The rail sleepers 10 are held at the correct spacing by
means of steel or
concrete cross ties 60 fixed to or cast into a rail sleeper 10 on either side.
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An optional feature is to place in-situ concrete 42 (Figure 6) between the
rail sleepers
so as to define a centre drain 32 between the sleepers. Where the centre drain
option is exercised, a preferred option is to fix a reinforcing mesh 34
between the rail
sleepers 10 to reinforce the centre drain 32 and effectively form a track
slab. Once the
s rail sleepers 10 are laid on the track bed, successive weld meshes 34 are
laced
together to form structural continuity between the sleepers 10.
The track structure 30 also includes one or more resilient mats 38 (Figure 5)
arranged
intermediate the bottom face 12.2 of the body portion 12 and the track bed.
The
to resilient mats 38 comprise of relatively soft polymers that are adapted at
least partially
to absorb dynamic or impact loading between the rail sleepers 10 and hard sub-
strata
such as tunnel floors, concrete bridges and the like, and to attenuate
structure-borne or
ground-borne noise and vibration.
is The track structure 30 also comprises at least one rock dowel or micro pile
40 (Figure 6)
located under a block formation 20 of the rail sleeper 10 for underpinning the
sleeper 20
in poor ground conditions and for fixing the steeper location on steep grades,
sharp
curves or the like. The rock dowel or micro pile 40 is installed through the
bore 22 and
comprises of an elongate bore extending vertically through the rail sleeper 10
and into
2o the ground underneath a block formation 20, the elongate bore 40 being
filled with
concrete, grout, crushed rock particles or the like.
The track structure 30 is adapted to accommodate slow and high-speed
installations,
and range from light axle load applications, such as mine tracks (in the order
of 10
2s tonne axle load in), to heavy haul applications in surface track (in excess
of 35 tonne
axle load).
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It will be appreciated that various other embodiments of the invention may be
possible
without departing from the spirit or scope of the invention as defined in the
claims.
