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Measuring and modeling the dynamic behavior of Danube Sands
Mesure et modélisation du comportement dynamique des sables du Danube
Ray R.P., Szilvágyi Zs.
Széchenyi István University, Győr, Hungary
ABSTRACT: The adaptation of Eurocode 8 and development of high speed rail system in Hungary has created a greater need to
define dynamic behavior of local soil groups. Danube sands compose an important segment of these soils and present the geotechnical
engineer with several design challenges. The soils are present at river crossings and major development parcels throughout Hungary.
Although the engineering behavior of these sands can vary over a wide range, they retain some common characteristics that will help
the engineer to make decisions about geotechnical and structural designs. Samples of Danube sands were brought in the laboratory for
dynamic testing, which included resonant column and torsional simple shear testing. This paper summarizes the dynamic behavior of
this typical local soil group with emphasis on the dynamic properties themselves. Researches will find the methods and approach to
evaluating properties helpful in their work while design engineers will understand how these properties are applied.
RÉSUMÉ : A cause de l’entrée en vigueur de l’Eurocode 8, et aussi du développement des lignes ferroviaires à grand vitesse, il était
plus en plus important de connaître le comportement dynamique des sols typiques du pays. Un partie de ces sols typiques sont des sols
alluviaux granulaires du Danube. Bien que les caractéristiques de ces sols varient très largement, ils ont des caractéristiques
communes aussi et leur connaissance peut aider fortement dans le dimensionnement des projets géotechniques et de structures. Des
échantillons de sables du Danube ont été testés en laboratoire, à la colonne de résonnance et à l’appareil de cisaillement simple en
torsion. Dans cette étude, nous résumons les propriétés dynamiques de ce sol typique. Les chercheurs porront trouver les méthodes
d’évaluation du comportement des sols et les ingénieurs de projets géotéchniques pourront comprendre comment utiliser ces
propriétés.
KEYWORDS: resonant column test, torsional simple shear test, dynamic soil behavior, dynamic soil testing, Danube sand
1 INTRODUCTION
In the last couple of decades the importance of numerical
modeling in Geotechnics has increased greatly and not only in
research, but in everyday practice as well. On the one hand this
is a result of the rapid and continuous progress of computer
technology; on the other hand the many advantages of achieving
more accurate and economical solutions help these approaches
to become more widespread. These calculation methods have
the great benefit of using advanced material models, which, if
used carefully and properly, allow for better modeling.
Many studies have shown that the accurate modeling of
stiffness degradation with strain (and stress) is a key aspect in
many dynamic as well as static geotechnical numerical
calculations (e.g. earthquake vibrations, high speed railway
induced vibrations, settlement calculations around retaining
walls or tunnels etc.). It has been recognized, that soils behave
linear-elastically only at very low strains (~10
-4
%) and as the
strains (and stresses) increase, the initially constant shear
stiffness (G
max
) decreases gradually while the damping or
hysteretic behavior becomes more pronounced (Figure 1).
Modulus reductions to 5-10% of the original, low-strain value
are common. Shown in Figure 1 are curves from Seed and Idriss
(1970) for sand and Vucetic and Dobry (1989) for clay (PI=0).
The level, at which this stiffness degradation starts is called
threshold level and depends on soil type. If the strains in the soil
increase above this level, non-linear behavior can be observed.
Several complex soil models have been developed to capture
this behavior of soils (Jardine 1980, Ramberg-Osgood 1948,
Benz 2008). In general these models define a modulus reduction
curve and a damping curve, and they can only produce accurate
results, if sophisticated laboratory and field test are used to
determine these key soil parameters.
Figure 1. Stiffness degradation and damping increase with shear strain
for sand and clay.
2 LABORATORY MEASUREMENT OF MODULUS
DEGRADATION
2.1
Resonant Column – Torsional Simple Shear (RC-TOSS)
Device Hardware
The device used in this study at Széchenyi István University
Győr has been built and used for earlier researches by the author
(Ray 1984, 2010; Ray and Woods 1987). In the last year, the
device has been rebuilt and calibrated in Győr and it is now
