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Slope stability of the Włocławek Dam frontal earth dam in the light of the
modernisation works carried out in the period 2000-2011
Stabilité de la pente du barrage en terre de Włocławek à la lumière des travaux de modernisation
exécutés dans la période 2000-2011
Leszczynski M., Lipiecki B.
Ove Arup & Partners
Popielski P.
Hydro-Engineering And Hydraulics Department, Warsaw University of Technology
The authors of this paper carried out an analysis of archival data associated with the more than 40 years of Włocławek Dam
exploitation for the needs of new dam design within the lower section of the Vistula River. The analysis was aimed at the issue of the
existing dam safety and covered all its elements including the frontal earth dam. Archival geotechnical investigation were analysed as
well as the monitoring results and all the modernisation and improvement works executed since the year 2000. As part of the task
slope stability analyses were carried out for the frontal earth dam for various filtration conditions accounting for changes resulting
from the modernisation works and improvements. The calculations were realised for variable sets of geotechnical parameters as a
result of the interpretation of available archival geotechnical data in form of a sensitivity analysis in order to facilitate the comparison
of the analysis outcome with the results of archival analyses done by others during the exploitation period of the structure. Within this
paper the background for performing the analysis has been described as to explain the safety issues related with the existing structure
in the light of the ongoing design of the new dam structure downstream.
Les auteurs de cet article ont conduit l’analyse des données concernant 40 ans d’exploitation du barrage de Włocławek, nécessaires
pour élaborer le projet de construction d’un nouveau barrage situé en aval sur la Vistule. L’analyse a pris en considération avant tout
la sécurité du barrage existant et tous ses éléments, y compris le barrage frontal en terre. On a analysé les informations
géotechniques, les résultats d’observation et tous les travaux de la modernisation exécutés après l’année 2000. On a exécuté les
calculs de la stabilité de la pente du barrage pour des conditions d’infiltration différentes. Les calculs étaient faits pour divers jeux de
paramètres géotechniques (obtenus par interprétation de données géotechniques d’archives), sous forme d’analyse de sensibilité. Ce
type de calcul a facilité la comparaison de nos résultats avec ceux d’analyses exécutées par d’autres pendant l’exploitation de
l’ouvrage. L’article contient la description de la base de calcul et l’explicitation des problèmes de la sécurité du barrage à la lumière
du projet de construction du barrage nouvel situé plus bas en cours du fleuve.
KEYWORDS: earth dam safety, seepage, piping effect, suffusion, internal erosion,
1
INTRODUCTION.
The analysed Dam structure is located at 674+500km chainage
of the Vistula River in Poland. It consists of earth frontal dam
(length of approximately 635m), 10 bay weir, fishpass,
hydropower plant and navigation lock.
The soil profile beneath the dam and weir foundation level is
formed by alluvial sands and partially by Tertiary deposits in
form of clays, high plasticity clays and sands. The hydropower
plant and navigation lock are founded on approximately 6 – 8m
thick Pliocene clays and high plasticity clays overlying Miocene
sands with lignite interbeddings. The earth dam body was
formed partially as hydraulic fill (its centre and bank side) and
partially as traditional fill (within the former river island zone).
The structure was originally designed as first of eight similar
dams working in a cascade, however originally assumed system
was never constructed, which basically resulted, in lack of
downstream support to the analysed structure as assumed in the
design process. In turn the structure has been operational since
its construction in 1970 under unfavourable conditions
compared to the design.
The key condition for establishment of cascade of dams
along the Vistula River was, that downstream water level for
each of the proposed dams to be formed by backwater from the
downstream structure.
2
STUDY
Lack of the next structure downstream from Włocławek as
discussed above induced major changes to the bottom of river
valley immediately below and further downstream from the
existing dam. Downstream erosion caused significant lowering
of the river bottom within 40km distance from Włocławek, with
obviously the most significant effect immediately below the
dam cross-section. The observed effects of downstream water
level lowering comprised among others:
Abasement of the phreatic level within the earth dam,
Increase of the hydraulic gradients below the weir and
hydropower plant,
Impact on hydropower plant blocks overall stability.
The induced areas of threats, to which Włocławek Dam has
been exposed within passing years are the following:
Decreasing density of the material within earth dam body,
Hydraulic contact between up- and downstream levels
within 6 of weir bays.
Since 1970s, when Włocławek Dam became operational, it was
subject of continuous documentary, investigation, observations
and modernisation works.
Within years of exploitation number of ground investigation
campaigns and technical condition assessments was undertaken,
starting from 1986, when first dynamic soundings through the
earth dam were executed, supplemented by CPTs and georadar
Slope stability of the Włocławek Dam frontal earth dam in the light of the
m d rnisation works carried out in the period 2000-2011
Stabilité de la pente du barrage en terre de Włocławek à la lumière des travaux de
modernisation exécutés dans la période 2000-2011
Leszczynski M., Lipiecki B.
Ove Arup & Partners
Popielski P.
Hydro-Engineering And Hydraulics Department, Warsaw University of Technology
