Work Package 2 is devoted
to lab testing of the track/embankment material. Characterisation of
the long-term non-linear behaviour of these materials (of the
order of millions of cycles) is the major target of this WP. CEDEX
is the leader of this work package.
This
WP plays particular attention to the behaviour of ballast,
sub-ballast and platform material. Tri-axial tests on railway track
material warrants non-standard experimental devices due to the large
size of the grains. Such tests are performed both in Norway by NGI
and in Spain by CEDEX. The equipment which used at NGI is the
so-called "vacuum tri-axial" setup.
The sample size in this
equipment is about 62.5 cm in diameter and 125 cm in height, thus
allowing testing of coarse-grained materials.
A vacuum triaxial works
on the principle that a controlled vacuum is applied internally to
the sample, which is confined in the membrane, and atmospheric
pressure in the laboratory thereby supplies the confining pressure.
Figure 1 displays a
sample after shear failure and Fig. 2 displays a set of typical
results from NGI’s vacuum tri-axial tests.
Figure 1: Testing of railway ballast by vacuum
tri-axial setup
Figure 2: Typical results from NGI's vacuum tri-axial testing with
1.1 million cycles
Similar tests are
performed on micro-ballast, sub-ballast and embankment material
obtained from the Guadalajara site in the 9 inches diameter
tri-axial cell available at CEDEX's Geotehcnical Laboratory. Four
tests, with 1 000 000 cycles each, are carried out on macro-ballast
using smaller size pressure cells.
Figure 3 shows a typical result from CEDEX’s tri-axial tests on sub-ballast.
Figure 3: Stress-strain data obtained in
1.000.000 cycles tri-axial test on sub-ballast
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