REPRINT getzner:Layout 1

18/8/08

12:29

Page 1

europeanrailway review
TECHNOLOGYKNOWLEDGEINNOVATIONREPRINT getzner:Layout 1

18/8/08

12:29

Page 2

Under Sleeper
Pads: improving
track quality
while reducing
operational costs
More traffic, increasing axle loads and higher speeds are just some of theongoing technical and economic challenges railway operators and track
managers around the world are faced with today. Under Sleeper Pads (USP) havebeen proven to extend the service life of the track superstructure and help toreduce Life Cycle Costs (LCC).
Harald Loy, System Engineer,
Getzner Werkstoffe GmbH

Systemlife of track superstructures. Moreover,

Under Sleeper Pads (USP) represent athey are installed to insolate vibrations, as

further development within the classic

a limited cost alternative to ballast mats.

elastic components used in the

They have been in use since the mid-1980s,

construction of permanent ways. They are

and are installed in regular mainline

additionally installed on the bottom

operation for train speeds of up to

surface of the sleepers and increase the

300km/h. They are also increasingly being

degree of vertical elasticity in the trackused in turnouts as well as to improvesuperstructure. The objective is to transmit

track geometry and lower vibrations.

the loads from the vehicles via the rails,
rail fasteners and the sleepers into thesuperstructure and the subgrade in the

Influence parameters of USP on
ballasted tracksmoothest, safest and most well

Ballasted track still continues to be the

distributed manner possible. Due tomost commonly used form of construction

the defined degree of elasticity, it isfor railway tracks. Due to the steady risepossible to reduce wear on the trackin axle loads and train speeds, however,system through lower dynamic forces,

operational loads are gradually increasing.

thereby improving the durability andAs the weakest link in the traditional track

cost-efficiency of the overall system.

superstructure, ballast is subjected to

The aim of USP is to extend the servicell

REPRINTED FROM EUROPEAN RAILWAY REVIEW ISSUE 4 2008

permanent dynamic settling. The loads

REPRINT getzner:Layout 1

18/8/08

12:30

Page 3transmitted by the sleepers are resulting inballast deterioration, caused by abrasion
and splintering, leading to breakage anddisintegration of the single ballast grains.
This damage to the ballast has adetrimental impact on the track geometry
and quality.
Targeted use of sleeper pads can help
retard this process in the following ways:‘‘Under Sleeper Pads
(USP) represent a further
development within theclassic elastic
components used in
the construction of
permanent ways’’

Figure 1: Under Sleeper Pads (USP) are integrated in the load transmission path within the track
superstructureballast. At the same time, the larger

point, all displacements caused by the test

contact surface area of the track frame

locomotive returned to their originalin the contact zones results in moreposition, at a different measurement point

even settlement.

a residual horizontal deformation ofWith the objective of measuring

maximum 0.1mm was found. In theresistance to horizontal displacement ofsection where sleepers were fitted withpadded sleepers, several studies are

relatively stiff pads, the residual

the sleeper and the ballast (5-8%

currently underway in Germany, Austria

displacement was up to 0.1mm and in awithout, 30-35% with sleeper pads at

and Switzerland. Due to the various

few cases up to 0.3mm. With extremely

methods of measurement, however, nosoft USP, residual deformations of up to

well-defined results are available yet.

0.2mm were measured, in a few cases up

I Increasing the contact area between

C=0.2 N/mm³)
I Reducing the pressure on the ballast(by 10-25%)
I Adjusting the bending line of the rail
I Stabilising the upper ballast layer
I Reduction of cavitations
I Lowering the impact force on theballast bed caused by “hanging”
sleepers
I Reducing vibrations in the ballast bed
and the transmission of such into the

Figure 2: Padded sleeper after 190 million load tonnes with indentations in the Sylomer® material

surroundings
Figure 2 shows a sleeper with a USP type
Sylomer® SLB 2210 G after 4.5 years inoperation. This sleeper was installed in
one of the most heavily used lines at Bad‘‘The aim of USP is toextend the service life of
track superstructures’’

to 0.6mm. Hence, the residual
deformations immediately following thepassage of the train were essentiallynegligible, compared to the measured
maximum displacement of the track frame

Krotzingen (Germany) and shows theindentations left by the ballast grain in the

While the assumption in Germany andload areas after 190 million load tonnes.

Austria is that there is no reduction of

Fundamentally speaking, one canThere are fewer indentations in the centre

resistance to horizontal displacement, in

expect to find fewer outliers in the dataof the sleeper as the track is not tamped

Switzerland a trend towards a reduction

with the use of USP and the fluctuations in

here. Despite the massive operational load,

was found, but this seems to depend on

the horizontal displacement resistance of

there was no perforation or otherthe product used.

individual sleepers are smaller. As a result,destruction of the elastic padding material.

