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Methodological approach for the stability analysis of the Po river banks
Méthodologie pour l’analyse de la stabilité des digues de la rivière Pô
Gottardi G.
1
, Madiai C.
2
, Marchi M.
1
, Tonni L.
1
, Vannucchi G.
2
1
DICAM University of Bologna, Bologna, Italy
2
DICEA University of Florence, Florence, Italy
ABSTRACT: The Po River is the major Italian watercourse, controlled with embankments along half its length. The Italian
Government has recently funded a number of activities aimed at the seismic hazard control, including the evaluation of the seismic
stability of about 90 km of embankments of the Po river. The paper describes the methodology developed in order to identify a
number of significant sections, their geotechnical models and the subsequent static and seismic stability analyses. The vast database
coming from hundreds of geotechnical investigations within the study area is described. Local seismic hazard and effects of site
conditions on the ground motion are taken into account in the definition of the expected seismic action. The safety conditions of the
embankments in static and seismic conditions are investigated as a function of the soil parameters variability and considering various
relevant river water levels. Eventually, a methodology aimed at developing stability maps of the investigated area based on the data
spatial variability is described.
RÉSUMÉ : Le Pô est le cours d’eau le plus important d’Italie, contrôlé par des remblais qui se déroulent pour presque la moitié de sa
longueur. Le gouvernement italien a récemment financé plusieurs études visant à évaluer le risque en cas de séisme et, en particulier,
les conditions de stabilité des digues de protection du Pô pour une longueur d’environ 90 kilomètres. L’article présente une
méthodologie conçue pour sélectionner les sections représentatives à analyser, définir un modèle fiable du sous-sol, évaluer le risque
de rupture des berges en conditions de chargement statique et sous sollicitation sismique. On décrit l’ensemble des plusieurs données
comprenant plus de 300 essais de pénétration statique, une centaine de forages, mesures géophysiques en forage et nombreux essais
de laboratoire. Les paramètres significatifs du séisme ont été choisis à partir du séisme prévisionnel ainsi que des conditions locales
du site. L’évaluation de la variabilité intrinsèque du sol permet d’utiliser des procédures de calcul probabilistes, de manière que la
sécurité des berges est définie en terme de probabilité de rupture plutôt que du facteur de sécurité habituel, faisant référence à
différents scenarios de crues.
KEYWORDS: riverbanks, stability analysis, in situ tests, seismic vulnerability, probabilistic approach.
1 INTRODUCTION
With a total length of 652 km across northern Italy, the Po
River is the major Italian watercourse (Figure 1). Over half its
length is controlled with embankments as protection measures
against heavy flooding. The stability of embankments is a
crucial issue for public safety and for the consequences that a
possible failure event may have on the territory and its
economy. Although the seismic hazard of the Po valley is not
very high, the related flood risk is extremely significant due to
the vulnerability of the levees and to the relevant exposure of
the territory. If levee failures occur following an earthquake
during a high water season, considerable flooding in the Po area
will occur.
Figure 1. The course of the Po River.
On the other hand, failures of the river bank under seismic
action that occur during the dry season might not immediately
lead to flooding but time and resources - generally limited - are
unlikely to be adequate before the arrival of the rainy season.
Recently, the Italian Government has funded a number of
activities aimed at the seismic hazard control, including the
evaluation of the seismic stability of about 90 km of
embankments of the Po River, promoted and coordinated by the
relevant Authority (Autorità di Bacino of the Po River -
AdBPO).
The project mainly aims, via a preliminary extensive survey
including site investigation and laboratory testing, at the seismic
microzonation of the area with assessment of local site
response, at the evaluation of the liquefaction potential and at
the stability analyses of the riverbanks, under static and seismic
conditions. The paper focuses on the methodology developed in
order to identify, along the portion of the embankment
investigated, a number of significant sections, their geotechnical
models and the subsequent static and seismic stability analyses.
The safety conditions of the embankments in static and seismic
conditions are investigated as a function of the soil parameters
variability and considering various relevant river water levels.
A probability distribution was assumed to represent the
parameters most affecting the stability and a Monte Carlo
procedure was then used to compute the probability distribution
of the resulting safety factors.
