Transport properties of the Callovo-Oxfordian clay rock under partially saturated conditions

International audienceA series of experiments were performed to characterize the permeability, the specific storage, the capillary pressure, the streaming potential coupling coefficient, and the electrical conductivity of a very low permeability Callovo-Oxfordian clay rock at different water saturations. The Callovo-Oxfordian formation is presently investigated as a potential host to store nuclear wastes because of its very low permeability (typically 10 nd at saturation) and high specific surface area. We first present the constitutive transport equations including an electrokinetic cross-coupling term in the generalized Darcy and Ohm constitutive equations. Then we present new experimental results using measurements of transient weight losses of samples submitted to a change in the relative humidity imposed by an automated humidity system in a hermetic chamber. These experiments are interpreted with a 1-D analytical model of the coupled hydromechanical and transport equations. The hydromechanical transport properties (relative permeability and specific storage) of this clay rock are investigated in the relative saturation range from 0.23 to 0.70. We demonstrate that below 30% in relative humidity, the flux of the vapor phase with respect to the flux of the liquid water phase cannot be neglected. The relative apparent permeability can be described by a simple power law relationship with the saturation. In addition, we measure the electrical conductivity and the streaming potential coupling coefficient at various saturations. The electrical conductivity is described by a model accounting for electrical double-layer contributions to surface conductivity. The measurement of the streaming potential coupling coefficient agrees with a power law model for the coupling coefficient versus the relative water saturation. A relationship between the exponent used to characterize the relative permeability and the second Archie's exponent used to describe the dependence of the electrical conductivity of the material with respect to the saturation is discussed

[Multiple cephalic deep granuloma annulare of children].

International audienceBACKGROUND:Deep granuloma annulare is a fairly rare variety of granuloma annulare. It is seen predominantly in children and mainly affects the anterior aspect of the legs and the top of the feet; cephalic presentation is rare. Below, we report three cases of deep granuloma annulare in children presenting solely at the cephalic extremity.PATIENTS AND METHODS:Case 1: a six-year-old boy presented 7 cutaneous nodules measuring 1 to 2cm that were flesh-coloured, insensitive to palpation, of hard consistency and deeply attached. The lesions were grouped together on the anterior half of the left temporal fossa. While spontaneous regression of the three nodules was noted in the month following cutaneous biopsy, these nodules recurred a few months later. Case 2: a four-year-old girl with five deep cephalic nodules measuring around one centimetre and the colour of normal skin were seen on her right temporal fossa. The child was lost to follow-up after biopsy. Case 3: a four-month-old infant was presenting some 15 deep cutaneous nodules arranged in linear fashion on the forehead next to the left temporal fossa. These nodules regressed spontaneously one month after biopsy. In all three cases, histological examination confirmed the diagnosis of deep granuloma annulare.DISCUSSION:There have been few published cases of multiple, cephalic, deep granuloma annulare at a single site in children. The condition has an extensive differential diagnosis that includes malignant tumours; in addition, histological confirmation is normally essential. Treatment is not qualified and therapeutic extension with clinical monitoring alone may frequently be recommended

Research Challenges Involving Coupled Flows in Geotechnical Engineering

Coupled fluid, chemical, heat, and electrical flows are common phenomena that arc relevant to a wide variety of applications in Geotechnical Engineering, including the use of engineered clay barriers for waste containment, electro-osmosis for soil consolidation, highly compacted bentonite buffers for high-level radioactive nuclear waste disposal, and electrokinetics for soil contaminant removal. among others. For all of these applications, a fundamental understanding of coupled flow phenomena is required, including the basis of the various phenomena. the potential effect of the phenomena on fundamental soil behavior, and the applicability of the phenomena in both natural and built environments. This chapter highlights some of the advances over the past approximate three decades, including the effects of osmotic phenomena (chemico-osmosis, electro-osmosis, and thermo-osmosis) on the mechanical behavior of clays, the formulations and measurement of coupled flow phenomena, the distinction between phenomenological and microscopic (physical-based) formalisms, and considerations with respect to both saturated and unsaturated soil conditions. Based on the description of these advances, research challenges pertaining lo the study of coupled flow phenomena for Geotechnical Engineering applications are identified