403
Oscillation of Acceleration Accompanying Shear Band and Subsequent Time-
Dependent Behavior in Overconsolidated Clay under Undrained Plane-Strain
Conditions
Oscillation de l’accélération accompagnant la formation de bandes de cisaillement et
comportement dépendant du temps dans une argile surconsolidée en déformations planes et
conditions non drainées.
Noda T.
International Member, Nagoya University, Japan
Xu B.
Student Member, Nagoya University, Japan
ABSTRACT: In this paper, a compression test on a rectangular overconsolidated clay specimen under plane strain, constant cell
pressure, and undrained conditions was simulated using a soil-water coupled finite deformation analysis code taking inertial loads into
consideration, and the following results were obtained: 1) In order to reproduce uniform deformation in a perfect specimen with no
initial geometric imperfection, it is necessary to have conditions in which the “permeability coefficient is zero” so that pore water
migration does not virtually occur, as well as to apply an initial distribution of velocity, acceleration and pore water pressure to the
interior as well as the boundary in accordance with the vertical velocity of the top/bottom ends so as to satisfy the undrained
conditions; 2) In specimens with initial geometric imperfection set to a very small amplitude primary cosine curve, when a vertically
symmetric vertical displacement was applied under displacement control from static conditions, shear banding occurred in the
specimen, and accelerations were generated from that part; 3) After the load became unstable, by changing to load control and
maintaining the load constant, creep behavior under undrained conditions was exhibited by the specimen.
RÉSUMÉ: Un essai de compression sur une éprouvette rectangulaire d’argile surconsolidée, en déformations planes et conditions non
drainées est modélisé en utilisant une analyse couplée en grandes déformations, prenant en compte les forces d’inertie. Cette analyse a
apporté les résultats suivants: 1) En vue de reproduire une déformation uniforme dans une éprouvette parfaite sans défaut géométrique
initial, il est nécessaire d’avoir des conditions dans lesquelles le « coefficient de perméabilité est égal à zéro » de telle sorte qu’il n’y a
aucun écoulement d’eau, ainsi que d’appliquer une distribution initiale de vitesses, d’accélérations et de pressions interstitielles à
l’intérieur ainsi qu’aux limites de l’éprouvette en accord avec la vitesse verticale de la base et du haut de celle-ci en vue de satisfaire
les conditions de non drainage ; 2) Pour des éprouvettes présentant un défaut géométrique initial de très faible amplitude, quand un
déplacement vertical symétrique est appliqué à déplacement contrôlé, des bandes de cisaillement se développent dans l’éprouvette et
des accélérations se développent à partir de là ; 3) Après que le chargement soit devenu instable, en changeant pour un chargement
contrôlé en effort et en maintenant l’effort constant, l’éprouvette présente un comportement de fluage en conditions non drainées..
KEYWORDS: imperfection, shear band, acceleration oscillation.
MOTS CLES : imperfection, bande de cisaillement, oscillation de l’accélération
1 INTRODUCTION
In bifurcation analysis or shear strain localization analysis of
soil specimens, calculations are normally carried out on a
uniform deformation field assuming quasi-static conditions that
ignore the effect of inertia forces (Ikeda et al. 2003, Wan et al.
1990). The authors have developed the GEOASIA code, which
is capable of performing analyses without distinction
dynamic/static problems, extending the static soil-water coupled
finite deformation analysis that has been carried out to date
(Asaoka et al. 2007, Noda et al. 2008). In this paper, the strain
localization problem of rectangular specimens of saturated
overconsolidated clay under undrained and constant side
pressure conditions was addressed, checking the conventional
solutions that were obtained under quasi-static assumptions and
taking the problem to be a dynamic problem that considers
inertial term. This paper introduces several phenomena such as
the generation of accelerations and time-dependent behavior
(creep) associated with the occurrence of shear banding as
newly found calculation results using GEOASIA.
2 CALCULATION CONDITIONS
Fig. 1 shows the finite element mesh and boundary conditions
used in the calculations. The calculation assumed 2-dimensional
plane strain conditions and a saturated rectangular specimen
with 3.5 cm wide and 8 cm high in the isotropic consolidation
state. The specimen was a fully remolded overcolsolidated clay.
As the elasto-plastic constitutive model in the analysis, the SYS
Cam-clay model (Asaoka et al. 2002), the degree of structure
was
R
*=1.0 and there was no effect of the initial anisotropy and
induced anisotropy (ζ
0
=0,
br
=0).
A
3.5cm
Impermeable
boundary
8.0cm
Rigidsmooth
pedestal
Constant
velocity
boundary
Traction boundary
(cell pressure
294.3kPa)
Fig. 1 Finite element mesh and boundary conditions
Table 1 shows the soil elasto-plastic constants and the set of
initial values used in the calculations. Apart from the
