251
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
1
Residual shear strength behavior of swelling soils
Comportement de force résiduelle de cisaillement des sols gonflants
Markou I.N.
Democritus University of Thrace, Xanthi, Greece
ABSTRACT: Three clay soils from North-Eastern Greece, presenting “high” or “very high” swelling potential, were used in this
investigation. The residual strength behavior of these soils was evaluated by performing ring shear tests on remolded specimens. The
specimens were prepared either with the optimum water contents resulted from Standard compaction test (26% - 31%) or with higher
water contents (46% - 47%), derived from the specimen moistures at the end of the preceding tests with optimum water contents.
Ring shear tests were performed using a Bromhead apparatus, according to the procedures described in BS 1377 – Part 7. The results
obtained from the consolidation stage of the ring shear tests conducted in swelling clays, do not present the typical form attained in
ordinary clays. Although the failure envelopes in residual state present curvature in some cases, they can be considered as linear for
effective normal stresses up to 250 kPa. The resulting values of residual friction angle do not exceed 14
o
and, in some cases, are
affected by the water content of the specimens used in the tests.
RÉSUMÉ: Trois sols argileux provenant du Nord-Est de la Grèce et présentant un potentiel de gonflement « haut » ou bien « très
haut », ont été utilisés dans le cadre de ce travail. Le comportement de la force résiduelle de cisaillement a été évalué à l’aide des
essais de cisaillement annulaire sur des échantillons remués. Les échantillons étaient préparés soit avec le pourcentage de contenu de
l’eau optimal, résultant par l’essai de compactage standard (26 %-31 %), soit avec des pourcentages de contenu de l’eau plus élevés
(46 %-47 %) qui dérivent par l’humidité des échantillons à la fin des essais précédents avec des contenus de l’eau optimaux. Les
essais de cisaillement annulaire ont été réalisés à l’aide de l’appareil de Bromhead, selon la procédure décrite dans BS 1377-Partie 7.
Les résultats obtenus par le stage de consolidation du cisaillement annulaire, conduits sur des argiles gonflantes, n’atteignent pas la
forme classique des argiles ordinaires. Bien que l’enveloppe de rupture présente une courbe dans quelques cas, elles peuvent être
considérées comme linéaires pour des contraintes normales effectives allant jusqu’à 250 kPa. Les valeurs résultantes de l’angle de
friction résiduelle, n’excèdent pas 14
o
et, dans quelques cas, elles sont affectées par le contenu de l’eau des échantillons utilisés lors
des essais.
KEYWORDS: soil behaviour, swelling soils, expansive clays, residual shear strength, laboratory investigation, ring shear tests
1 INTRODUCTION
The residual shear strength of cohesive soils plays a part in the
stability of old landslips, in the assessment of the engineering
properties of soil deposits which contain pre-existing shear
surfaces, and in the assessment of the risk of progressive failure
in stability problems in general. Extensive investigations on the
residual strength have been carried out and directed towards: (a)
developing suitable laboratory techniques for its measurement,
(b) identifying the influence of geomechanical features on the
residual strength, (c) understanding the basic mechanisms
involved in the mobilization of shear strength during the
residual stage of deformation and (d) establishing correlations
with soil index properties. Although the residual strength has
been studied in the laboratory using experimental techniques
such as the triaxial test procedure proposed by Chandler (1966),
the ring shear test and the multi-reversal direct shear test are
widely used to measure the residual strength of soils. Published
results (Lupini et al. 1981, Skempton 1985) show that residual
shear behavior changes significantly as the clay content of
cohesive soil increases, and that a change in shearing
mechanism also occurs. Apart from the clay fraction, the
mineralogy of the clay also has an effect on residual strength,
especially when the clay fraction is large (Kalteziotis 1993). A
number of correlations between residual strength and clay
fraction, plasticity index and liquid limit have been proposed
(e.g. Skempton 1964, Lupini et al. 1981, Hawkins and Privett
1985, Skempton 1985, Mesri and Cepeda-Diaz 1986), but
Lupini et al. (1981) suggested that all these correlations can not
be general.
Soils containing expansive clay minerals, called swelling or
expansive soils, have created problems of uplift and instability
on many structures, because there is an opportunity for water to
become available and thus facilitate the expansion (swelling) of
the clay minerals. Swelling clays are often subject to extreme
changes in shear strength because of extreme moisture changes.
In addition to the strength factors related to the minerals
involved, the interrelation of moisture, density and load plays an
important part in the strength (Gibbs et al. 1960). Swelling soils
also exist in Greece and have created a number of problems
and/or failures in projects (Christodoulias and Gasios 1987,
Stamatopoulos et al. 1989). Therefore, the properties and the
swelling characteristics of swelling soils from Greece were
investigated (Xeidakis 1993, Tsiambaos and Tsaligopoulos
1995, Kollaros and Athanasopoulou 1997), preventive and
corrective measures against swelling were applied
(Christodoulias and Gasios 1987, Stamatopoulos et al. 1989)
and the treatment of swelling soils using various methods for
reducing swell potential and increasing strength was examined
(Stamatopoulos et al. 1992). It is, therefore, of merit to
investigate the residual shear strength behavior of swelling
soils. Toward this end, a laboratory investigation was conducted
in order to evaluate the residual shear strength parameters of
selected swelling soils having different moisture contents and
the results obtained and observations made, are reported herein.
résistance résidu lle au cisaillem nt de s ls gonflants
