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

Coherence susceptibility as a probe of quantum phase transitions

We introduce a coherence susceptibility method, based on the fact that it signals quantum fluctuations, for identifying quantum phase transitions, which are induced by quantum fluctuations. This method requires no prior knowledge of order parameter, and there is no need for careful considerations concerning the choice of a bipartition of the system. It can identify different types of quantum phase transition points exactly. At finite temperatures, where quantum criticality is influenced by thermal fluctuations, our method can pinpoint the temperature frame of quantum criticality, which perfectly coincides with recent experiments.Comment: Accepted versio

On-sample water content measurement for a complete local monitoring in triaxial testing of unsaturated soils

To provide a complete local monitoring of the state of an unsaturated soil sample during triaxial testing, a local water content measurement device was adapted to a triaxial device comprising the measurement of local displacements (Hall effect transducers) and suction (High capacity transducer). Water content was locally monitored by means of a resistivity probe. The water content/resistivity calibration curves of an intact natural unsaturated loess from Northern France extracted by block sampling at two depths (1 and 3.3 m) were carefully determined, showing good accuracy and repeatability. The validity of two models giving the resistivity of unsaturated soils with respect to their water content was examined

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

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