INCREASING TUNNEL LOADING GAUGE WITHOUT LOWERING THE INVERT.

lifegunbarrelcityUrban and Civil

Nov 26, 2013 (3 years and 10 months ago)

77 views

INCREASING TUNNEL LOADING GAUGE WITHOUT LOWERING
THE INVERT.


Paper presented to Railway Engineering 2001 Conference

by Professor Lewis Lesley,




Dr. Fouad Mohammad,

Dr. Hassan Al Nageim




School of Civil Engineering,

School of Built Environment,



Univ
ersity of Nottingham,

Liverpool JM University,




Nottingham NG7 2RD

98 Mount Pleasant,

Liverpool L3 5UZ



KEYWORDS: Loading gauge, tunnel invert, LR55 track, track loadings, foundation
behaviour


ABSTRACT


With few exceptions railway tunnels in the UK w
ere built to 19th century loading gauges,
before the advent of piggyback euro standard HGV trailers, super cube ISO maritime
containers, or electrification. Justifying the capital cost for the reconstruction of tunnels to
larger loading gauges is difficult
, even where "free" money from the EU is available. The
alternative of lowering the invert is difficult, especially where tubular tunnels are
involved. In any case only limited enlargement can be achieved.


Some rail lines in the UK can carry 8ft 6in high
ISO containers, and with low floor
wagons, 9ft 6in high containers. Neither the next generation of 10ft 6in high containers
already in wide international use, nor 4m high, 2.5m wide and 12m long road trailers
piggyback can be accommodated, without tunnel l
oading gauge enlargement.


This paper describes the development work of the LR55 track system, which can provide
at least 300mm more head room in existing tunnels, within the existing invert. The LR55
track system is based on highway structural design phil
osophy and has been subjected to
a battery of tests, including 80 tonne axles and 3m diameter tube tunnel loading.



1.0

INTRODUCTION


Since George Stephenson built railways, the sleeper with rails fixed either directly or on a
base plate, has been the pri
ncipal method of transmitting train loads into the sub soil via
an elastic ballast. Brunel's longitudinal sleepers only found favour for bridges. Higher
axle loads and train speeds, and the desire for better track standards with reduced
maintenance costs,
has seen traditional sleeper tracks improved incrementally with
heavier rails, stronger fastenings, bigger sleepers and deeper ballast. On open tracks these
improvements have been able to cope. In tunnels the situation is different, since the depth
of bal
last is constrained by the level of the invert, and so therefore are axle loads and
speeds which can be accommodated, witnin a given loading gauge. In double track
tunnels extra loading gauge can be won by singling but then there is a loss of train
capaci
ty, unless a new parallel tunnel is built. This paper discusses a new track system
which requires a shallow foundation depth, even for the heaviest axle loads and high train
speeds, and therefore promises larger loading gauges within existing tunnel inver
ts.



2.0

DESCRIPTION OF LR55 TRACK SYSTEM


Traditional track systems use bottom supported rails, which then need strong fastenings to

sleepers to prevent overturning from lateral wheel loads. With discrete support on
sleepers, trains experience regular ha
rd spots at the sleepers, which are a cause of the
formation of short wave corrugations on rail heads. Because spacing between sleepers is
an order of magnitude larger than the sleeper width, ballast must be considerably deeper
than that required for cont
inuously supported rails. Finally rails and sleepers have to be
adjusted together for line and level.



2.1

LR55 track components

There are six components to the LR55 track system (Fig. 1):


(a)

compacted highway type base

(b)

prefabricated concrete suppor
t troughs

(c)

gauging bars between troughs

(d)

ballast outside and between troughs

(e)

low profile, top supported rail

(f)

elastomeric grout to bond and support the rail in troughs




















Figure 1. LR55 track system components



2.2

Track base

There is worldwide experience and expertise in the design and installation of compacted
highway bases. The bearing quality, elasticity and life of such bases is well understood.
There are many highway contractors competent to lay quickly such bases. These
bases
can be laid with a very high tolerance of material quality, and line and level. This is
important, as the pre cast concrete support troughs sit directly on the base. The level of
base, together with the prefabrication tolerance of the troughs determ
ines the first order
accuracy of the ultimate line and level of the track. The troughs are gauged together by
bars, although the mass of the ballast, the lateral stiffness of the troughs and large trough
sides, provide substantial lateral restraint to the
track.



2.3

Concrete Support Troughs

The support troughs are vertically and laterally stiff. This is important as the rail is less
stiff vertically than girder rails (eg. UIC60). The wide base of the trough, and the
continuous support, means that the tr
ough pressure into the track base typically lies
between 150 and 250 MPa, for 25 tonne axles loads, depending on the stiffness of the
base. Even a weak base however, like sand has a load capacity of about 5000 MPa, an
order of magnitude greater than the im
posed pressure.


