719
Numerical Investigations on Vibratory Sheet Piling in Embankments using
a Multi-Phase Material
Études numériques des effets de vibrofonçage sur les berges en utilisant une approche
multi-phasique
Hamann T., Grabe J.
Hamburg University of Technology, Institute of Geotechnical Engineering and Construction Management
ABSTRACT: The influence of vibratory driving on the surrounding soil is difficult to predict due to complex mechanical processes in
the soil. Effects like soil compaction, subsidence or a temporary reduction of the soil's shear strength can occur as a result of the
dynamic loading. In case of water saturated soil additional effects like excess pore water pressure or soil liquefaction can occur. When
driving piles in the area of embankments these effects can cause great deformations of the embankment and the driven pile. In this
paper the lateral drift of a sheet pile wall due to the installation process in the area of an embankment is simulated by use of the finite
element method using a coupled 2-phase approach to consider the development of excess pore water pressure and the resulting
effects. The deformation mechanism and the mechanical processes in the soil are investigated. Further the calculated deformations of
the sheet pile are compared to measurement data. A comparison of the results of a fully drained analysis and a coupled analysis
considering the development of excess pore water pressure is done.
RÉSUMÉ : L'influence du vibrofonçage sur le sol environnant est difficile à prévoir en raison de phénomènes mécaniques complexes
dans le sol. Les effets tels que la compaction du sol, l'affaissement ou la réduction temporaire de la résistance au cisaillement du sol
peuvent se produire sous l’effet d’une charge dynamique. Dans le cas d’un sol saturé en eau, des effets supplémentaires tels que des
surpressions interstitielles ou la liquéfaction des sols peuvent se produire. Lors de l’installation de pieux à proximité d’une berge, ces
effets peuvent causer de grandes déformations de la berge et du pieu. Dans cette étude, le déplacement latéral d'une paroi de
palplanches dû au processus d’installation à proximité d’une berge est déterminé en utilisant la méthode des éléments finis. Une
approche biphasique est utilisée pour estimer le développement de la surpression interstitielle de l’eau et des effets qui en résultent. Le
mécanisme de déformation et les phénomènes mécaniques dans le sol sont étudiés. Les déformations calculées pour la palplanche sont
comparées aux résultats de mesure. Pour finir, la comparaison des résultats d'une analyse parfaitement drainée et d’une analyse
biphasique est effectuée.
KEYWORDS: water saturated soil, soil liquefaction, two-phase approach, finite element method, installation process
1 INTRODUCTION
The influence of vibratory driving on the surrounding soil is
difficult to predict due to complex mechanical processes in the
soil. Effects like soil compaction, subsidence or a temporary
reduction of the soil's shear strength can occur as a result of the
dynamic loading. In case of water saturated soil additional
effects like excess pore water pressure or soil liquefaction for
water saturated loosely layered sands can occur. In particular,
during driving of piles in embankments, such as railway
embankments or shoreline stabilisations, these effects can
influence the stability of the embankment and lead to a lateral
drift of the driven pile or large deformations of the
embankment. In practice, pile driving guides are usually used to
prevent a drift of the pile during installation.
The finite element method provides a powerful tool for
investigation of mechanical processes in soil during vibratory
driving. Deformations of the embankment and the pile as well
as the reaction forces can be predicted to design a pile driving
guide.
In this paper, the lateral drift of a sheet pile wall of a quay wall,
which has occurred due to the installation process, is simulated
numerically. The soil is modeled by the use of a dynamic
coupled 2-phase approach to investigate the mechanical
processes in the soil and the development of excess pore water
pressure during the vibratory driving. The deformation of the
sheet pile and the soil as well as the reaction forces of a pile
driving guide are investigated and compared with in-situ
measured data. In previous three-dimensional calculations
(Hamann and Grabe 2012a, Hamann and Grabe 2012b), in
which the coupled approach was not yet available, fully drained
conditions were assumed for simplification. In this paper
simulations assuming coupled conditions with a predefined
permeability and simulations assuming drained conditions are
carried out and compared with each other to analyse the
influence of excess pore water pressure on the deformations and
reaction forces.
2 CONSIDERED CASE OF DAMAGE
As part of a power plant expansion a sheet pile wall acting as a
new waterfront was built up in the area of an embankment
consisting of sand. The sheet piles of type “AZ 41-700” were
vibrated as double piles with a vibratory frequency of
f =
36 Hz
using an upper and lower pile driving guide as shown in Figure
1.
During the vibratory driving a lateral drift of the pile and the
pile driving guide occurs. At the investigated cross section of
the embankment horizontal deformations into the direction of
the waterside of
u
h
= 13 cm at measuring point 1 and
u
h
= 9 cm
at measuring point 2 were detected due to the installation
process.
3 NUMERICAL MODELING
The described case of damage is simulated numerically by use
of the finite elmente software Abaqus/Explicit (Dassault
Systèmes 2009). A total stress analysis is carried out to consider
