3433
General Report
Shallow foundations
Rapport général
Fondations superficielles
Zerhouni M.I.
ARCADIS ESG – Le Plessis-Robinson - France
Demay B.
TRACTEBEL ENGINEERING- Gennevilliers - France
ABSTRACT: Ten papers, from different countries, were accepted to this Discussion Session on Shallow Foundations. This General
Report reviews and summarizes the main contents and objectives of each of the submitted papers. This review shows that different
themes are treated and studied. Most of them are related to the improvement of models for predicting settlements of shallow
foundations in granular soils and in clayey soils. Accuracy and uncertainties in estimating settlements are assessed through
probabilistic analyses in four of the accepted papers. The definition and the determination of moduli and elastic soil properties are also
studied, like for instance the use of measured non-linear dynamic properties of soil. One paper addresses the settlement reduction by
aggregate piers (stone columns) and defines, through a full scale loading program, the corresponding “improvement factor”. Another
theme related to the eccentrically and inclined loading of shallow foundations is treated in three papers. The interaction of nearby
footings submitted to inclined loading is studied through Finite elements analyses. Foundations submitted to dynamic loadings are
also emphasized through a paper presenting the study of an improved type of foundation combining massive block and plates.
RÉSUMÉ : Dix articles provenant d’auteurs de différentes nationalités ont été acceptés pour cette session de discussion sur les
Fondations superficielles. Le présent rapport fournit une synthèse du contenu et des objectifs de chaque article. La revue montre que
différents sujets ont pu être abordés. La plupart porte sur l’amélioration des modèles de prédiction des tassements de fondations aussi
bien dans les sols granulaires que dans les sols argileux. La précision et les incertitudes associées à l’estimation des tassements sont
évaluées au travers d’analyses probabilistes dans quatre des articles présentés. La définition et la détermination des modules et des
propriétés élastiques des sols, comme par exemple, l’utilisation des propriétés dynamiques non linéaires, mesurées sont également
abordées. Un article traite de l’amélioration des tassements par des colonnes ballastées et définit, sur la base d’un important
programme de chargement de semelles en vraie grandeur, les facteurs de réduction des tassements. Trois des articles de la session
concernent les semelles soumises à des charges inclinées et excentrées. L’interaction entre semelles rapprochées soumises à des
charges inclinées est également étudiée par l’intermédiaire de modélisations aux éléments finis. Les fondations soumises à des
chargements dynamiques sont également abordés par la présentation d’un système combinant un bloc massif associé à une ou
plusieurs dalles.
KEYWORDS: shallow foundation, settlement, probabilistic approach, dynamic properties.
1 INTRODUCTION.
This general report reviews and summarizes the main
contents and objectives of each of the papers submitted to the
Shallow foundation session. Different themes are covered and
studied by these papers.
Most of them are related to the study of settlements under
shallow foundation either in granular soils or in clayey soils.
The definition and the determination of moduli and elastic
soil properties are also studied. The use of non-linear dynamic
properties, measured in-situ, to predict settlement is covered in
one of the submitted papers.
Accuracy and uncertainties in estimating settlements are also
assessed through probabilistic analyses.
The settlement reduction by using aggregate piers (stone
columns) and a proposal for the definition, through the results
of a full scale foundation loading program, of the corresponding
“improvement factor” is given.
Another theme subject is related to the eccentrically and
inclined loading of shallow foundations. The interaction of
nearby footings submitted to inclined loading is studied through
Finite elements analyses.
Foundations submitted to dynamic loadings are also
emphasized through a paper presenting a study of an enhanced
type of foundation combining massive block and plate.
2 SETTLEMENT OF SHALLOW FOUNDATIONS
2.1
Settlement measurements
In the paper of
Dapena &
al
.
from Spain, the settlements of
major-scale shallow foundations of large biodigesters tanks of a
Waste Water Treatment Plant have been recorded over the first
ten years after they have been put in operation and loaded.
These biodigesters are located on top of a layer of dark gray
silty clay alluvial sediments between 15 and 20 m thick
Dapena
& al
. discuss the amount of settlement recorded over
the first 10 years and how it has developed over time. It also
identifies how the pools have behaved differently, delimiting
the areas with similar settlement rates.
The measured settlement values vary between 50mm and
200mm (figure 1).
They show (figure 2) that the settlement s, which occurs with
time, fits the model s = a
ta
+ b, where ta is the time in years
since the tank has been full.
Coefficient “a” is related to the rate of settlement and its
distribution is similar to the settlement values.