Support Troughs are manufactured and delivered to site in lengths to suit handling and
installation to the required quality. At this stage it would seem sensible that support
troughs would be 6m long, which weigh about 600kg. Longer Suppo
rt Troughs could be
tried as part of an optimisation exercise balancing import material costs against site
handling and adjustment. On curves, support troughs are laid as tangents to the required
radius and design super elevation for the train speeds expec
ted. Simple mechanical links,
fix the ends of support troughs together, until the application of a bonding grout
permeates between the trough ends and bonds the troughs together.


There are various methods available for prefabricating the support troughs.
Many
manufacturers are capable of producing the troughs to the required quality of concrete and
dimensional tolerance. Pre
-
stressed tendons primarily fulfil the function of ensuring that
troughs can be delivered to site intact. Most of the track testing h
owever has been
undertaken satisfactorily with unreinforced troughs.


2.4

LR55 rails

The LR55 rail is top supported in the pre
-
cast concrete trough. This makes the rail very
stable and highly resistant to overturning. About 60% of the wheel loads are trans
mitted
on the running side rail flange, about 30% on the non running side flange, and 10% by the
rail base. The rails weight about 55kg per linear metre and therefore have similar
electrical resistivity to girder rails of similar weight. Lateral train load
s are accommodated

by shear compression of the elastomeric bonding grout, and the lateral stiffness of the
troughs and track construction.


The LR55 rails are welded into long strings and pre tensioned longitudinally to
compensate for ambient temperature v
ariations. The rail welds are located away from
joints between the support troughs, to prevent hinges being created. The rails are
supported temporarily either by stands, or wedges of pre
-
cured bonding material. The
rails are adjusted for line, level and g
auge.


Once the rails are to line, level and gauge, they are bonded into the concrete support
troughs by elastomeric grout. This is the second order determinant of track accuracy. It
should be possible to achieve a tolerance of 0.1mm. There is no mechani
cal connection
between rail and trough, with the rail continuously supported vertically and restrained
laterally by the elastomeric grout, rail/wheel interface forces are almost constant along
the track. This should mean a better ride for vehicles (and th
eir loads) as well as reducing
the incidence of long, medium and short wave length corrugations along rail heads.


The LR55 rail is made with a built in continuous check rail. This should reduce
derailments, especially by flange climbing over the rail hea
d, since the other wheel on the
axle will be restrained laterally by the check rail. In the event of a derailment, trains
cannot drop because the track formation is level with the top of the rail. This also means
that derailed trains are unlikely to overtu
rn off the track.


Finally on curved tracks with high speed running, gauge corner cracking is less likely to
occur, since the centrifugal wheel forces are shared between outside and inside wheels on
the curve. In the less likely case of cracks progressing
to failure, as occurred in October
2000, the bonding and support trough which surrounds the rail will prevent it falling
apart, and thus denying the derailment mechanism which had tragic consequences at
Hatfield. This continuous support for the rail, means

that the more common weld failure
need not be so critical, since the broken rail ends will be restrained and kept together.



2.5

Elastomeric Grout

The rails are bonded into the support troughs with an elastomeric grout which transmits
the static and dyna
mic forces from wheels through the trough into the rail base.
Polyurethane elastomers are now widely used in rail application, eg. noise reducing base
plates. There are many proprietary polyurethane bonding grouts available "off the shelf",
fully tested fo
r the climatic and loading conditions experienced in railway environments.



3.0

COMPLETED MODELLING


3.1

Modelling

Static and dynamic load models were examined. Wheel loads rolling along and across the
rail have been modelled. The outputs of the models ar
e:


-

rail deflection


-

trough deflection


-

shear forces in rail


-

shear forces in trough


-

bending moments in rail


-

bending moments in trough


-

pressure at base of trough



3.2

Analytical Models

Modelling conventional railways has been undertaken b
y considering the rails as a single
layer beam, and the sleepers and ballast as a homogeneous elastic foundation. In the
LR55 track system the rail is continuously supported in a concrete support trough. This is
better represented as multi layer beams wit
h elastic foundations. Here the rail and the
support trough are considered to be beams, and the elastomeric grout and sub
-
base as
elastic foundations with different moduli. Analytical models can only solve a limited
number of idealised problems. The bounda
ry conditions of these were discussed by
Hetenyi (1946). Timoshenko et al (1932) had earlier analysed the stresses in railway
tracks in the same way.


