TENAX Kunststoffe GmbH - extrudierte Netze und Gitter aus Kunststoff

TENAX Kunststoffe GmbH • Schloßstraße 13 • 88131 Lindau - Deutschland
Tel (+49) 08382-93040 • Fax (+49) 08382-930430 • E-mail: info@tenax-net.de
CASE HISTORY
Railroad line Trieste Vienna: railway
ballast stabilization by means of
geosynthetics
PRODUCT
TENAX LBO 401 SAMP
bi-oriented geogrids
PROBLEM
The railroad line Trieste Vienna, is
crossing the Slovenian territory on
very poor foundation soils (soil
foundation modulus always lower
than 20 MPa and locally equal to 5-
10 MPa). On such conditions of
excessive settlements, a drastic
reduction of the trains were forced
to travel at a low speed of 40-50
km/h) until major reconstruction
was completed. Since it was
necessary to substitute only one
track at a time, increasing the traffic
on the adjoining track, the
possibilities to remove poor
superficial soil (clayey silt and clay)
were very little (limited to the first
0.60 m). In order to assure the
minimum soil elastic modulus
required by the Slovenian Railway,
it was necessary to stabilize the
foundation layers (50 MPa) by using
TENAX geogrids.
SOLUTION: ŠENTJUR-CELJE
Specifically, in the track section
between the cities of Sentjur and
Celie, bioriented geogrids in PP
TENAX LBO 401 SAMP were used to
stabilize the railways foundation.
TENAX LBO 401 SAMP geogrids are
manufactured from polypropylene
(PP) by a patent extrusion process
and successively oriented in both
Compaction of the foundation base
Installation of the geotextile and
geogrid layers
Installation of the first course of 0.30
cm granular material
Typical cross section

MD and TD directions thus creating
biaxial geogrids.
After the removal of the ballast and
partial foundation soil, the
foundation was compacted by
means of a compactor roller (photo
n. 1); then a geotextile, a TENAX
LBO 401 SAMP geogrid (photo n. 2)
and 60 cm layer of granular
material were placed (laid and
compacted in two different lifts)
(photo n. 3) and successively
covered with 30 cm of ballast. A
nonwoven geotextile below the
bioriented geogrid in PP to has been
installed at the base of the ballast.
The geotextile provides the filtering
effects between the foundation soil
and the ballast, while the geogrid
prevents the geotextile from
excessive deformation and stiffening
the subbase (reinforcement and
separation functions).
In this way the so called risk of
"pumping" of fine particles of the
foundation inside the granular
material of the ballast, due to the
compression and decompressing
cycles caused by the rapid passage
of trains, was avoided.
The grain size variation, due to the
increasing portion of the fine
fraction, generates a progressive
water retention within the ballast,
with consequent greater
settlements. Besides, the separation
layer at the toe of the ballast allows
a filtering action between the ballast
and the foundation soil, avoiding the
capillary raise from foundation.
CONCLUSIONS
The embankment was completed in winter of 1996 and the railway line is
fully operative. The geogrids installed were monitored by means of
extensometers to verify the local shear stresses acting on the
reinforcement. The low mobilised geogrid strains show that the geogrid is

fully performing within the reinforced section as a rigid load transfer
platform; thus minimizing the shear displacement and consequent loss of
bearing capacity and settlements.
TENAX Kunststoffe GmbH • Schloßstraße 13 • 88131 Lindau - Deutschland
Tel (+49) 08382-93040 • Fax (+49) 08382-930430 • E-mail: info@tenax-net.de