Investigating the Swelling Pressure of Compacted Crushed-Callovo-Oxfordian Claystone

International audienceThis paper presents an experimental study on the swelling pressure of heavily compacted crushed Callovo-Oxfordian (Cox) claystone at a dry unit mass d = 2.0 Mg/m3 using four different methods: constant-volume, swell-reload, zero-swell and adjusted constant-volume method. Results show that the swelling pressure varies in the range of 1-5 MPa and depends significantly on the test method. From the constant-volume tests, it is observed that the swelling behaviour during wetting is a function of the suction and depends on both the hydration paths and wetting conditions (e.g. vapour-wetting or liquid-wetting). The swelling pressure decreases significantly with saturation time. To identify the microstructure changes of specimens before and after wetting, mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) tests were performed. It is observed that, after wetting, the large inter-aggregate pores observed in the as-compacted specimen are no longer apparent; the whole pattern is characterized by a general swell of hydrated clay particles, rendering the soil more homogeneous. Results from MIP indicated that wetting caused a significant reduction of the entrance diameter of the dominant inter-aggregate pores from 2.1 to 0.5 m whereas intra-aggregate pores were not significantly influenced

Electrically switching transverse modes in high power THz quantum cascade lasers.

The design and fabrication of a high power THz quantum cascade laser (QCL), with electrically controllable transverse mode is presented. The switching of the beam pattern results in dynamic beam switching using a symmetric side current injection scheme. The angular-resolved L-I curves measurements, near-field and far-field patterns and angular-resolved lasing spectra are presented. The measurement results confirm that the quasi-TM(01) transverse mode lases first and dominates the lasing operation at lower current injection, while the quasi-TM(00) mode lases at a higher threshold current density and becomes dominant at high current injection. The near-field and far-field measurements confirm that the lasing THz beam is maneuvered by 25 degrees in emission angle, when the current density changes from 1.9 kA/cm(2) to 2.3 kA/cm(2). A two-dimension (2D) current and mode calculation provides a simple model to explain the behavior of each mode under different bias conditions

Self-potential dataset for mapping groundwater flow patterns in the Chaîne des Puys (Auvergne, France)

The present Self-Potential (SP) dataset acquired in the Chaîne des Puys is the result of four decades of measurements carried out by master's students, PhD students, researchers, and engineering offices under the auspices of the Laboratoire Magmas et Volcans (LMV) and the Observatoire de Physique du Globe de Clermont-Ferrand (OPGC). Acquired in the 1980s by Maurice Aubert and his collaborators (e.g. [1–3]), this Self-Potential dataset was completed as part of the CAPRICE project focused on the hydrosystem of the Chaîne des Puys. The methodology and equipment used for data acquisition has remained unchanged since the first measurement in 1987. As a result, this dataset compiles more than 20,000 SP measurements and covers an area of almost 200 km².The SP data are intended to serve as the basis for geological models, coupled with geological and other geophysical data, according to the method described in Aubert and Atangana, 1996. After interpolation, SP data can be used to identify preferential groundwater flow paths and to delineate the surface of hydrogeological watersheds. As indicated in the literature, they also be used to identify possible recharge zones or areas of permeability contrast

Les troubles sémantiques au stade prodromal de la maladie d'Alzheimer [Semantic deficits in prodromal Alzheimer's disease]

International audienc

Water retention and transfer properties of a Green roof volcanic substrate

The water retention curve and the hydraulic conductivity function of a volcanic coarse granular material used as a substrate in an urban green roof in the Paris area was carried out on a newly developed device, in which low suctions were controlled. In the same cell, a hanging column system was used for controlling smaller suctions (up to 32 kPa) and the axis translation technique for larger suctions (up to 50 kPa). Water exchanges were monitored in connected tubes by using a high accuracy differential pressure transducer. The step changes in suction were also used to determine the hydraulic conductivity function by means of Gardner’s method, accounting for the impedance effects due to the high air entry value ceramic porous disk with Kunze and Kirkham’s method. van Genuchten and Brooks and Corey models were used for the water retention curve, but the hydraulic conductivity functions derived from these expressions appeared to lead to a significant under-estimation, confirming the need of operational and simple device for the experimental determination of the hydraulic conductivity function

A new hollow cylinder triaxial cell to study the behavior of geo-materials with low permeability

International audienceA new hollow cylinder triaxial cell (60 mm internal diameter and 100 mm external diameter) has been designed to study the behavior of low permeability saturated geo-materials such as stiff clays or argillites under controlled temperature and pore pressure conditions. The main advantage of this device is the short drainage path allowed by the hollow cylinder geometry that is reduced to half the thickness of the sample (10 mm)--four times less than that of standard full cylinder samples of 78 mm height. The reduced drainage path allows a significantly faster resaturation procedure of initially unsaturated samples compared to conventional full cylindrical samples. It also permits the achievement of drained conditions (i.e. negligible excess pore pressure during testing) with a higher loading rate. A numerical simulation of the saturation process demonstrates that the resaturation of the hollow cylinder clay sample can be achieved almost 30 times faster than in standard full samples that are drained at one end, and about seven times faster than in samples drained at both ends. Appropriate loading rates to be used in drained tests on stiff clays and argillites are also discussed based on a numerical simulation of the isotropic compression test. The effect of the deformability of the drainage system on the measured parameters during undrained tests is also analyzed. A correction method is proposed, based on the work of Bishop, by considering the deformability of the porous elements and of the drainage system