3.3

Finite Element Method

The use of the Finite Element Method (FEM) allows a wider range of problems to
be
solved, with different loading and boundary conditions, and non
-
linear foundation
properties. These were applied to railway problems by Fateen (1972) and explored by
Miranda et al (1996).


The analysis of the LR55 track system using FEM is based on a st
iffness approach for
solutions, the nodal displacements are assumed to be the basic unknowns. The nodal
equilibrium may be expressed by the stiffness matrix equation (1):




[K].{∂} = {P}








(1)


where


[K] = global stiffness matrix of the structure



{∂} = unknown displacement vector of the structure



{P} = applied load vector on the structure.


Solving this equation with FEM requires the track to be divided into a number of
elements. The contribution of the track base to shear resistance in the stif
fness matrix is
so small and unreliable that it can be ignored. The stiffness matrix of the LR55 track is
therefore the assembly of the stiffness matrices of all its components.


3.3.1

Rail and concrete beam elements

The steel rail and concrete support tro
ugh can be treated as conventional beam elements,
with two nodes per element. Each node has three degrees of freedom; horizontal
displacement (u), vertical displacement (v) and rotation about the z
-
axis (ø). This
produces a stiffness matrix, which is there
fore 6 x 6. Przemieniecki (1968) discussed the
coefficients of the stiffness matrix.



3.3.2

Pad Spring Elements

The elastomeric grout acts like a pad and is represented by a number of discrete vertical
and horizontal springs. Each spring has one degree o
f freedom per node which is
displaced in the axial direction. The vertical springs are assumed to be of a Winkler type,
Selvadurai (1979). These can be defined as equ. (2)





K1v =

Ep W





hp







(2)






Where:



Ep = elastomeric pad Youn
g's modulus



W = rail width




hp = thickness of elastomeric pad


The two ends of the grout vertical spring elements are free to displace, so the stiffness
matrix is 2 x 2 in the form :






vi vj






1
-
1


vi


[K]e = K1v








(3)




-
1 1


vj




3.3.3

Track base vertical spring elements

The track base foundation can also be considered to consist of Winkler type vertical
springs. Each spring having one degree of freedom. The stiffness of each spring is then
equ. 4:



K2 = k2 L









(4)

where:


k2 = track base modulus



3.3.4

Input assumptions

These equations were used to predict the behaviour of the LR55 track specified with the
following characteristics:



TABLE 1


PROPERTIES OF THE LR55 TRACK SYSTEM




Element SectionArea

Moment of Inertia

Young's Modulus Self weight





m2 x 10
-
4


m4 x 10
-
8



(N/mm2) x 104


(kN/m)




Rail


67.2


337.3



20



0.53



Trough 472




8260



2



1.13




The tr
ack base modulus is assumed to be 20 N/mm2 and the Young's modulus of the
elastomeric grout is assumed to be 2.42 N/mm2 . The grout is assumed to be uniformly
20mm thick. The applied wheel load is 122.6 kN, equivalent to the 25 tonne maximum
axle load pe
rmitted on Britain's railways.



3.3.5

Deflection

The maximum deflection of the LR55 rail under the above conditions is 7.8mm, and
occurs at the point of wheel loading. The deflection decays to zero over a distance of 2m
from the point of load. There is t
hen a negative deflection (hogging) where the rail rises
above the neutral position by up to 0.1mm over a further 2m length.


Similar characteristics can be seen in the behaviour of the concrete support trough,
although the deflection is much less. Immedi
ately under the wheel load deflection is at a
maximum, of only 3mm. Again there is a hogging of 0.1mm between two and four metres
from the load. These two calculations show that at the point of load the rail is depressed
into the grout and trough by about
5mm. This is below the 6mm figure specified for
American main line railways . (Fig. 2)



3.3.6

Bending moment

The maximum bending moment in the LR55 rail occurs, as would be expected, under the
wheel load. Here it has a value of about 20kN.m and then decl
ines away from the load to
zero 0.5m away. It continues to decrease to a negative moment of about 4kN.m , a metre
from the wheel load. The moment increases and approaches the neutral axis smoothly
regaining neutrality about 3m from the load.



For the co
ncrete support trough there is a similar picture, except that the bending
moments are much less. Under the wheel load it is 7kN.m, and the maximum hogging of
2kN.m about 1.5m from the load. However in the case of a FEM for a trough only 4m
long, the end e
ffects of the more rigid trough show that hogging continues to decrease to
a value of
-
6kN.m. (Fig. 3 )





























Figure 2. Deflection of LR55 rail and support trough under 25 tonne axle load



























Figure 3. Bending

moment of LR55 rail and support trough under 25 tonne axle
load


In all cases, the FEM and analytical model results closely agree. Given the complexity of
the FEM, for first order approximations the analytical beam model gives very satisfactory
results.