In displacement measurements carriedof up to 2.5mm.

the track geometry in the horizontal plane

The indentations in the elastic layer, whichout by the University of Innsbruck on

is more homogeneous on the whole, which

are desired in order to ensure sufficienttight radius curves (R=230 to R=265 m)1

has a favourable impact on the stability ofresistance against horizontal displacement

the average amounts of the horizontal

the continuous welded rail.

(i.e. rail buckling), help to stabilise the top

track displacement were measured at

The current trend for reducing wear

ballast layer. Dynamic loads arevarious points based on five passes foron the ballast and adequately stabilisingtransferred into deeper areas of theeach direction of travel. For one reference

the track frame is to use somewhat stiffer

www.europeanrailwayreview.com

ll

REPRINTED FROM EUROPEAN RAILWAY REVIEW ISSUE 4 2008

REPRINT getzner:Layout 1

18/8/08

12:30

Page 4

pads (bedding modulus of C ≥ 0.2 N/mm³)

positive experiences from measurements

additional financial impact and result inwith a large degree of plasticity.

during the period 2001-2008 on a test

significant cost savings.

On the whole, an extension in service

track section in Markersdorf (Austria)2.

With regard to wear and tear on thelife of the entire system can be achieved

The quality is represented by the

track system, the measurements carried

due to the further development andaveraged standard deviation of theout at the University of Innsbruck indicate

optimisation of ballasted track using

longitudinal rail level.

that in tight radius curves the formation ofrail corrugation can be retarded on thepadded sleepers.

surface of the interior rail1. Railcorrugation occurs as a function of speed,
radius and cant. The vertical stiffness ofthe track also influences the formation anddevelopment of such corrugation overtime. Rail corrugation generally leads toincreased dynamic loads on the
superstructure, which can result in
deterioration of the track geometry anddestruction of the rail fasteners, thesleepers and the ballast. With USP, theaverage depth of the corrugation in thetest curves increased less quickly than in
the standard track superstructure andwas approximately 50% less after a grossFigure 3: Standard deviation of the longitudinal rail level as a measurement of track geometry quality

load of 25 million tonnes (see Figure 4).
For sleepers equipped with USP, theIncreased track quality with
Sylomer® USP‘‘Ballasted track still
continues to be themost commonly used
form of construction for
railway tracks’’

USP made of Sylomer have been tested®

and used by the major rail operators in
Europe for over 15 years. These
Polyurethane (PUR) elastomers are
extremely resilient and exhibit very little

average depth of the corrugation was
0.075 – 0.1mm and thus was considerably
lower than the values for the unpadded
sleepers exhibiting an average corrugation
depth of 0.15 – 0.18mm. The averagecorrugation length was also shorter in thesection with pads than at the reference
measurement points.

dynamic stiffening. Along withimprovement in the quality of the track

In locations where low construction

In some tight radius curves withgeometry and track stability, one key

height is expedient or necessary, forpadded sleepers, no rail corrugation has

insight gained from the long-term use isexample in tunnels with low overhead

been detected, even after several years.

the possibility in reducing the height of theclearance, or on bridges to reach sufficientballast bed. Figure 3 shows the initial

bedding conditions, USP can have an

Wear on the rail pads was alsostrongly minimised. In respect of track
settlement, an improvement on the orderof 40-70% can be achieved compared toconventional ballasted track systems3.
Long-term experience shows that the useof padded sleepers significantly reduces
maintenance expenses for thesuperstructure and increases the intervals
between tamping.

Reduction of vibrations
A significant reduction in vibrations isfound especially for frequencies above 40
Hz. First of all, this has a beneficial effecton the stability of the ballast, because theballast frame is sensitive mainly to
Figure 4: Development of rail corrugation on the railhead is delayed over time with USPll

REPRINTED FROM EUROPEAN RAILWAY REVIEW ISSUE 4 2008

medium-frequency vibrations in the rangeof 50-150 Hz, and consequently exhibits a

REPRINT getzner:Layout 1

18/8/08

12:30

Page 5stronger tendency to ‘liquefaction’ andthus become instable4. Tests in Germany
have shown that the use of USP results insignificantly improved vibration behaviour
compared to traditional ballasted track5.
With various test installations mainlyin Europe, an insulation of between 8 to
15 dB was found in the relevant frequency
range – concerning the insertion loss. The
greater the elasticity of the material used
and the lower the bedding modulus, thegreater the insulating effect of mitigation
against structure-borne noise.
Due to the reduction of higher
frequency vibrations and structure-borne

