1129
Expression of mechanical characteristics in compacted soil with soil/water/air
coupled F.E. simulation
Expression des caractéristiques mécaniques des sols compactés par une simulation couplée
sol/eau/air par éléments finis
Kawai K., Iizuka A.
Kobe University
Kanazawa S.
Chuo University
ABSTRACT: Results obtained in a lab compaction test are difficult to apply to the design and compaction control at an actual
geotechnical engineering site. This is attributed to the fact that the mechanism for compaction has not been explained using the
principles of soil mechanics. The main theme of this study is interpretation of the compaction mechanism with unsaturated soil
mechanics. Here, static compaction tests were simulated with soil/water/air coupled finite element analysis code DACSAR-MP.
Consequently, the shape of the compaction curve was successfully expressed. Moreover, the effects of compaction on compressibility
and permeability of compacted soil could be reasonably explained. Additionally, shear deformation was applied to the specimen
obtained from static compaction simulations in soil/water/air coupled analysis. The relationships between shear strength and
compaction curve showed good agreement with the actual behavior.
Résumé : Les résultats des essais de compactage obtenus dans un laboratoire sont difficilement applicables à la conception et au
contrôle de compactage dans des sites géotechniques d’ingénierie réels. Ceci peut être attribué au fait que le mécanisme du
compactage n’a pas été expliqué à partir des principes de la mécanique des sols. Le principal thème de cette étude est de définir le
mécanisme de compactage en considérant les principes de base de la mécanique des sols non saturés. Dans ce cadre, nous avons
simulé le compactage statique avec de la terre, de l’eau ou de l’air doublé d’une analyse par éléments finis, code DACSAR-MP.
Ainsi, nous avons pu mettre à jour avec succès la forme de la courbe de compactage. De plus, nous avons réussi à expliquer
scientifiquement les effets du compactage sur la compression et la perméabilité des sols compactés. En outre, les essais de
cisaillement ont été simulés sur l’éprouvette obtenue à partir de la simulation d’un compactage statique couplée sol/eau/air . Les
relations entre la résistance au cisaillement et la courbe de compactage sont parfaitement en accord avec le comportement réel. .
KEYWORDS: Compaction, Unsaturated soil, Soil/water/air coupled simulation
1 INTRODUCTION
Most onshore earth structures, such as the earth dam or
embankments and river levees, are constructed by compaction.
It is generally known that the maximum dry density appears at
the optimum water content under constant compaction load.
This relationship is called compaction curve. In previous
research, the characteristics of compacted soil were compared
with the compaction curve (see Fig. 1). Water content at the
extremal values of mechanical characteristics was found to be
different from the optimum water content of the compaction
curve. This means that increase in dry density does not directly
influence increase in shear strength or a decrease in
compressibility and permeability. Moreover, in-situ tests (e.g.
Proctor: 1933) and/or experimental construction are actually
needed for construction of compacted earth structures since
compaction effects are dependent on the method of compaction.
In this study, the relationship between characteristics of
compacted soil and the compaction curve is expressed using
soil/water air coupled F. E. Simulation to clarify the compaction
mechanism and the characteristics of soil induced by
compaction.
2 NUMERICAL MODELS IN SOIL/WATER/AIR
COUPLED ANALYSIS
In this study, the soil/water/air coupled F. E. analysis code,
known as DACSAR-MP, is used for simulations. The numerical
models applied to DACSAR-MP are detailed as follows:
2.1
Constitutive model for unsaturated soil
Figure 1. Characteristics of compacted soil with compaction curve
(Kuno: 1974)
q
p
0
e
S
sat
p
sat
ap
1
e
S
0
e
S
Figure 2. Yield surface of constitutive model for unsaturated soil