3.4

Noise and vibration transmission modelling.

A mass
-
sping
-
mass
-
spring model for noise and vibration attenuation from wheel/rail
interaction into the ground has been constructed. This predicts a 30dB reduction in the
range 0
-

20 Hz, and 50dB reduction i
n the >100Hz range compared to girder rails on
sleepers in ballast. This is due to two main factors. There is no rail web to act as a
sounding board. Secondly the mass
-
spring
-
mass
-
spring transmission path provides the
optimum attenuation, with noise and vi
bration energy absorbed by warming of the
elastomeric grout.



3.5

Thermal Forces

The effects of temperature variations in the LR55 rail, elastomeric grout and concrete
support trough was modelled by differences in expansion (and contraction), on the
equ
ilibrium in the track. These exert shear forces along the LR55 track, between rails and
bond, and bond and trough. Further forces act in extension (or compression) between the
rail and bond, and bond and trough. For the temperature range examined neither o
f these
family of forces will result in bond failure.


3.6

Laboratory Tests

A series of physical tests were undertaken in the Civil Engineering Structures Laboratory
of the Liverpool JM University. The tests used a standard hydraulic press able to deliver
up to a 500kN (about 50tonne) load, either statically or dynamically. Track samples 1m
and 6m long were tested with static and dynamic loadings. In all cases the tests pieces
were instrumented with strain and displacement gauges. The applied loads were
me
asured with a load cell. All data were recorded with a computer, which was used to
analyse the results obtained. Tracks were also tested on a variety of base materials and a
range of ambient temperatures from
-
10oC to +60oC. Half of the tests were conduct
ed
with the tracks under water to check for elastomeric bond delamination and track failure
by pumping. Two tests to destruction were undertaken, to examine the behaviour of the
track in failure mode.


3.6.1

Description of Rail Samples Tested

Sample rails,

1 metre long were cast by Edgar Allen Engineering Ltd. from standard
manganese steel used for normal rails, points, switches and crossings. The rails had three
different depths 60mm, 70mm and 80mm. The first and third samples had plain rounded
bases (as
in Fig.1), while the second had notches in the rail side (Fig.4). A further cast rail
80mm high and 6m long, with a rounded base was made for foundation failure testing.



















Figure 4. LR55 rail profile with notched sides


The 1m long rails we
re bonded into a weak mix unreinforced cast concrete support
troughs using either rubber filled polyurethane grouting (KC330) provided by SIKA Ltd,
or System 6 polyurethane grouting provided by ALH Ltd. Attached to the underside of the

rails were strain ga
uges which were placed 0.2, 0.5 and 0.7 metres along the length of the
rail, in the centre line.


Some of the tests were conducted in dry conditions. In others the rail and concrete base
were covered by 25mm of water retained by a tank created around the c
oncrete base and
sealed with silicon mastic.


The 6m long sample was comprehensively strain gauged along the length of the rail and
the support trough, on the top, sides and bottom.




3.6.2

Description of the Test Rig

The 1m rails embedded in their concre
te bases were mounted on the hydraulic impulse
press normally used to test highway pavement specimens. A load cell was placed over the
centre of the upper surface of the rail and loads imposed which could be raised in 0.1 kN
steps. The load into the rail h
ead was imposed using a large steel ball to replicate a rail
wheel. Imposed loads were both static and dynamic. The strain gauges plus a
displacement gauge at the centre of the rail were connected to a data logging system.


3.6.3

The Endurance Testing Proc
edure

At the start of each test, increasing static loads were imposed in incremental steps from
0.0 to 100 kN and reference readings from the displacement and strain gauges taken. The
rail was then subjected to 1.25 million cycles of sine wave dynamic impu
lses with a
frequency of 15Hz, and a maximum load of 50 kN.


A further graduated load test up to 100 kN was then undertaken. The rail was then
subjected to another 1.25 million cycles. Lastly the graduated load was repeated. The
before, middle and after r
esults were then plotted for comparison, to determine what
deterioration of the track had occurred. 15Hz was selected to represent an operating train
speed of over 100 km/h.


This procedure was then repeated for a further 2.5 million cycles with the sampl
e rail
submerged in water. Giving 5 million cycles in total for the sample. The other 1m rail
samples were subjected to the same procedures as the initial rail, each having 2.5 million
cycles, dry and 2.5 million cycles wet. Giving an accumulated total of
15 million cycles
for the initial three rail samples examined.


