Swelling behaviour of compacted Maryland clay under different boundary conditions

This paper presents an experimental study on the swelling response of compacted Maryland clay specimens subjected to hydration under a range of boundary conditions. The research is multi-scale with swelling tests complemented by comprehensive mercury intrusion porosimetry analyses. The objective of the experimental programme is to establish the locus of final swollen states (in terms of void ratio and swelling pressure) and assess its robustness by testing a range of boundary conditions or combinations thereof. Five initial soil conditions were tested and swelling was generated by flooding or incremental suction reduction by way of the osmotic technique. The paper shows that, for a given soil condition, there is no influence of the stress–volume path on the final swollen state. This observation was corroborated at the microscopic level by the mercury intrusion porosimetry. It was concluded that the effect of different stiffness can actually be analysed in terms of the maximum stress applied to the specimen. In particular, a clear correlation was identified between the macroscopic strains and the confinement applied during the test, regardless of the boundary conditions. Also, the conceptual model relating the water ratio and micro void ratio proposed by E. Romero and co-workers in 2011 was found to prevail, regardless of the boundary conditions.Peer ReviewedPostprint (author's final draft

Hydro-Mechanical Modelling of Multiphase Flow in Coalbed by Computational Homogenization

peer reviewedA multiscale model is developed for the modelling of coalbed methane (CBM) production. CBM recovery is known to be a highly coupled and multiphase problem. The finite element square method is used to integrate a fracture-scale model in a multiscale scheme. This method consists to localize the macroscale deformation to the microscale, then resolve the boundary value problem on the microscale with finite elements, then homogenize the microscale stresses to compute macroscopic quantities, and finally resolve the boundary value problem on the macroscale with finite elements. This approach has the advantage that it does not require to write some constitutive laws at the macroscale but only at the REV-scale. The multiscale model is therefore appropriate for reservoir modelling. The model is developed and implemented in a finite element code and the simulation of a synthetic reservoir is considered

A New Technique for Deep in situ Measurements of the Soil Water Retention Behaviour

In situ measurements of soil suction and water content in deep soil layers still represent an experimental challenge. Mostly developed within agriculture-related disciplines, field techniques for the identification of soil retention behaviour have been so far employed in the geotechnical context to monitor shallow landslides and seasonal volume changes beneath shallow foundations, within the most superficial ground strata. In this paper, a novel installation technique is presented, discussed and assessed, which allows extension of the use of commercially available low-cost and low-maintenance instruments to characterise deep soil layers. Multi-depth installations have been successfully carried out using two different sensor types to measure the soil suction and water content up to 7\u2009m from the soil surface. Preliminary laboratory investigations were also shown to provide a reasonable benchmark to the field data. The results of this study offer a convenient starting point to accommodate important geotechnical works such as river and road embankments in the traditional monitoring of unsaturated soil variables

Advances in constitutive modelling of jointed rock hydro mechanical interactions at laboratory scale

Cette étude s’inscrit dans une recherche multi échelles basée sur des expérimentations in situ et des essais de laboratoire. Les essais, injections radiales d’eau au centre de l’éponte inférieure, sont fait à contrainte normale constante de 0 à 110 MPa et pour des pressions de 0 à 4 MPa. Quatre essais hydromécaniques ont été réalisés au laboratoire L3S sur des échantillons de calcaire fracturé (deux diaclases et deux joints de stratification). L’analyse des mesures montre une corrélation entre les variations de la surface de contact et le débit hydraulique dans la fracture. La modélisation hydromécanique réalisée à l’aide du code 3DEC peut être améliorée à partir de l’analyse précédente à travers la modification de la relation entre l’ouverture hydraulique et la fermeture mécanique du joint. L’écart entre les valeurs mesurées et calculées est lié en particulier à la dégradation des aspérités de la fracture sous forte contrainte et à la turbulence des écoulements non prises en compte dans la modélisation

