Chemo-mechanical behaviour of non-expansive clays accounting for salinity effects

Changes in the chemistry of the pore fluid are known to impact on the hydro-mechanical behaviour of clays. Experimental evidence collected in the last decades led to the formulation of constitutive chemo-mechanical models for expansive soils used in engineering practice for the containment of pollution, such as bentonite. Less attention has been paid to modelling the chemo-mechanical behaviourof non-expansive clays, less frequently used for geoenvironmental applications, but equally exposed to chemical changes. Key differences between the impact of salinity on the fabric of expansive and non-expansive clays are pointed out. At the macroscopic scale, an increase in salinity causes a translation of the Normal Compression Line of non-expansive clays to higher void ratios, which in some cases is also accompanied by an increase in compressibility. The opposite occurs for expansive clays. These experimental evidences provide the basis for a chemo-mechanical model formulated in the frame of elasto-plasticity with generalised hardening, whose yield surface expands with pore fluid concentration. The model is validated against experimental results, both original and from the literature. Simulation results compare very well with those of tests performed on reconstituted, compacted and intact samples

Nefroprevención en el paciente muy anciano

Nephroprevention consists of a set of measures to attempt to prevent or slow kidney damage. Primary nephroprevention is the term used when such measures seek to reduce the risk of  installing an acute renal failure; and secondary prevention or nephroprotection is used when attempting to slow the progression of chronic renal failure. Regarding nephroprotection, the measures implemented for this purpose in young and very elderly (age>75 years) patients are often similar, based on the modulation of the diet, blood pressure levels, hemoglobin and glycosylated hemoglobin, and the type and dose of medication delivered. However, given that those objectives can induce complications in the very elderly, less strict targets must be sought,while respecting certain well-defined limits.La nefroprevención es un conjunto de medidas destinadas a intentar prevenir o ralentizar el daño renal, soliéndose emplear el término nefroprevención primaria cuando dichas medidas buscan reducir el riesgo de instalación de una insuficiencia renal aguda; y el de prevención secundaria o nefroprotección, cuando pretenden enlentecer la progresión de una insuficiencia renal crónica. Con respecto a la nefroprotección, las medidas implementadas para tal fin, en pacientes jóvenes y muy ancianos (edad >75 años), suelen ser similares, basadas en la modulación de la dieta, cifras de tensión arterial, valores de hemoglobina y hemoglobina glicosilada, así como en el tipo y dosis de medicación suministrada. Sin embargo, dado que dichos objetivos pueden inducir complicaciones en los muy ancianos, deben muchas veces buscarse objetivos más laxos, aunque respetando ciertos límites bien definidos

Numerical investigation on water exchange of shale samples

Interest in the hydraulic and mechanical characterization of shales has grown in recent years, because of their application in the context of energy geotechnics. In the frame of nuclear waste disposal shales are considered as host formations for the placements of nuclear waste at high depths. In the frame of hydrocarbon production they are considered as unconventional reservoirs, from which extracting natural gas. Understanding how fluids flow through shales is then a key aspect for both fields of application. This paper focuses on the analysis of the transport of water vapour through laboratory samples. After reviewing the balance and flow laws that govern the transport of fluid in unsaturated porous media, a simplified model is put forward. The model was implemented in a commercial finite element code, and it was used to reproduce the results of a literature study on wetting and drying of Opalinus Clay shale samples, imposed through the vapour equilibrium technique. Back analysis of the water content and volume strains of these specimens suggests that existing models underestimate the actual flow rate of water vapour which takes place at low suctions. The current interpretation also seems to be consistent with microstructural investigations on the interconnection between large pores of this material