2617
The reinforcement of soils by dispersed oversized particles
Le renforcement des sols par les particules trop grandes non réparties uniformément
Vallejo L.E., Lobo-Guerrero S., Seminsky L.F.
Department of Civil & Environmental Engineering, University of Pittsburgh, Pittsburgh PA, USA
Caicedo B.
Departamento de Ingenieria Civil & Ambiental, Universidad de los Andes, Bogota, Colombia
ABSTRACT: Soils containing dispersed large particles (greater than # 4 sieve) form part of many engineered fills, glacial tills, debris
flows, and residual soil deposits. Very little is known about the effect that the large particles have on the shear strength of the soil-
large particles mixtures. In this study, the influence of the large particles on the shear strength of the mixtures was evaluated
experimentally and numerically. The experimental analysis used direct shear tests on simulated granular materials containing large
dispersed particles. The numerical analysis used the Discrete Element Method (DEM). The laboratory and the DEM simulation
results indicated that the shear strength of the mixtures increased with the concentration (C
a
) of the simulated large particles in the
mixtures. Also, this study established that the shear strength of the simulated granular materials with dispersed large particles, S
c
, can
be obtained if one uses the following relationship: S
c
= S
m
(1 + M C
a
). In this relationship, S
m
is the shear strength of the simulated
soil matrix in which the large particles are dispersed, and M is a constant that varied between 1 and 2 for the numerical and laboratory
analyses.
RÉSUMÉ :
Les sols contenant des particules dispersées de grande taille (supérieure à tamis # 4) constituent la majorité des remblais,
argiles glacières à blocs, des coulées d’éboulis et
des dépôts résiduels de sol utilisés dans la construction. Peu de travaux existent sur
l'effet que les grosses particules ont sur la résistance au cisaillement des mélanges de particules de sol de grande taille. Dans cette
étude, l'influence des grosses particules sur la résistance au cisaillement des mélanges a été évalué expérimentalement et
numériquement. L'analyse expérimentale utilisée essais de cisaillement direct sur simulées matériaux granulaires contenant de grandes
particules dispersées. L'analyse numérique utilisé la méthode des éléments discrets (DEM). Les essais en laboratoire et les résultats
des simulations ont indiqué que la résistance au cisaillement des mélanges augmente avec la concentration (Ca) des particules de
grandes tailles simulées. En outre, cette étude a établi que la résistance au cisaillement des matériaux granulaires simulées avec des
grosses particules dispersées, S
c
, peut être obtenu si l'on utilise la relation suivante: S
c
= S
m
(1 + M Ca). Dans cette relation, S
m
c'est
la résistance au cisaillement de la matrice du sol simulé dans lequel les grosses particules sont dispersées, et M est constante qui varie
entre 1 et 2 pour les analyses numériques et de laboratoire.
KEYWORDS:granular mixtures, shear strength, laboratory tests, DEM analysis.
1INTRODUCTION.
Materials forming part of natural slopes and engineered fills
have a distinct structure, this consisting of a mixture of a soil
matrix (sand) and large particles of gravel that are dispersed
(fragments do not interact) in the soil matrix . The rock
fragments are composed of materials larger than the No. 4 sieve
(Magier and Ravina, 1982; Poesen and Lavee, 1994; Fragaszy
et al. 1992; Budiman, et al., 1995 and Vallejo 1989, 2001) (Fig
1). Soil Mechanics has dealt mainly with the study of three
main soil types: sands, silts, and clays. However, mixtures of
soils such as those shown in Fig. 1 are more commonly found in
nature and in earth construction projects than pure sands, silts
and clays. Since the determination of the mechanical properties
(i.e. shear strength) of mixtures such as those depicted in Fig. 1
has heretofore received scant attention, such an investigation is
indeed called for. This study reports on the mechanisms
involved with the shear strength of simulated granular materials
with dispersed oversized particles.
2 LABORATORY TESTING PROGRAM
2.1
Equipment and simulated granular materials
For the purpose of understanding the mechanisms involved in
the shear strength of granular materials with dispersed large
particles an open face, two-dimensional direct shear apparatus.
Figure 1.Natural slope in Wisconsin made of a soil-rock mixture
was used (Fig. 2) This apparatus is called the Plane stress Direct
Shear Apparatus (PSDSA) (Vallejo, 1991). The granular matrix
will be simulated by a mixture of wooden sticks. Wooden sticks
are strong and can be easily shaved into polygons as their cross
sectionalareas. These polygons resemble the profiles of actual