High Capacity Tensiometers: performance and behaviours

High capacity tensiometers (HCT) allow the direct measurement of soil matric suction, and their major limitation is the occurrence of cavitation. In this paper HCT designs using different ceramic filters with varied air entry values (AEV), varied reservoir sizes, and different pressure transducers are assessed as to determine the impact that each component may have in the HCT performance. Moreover, the effectiveness of first saturation and resaturation processes is discussed in relation to the time required to prepare/recover HCTs. The results obtained with the different designs show that the measuring range is directly linked to the AEV of the ceramic filter and that the choice of materials used for the various components may affect the reliability of measurements in field installations if the thermal performance is not accounted for in the calibration procedure. The use of a 1hr high vacuum pre-stage followed by overnight water pressurisation at pressures equal or above the AEV of the ceramic filter was found to be the quickest process to fully saturate an HCT for the first time. While resaturation time for an HCT can be reduced to as little as a few minutes if the HCT is resaturated immediately after cavitation has occurred.Postprint (published version

Lyapunov spectrum of asymptotically sub-additive potentials

For general asymptotically sub-additive potentials (resp. asymptotically additive potentials) on general topological dynamical systems, we establish some variational relations between the topological entropy of the level sets of Lyapunov exponents, measure-theoretic entropies and topological pressures in this general situation. Most of our results are obtained without the assumption of the existence of unique equilibrium measures or the differentiability of pressure functions. Some examples are constructed to illustrate the irregularity and the complexity of multifractal behaviors in the sub-additive case and in the case that the entropy map that is not upper-semi continuous.Comment: 44 page

Fractal analyses reveal independent complexity and predictability of gait

Locomotion is a natural task that has been assessed for decades and used as a proxy to highlight impairments of various origins. So far, most studies adopted classical linear analyses of spatio-temporal gait parameters. Here, we use more advanced, yet not less practical, non-linear techniques to analyse gait time series of healthy subjects. We aimed at finding more sensitive indexes related to spatio-temporal gait parameters than those previously used, with the hope to better identify abnormal locomotion. We analysed large-scale stride interval time series and mean step width in 34 participants while altering walking direction (forward vs. backward walking) and with or without galvanic vestibular stimulation. The Hurst exponent α and the Minkowski fractal dimension D were computed and interpreted as indexes expressing predictability and complexity of stride interval time series, respectively. These holistic indexes can easily be interpreted in the framework of optimal movement complexity. We show that α and D accurately capture stride interval changes in function of the experimental condition. Walking forward exhibited maximal complexity (D) and hence, adaptability. In contrast, walking backward and/or stimulation of the vestibular system decreased D. Furthermore, walking backward increased predictability (α) through a more stereotyped pattern of the stride interval and galvanic vestibular stimulation reduced predictability. The present study demonstrates the complementary power of the Hurst exponent and the fractal dimension to improve walking classification. Our developments may have immediate applications in rehabilitation, diagnosis, and classification procedures

Development and Validation of a New Near-Infrared Sensor to Measure Polyethylene Glycol (PEG) Concentration in Water

A near-infrared absorption based laser sensor has been designed and validated for the real-time measurement of polyethylene glycol (PEG) concentration. The wavelength was selected after the determination of the absorption spectrum of deionised water and PEG solutions using a Varian Cary 6000i spectrophotometer, in order to limit the influence of PEG molecular mass on the absorption measurement. With this new sensor, the water is treated as the attenuating species and the addition of PEG in water reduces the absorbance of the medium. The concept was validated using three different PEG types (PEG 6,000, 20,000, and 35,000) and it was found that the results follow Beer Lambert’s law. The influence of temperature was assessed by testing the PEG 20,000 at four different temperatures that could be encountered in a laboratory environment. The data show a slight temperature influence (increase of absorbance by 8% when the temperature rises from about 20 to about 29 degrees). Following the validation phase conducted ex situ, a prototype of an immersible sensor was built and calibrated for in situ measurements