The 6m long rail sample bonded into a 6m long concrete support trough was placed on a
prepared sub base over 1m deep, to replicate the rail sub soil. This sample was subjected
to static and dy
namic loads as for the 1m long samples. This sample was also tested with
a 1m wide void in the sub base immediately under the point of load application.This was
to determine the ability of the LR55 system to resist weak and collapsed foundations and
sub ba
ses. All tests on this sample were undertaken with 25 tonne axle loads.


3.6.4

Simulated loads


Simulated axle loads up to 80 tonnes were used on the LR55 track without failure. Cyclic
loadings with 25tonne axle loads using a 15Hz frequency (simulating a p
assing speed of
about 30m/sec. ). In total all track samples were subjected to about 30million axle loads,
without showing any signs of failure.


3.6.5

Static tests.


Static axle loads have been tested without failure up to 80 tonne, and dynamic axle loads

of 25 tonnes. Track samples have been subjected to endurance tests of 30 million axles
passing at simulated speeds of over 100km/hr. Samples have been tested under water to
ensure no penetration, or failure from pumping or frost damage.


One track sample
was tested in a temperature chamber, where the ambient temperature
was varied from
-
10oC to +60oC. This allowed both the performance of the track to be
examined under different temperatures but also the variation of stiffness to be examined,
of the elastom
eric pad between rail and concrete support trough.


All tests have been undertaken on 8 different track samples at up to the equivalent of 80
tonne axle loads. Two different PU grouts (SIKA KC330 and ALH System 6) have been
tested for performance. Three di
fferent rail heights (60mm, 70mm and 80mm) were
tested, as well as rails having notches in the lower rail side to determine what difference
of performance resulted. After these tests, the 80mm rail section was selected for further
testing, without side not
ches. The analytical structural models have been validated on a
6m long track sample.


3.6.6

Dynamic tests

Tests were undertaken at a simulated train operating speed of over 100km/hr with an
equivalent of at least a 20 tonne axle load. This was achieved wi
th a load of 100kN
applied sinusoidally at a frequency of 15Hz. In total some 30 million passing axles have
been simulated. About 10 million axle loads were tested with the track samples flooded,
to determine the degree of water penetration and possible fa
ilure. No water penetration or
failure was recorded.


One sample was tested dynamically in a temperature chamber in the range
-
10oC to
+60oC. This recorded the hardening at lower temperatures and the softening at higher
temperatures of the bonding PU gro
ut. This did not impair the performance of the track
system, which showed no signs of premature failure, having previously been tested under
wet and dry conditions (3.2.3).

3.6.7

Test results

These results have shown that from laboratory tests using a hyd
raulic impulse press to
simulate 126 kN loads at 15Hz, equivalent to over 100 km/h, sections of LR55 low
profile rail with different rail depths were able to withstand and recover from the loads
imposed, which were equivalent to maximum main line railway
standards. A total of 30
million simulated axle loads were imposed. The behaviour of the PU bonding grout
replicated earlier tests at the University of Calgary (Shrive & Ameny 1987). The PU grout
was able to withstand the ingress of water from 2.5 million

cycles submerged for each
sample tested.


The rail and bonding material behaved according to Hooke's Law, and no evidence
emerged that the elastic limit was approached for any of the samples. Nor was there any
evidence of a deterioration in the performanc
e of the PU grout, which continued to
behave elastically. However, these laboratory tests did not simulate a rolling axle passing
along the rail or the impact of sine wave deformation and harmonics created by adjacent
axles.



3.6.8

Failure tests.

Destruc
tive tests were also undertaken. A one metre sample was supported at each end as
a simple beam. It was loaded in its centre to failure. The load was increased in 10 kN
increments. The track failed at 296 kN, a simulated axle load of about 58 tonne . The
concrete of the trough failed in tension. The bond between the polyurethane grout and
both the LR55 rail and concrete support trough did not fail.


A second destructive test was of the strength of the PU grout to resist the rail pull out
from the trough. T
his also determined the resistance of the PU grout to thermal expansion
forces of the rail to high ambient temperatures, which could cause the rail to be displaced
from the foundation support trough. The test involved pulling out, with an incrementally
inc
reasing load, a 1m long rail from its trough. The one metre long sample failed at a pull
out load of 29kN (about 3 tonnes). Again the concrete in the trough failed in tension. The
elastomeric bond held. This means that the LR55 can resist thermal expansion

from
atmospheric conditions experienced in a 70oC temperature range .


In both cases the elastomeric grout did not fail. The grout remained bonded to the LR55
rail and to the concrete trough. The concrete troughs failed in tension. Both tests indicate
con
siderable over capacity compared to loads to be met in normal railway operation.


