191
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
1
Laboratory testing of geomaterials: time effects and other peculiar observations -
General Report of TC 101 (session 1)
Essais de laboratoire sur les géomatériaux: Effets du temps et autres observations spécifiques -
Rapport général du TC 101 (session 1)
E. Ibraim
University of Bristol, Bristol, UK
ABSTRACT: This paper presents a General Report of 29 written contributions submitted for one of the parallel sessions entitled
“
Time effects and other peculiar observation
”
of the Technical Committee 101: Laboratory Stress Strength Testing of Geomaterials.
The origin of the authors shows a wide geographical distribution. The General Report reviews these contributions and presents the
current research directions mainly in relation to the experimental behaviour as well as the key outcome results. The topics covered by
the written contributions have been grouped within the following thematic strands: time effects, expansive soils,
consolidation/compressibility and crushable granular soils.
RÉSUMÉ : Ce document présente un rapport général des 29 contributions écrites pour l'une des sessions parallèles « Effets du temps
et autres observations spécifique », soumis au Comité Technique 101: Essais de laboratoire des géomatériaux. L'origine des auteurs
montre une large répartition géographique. Le rapport général examine ces contributions et présente les axes de recherche actuels
principalement en ce qui concerne le comportement expérimental ainsi que les principaux résultats. Les sujets couverts par les
contributions écrites ont été regroupées dans les volets thématiques suivants: les effets du temps, sols gonflants,
consolidation/compressibilité et sols granulaires avec rupture des grains.
KEYWORDS: clay soils, time effects, creep, strain rate, consolidation, expansive soil, shrinkage, swelling, breakage, sand.
1 INTRODUCTION
This paper presents a summary in the form of a General Report
of the topics, current research directions and key outcomes of
the written contributions submitted to the Technical Committee
101: Laboratory Stress Strength Testing of Geomaterials
Session. TC101 promotes and actively encourages co-operation
and exchange of information concerning research and
developments in advanced laboratory geotechnical testing,
including apparatus, techniques and interpretation, and their use
in practical geotechnical engineering, site characterisation
studies and ground modelling approaches.
TC101 session contains a total of 58 written contributions.
Their presentation is organised in two parallel sessions of 29
papers each on
Time effects and other peculiar observations
and
Strength properties and treated soils
. This General Report
refers only to the papers selected for the former session.
The origin of the authors clearly shows a wide geographical
distribution, 12 contributions from Europe, 12 from Asia, 3
from North and South America, and 2 from Australia and New
Zealand. Japan, China and France are leading in terms of
number of contributions with 5, 4 and 3 papers, respectively.
Although the papers in this session explore mainly the
experimental aspects of the behaviour of fine and granular soils,
the analysis and interpretation are enhanced due to
complementary use of various analytical and constitutive
modelling approaches. In general, there is a great concern for
conducting multi-scale investigations, including soil structure
analyses and correlation with macro soil response. Reference to
practical applications is also considered.
Despite some inherent heterogeneity, the topic covered by
the written contributions can be grouped within the following
thematic strands:
Time effects: creep, strain rate effects in fine soils;
Expansive soils: swelling/shrinkage characterisation;
Consolidation/compressibility (loading and unloading);
Crushable granular soils.
The following sections develop the issues with reference to
the written contributions.
2 TIME EFECTS
Of all aspects of settlement analysis, the issue of creep and
secondary consolidation is one of the area in which least
progress has been made in terms of fundamental understanding
and in the incorporation of research into practice. While the
existence of creep complicates the predictions of the magnitude
of settlement of structures founded on clay soils, further
difficulties arise from the fact that the concerned elapsed time
under the constant load following the end of the construction in
a full-scale soft clay deposit is usually very long. As a
consequence, the settlement rates are very low, significantly
lower than those that can reasonably be measured in
conventional laboratory testing (Leroueil 2006). In order to
overcome this exertion and evaluate the creep process at very
low strain rates as observed in the field (order of 10
-10
%/s), a
new laboratory one-dimensional compression test method is
proposed by Kawabe and Tatsuoka (2013). The test procedure
consists of application of multiple unloading/reloading (UL/RL)
cycles with several sustained - creep - loading (SL) stages.
Figure 1 summarises the relationships between the creep strain
(for three hours) and the stress ratio between the stress at the
start of (UL) or (RL),
UL
or
RL
, and the stress at each (SL)
stage,
SL
obtained during multiple UL/RL cycles and several
numbers of SL stages on two samples of reconstituted soft
clays. The creep strain rates recorded during UL and RL cycles
are smaller than those during primary loading and they can
reach a very low level. Based on relations of this type, the stress
ratio corresponding to
a(creep)
Δ
= 0 can be deduced and based
Ibraim E.
