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Bridge foundation on very soft alluvia with stone column ground improvement
Fondation de pont sur alluvions très mous et amélioration du sol avec des colonnes ballastées
Vlavianos G.J.
,
Marinelli A.K.
Ministry of Development, Competitiveness, Infrastructure, Transport and Networks, Greece
Andrianopoulos K.
Foti S.
Geosynolo Ltd.
ABSTRACT: The present paper proposes technical solutions for a road design project comprising both bridges and high
embankments in the Region of Western Greece, where major geotechnical issues had to be dealt with. The very low P-y reaction of
the soft silty clays and the eventual liquefaction of the silty sand layers embedded within the foundation soil, the high ground water
table and the high seismicity of the area, led to the decision to improve the top part of the natural soil given the necessity for an
acceptable solution in terms of both dimensions and cost. Among other possible methods of soil improvement, the application of stone
columns followed by preloading was selected. A comparative parametric stability analysis of the bridge embankments and the pile
foundations for bridge piers, with or without the presence of stone columns, quantified the benefits from the proposed ground
improvement method and verified that the completion of this project is feasible within acceptable performance, safety and cost limits.
RÉSUMÉ : La communication propose des solutions techniques pour l’élaboration d’un projet de route qui comprend des ponts et des
remblais de grande hauteur dans la région de la Grèce occidentale où il a fallu faire face à des problèmes géotechniques importants.
La très faible résistance des argiles limoneuses molles aux sollicitations horizontales et la liquéfaction éventuelle des couches du
terrain formées de sables limoneux qui sont contenues dans le sol de la fondation, la nappe phréatique élevée et la haute séismicité de
la région, ont conduit à la décision d’améliorer la partie supérieure du sol naturel en prenant en considération la nécessité de trouver
une solution acceptable en ce qui concerne les dimensions et le coût. Parmi d’autres méthodes d’amélioration du sol, il a été choisie
l’utilisation des colonnes ballastées suivie d’un préchargement du sol. Une analyse paramétrique comparative de stabilité des remblais
des ponts et des fondations des piliers des ponts avec ou sans la présence des colonnes ballastées, quantifient les bénéfices obtenus par
l’utilisation de la méthode d’amélioration du sol proposée et vérifie que l’achèvement de ce projet est réalisable avec une performance
acceptable en termes de sécurité et de coûts
KEYWORDS: road project, bridge foundation, soft alluvia, liquefaction, ground improvement, stone column, preloading.
1 INTRODUCTION
A significant project for road infrastructure is currently under
way in western Greece, perfecture of Aitoloakarnania,
concerning the construction of a 13,1km part of a public
provincial road connecting the municipality of Astakos to the
bridge of Gouria.
Owner of the project is the Greek State and the Supervising
Authority is the Directorate of Studies for Road Works, General
Directorate of Road Works, Ministry of Development,
Competitiveness, Infrastructure, Transport and Networks.
Following the necessary competitive procedure, the design of
the project was assigned to a joint scheme of specialized design
offices, covering the involved scientific areas.
This paper focuses on the technical solutions proposed for
the geotechnical issues that arose with reference to the stability
of embankments and bridge foundation.
2 PROJECT OVERVIEW
The importance of this project lies in its expected contribution
to the improvement of road access towards western
Aitoloakarnania and mainly the touristic zone of Astakos-
Mytikas-Palairos. It is also anticipated to take over some of the
traffic load of other local axis and to support the increase in use
of an existing tunnel nearby. What is more important though, is
the expected traffic load assumption for the shipbuilding and
industrial zone of Astakos, which in the future will be the base
for development in the whole area.
The realization of the project will improve the accessibility
of the area and will facilitate road connection between cities and
existing or planned infrastructure, decreasing time demands and
improving safety and comfort requirements
This road axis under study forms a part of the connection of
Astakos and the port of Platygiali with the major motorway of
“Ionia Odos”, passing through the bridge of Gouria and the
existing tunnel of Saint Elias. The road section is 11,0m wide (1
lane per direction). From geotechnical point of view, it is to be
mentioned that the whole project comprises 6 bridges (15-105m
long) and a significant length of embankments between 2 and 7
meters high.
Major geological and geotechnical issues that arise for the
last 10km of the road are related to the very low altitude of the
ground and the lack of inclination, the high ground water table,
the insufficient drainage system and the presence of silty clays
and sands, often with high content of organics. The whole
situation is aggravated by the liquefaction potential of the silty
sand layers embedded within the foundation soil, in connection
with the high seismicity of the area.
During the preliminary design stages, it became obvious
that the most significant geotechnical problems for the
realization of the project would be related to the load bearing
capacity of the soil, the expected subsidence under static
loading and the eventual liquefaction phenomena.
3 GEOTECHNICAL CONDITIONS
The area where the bridge foundation will be constructed
consists of soft and compressible saturated alluvial soils, while
the water table is located at ground level. The prevailing