3.6.9

Electrical Resistivity

The control of stray currents in normal conditions is determined by the electrical
resistivity of tracks. One metre long track samples in the lab
oratory measured better than
20,000 mega Ω resistance. The resistivity of both PU grouts tested were similar. This
translates in the field to over 10,000 Ωkm resistivity, and would suggest negligible stray
currents in normal conditions.



3.7

Site Testing

Two field trials have been successfully mounted.




3.7.1

Rotherham Bus Station.

A 10 metre length of LR55 track was installed in March 1993 in the entrance to
Rotherham Bus Station, were buses crossed, turned around and passed along the rail. The
trial
was concluded in Sept. 1995 after about 2 million buses had impacted on the LR55
trough. It was laid in three support troughs; 2.5m, 3.0m and 5.0m long to determine the
behaviour of different trough lengths under load.


The rail and trough were instrument
ed with strain gauges and the results captured on a
data logger. Regular analysis of this data showed that the track remained in good
condition. After a year all gauges had exceeded their design life but continuing visual
monitoring confirmed that the LR55

track had not deteriorated or failed. This trial
represented about 30 years traffic in a typical urban radial road.


This was also confirmed by a trench dug under the site in Sept. 1994 to expose the track
construction. The concrete trough showed no signs

of failure or deterioration. This was
inspected by interested parties including the Railway Inspectorate, public utility
representatives etc. The trench showed the shallow construction of the track and that the
LR55 track is self supporting over trenches
(or foundation voids).



3.7.2

South Yorkshire Supertramway.

Over a weekend in March 1996 a length of LR55 track was installed on a single track
section of the Supertramway where a conventional girder railed track had failed after only
two years. The LR55
installation was at a point where some 300 LRVs and 100 HGVs
impact per day ( a total of about 120,000 vehicles pa, or about 6million tonnes pa). A
failure of this sample would halt the main line to Meadowhall. The track was installed
one rail per night t
ime possession, without interruption of day time rail service or road
traffic. This installation has been monitored regularly, and the alignment measured for
stability. The installation was accepted by South Yorkshire Supertram Ltd. into its
maintenance re
sponsibility in Sept. 1996. The LR55 track continues to give a satisfactory
performance


3.7.3

Heavy Rail application

A presentation and discussions have been held with Deutsche Bahn for the use of the
LR55 track system in one of two particular uses:

(a)

L
ow cost, low maintenance, low traffic branch lines

(b)

High Speed slab track, with troughs for easy rail replacement, and train
containment in case of derailment.



The development and testing work have been undertaken to mainline railway standards.
Even
at 25 tonne axle loads, the pressure at the base of the foundation trough is low
(<250 mPa), and by distributing loadings over a wide area, means that track should have a
longer life than conventional sleepered track. Gauge maintenance is achieved by a
com
bination of ballast resistanc, trough stiffness and gauge bars between the support
troughs.



4.0

APPLICATION TO TUNNEL LOADING GAUGE ENHANCEMENT


The total height of the LR55 track system above the sub soil/sub base is only 200mm.
This is at least 300mm
lower than sleepered tracks. A lower track height means that a
larger loading gauge is achievable in tunnels without the need to lower the invert or
reconstruct the tunnel. (Fig. 5).


The LR55 track with a level track surface also provides other benefits
for tunnels. These
include:


(1)


safer staff working conditions


(2)


safer emergency train evacuation


(3)


ability to use road maintenance or rescue vehicles without modification


4.1

Tubular tunnels

The LR55 track benefits of increasing loading gauge
are available for tubular tunnels,
where the cost of lowering the invert would be considerable and disruptive. Indeed a
section of London Underground tube tunnel (3 m diameter) was replicated in the
Structures Laboratory at Liverpool JM University to inves
tigate the stresses in the lower
tunnel sections and the ground around the tunnel. (Fig. 6) As in the above tests, this
showed that the LR55 track could create an increase in tunnel loading gauge height of
over 300mm, without increasing the stress in the
tunnel segments, or overloading the
surrounding ground. A (temporary) transition section between LR55 and sleepered track
has been designed to enable relaying with LR55 to be undertaken on a progressive basis
with short possessions if necessary.








F
igure 5. LR55 track in existing tunnel with enlarged loading gauge








increased loading gauge
gaugegauge




Figure 6. LR55 track system in tube tunnel to enlarge loading gauge



4.2

Other tunnels

Masonry tunnel walls with strip foundations , or built onto bedrock represent a different
structural challenge for increasing loading gauge. While lowering the invert is physically
possible to achieve, the cost of disruption while the operating railway is closed or
curtailed makes this also difficult to achieve. The advantage of the LR55 track
is that it
can be laid in place of existing tracks on the same possession basis, with immediate
reopening of tracks, albeit at temporary lower speeds to accommodate the transition
between LR55 and remaining sleepered tracks. The increased head room and lo
ading
gauge is particularly relevant to new rail freight traffics, eg. piggyback, and the new 10ft
6in high ISO containers. (Fig.7) now in use on maritime trades.




















