3,241 research outputs found
Modelling the thermo-mechanical volume change behaviour of compacted expansive clays
Compacted expansive clays are often considered as a possible buffer material
in high-level deep radioactive waste disposals. After the installation of waste
canisters, the engineered clay barriers are subjected to
thermo-hydro-mechanical actions in the form of water infiltration from the
geological barrier, heat dissipation from the radioactive waste canisters, and
stresses generated by clay swelling under almost confined conditions. The aim
of the present work is to develop a constitutive model that is able to describe
the behaviour of compacted expansive clays under these coupled
thermo-hydro-mechanical actions. The proposed model is based on two existing
models: one for the hydro-mechanical behaviour of compacted expansive clays and
another for the thermo-mechanical behaviour of saturated clays. The elaborated
model has been validated using the thermo-hydro-mechanical test results on the
compacted MX80 bentonite. Comparison between the model prediction and the
experimental data show that this model is able to reproduce the main features
of volume changes: heating at constant suction and pressure induces either
expansion or contraction; the mean yield stress changes with variations of
suction or temperature
Development of a Large Scale Infiltration Tank for Determination of the Hydraulic Properties of Expansive Clays
International audienceA large-scale infiltration tank was developed to study the water transfer in compacted expansive clay. Volumetric water content sensors were buried in a soil column for water content monitoring during infiltration. In addition to water content, soil suction and temperature at various locations and the heave at the soil surface were also monitored. Emphasis was put in minimizing the effect of sensors installation on water transfer and soil deformation. The results obtained for 338-days of infiltration were presented in terms of changes of suction, volumetric water content, temperature and the soil heave. Based on the recorded data, the performance and limitation of different suction and volumetric water content sensors and the adopted test procedure were analyzed. The recorded data on soil suction and volumetric water content were finally analyzed for determining the unsaturated hydraulic properties of soil such as the water retention curve and the unsaturated hydraulic conductivity. Note also that the results constitute useful data for further physical analysis or numerical models calibration
An evaluation of the osmotic method of controlling suction
Experimental techniques of testing the mechanical properties of unsaturated
soils are complex and difficult to conduct. As a consequence, complete sets of
parameters that characterise the behaviour of unsaturated soils remain scarce
and necessary. In this context, it has been found useful to gather the
information obtained after some years of practice of the osmotic technique of
controlling suction. As compared to the more documented axis-translation
technique, the osmotic technique has its own advantages and drawbacks that are
discussed in this paper, together with some potential future developments. The
osmotic method has been developed by soil scientists in the 1960s and adapted
to geotechnical testing in the early 1970s. This paper presents the osmotic
technique and comments on its advantages (including suction condition close to
reality and higher suctions easily attained) and drawbacks (including some
concern with the membrane resistance and some membrane effects in the
suction/concentration calibration). Various applications to geotechnical
testing are presented such as the determination of the water retention curve,
oedometer and triaxial testing procedures and the determination of the
permeability of unsaturated soils. Recent developments, that include the
extension of the method up to high suctions (10 MPa) are also described,
together with some recent and novel applications such as data from high
controlled suction oedometer compression test and the determination of the
oil/water retention properties of oil reservoir chalks
The influence of changes in water content on the electrical resistivity of a natural unsaturated loess
Non-destructive methods of measuring water content in soils have been
extensively developed in the last decades, especially in soil science. Among
these methods, the measurements based on the electrical resistivity are simple
and reliable thanks to the clear relationship between the water content and the
electrical resistivity of soils. In this work, a new electrical resistivity
probe was developed to monitor the change in local water content in the
triaxial apparatus. The probe is composed of two-pair of electrodes, and an
electrical current is induced through the soil at the vicinity of the contact
between the probe and the specimen. Some experimental data on the changes in
resistivity with the degree of saturation were obtained in specimens of a
natural unsaturated loess from Northern France. Two theoretical models of
resistivity were also used to analyze the obtained data. Results are finally
discussed with respect to the loess's water retention properties
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