3497
Soil-Geosynthetic Interface Shear Strength by Simple and Direct Shear Tests
Détermination de la résistance au cisaillement de l’interface sol – géosynthétique par des essais de
cisaillement simple et direct
Vieira C.S. & Lopes M.L.
Civil Engineering Department, Faculty of Engineering, University of Porto, Portugal
Caldeira L.
National Laboratory of Civil Engineering, Lisbon, Portugal
ABSTRACT: Soil-reinforcement interaction mechanism has an utmost importance in the design of reinforced soil structures. This
mechanism depends on the soil properties, reinforcement characteristics and elements (soil and reinforcement) interaction. In this
work the shear strength of an interface between siliceous sand and a high strength geotextile was characterized through direct and
simple shear tests. The direct shear tests were performed on a large scale direct shear apparatus. The scale effect of the direct shear
box was also analysed. Unreinforced sand and one layer reinforced sand were characterized trough simple shear tests.
Notwithstanding the differences between the shear strength characterization through simple shear and direct shear tests, it was
concluded that the shear strength of the reinforced sand is similar to the interface direct shear strength.
RÉSUMÉ : Le mécanisme d’interaction sol – renforcement a une importance extrême dans le dimensionnement des structures avec
des sols renforcés. Ce mécanisme dépend des propriétés du sol, des caractéristiques du renforcement et des éléments (sol et
renforcement) d’interaction. Dans ce travail, la résistance au cisaillement de l’interface entre une sable siliceux et un géotextile de
haute résistance a été caractérisée à travers des essais de cisaillement simple et direct. Les essais de cisaillement direct ont été réalisés
sur un appareil de cisaillement direct de grande dimension. Du sable sans renforcement et une couche de sable renforcé ont été aussi
caractérisés avec des essais de cisaillement simple. Nonobstant les différences entre la caractérisation de la résistance au cisaillement
à travers des essais de cisaillement simple et direct, on a conclu que la résistance au cisaillement du sable renforcé est similaire à la
résistance au cisaillement direct de l’interface.
KEYWORDS: Soil Reinforcement; Soil-Geosynthetic Interfaces; Direct Shear; Simple Shear.
1 INTRODUCTION
Soil-reinforcement interaction mechanism has an utmost
importance in the design of reinforced soil structures. This
mechanism depends on the soil properties, reinforcement
characteristics and elements (soil and reinforcement)
interaction. The accurate identification of the interaction
mechanism and the choice of the most suitable test for its
characterization are important factors. Figure 1 presents a
potential failure mechanism of a reinforced soil slope. In the
upper part of the retained reinforced soil mass, the
reinforcement is pulled out, so the soil-reinforcement interaction
can be best characterised by laboratory pullout tests. Near the
base of the slope, soil sliding is expected and the interaction
between the two materials is better characterized trough direct
shear tests.
Pullout test
F
σ
σ
τ
Direct Shear
test
Figure 1. Potential failure mechanism of a reinforced soil slope and the
most suitable laboratory tests to soil-reinforcement characterization.
Numerous experimental studies have been conducted to
investigate the shear behaviour of soil-geosynthetic interfaces
through direct shear tests (Vieira
et al.
2013; Liu
et al.
2009;
Hsieh and Hsieh 2003; Lee and Manjunath 2000). The use of
the simple shear device to characterize interfaces behaviour is
very scarce and is limited mainly to sand-steel interfaces
(Uesugi and Kishida 1986; Evgin and Fakharian 1998). In this
work, simple shear tests were used to characterize the behaviour
of a dry sand reinforced with a high strength geotextile.
2 MATERIALS
In the laboratory study herein presented, the interface between
siliceous sand and a high strength geotextile (geocomposite
reinforcement) was characterized. According to the Unified Soil
Classification System, the sand is classified as SP - poorly
graded sand and it was referred as SP49. This sand has mean
diameter of 0.45 mm, uniformity coefficient of 1.9 and
coefficient of curvature equal to 0.9.
The geocomposite is a high strength composite geotextile,
consisting of polypropylene continuous filament needlepunched
nonwoven and high strength polyester yarns (unidirectional
reinforcement), with a nominal strength of 100 kN/m and
elongation at nominal strength of 13%. This geocomposite was
referred as GC100.
3 DIRECT SHEAR TESTS FOR SAND/GEOSYNTHETIC
INTERFACE CHARACTERIZATION
3.1
Large scale direct shear device
The conventional direct shear device can only accommodate
small size specimens, which imposes serious limitations in
terms of reproducing real conditions. Based on this evidence, a
large scale direct shear test device able to perform load and
i ira C.S., Lopes M.L.