Figure 7. LR55 tracks accommodating larger loading gauge for freight train
s



5.0

OTHER RAILWAY APPLICATIONS OF LR55 TRACK SYSTEM


The LR55 track system, while providing a specialist solution to increasing tunnel loading
gauge without lowering the invert, does have other practical applications for main line
railways, some of whi
ch are topical.


5.1

Gauge corner cracking and other rail failures

This is a well known phenomena (eg. Profillidis 2000, p.104), and different railway
administrations have adapted a variety of treatments to prevent rail failures through
microscopic cracks
progressing to catastrophic failure. Rails fail for other reasons, eg.
weld failure, fishplate failure. In 1960 rail breaks in Britain averaged 200 per annum (Hall
1992). However within ten years the figure had increased to over 400 breakages pa., in
spite

of a smaller network. In addition there were over 200 weld breaks on CWR. By the
late 1980's the rail breaks had decreased to 350pa while the CWR weld failures had
increased to over 250 pa. Inspite of ultra sonic testing, microscopic cracking can
occasio
nally progress to complete failure as at Hatfield (Oct. 2000) with tragic
consequences. Unfortunately a rail failure is one of the few examples in railway
technology which is not "fail safe". If a rail physically fails, trains derail.


In the LR55 track

system, the rails are completely retained in the elastomeric grout, which
is itself contained by a substantial and stiff concrete trough. If a rail (eg. weld) should
break, the rail ends will be restrained. This is due to the continuous support of rails
in the
LR55 system. So the location of a random rail failure will be immaterial, the rail ends
will remain nearly to line and level, and thus passing rail wheels should stay on the rail.
Further the train wheels on the other rail are also restrained by th
e continuous check rail,
so that if the failed rail is being pushed outwards , the wheels (and train) cannot follow.


Should a rail failure lead to a derailment in the LR55 system, the rail vehicle will arrive
on the ballast which is a rail height. Trains
are therefore unlikely to fall over, which is
another cause of casualties in many rail crashes.



5.2

High speed tracks

High speed tracks using heavier sleepers and rails, together with deeper ballast require
considerable and regular maintenance to provide

an acceptable line and level for a
comfortable ride for passengers. There is a trade off between low first and high
maintenance costs, and high first and low maintenance costs. In an attempt to make the
latter more economically attractive, a study has bee
n undertaken with the LR55 track as
part of a slab track system (Fig. 8).










PU grout injected






LR55 rail in trough


ballast


LR55 trough


















Sub soil










Figure 8. LR55 track in slab foundation for high speed trains


Continuo
us reinforced concrete slabs have long been in use for highway applications, and
specialist machines, eg. slip form paviour, mechanise the production of the slab to a high
tolerance of line and level. The slab is structurally more stable than sleepered rai
ls, since
the slab is very stiff in the lateral plane, across the track, which is most sensitive to
movements out of alignment. Indeed this technique as a continuous extrusion of concrete
can be modified to provide any profile. This was used in Sheffield t
o provide the track
bed for the new light rail system. The slab must however be correctly laid, since this
determine the line of the rails.


The advantage of marrying the LR55 track system to a continuous slab can be
summarised as follows:

(1)

high toler
ance for rail line, level and gauge

(2)

reduced chances of derailment due to continuous check rail

(3)

in derailment train does not fall off track,

(4)

minimal slab damage in the case of derailment and thus

(5)

no needed to replace slab after (train) accid
ent

(6)

ease of rail replacement after accident.

In the light of the Hatfield crash, slip formed slabs for curves combined with LR55 would
reduce maintenance costs and the risks of derailment.


5.3

Low maintenance cost branch lines

For branch lines the dy
namic challenges on the track are rather less than on high speed.
Nevertheless the track must be able to accommodate 25 tonne axles at low speed. For
branch lines low first cost and low maintenance costs must combine to improve the
overall economics in the

face of lower traffic volumes. This could be particularly
important where closed line restoration is being considered. Here a variation of the LR55
principle has been developed exploiting highway construction technology (Fig. 9).




















