Under Ballast Mats

1 Functional Principle

Under ballast mats made of theGetzner materials Sylomer® and
Sylodyn® limit the static and dynamic
forces exerted on the ballast bed byrailway operations.

The most important applications
are:Getzner under ballast mats havea multi-layer structure:— Isolation of structure-borne noise on
railway lines in densely populated
regions: local transport railways andstandard-gauge railways in thevicinity of buildings.

— Load distribution layer
The top layer of the mats consistsof a geotextile or fleece with highstretch and tear resistance. This layer
deforms under the load of the ballast.
The ballast rocks are embedded andtheir positions are stabilized by theincreased contact surface. Forces
introduced to the mat are distributed
over the full area and transmitted tothe underlying resilient layers.

— Protection of structures and buildings sensitive to vibrations or withelevated vibration protection requirements such as concert halls, museums, hospitals, historic structures orvibration-sensitive laboratory, testingor measurement equipment.
— Reduction of the emission of secondary air-borne sound on bridge
structures.
— Increased track geometry stability
and reduction of ballast compression
decrease the maintenance costs forheavily laden track sections.

— Resilient layer
The resilient layer consists of microcellular polyurethane materials. The
materials are volume-compressible,
meaning that no profiles or cavities
are required for shaping. Dependingon the mat type, the resilient layer iscomprised of one or two layers, eachwith a density specifically selected
to yield the desired overall static anddynamic stiffness.

32 Engineering
ServiceGetzner has developed a specialized
computational model for the installation of under ballast mats that allows
for reliable prediction of the achievable vibration reduction.

ultiple series of tests by various
railway operators under a variety
of test conditions have shown that
Getzner’s predictions correspond to
the actual results. As part of Getzner’s
service to its customers, experts
generate separate predictions for eachapplication and mat type.

M

Additional examples of the comprehensive service offered by Getzner include
the creation of CAD installation plans,
specific calculation models for determining rail deflection, individual on-site
construction support or installation
instructions for the mats. The state-ofthe-art testing laboratory helps makethis possible.
In close cooperation with customers
and various research and testing agencies, Getzner continuously modifies
and tests its product selection. The
engineers, product managers andphysicists at Getzner are constantly
focused on the rising expectations of
the market and of customers.
Under ballast mats made of Sylomer®
and Sylodyn® have proven their quality
on operational track sections manytimes over the past few decades.

4

Tests and measurements
are available from the following institutes (excerpt):— Chair and Testing Institute for Construction of Transport Routes at theMunich University of Technology— TÜV Rhineland, Cologne, Central Department of Vibration Technology andVibration Protection— Deutsche Bahn, Testing Institute— Arsenal Research, Vienna— Müller BBM GmbH, Planegg near Munich— ISMES Spa, Bergamo, Italy— Institute for Road and Rail Transportation, Berlin University of Technology— Prof. Peter Steinhauser, Civil Engineer for Technical Physics, Vienna— Ruthishauser Engineering Office for Construction, Transportation and theEnvironment, Zurich— EMPA, Federal Materials Testing and Research Institute, Dübendorf— Fritsch, Chiari & Partner Ziviltechniker GmbH, Vienna
Research and test reports are available upon request.

5

3 Technical
Product Information

Bedding modulus andstatic stiffness

Effectiveness andinsertion loss

The correct stiffness of a mat depends on the application, the superstructure design (ballast bed height,
sleeper area and spacing, rail type)
and the operating conditions (axleload, maximum speed).

The effectiveness of a under ballast
mat can be seen in the form of areduced structure-borne sound level.

he measure of stiffness is thebedding modulus, given in N/mm3.
This value is largely responsible fordetermining the rail deflection during
train passes. If the recommendations
are observed, the rail deflection is
generally less than 3 mm and less than
1.5 mm for high-speed traffic.

T

The following parameters are
particularly important:— Unsprung mass of the bogie— Dynamic stiffness, damping and massof the ballast superstructure excluding the mat— Dynamic stiffness and damping of
the mat (depends on load, frequency
and amplitude)— Vibration resistance (impedance)of the substructure

his measure is referred to as“insertion loss” and is indicated as
the difference of 1/3-octave levels(cumulative level within a 1/3-octave
frequency band) as a function of the
1/3-octave band center frequency. The
effectiveness is not determined solely
by the under ballast mat; rather, it
results from the characteristics of theentire system – from the vehicle to thesubstructure.

TSpecific load [N/mm2]

Getzner determines the actual deflection in the individual case by calculating the bending line of the rails.
0.20

0.15

0.10
Cstat=0.03 N/mm3

0.05

Spring load def lection curve for
Sylodyn® DN 335 under ballast mat

0.02
0
0

6

1

2

3

4

5

6

7

8

9

10
11
12
Deflection [mm]effective in the frequency range
corresponding to the wheel/rail superstructure resonance for a superstructure without mats. Depending on thebedding stiffness, this is between
approx. 50 Hz and 80 Hz.

Prediction model
y considering the entire system
and including the various structural factors, Getzner is able to apply
a prediction model to calculate theeffectiveness of a measure in advance.

B

not applicable to other types of underballast mats (examples: compact elastomer mats with profiling or interior
cavities).

In most applications, the effectivenessin the frequency range under about
80 Hz is particularly important sincethese low-frequency vibrations arevery strongly stimulated. Buildings andbuilding elements can easily be stimulated within this frequency range, as
can be seen in the natural vibration ofceilings and walls.

