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

The Ljapunov-Schmidt reduction for some critical problems

This is a survey about the application of the Ljapunov-Schmidt reduction for some critical problems

Effects of curing on the hydro-mechanical behaviour of cement-bentonite mixtures for cut-off walls

Cement-bentonite cut-off walls are commonly employed in geoenvironmental applications to limit ground water flow and pollutant transport. The wide diffusion of this artificial material in the current practice is not only due to its low permeability, but also to its simplicity of use. In this paper, experimental evidences about the role of curing on the hydro-mechanical behaviour of cement-bentonite mixtures are presented. Different curing times and curing conditions (representative for either water saturated or hydrocarbon polluted soils) have been considered, and their effects on both hydraulic conductivity and mechanical response in oedometer and triaxial conditions have been assessed. A unified hydro-mechanical framework, accounting for the changes of material fabric occurring with curing time and environment, is formulated. The hydraulic conductivity is very well predicted by a Kozeny-Carman like equation, whereas the mechanical behaviour is finely reproduced via an enhanced elastic–plastic constitutive model