2715
Pylon foundation of a cable stayed bridge at the motorway ring road of Wrocław
Fondation d’un pylône du pont suspendu du périphérique de l’autoroute de Wrocław
Dembicki E., Cudny M., Krasiński A., Załęski K.
Gdańsk University of Technology, Faculty of Civil and Environmental Engineering,
Department of Geotechnics, Geology and Maritime Engineering
ABSTRACT: The largest bridge of the motorway ring road of Wroclaw is a cable stayed bridge over the Odra river near Rędzin. Due
to hydrogeological conditions of the ground it was not convenient to use standard bored piles of high length. Instead shorter piles
were applied with additional improvement by cement injections at the pile toes. This decision was possible by extending ground
investigation program and application of numerical modeling of the soil-structure interaction with nonstandard material models of the
overconsolidated clayey deposits. Sufficient stiffness and bearing capacity of piles was approved by field tests. Overall performance
of the foundation was monitored during construction and after completion of the bridge. Comparison of settlements predicted during
design and obtained in the monitoring is presented and discussed.
RÉSUMÉ : La plus grande construction sur le périphérique de l’autoroute de Wrocław est le pont suspendu sur le fleuve Odra à
Rędzin. L’utilisation des pieux normalisés de grandes longueurs a été jugée inconvenable à cause des conditions hydro-géologiques.
Les pieux de grands diamètres raccourcis avec un renforcement de la base par l’injection de ciment ont été donc utilisés. Une telle
solution a été rendue possible grâce à un programme élargi de caractérisation du sous-sol ce qui a permit de réaliser les calculs du
projet en utilisant des modèles de comportement non standards adaptés aux matériaux à grains fins surconsolidés. La rigidité et la
résistance correspondante des fondations sur pieux ont été confirmées par les essais de chargement in situ. Le comportement de la
fondation en entier a été contrôlé durant sa construction et durant la période d’exploitation après la fin des travaux. Les déplacements
de la fondation évalués en cours de projet et après, par observation, ont été présentés et discutés.
KEYWORDS: piled-raft foundations, pile foundations, finite element analysis
1
INTRODUCTION
Main section of the bridge of 612m length will be suspended
from a single pylon of 122m high. Large loading from the pylon
structure causes the design of the foundation to be a challenging
geotechnical problem due to high level of loads to be safely
transmitted into the subsoil. In the case of the cable-stayed
bridge over the Odra river the highest characteristic vertical
load, considered among various combinations of loads analysed
by the designer, transmitted onto the support was estimated to
be 776.0 MN. Dimensions of the bridge makes it the highest
object of that type in Poland.
2
SOIL AND WATER CONDITIONS
Designed foundation will be placed in the central part of
Rędzin Island within the main Odra river bed. The island is
connected with the river banks and mainland through two
Rędzin locks, which are located ca. 70 m north and through
historical weir, located ca. 110 m south-west. The area
designated for foundation is 67.4 m x 28.0 m.
The terrain under foundation is basically flat with mean
elevation of 112.8 m a.s.l. From the geomorphological point of
view it is located in Wrocław-Magdeburg ice-marginal valley
(Odra River valley), 10 km wide and filled with Pleistocene and
Holocene river sediments with several terraces at various levels.
The surface layer of fills and normally consolidated river
accumulation formations 2.0 m thick lies on dense coarse
material of the thickness of 6-7 m with unconfined water table
at the mean elevation of 107.6 m a.s.l. Below coarse sediments
there are fine soils of tertiary origin represented by clays and
locally silty sands. In this continuous, 15 m thick layer local
water percolations are observed. Below it, thin layer (2.5 m) of
silty sands and sandy silts with confined water table under high
pressure was found.
Table. 1:
Characteristic values of basic geotechnical parameters
Layer Soils
(
’)
[kN/m
3
]
’
[
o
]
c
’
[kPa]
E
oed
[kPa]
IIa/IIb
Cl, siCl,
Si
21,0/11,0
15,0
5,0
30 000
0,20
IIIa
MSa,
CSa,
FSa
19,0/10,0
33,0
1,0
85 000
0,20
IIIb
MSa,
CSa,
grCSa
20,0/10,0
35,0
1,0
150 000
0,15
IIIc
grCSa,
Gr
20,0/10,0
35,0
1,0
220 000
0,15
Va
Cl, siCl,
21,5/11,5
23,0
18,0
40 000
0,20
Va*
Cl, siCl,
21,5/11,5
23,0
18,0
100 000
0,20
Vc
siSa
20,5/11,0
32,0
1,0
85 000
0,15
To the depth of 50 m below the subsoil surface there were no
weak soils found. Tertiary clays are characterized by good
strength and stiffness. The only problem related to the depth of
the pylon foundation are local water percolations and high water
pressures in confined aquifers. The most unfavorable foundation
and execution conditions have been assumed for the further
calculations and analyses, see Figure 1 and Table 1.
