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Dynamic shear modulus and damping of compacted silty sand via suction-controlled
resonant column testing
Propriétés dynamiques d'un sable limoneux par des tests en colonne de résonance sous aspiration
contrôlée.
Hoyos L.R., Cruz J.A., Puppala A.J., Douglas W.A., Suescún E.A.
University of Texas at Arlington, Arlington, Texas 76019, USA
ABSTRACT: Dynamic properties of unsaturated soils, particularly shear modulus and material damping, play a fundamental role in
the analysis/design of critical geotechnical infrastructure resting on unsaturated ground, or made of compacted unsaturated soils, when
subjected to static and dynamic loads. This paper introduces a proximitor-based resonant column device with self-contained bender
elements suitable for testing soils under controlled-suction conditions via the axis-translation technique. A series of suction-controlled
resonant column and bender element tests were conducted on several statically compacted samples of silty sand under net stresses and
suction states ranging from 50-400 kPa. Particular attention was devoted to the influence of suction over the frequency response
curves and cyclic hysteretic stress-strain loops. The results confirm the influence exerted by the stress/suction history experienced by
the soil, in terms of dynamic shear modulus and damping.
RÉSUMÉ: Les propriétés dynamiques des sols non saturés, en particulier le module de cisaillement dynamique et l'amortissement,
jouent un rôle clé dans l'analyse et la conception de l'infrastructure civile sous des charges statiques ou dynamiques. Dans cet article,
un appareil de colonne de résonance a été utilisé pour tester des échantillons de sol non saturé dans des conditions contrôlées
d'aspiration. Les essais en colonne de résonance ont été effectués sur des échantillons de sable limoneux compacté statiquement, sous
des succions de 50-400 kPa. Les résultats confirment l’influence des chemins de contrainte et des succions sur les échantillons de sol,
en termes de module dynamique de cisaillement et d'amortissement.
KEYWORDS: unsaturated soil, matric suction, axis-translation, resonant column test, shear modulus, damping, cyclic hysteretic loop.
1 INTRODUCTION
Dynamic properties of unsaturated soils, particularly shear
modulus and material damping, play a fundamental role in the
analysis/design of critical geotechnical infrastructure resting on
unsaturated ground, or made of compacted unsaturated soils,
when subjected to static or dynamic loads. Most conventional
soil testing techniques, however, cannot capture this very small-
strain behavior and thereby considerably underestimate the true
soil stiffness. Several efforts have been reported since the early
1980’s to study the effects of capillarity and saturation on small-
strain stiffness of unsaturated soils via resonant column (RC) or
bender element (BE) testing, including Brull (1980), Wu et al.
(1984), Qian et al. (1991), Marinho et al. (1995), Picornell and
Nazarian (1998), Cabarkapa et al. (1998), Cho and Santamarina
(2001), Mancuso et al. (2002), Inci et al. (2003), Kim et al.
(2003), Mendoza et al. (2005), Cabarkapa and Cuccovillo
(2006), Vassallo et al. (2006), Sawangsuriya et al. (2008, 2009),
Ng et al. (2009), and Khosravi et al. (2010).
The BE technique has proved a feasible way to investigate
unsaturated soil stiffness at very small shear strain amplitudes.
However, there is a great need for assessing the suitability of
this technique, particularly for unsaturated soils, as compared to
more fully-standardized procedures such as the resonant column
and simple shear test methods.
This paper introduces a suction-controlled proximitor-based
resonant column apparatus which features self-contained BEs
for the simultaneous testing of soils under both techniques.
Particular attention is devoted to the influence of suction over
the frequency response curves and cyclic hysteretic stress-strain
loops. The results highlight the critical influence exerted by the
stress/suction history experienced by the soil in terms of both
dynamic shear modulus and damping.
2 RC/BE DEVICE: MAIN FEATURES
The model THS-100 resonant column cell features a reinforced
acrylic chamber of 1000 kPa confining pressure capacity. The
bottom pedestal, for samples of 70-mm diameter, features a full
set of HAEV (5-bar) ceramic disks, as well as one BE crystal
(receiver) for shear-wave velocity readings: Figure 1(a). The top
cap features a full set of coarse porous stones, for uniform pore-
air pressure application/control, and also one BE transmitter. An
electrical servo motor actuator is used for the application of
torsional loads with +/– 2 3.3 kN-m (peak) capacity, and 300-
Hz frequency range.
The input torque is measured in pfs (percent of full scale)
units, with 100 pfs equivalent to a 10 kN-m torque. Mounted on
an internal floating frame, thus allowing for large vertical
deformations, the actuator includes a servo amplifier for closed-
loop control of torsional loads, and one proximitor mounting
acting as the internal angular displacement transducer: Figure
1(b). A model PCP-15U pressure panel is used for direct control
of pore-air pressure u
a
through the top cap, with dual pressure
regulators/gauges for precise measurement/control of matric
suction, s = u
a
(u
w
= 0).
Figure 1. THS-100 resonant column cell with self-contained BEs.