Figure 5: Measurements of insertion loss of tracks with Under Sleeper Pads in various countries

noise in particular, elastic USP represent a
cost-effective alternative to ballast mats,especially for situations without very‘‘The Technical Universityof Graz has carriedout various studies on
the cost-efficiency ofrailway tracks’’2 to 2.5. Even taking a conservative view

investment costs, the interest rate on thethis can at least double the service life ofcapital employed should be approximately

the ballast. It should be recalled that,

5% in order to be profitable. Whiledepending on the quality of the stones

padded sleepers initially are a cost-used, ballasted track can usually be

increasing factor, the technical andtamped about 10 times on an average. As

economic impacts demonstrated must bea result, the service life of the track is

specifically considered. In addition tohighly dependent on the condition of thebeing a very economical and effective

stringent requirements. At the same time,
it is also possible to compensate local
inhomogeneities in the track withoutchanging the sleeper design. Based on theexperience gained so far, a significant
advantage is generated using a simple,
thoroughly tested system. Generally, no
substantial changes are determined withregard to primary airborne noise.

Life Cycle Cost (LCC) – Aspects
Based on the available measurement datafrom rail lines with padded sleepers, theTechnical University of Graz has carriedout various studies on the cost-efficiencyof railway tracks. These studies werebased on investigation of LCC aspects6. In

Figure 6: Assembling mesh ensures strong bond between the elastic pad and the concrete sleeper

order to do this, measurement data on
track geometry quality was analysed overballast. In determining cost-effectiveness,

option to reduce maintenance costs, thea period of eight years. It was found thatthe costs stemming operational disruption

basic aspect that should be taken into

the desired goal of maintenance planning,

due to maintenance work are also taken

account in this regard is the extension ofi.e. to reduce LCC for the track, can beinto account (e.g. track closures, zones of

the useful life of the track.

achieved most effectively by extending the

reduced speed). In this regard, it has been

service life, with a corresponding

found that the higher the traffic loads andreduction in depreciation. Use of sleepers

the more strongly a track section is used,

Secure bonding using an
assembling meshwith pads can extend the intervals

particularly for tight curves, the more

USP made out of PUR elastomers are

between tamping by a minimum factor of

cost-effective USP are. At the present

available as standard products in tightly

www.europeanrailwayreview.com

ll

REPRINTED FROM EUROPEAN RAILWAY REVIEW ISSUE 4 2008

REPRINT getzner:Layout 1

18/8/08

12:30

Page 6

Figure 7: Installation of padded sleepers

graduated levels of stiffness with bedding

DBS 918 145 – 017 on a norm-ballast-

the one hand, bonding the pads helps tomodulus ranging from C=0.02 N/mm³

plate). Prior to installation, the elastic

ensure safe transport and on the otherto stiffer than C=0.30 N/mm³ (measured

components must be bonded to the entire

hand, the pads must be tightly andas per German railway standard

bottom surface of the concrete sleeper. On

strongly bonded to the sleeper during theirservice life. This is necessary in order forthe pad to be able to transmit theServiceslongitudinal and lateral forces and towithstand tensile loads, for example whenGetzner does more than just merely deliver top quality, elastic track components – the company
also offers a full range of services that help its partners and customers to find the most effective
and efficient solutions for their specific application needs.
These services include:I
Design calculations
I
Calculation of insertion loss and efficiencyI
FE (finite elements) calculations and simulations
I
Vibration, mechanical and acoustic measurements
I
Precision measurements on the company's large scale testing facilityIOn-site installation consultation
I
Full-scale installation of ballast matsthe track frame is lifted for maintenancework. In the past, USP were bonded to thesleepers following production using anadhesive. The current trend, however, is tointegrate the pad into the production of
the sleeper itself. A strong bonding layer isused for this purpose. One excellent wayof ensuring this is the use of an assemblingmesh incorporated into the sleeper
whereas the upper half of the thickness of

The outstanding engineering services offered by Getzner reflect the company's expertise andknow-how, highlighting its role as a competent partner for its customers.
The company's large team of experts, wide range of testing facilities and vast experience are
made available to its partners world wide. By using the company's large scale testing facility,
Getzner is able to imitate real-life situations and gain additional experiences.
Source: www.getzner.com

the mesh extends out of the pad, whichthen is pressed into the bottom of thesleeper. This method works with varying
degrees of wetness of the concrete and it is
not necessary to vibrate the mesh into theconcrete, depending on the specificll

REPRINTED FROM EUROPEAN RAILWAY REVIEW ISSUE 4 2008

REPRINT getzner:Layout 1

18/8/08

12:30

Page 7production process used. Basically,work is required at the track installation

bonding of Sylomer® or Sylodyn® sleeper

site. The installation of the sleepers ispads is possible with all types ofquick and unaffected by weather

2. Schilder, R.: USP – Under Sleeper

production processes commonly used for

conditions (which could affect thePads, Schwellenbesohlungen.

the manufacturing of concrete sleepers,

adhesion), hindered in no way whatsoever

Getzner Bahnfachtagung

regardless of whether the principle ofby the use of USP.