Figure

9. LR55 tracks for branch lines


The starting point will be the laying of a standard road base, the thickness determined by
the CBR of the subsoil, the annual train tonnage and the required track base life. The
compacted road base will have a high bearing

strength together with elastic structural
properties. The base can be laid to a high line and level tolerance. On this base, sit the
LR55 support troughs directly. The troughs are joined by gauge bars to provide track
gauge. The LR55 track on road bases h
ave been tested without failure up to static axle
loads of 80 tonnes. The LR55 troughs are stiff in the vartical and horizontal plane and
across the track. To provide further resistance to the track going out of alignment, ballast
is laid outside and betwe
en the troughs to anchor the track on its base. Finally the rails are
bonded into the support troughs and a very high level of line, level and gauge tolerance
can be achieved at this stage. This improves ride stability and therefore reduces of the
mechanis
ms for track being pushed out of alignment, rail damage or premature failure.


5.4

Level crossings

There will be railway level crossings for the foreseeable future. Level crossings are the
responsibility of the rail infrastructure owner. Level crossings ar
e a perennial cause of
problems and complaints, especially for road traffic crossing the rail line. This arises as
road pavements are not tied into rail tracks and therefore heavy road vehicles can cause
the misalignment of both road and rail ways. The LR5
5 track addresses this directly by
making the road pavement the foundation for the rail line (Fig. 10). A transition rail has
been designed to accommodate the joining of LR55 rails to all current girder rail profiles.






















Figure 10. LR55 t
rack for Level Crossings



6.0

CONCLUSION


The LR55 track system provides a number of unique opportunities to improve the safety,
infrastructure and economics of railways. These can be summarised as follows:


(1)

loading gauge enhancement in tunnels and un
der bridges without lowering inverts

(2)

high speed curves to reduce gauge corner cracking failures

(3)

high speed tracks to reduce costs and improve alignment

(4)

low cost branch line (re)tracking

(5)

low maintenance level crossings.


The LR55 track is a
s radical a change in rail track technology, just as the Vignoles rail
was to bull head railed tracks in the 19th century. The short and long term economic
advantages are probably greater, especially the opportunity created to attract freight
traffics whic
h cannot at present be carried by rail.



References


Al Nageim H.K. & Lesley L.

Investigating the structural reliability of a new low profile rail system under simulated
environment.

Proceedings of 18th Energy Sources Conference,

ASME International, Stru
ctural
Dynamics and Vibration. Houston Texas USA Vol. 170. 71
-
77


Fateen S

A finite element analysis of full depth asphalt railway tracks.

MSc Thesis,

University of Maryland. 1972


Hall, S,

Railway Disaster
-

cause and effect. Vol. 2. p.195

PRC Ltd. 1992
,

ISBN 1 85648 049 6



Hetenyi M

Beams on Elastic Foundation.

University of Michigan Press. 1946


Lesley L

Light rail transit developments in the UK.

Rail Engineering International,
1993 Vol. 3. 2
-
4


Lesley L & Al Nageim H.K.

Transmission of vibration and
the conditions of resonance in the LR55 track system.

Proceedings of 18th Energy Sources Conference,

ASME International, Structural
Dynamics and Vibration. Houston Texas USA Vol. 170. 233
-

236


Miranda C & Nair K

Finite beams on elastic foundations.

Jour
nal of Structural Division

ASCE.

1996 Vol. 92 No. ST2 131
-
142


Mohammad F, Al Nageim H.K., Lesley L & Pountney D.

A theoretical analysis of LR55 track system as Multi layer Beams on elastic Foundations:
An Analytical Approach.

Proceedings of International

Symposium on Theories and Applications of Traffic and
Transportation Systems Engineering.

Beijing, PR China 12
-
13 July 1996. 113
-
126


Profilliddis, V.A., Railway Engineering

Ashgate, Aldershot, UK 2000

ISBN0 7546 1279 1



Przemieniecki J.S.

Theory of Mat
rix Structural Analysis.

McGraw
-
Hill. New York USA 1968


Selvadurai A.P.S.

Elastic Analysis of soil
-
foundation interaction.

Developments in Geotechnical Engineering.

Elsevier Science Publisher.1979



Shrive, N.G. & Ameny, P,

Tests of resilient track supp
ort materials for City of Calgary Light Rail Transit,

University of Calgary Aug. 1987


Timoshenko S & Langer B.F.

Stresses in Railroad Tracks.

Transactions of the American Society of Mechanical Engineering.

USA 1932 Vol. 54 277
-
302




Figures


1.

plain LR5
5 track


2.

LR55 track displacement


3.

LR55 bending moment under load


4.

notched LR55 track



5.

rail branch line


6.

high speed rail


7.

tunnel loading gauge


8.

tube tunnel cross section


9

piggy back in tunnels


10.

high speed track


11.

branch lines


12.

level crossings