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General Report of TC 106
Unsaturated soils
Rapport général du TC 106
Sols non saturés
Jommi C.
Department of Geoscience and Engineering, Delft University of Technology, Delft, The Netherlands
Department of Civil and Environmental Engineering, Politecnico di Milano, Milano, Italy
ABSTRACT: This general report summarises the contributions on unsaturated soil mechanics submitted to the Discussion Session of
TC106 – Unsaturated soils –at the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering held in Paris in
September 2013. The thirty-five papers collected under the framework of unsaturated soil mechanics cover a broad spectrum of
problems and procedures at varying scales. Much attention is devoted to issues related to experimental techniques and procedures for
hydro-mechanical characterisation of unsaturated soils, with special attention to retention behaviour. Swelling, shrinkage and
eventually cracking are the processes which seem to capture most of the attention in view of the performance of engineering systems.
A few contribution deal with constitutive and numerical approaches, while only a couple of papers introduce unsaturated soil
mechanics into engineering practice. While innovative efforts are mainly addressed to experimental techniques in the laboratory, the
most challenging issues in future perspective appear to be related to the assessment of unsaturated geotechnical systems in the field,
including contaminated soils and mine tailings, besides to more traditional applications dealing with compacted soil structures and
soil-atmosphere interaction.
RÉSUMÉ : Ce rapport général résume les contributions sur les sols non saturés soumis à la Session de Discussion du TC106 - Sols
non saturés - du 18ème Congrès International de Mécanique des Sols et de Géotechnique tenu à Paris en Septembre 2013. Les trente
cinq articles collectés couvrent un large spectre de problèmes et de procédures à des échelles variées. Beaucoup d'attention est portée
aux aspects concernant les techniques expérimentales et les procédures de caractérisation hydro-mécanique des sols non saturés, avec
une attention spéciale pour les propriétés de rétention. Le gonflement, le retrait et la fissuration sont les problèmes qui semblent les
plus étudiés dans les applications géotechniques. Quelques contributions concernent les approches constitutives et numériques, alors
que seulement une paire d’articles introduit la mécanique des sols non saturés dans la pratique. Alors que des efforts novateurs
concernent principalement l'évaluation des techniques expérimentales dans le laboratoire, le défi des prochaines années semble
concerner l'évaluation des systèmes non saturés sur le terrain, incluant les sols contaminés et les résidus, en plus des applications plus
traditionnelles liées aux structures en sol compacté et aux interactions entre le sol et l'atmosphère.
KEYWORDS: unsaturated soils, laboratory and field testing, hydro-mechanical behaviour, assessment of geo-engineering systems
1 INTRODUCTION.
The number of papers presented to the Discussion Session
organised by the Technical Committee TC106 testifies the
interest of the geotechnical community in geo-engineering
problems related to unsaturated conditions. Papers on a broad
spectrum of aspects of unsaturated soils behaviour, coupled
hydro-mechanical processes, laboratory developments, field and
laboratory experimental techniques, and geotechnical problems
have been submitted. Researchers from all the continents
contribute to the session, although most of them come from
Europe, Asia – with the relevant participation of Japan with six
papers – and North America.
The thirty-five papers submitted to the Discussion Session
are summarised in Table 1, where a list of selected keywords
tries to provide a first glance on the topics which are capturing
most of the attention at present. It appears that lot of effort is
addressed to the hydraulic characterisation of unsaturated soils,
especially for what concerns experimental techniques and
procedures for the description of water retention behaviour, at
increasing scale, from the laboratory to the field and possibly
the regional scale. It might be argued that the first season of
unsaturated soil mechanics, in which the attention has been
focussed almost exclusively on the role of suction on the
mechanical behaviour of unsaturated soils, has come to an end.
The contributions presented to this conference suggest that the
mutual influence between the hydraulic history, in terms of both
suction and a measure of the amount of water retained in the
pores, and the strain history of the soil is considered of
paramount importance to understand and describe the peculiar
features of geo-engineering problems related to unsaturated
soils.
The hydro-mechanical behaviour of compacted soils is still
under investigation, both in static and dynamic conditions,
together with improvement techniques. Theoretical and
constitutive approaches are being evaluated as an extension to
unsaturated conditions of approaches previously conceived for
saturated soils. Coupled thermo-hydro-mechanical finite
element formulations are being consistently used, both to assess
the performance of new hydro-mechanical models, and to
predict the response of engineering systems.
Problems which have accompanied the history of
unsaturated soil mechanics, like constructions on expansive
soils or slope stability under rainfall infiltration, still deserve
some attention. Studying the conditions leading to cracking and
proper tracking and modelling of the cracking process is the
present challenge for unsaturated soils undergoing significant
volume changes, especially in view of climate changes. To this
end, the effects of vegetation on the behaviour of upper soil
horizons are being studied, to provide simple but effective
models for water balance and vertical displacements, accounting
for soil properties. Future challenges also come from fields
related to environmental geotechnics, like mine tailings and
waste repositories, where unsaturated soil mechanics is starting
to be exploited in a consistent way.