Schwarzenberg/Vorarlberg,Öffentlicher Verkehr der Universität
Innsbruck, 2001

14.-16.11.2007

immediate demoulding or later

3. Plica, P.: Das Kräftespiel imdemoulding is applied. Positive

Summary

experiences have also been gained with

Increasing operational loads on railways

Schotteroberbau mit besohlten

self-compacting concrete. The very goodrequire further development of theSpannbetonschwellen. Getzner

mechanical bonding between the sleeper

ballasted track system. The installation of

Bahnfachtagung

pad and the concrete has been

precisely defined elastic components can

Schwarzenberg/Vorarlberg,

demonstrated by pull-off tests in thehelp to meet the requirements such aslaboratory. The average pull-off

satisfactory elastic behaviour for the

resistance of Δ σR=0,50 N/mm² 7 asprevention of track settlement, reduction

Zukunftsperspektiven zum

required by the German railway standardof vibrations and structure-borne noise

Eisenbahnoberbau. EI Der

is ensured by the use of above described

and lower track maintenance costs. In the

Eisenbahningenieur (43) 3/1992,

assembling mesh.

future, increased use of Sylomer® andIn order to increase the resilience

Sylodyn® sleeper pads promises an

14.-16.11.2007
4. Eisenmann, J., Leykauf, G.:

S. 130-139.
5. Leykauf, G., Stahl, W.:against the contact of ballast grains andexcellent cost-benefit relationship. Elastic

Untersuchungen und Erfahrungen mit

their sharp edges, it is also advantageous

pads help to mitigate the forces in thebesohlten Schwellen. EI Der

to install an additional load deflection andcontact zone between the concrete sleeper

Eisenbahningenieur (55) 6/2004,

protective layer on particular highly elastic

and the ballast grains and at the same time

S. 8-16.

pads. A felt-like material (geo textile) has

protect the surrounding ballast from theproven very effective in protecting theimpact of the strong dynamic forces.

Gleisen – Wirtschaftliche Bewertung

active elastic layer from damage caused byConsequently, the superstructure is subject

auf Basis einer

the track operation.

to considerably lower forces than is theLebenszykluskostenbetrachtung.

case with traditional concrete sleepers.

Getzner Bahnfachtagung

Introduction of an elastic layer beneath

Schwarzenberg/Vorarlberg,‘‘In the future, increased
use of Sylomer® and
Sylodyn® sleeper pads
promises an excellent
cost-benefit relationship’’the sleeper does not require any
modification of the rail profile or special

6. Veit, P.: Schwellenbesohlung von

14.-16.11.2007
7. DB Systemtechnik: DBS 918 145-01:

rail fastening systems which might beTechnische Lieferbedingungen –necessary when extremely soft rail pads

Spannbetonschwellen mit elastischer

or baseplate pads shall be used.

Sohle – Elastische Schwellensohlen,

Furthermore, the material and installation(Jan. 2004)

costs are far less compared to theOn-site installation of padded
sleepers

installation of ballast mats. LCC studies

Due to the strong mechanical adhesion

systems using padded sleepers can be a

between the elastic pad and the bottom ofvery cost-effective option. Accordingly,

the concrete sleeper, standard installation

Under Sleeper Pads represent anprocedure will be used for the padded

economical alternative for retrofitting

sleepers and there are no restrictions on

measures, helping to underpin investment

track maintenance. Transition zones inin the tracks of the future.

confirm that the installation of track

which the bedding modulus values ofthe subgrade beneath the sleepers change

Reference

can be compensated by the use of USP

1. Prager, G., Kopp, E.:biography

with varying degrees of stiffness. It is

Schlupfwellenmessungen am

also possible to even out the geometricallyStandardoberbau und am Oberbau mit

induced differences in stiffness withinbesohlten Schwellen in Hieflau (n.v.).

turnouts with their indifferent long

Institut für Infrastruktur,

sleepers. Pre-installation by the sleeper

Arbeitsbereich Eisenbahnwesen und

manufacturer ensures smooth progress

Harald Loy
Harald Loy graduated from the Technical
University of Munich as a Civil Engineer. Since
2005, Mr. Loy has been employed in the
System Development Department at Getzner
Werkstoffe GmbH in Austria, specialising inrailway track applications.

at the construction site. No additional

www.europeanrailwayreview.com

ll

REPRINTED FROM EUROPEAN RAILWAY REVIEW ISSUE 4 2008

REPRINT getzner:Layout 1

18/8/08

12:30

Page 8