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Rainfall-induced collapse of old railway embankments in Norway
Influence des precipitations sur l’instabilité d’anciens remblais ferroviaires en Norvège
Heyerdahl H., Høydal Ø., Nadim F., Kalsnes B.G.
Norwegian Geotechnical Institute
Børsting T.
Norwegian National Rail Administration
ABSTRACT: During the second half of year 2011 heavy rainfall caused dramatic damage on railway foundations in Southern
Norway. Most of the railway foundations affected are old, generally constructed between 1850 and 1950 at a time when construction
work was done manually, and soil materials from cuts in local natural deposits were utilized for construction of nearby embankments.
Quality of culverts and embankments therefore does not correspond to modern construction standards. As a consequence the
embankments do not perform well during intense and prolonged rainfall as demonstrated in the fall of 2011. In some cases, low
capacity of old culverts caused rise in water levels upstream of embankments, followed by internal erosion and ended in complete
destruction of embankments. However, the collapse of several embankments was not related to this factor. The geotechnical
behaviour of some of the collapsed embankments, constructed of sandy, silty and clayey material was studied, and the results for one
of these are presented in this paper. Unsaturated flow properties were taken into account to explain the behaviour. .
RÉSUMÉ: Au cours de la seconde moitié de l’année 2011, suite à d’intenses précipitations, un certain nombre de voies ferrées et leurs
fondations ont été endommagées dans le Sud de la Norvège. La plupart des ouvrages touchés étaient anciens et avaient été construits
dans les années 1850-1950, à une époque où les travaux se faisaient à la main et où les matériaux employés pour la construction des
remblais étaient prélevés sur des chantiers à proximité. La qualité de ces ouvrages ne correspond donc pas aux standards actuels de
construction. Par conséquent, ils ne sont pas toujours en mesure de résister à de fortes et longues périodes de pluie, comme cela s’est
démontré à l’automne 2011. Dans certains cas, la faible capacité des drains a entraîné la montée du niveau d’eau en amont des digues,
provoquant l’accélération de l’érosion interne et, au final, la destruction complète de la structure. Dans certains cas néanmoins, le
phénomène s’explique par d’autres causes. Le comportement géotechnique de certains des ouvrages ayant été détruits, lesquels sont
généralement construits sur des sols sableux, silteux et argileux, a été étudié et est présenté dans cet article. Les écoulements non
saturés ont été pris en compte pour expliquer les phénomènes observés.
KEYWORDS: railway, stability, embankment, culvert, rainfall, retention curve, permeability, grain size distribution
1 INTRODUCTION
The railway infrastructure in Southern Norway suffered serious
damage during the second half of 2011. The damages, often
leading to complete destruction of sections of the railway, were
caused by prolonged and intense rainfall. Monthly rainfall of
>150 % of normal values were observed, with estimated periods
of 30-50 years. NGI assisted on a number of occasions where
railroad infrastructure was damaged. Cases were distributed
over a large geographical area and on most major railway lines
in Southern Norway. In this paper, typical damages are
discussed. A case study of a failed railway embankment is also
presented, with special emphasis on the geotechnical behaviour.
2 OLD RAILWAYS AND DAMAGES
2.1
Some features of existing railway infrastructure
Railway lines constructed between 1850 and 1950 constitute the
major part of present railway infrastructure in Norway. Some
modernization as widening of embankments has been done,
some culverts have been renovated, new ballast types
introduced, however, much of the original substructure, 50-150
years old, remains more or less unaltered. Documentation from
the construction phase shows that the principal of mass balance
along the railway was used. Manual labour and mass transport
by wheel barrows prevented long distance transport, and
prohibited the use of materials from e.g. remote stone quarries.
Soil from cuts was placed in nearby embankments; hence,
materials as clay, silt and sand are today encountered in the
railway embankments. Culverts passing under the railway were
typically constructed by dry masonry of rectangular hewn
blocks of stone. Some culverts have been modernized as part of
maintenance or after damage, often by inserting plastic pipes
into old stone culverts. This reduces the cross section, and flow
capacity may be reduced, although smoother surface partly
compensates for reduced cross section. Inspection however
shows that even after operating times of >100 years many
culverts are in surprisingly good condition.
2.2
Types of damages
In the following description of damages, direct hit on the
infrastructure from landslides initiating outside the railway is
excluded. The discussion is limited to damages on railway
infrastructure due to extraordinary rainfall in the second half of
year 2011. Observed damages are categorized in a few main
groups: 1. Damages related to culverts.2. Damages related to
flooding. 3. Damages related to embankment slope failure.
2.3
Damages related to culverts
Embankment collapses caused by inadequate performance of
the culverts is a well-known phenomenon along existing
railways. Depending on the soil type in the embankments,
complete destruction of embankments may occur surprisingly
quickly. In pioneering days of railway engineering, culverts