The model assumes that the “dynamic
stiffness” and the “loss factor” aresufficient for a nearly complete description of the dynamic properties of theunder ballast mat in the relevant load
and frequency range.
Getzner under ballast mats satisfy thiscondition because the dynamic stiffness is only minimally dependent on
frequency, load and amplitude. The
under ballast mats are particularly

Due to the advanced technology ofGetzner under ballast mats, the values
for their effectiveness based on
experience and prediction models are

Dyn. bedding modulus [N/mm3]

Load and frequency dependence ofdynamic stiffness (from: MüllerBBM, Report No. 32242/12)

0.06

F' = 0.06 N/mm

Under ballast mat: Sylodyn® DN 335
Sample dimensions: 200 x 200 x 35 mm3

F' = 0.01 N/mm2

Load F' = 0.03 N/mm2
2

F' = 0.10 N/mm2

0.04

0.02

0

40

80

120

160

200
Frequency (Hz)7

4 Long-Term
Behavior

Long-term behavior under
the harshest conditions
Getzner under ballast mats exhibit
extremely high effectiveness evenafter years of exposure to operationalloads. This has been proven by astudy evaluating the long-term
properties of Getzner under ballast
mats.
fter more than 16 years of operation and a daily load of roughly
150 000 tons, samples were removed
from the superstructure and subjected
to various tests. The test results
showed that the under ballast mats still
exhibited outstanding functionality.
Despite more than 16 years of use, theunder ballast mats from Getzner still
had an impressive, constant stiffness
behavior. In verification measurements
on samples that had lain in silty subsoil
for over 20 years, no contamination
was found inside the mats.

A

Getzner under ballast mats retain theirfunction even under extreme conditions. Environmental influences such ascomplete flooding, frost or heavy
soiling of the ballast bed with sand or
material worn away from the ballast
rocks cannot affect the mats.

8

Quote from the test report byan external testing institute:“... The Sylomer® B 851 under ballast
mat superbly withstood the extremely high operating loads totalling over
760 million tons within a period of
more than 16 years.”5 Installation Technology
and Retrofitting

Delivery form
and installation
Getzner manufactures under ballast
mats in a uniform width of 1.50 m. The
mat sheets are cut to the local track
width before leaving the factory.

The mat covering is fully functional
immediately after laying – in otherwords, even without the mats being
bonded to the subsoil.

fter being cut to size, the mats arerolled up and packaged. After the
installation position has been marked
on the mat, it is delivered directly tothe construction site. Starting from amat thickness of 35 or 40 millimeters,
it is sometimes useful to deliver themats in two separately rolled layers toallow for easier handling.

Rubber-tired construction vehicles candrive over the mat covering with noproblems. If the mats are not covered
with ballast immediately after laying, it
is useful to secure the position of themats through partial bonding with thesubsoil (construction site traffic, incoming water). Getzner uses solvent-freeadhesive, such as 2-component PUR
adhesives, for this task. The bonding
takes place so that any water that may
have penetrated under the mats canflow or seep to the next drain inlet.

A

The mat rolls are distributed and laidout at the destination site according totheir labeling. Any fine adaptations
necessary are performed by inserting
fitting blocks or by cutting the matsto the correct size and shape, which
may be necessary in the area of
curves.
The continuous further development of
installation techniques by Getzner has
now made it possible to thermally glue
the upper layer of the individual matsand the fitting blocks together.

10

Requirements forthe subsoil
Getzner under ballast mats lie on thesubsoil with full surface contact.
Because they are flexible and elastic
in all directions, they largely adapt tothe contour of the subsoil.
ince the mat optimally adapts tothe subsoil beneath, sharp-edged
recesses or bumps in the laying
surface can damage the mats. Concrete decking must first be scraped orsmoothed to an approximate evenness. No special measures are required for laying Getzner under ballast
mats on subsoil of compressed gravel(sub-grade), on a cement-paved support layer or on a bitumen support
layer.

S

When existing track sections are
retrofitted with mats, the laying
surface frequently consists of old

Retrofitting existing
track sections
ballast. In this case, it has proveneffective to provide a load distribution
layer on both sides of the mat.

Sylomer® and Sylodyn® are free ofsoftening agents and other oils. If theunder ballast mats are to be bonded,
the subsoil must first be dry and swept
clean.

If the mats are subject to constant andextensive water exposure, drainage
mats can be laid under the mats in a
linear arrangement. To avoid soundbridges in the area of the water
channels, the grills or grates arecovered with perforated under ballast
mats; however, these can also beelastically supported themselves.

nder ballast mats made of Sylomer®
and Sylodyn® have also proventhemselves well in sensitive areas withthe highest requirements for vibration
protection as well as under extreme
structural conditions.

U

The retrofitting procedure fromGetzner has been tested frequently inpractice and ensures rapid construction progress. Because it is not necessary to remove the entire track panel,
only short track closure times are
required for the installation. Since it is
not possible to adapt the size of themats in advance, they must be cut
on-site to the exact lengths required.
They can be cut with simple, widely
available carpet cutters.

The Getzner under ballast matsdelivery program naturally also
includes detailed, written installation
instructions as well as the adhesive
required for laying. If the laying surface
is coated with plastic (e.g. epoxy resin
for steel bridges), no special measures
are required.

Profile
Peg
00

m

m

Side wall mat

10

Under ballast mat
Peg

Getzner under ballast mats are
particularly valued in many retrofitting projects due to their low weightand easy installation.

Drainage solution
e.g. with geotextile

If the signs of wear on the superstructure are not too extreme after years ofoperational loads without under ballast
mats, it is naturally possible to reinstall
all components. Rails, sleepers, rail
fastenings and ballast do not have tobe replaced, as is the case for othervibration-related refurbishment measures. Getzner trumps with economy
and efficiency.

Drainage openings
drilled on-site

Drainage principle:
Sylomer ® and Sylodyn®
under ballast mats11

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