Cortical electrophysiological markers of language abilities in children with hearing aids: a pilot study

Objective. To investigate cortical auditory evoked potentials (CAEPs) in pediatric hearing aid (HA) users, with and without language impairment. Design. CAEPs were measured in 11 pediatric HA users (age: 8–12 years) with moderate bilateral sensorineural hearing loss (HL); participants were classified according to language ability. CAEPs were also measured for a control group of 11 age-matched, normal-hearing (NH) children. Results. HL children without language impairment exhibited normal CAEPs. HL children with language impairment exhibited atypical temporal CAEPs, characterized by the absence of N1c; frontocentral responses displayed normal age-related patterns. Conclusion. Results suggest that abnormal temporal brain function may underlie language impairment in pediatric HA users with moderate sensorineural HL

A new approach of accounting for impedance effects in Gardner’s method of determining the hydraulic conductivity of unsaturated soils

Based on tests carried out on a specific device allowing to determine the water retention and transport properties of granular media at low suctions, an alternative approach to Kunze and Kirkham’s method of accounting for the impedance effects due to the high air entry value ceramic disk when using Gardner’s method is proposed. Impedance effects are accounted for by proposing analytical solutions to the equations governing water transfers occurring within the specimen and the ceramic disk. By using some experimental data obtained on a volcanic granular substrate used for urban green roofs, the method is successfully compared to Kunze and Kikham’s graphical method. Its advantages are to be simpler of use and not operator dependent. A detailed examination of the performance of our method compared to those of Gardner and Kunze and Kirkham is carried out based on experimental data, that confirm its validity

A Device for the Simultaneous Determination of the Water Retention Properties and the Hydraulic Conductivity Function of an Unsaturated Coarse Material; Application to a Green-Roof Volcanic Substrate

International audienceThe determination of the water retention curve (WRC) and hydraulic conductivity function (HCF) of a specific volcanic coarse granular material used as a substrate for urban green roofs in Europe was carried out on a newly developed specific device in which low suctions, typical of coarse granular materials, were controlled. Smaller suctions (up to 32 kPa) were imposed by using a hanging column system, and larger suctions (between 32 and 50 kPa) were imposed by using the axis translation technique in the same cell. The changes in suction during the tests were monitored by using a high accuracy differential pressure transducer. They were also used to determine the HCF by means of both Kunze and Kirkham’s and Gardner’s methods. The former technique was used at low suctions (<4 kPa) to account for the impedance effects due to the high air entry value ceramic porous disk and the latter was used between 4 and 50 kPa. Good comparability was observed in the data from both methods, demonstrating the good performance of the device. The mathematical expressions of the WRC of van Genuchten and Brooks and Corey were used, and a good fitting with our experimental data was obtained. Conversely, the HCFs derived from these expressions appeared to lead to a significant underestimation, confirming the need of an operational and simple device for the experimental determination of the HCF. Also, this material proved to be an appropriate material for green urban infrastructures, because of its lightweight, satisfactory water retention capability and hydraulic conductivity

Two Improvements to Gardner's Method of Measuring the Hydraulic Conductivity of Non‐saturated Media: Accounting for Impedance Effects and Non‐constant Imposed Suction Increment

International audienceGardner's (1956, https://doi.org/10.2136/sssaj1956.03615995002000030006x) transient method of measuring the hydraulic conductivity function of unsaturated media has been largely used, together with the improved graphical method proposed by Kunze and Kirkham (1962, https://doi.org/10.2136/sssaj1962.03615995002600050006x) to account for the impedance effect resulting from using a low hydraulic conductivity ceramic disk in porous plate testing. These methods are nowadays seldom used, since they have been replaced by numerical back analysis and methods for parameter optimization. Based on tests carried out on a specific device allowing to determine the water retention and transport properties of water in a coarse granular media at low suctions (up to 50 kPa), it was found necessary to account (i) for impedance effects and (ii) for the effects of nonconstant suction increments, as is often the case when using the hanging column technique. A new method is proposed to account for impedance effects, based on an analytical solution of the equations governing water transfer. The validity of this method is tested by considering experimental data from three distinct materials: a coarse green roof volcanic substrate, poorly graded sand, and undisturbed silty clay. Compared to the graphical method Kunze and Kirkham's method, it is less operator‐dependent and hence more objective. It is also simpler than numerical back analysis methods, since it does not require any use of numerical code or parameter optimization algorithm, providing a more direct and reliable access to the hydraulic conductivity. An analytical solution is also proposed to solve the problem resulting from the application of a nonconstant suction increment