Ratarakenteen vesipitoisuuden vaikutus pysyvien siirtymien muodostumiseen

Tutkimustuotos: Tutkimusraportti


Frost-heave measurements stations have been maintained on Finnish railway network from 2008 by Tampere University (previously Tampere University of technology). The measured quantities were track vertical displacements, temperatures
from different depths and some stations had also soil water content sensors. In
this study, the measurement data was collected and combined, and the main focus
was to analyze track vertical displacement behavior.
In the recent research project (Latvala 2021), large differences between the loading resistance of different sub-ballast samples were observed in cyclic loading triaxial test. Material with small average grain size (<0,7 mm) was recognized to be
sensitive for increasing water content specially, if the material also includes fines
and the uniformity coefficient is small (<5). These conditions can decrease track
loading resistance. The vertical stress addition initiated by trains was found to be
small with axle weights of passenger trains and therefore the practical differences
between different sub-ballast materials remains small. The differences were found
to be much larger with axle weight of freight traffic especially, if the upper part of
sub-ballast layer has high saturation degree. These observations were verified in
this study by analyzing the long-term vertical displacement data from frost-heave
measurements stations.
Significant differences in the stability of track’s vertical positions were observed
between different monitoring sites. It seems that the influence of sub-ballast water
content on displacement on unfrozen structure is so small that it cannot be distinguished from other deformation-causing factors. The result was partly expected,
because the traffic volumes and actual axle weights are small at many frost-heave
measurements stations. The thaw settlement was found to cause permanent displacements of several millimeter at the sites, where significant frost heave occurred. The simplified reason for this is probably the bulking of the structure layers
due the expanding ice lenses with local spots of saturated structure.
The track structure is a complex entity, where the water content of sub-ballast
layer is only one factor. Although some vertical displacements were observed at
measurement sites, their magnitude was not too large in any of the frost-heave
monitoring sites. It is likely that it is not possible to significantly reduce the track
displacements caused by trains by lowering the water content of sub-ballast layer.
Vertical displacements could occur more than observed if the traffic consist mainly
of heavy freight-traffic and the water content on upper part of very small grained
sub-ballast layer is high. This conclusion is similar with previous studies.
Julkaisun otsikon käännös Effect of the track structure’s water content on the formation of permanent displacements
ISBN (elektroninen)978-952-405-091-3
TilaJulkaistu - syysk. 2023
OKM-julkaisutyyppiD4 Julkaistu kehittämis- tai tutkimusraportti taikka -selvitys


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