Impatti, adattamento e vulnerabilita Le cause e le responsabilita dei cambiamenti climatici sono state trattate sul numero di ottobre della rivista Cda. Approfondiamo l’argomento presentando il documento: “Cambiamenti climatici 2007: impatti, adattamento e vulnerabilita” votato ad aprile 2007 dal secondo gruppo di lavoro del Comitato Intergovernativo sui Cambiamenti Climatici (Intergovernmental Panel on Climate Change). Si tratta del secondo di tre documenti che compongono il quarto rapporto sui cambiamenti climatici.

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Climate Change 2007: Impacts, Adaptation and Vulnerability.

This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (±10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan et al. [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise.

A Benchmark Study on the Thermal Conductivity of Nanofluids

Keywords: Mecanique des sols ; Drainage ; Ecoulement souterrain Reference Record created on 2004-09-07, modified on 2016-08-08

Applications of soil physics.

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Analysis of observed chaotic data

http://www.saetaequina.com/files/1-s2_0-S0950061811006763-main.pdf

A simple review of soil reinforcement by using natural and synthetic fibers

A new constant volume cell was developed, allowing the measurement of swelling pressure without any strain adjustment and any effect of the stiffness of the testing device. By employing this new cell, the swelling behavior of compacted soil specimen under different suctions (57, 38, 9 and 0 MPa) was investigated. The results show good repeatability, indicating the reliability of the new cell and validating the test procedures adopted. Moreover, the developed cell is quite convenient to study the long-term swelling behavior of soil since no load adjustment is necessary. The obtained results show that, during the progressive wetting by applying successively the suctions of 57, 39, 9 and 0 MPa, the swelling pressure increases to 0.17, 0.31, 0.46 and 0.89 MPa, respectively. The swelling pressure and the time required to reach equilibrium are function of suction. Vapour-wetting and water-wetting show different hydration mechanisms and result in different swelling behavior: the swelling pressure develops slowly and gradually to finally reach stabilization upon vapour-wetting, while it increases quickly to a peak value and followed by a small decrease upon water-wetting.

A New Apparatus for the Measurement of Swelling Pressure Under Constant Volume Condition

The swelling characteristics of bentonite play a very important role in ensuring the long-term stability and isolation of high-level radioactive waste (HLW) repositories. A custom-made test apparatus, capable of providing a range of boundary conditions, was designed to investigate the swelling behavior of bentonite. The imposed boundary conditions include constant mean stress (CMS), constant volume (CV) and an intermediate flexible boundary condition called constant stiffness (CS), which applies stress as a specified function of volume increase. The results show that boundary conditions significantly affect the swelling strain and swelling pressure of the bentonite tested. More specifically, the relationship between the range of boundary conditions provided and the corresponding swelling pressures are: CV > CS > CMS, while the relationship between the range of boundary conditions and the corresponding swelling strain is CMS > CS > CV. Based on these results, several swelling equilibrium limit (SEL) curves are developed to index the effect of boundary conditions on soil swelling potential. The methodology can be used to predict the final stress and volume states of bentonite during fluid infiltration under the range of boundary conditions possible in HLW repositories.

Influence of Stress-Strain Boundary Conditions on the Swelling Behavior of Bentonite

Drying‐induced soil curling is commonly observed in nature. In order to investigate the change of water distribution in soil caused by drying and curling, a series of drying tests is performed on thin soil layers in the laboratory. A discrete element model (DEM) is then proposed to simulate soil desiccation curling. The outermost particles are selected as the surface of the model to address the importance of surface evaporation. Moisture distribution change during drying is governed by both surface evaporation and moisture exchange between DEM particles. The results show that the model can capture the main features of the soil curling process from concave curling ( ∪ $\cup $ ) to convex curling ( ∩ $\cap $ ). The model enables variation in moisture gradient during the drying process. The trend of the curling development obtained from the model agreed well with the laboratory observation. A newly exposed surfaces in the model can provide a more realistic moisture distribution and influence the curling behavior. Generally, the drying‐induced soil curling process and extent are associated with the change in moisture gradient along the depth. The movement of tensile stress concentration change from the upper layer in the early drying stage to the lower part of the sample in the late drying stage is the intrinsic mechanical factor responsible for the initial concave curling deformation and the subsequent fallback and convex curling phenomenon. Curling deformation in the present model is compared with other existing explanations on desiccation curling. The influences of evaporation rate and hydraulic conductivity on the model performance were also discussed. It is found that a higher evaporation rate and a lower hydraulic conductivity would result in a higher extent of curling during drying.

Modeling of Drying‐Induced Soil Curling Phenomenon

An efficient microbial sealing of rock weathering cracks using bio-carbonation of reactive magnesia cement

• A new method to measure water content at soil surface is developed based on infrared thermal imaging technology. • The method is based on infrared thermal imaging technology. • For a given over-saturated soil, the interfacial temperature difference is a constant value. • The unsaturated water content is linearly related to the interfacial temperature difference. • The proposed method is validated using a cracked soil sample. In this study, infrared thermal imaging technology is adopted to measure water content at soil surface by calibrating the linear relationship between water content at soil surface and interfacial temperature difference of a given soil type. The method is suitable for the soil surface which is unsaturated. First of all, the theoretical considerations of the new method are introduced. Infrared thermal imaging technology can directly measure soil surface temperature and the difference between the soil surface temperature and the ambient temperature is named as the interfacial temperature difference. For over-saturated soils, at a certain environmental condition, the interfacial temperature difference of a given soil type is a constant value. For unsaturated soils, there is a linear relationship between water content at soil surface and interfacial temperature difference. For the tested four types of soils with different textures, all the values of R 2 for the linear fitting are greater than 0.9. Then, the water content at soil surface can be calculated based on the surface temperature measured by the infrared camera. Moreover, in this study, a cracked soil sample with an uneven surface water content field is tested for validating the feasibility of the proposed method. There is a good match between the data measured by the proposed method and traditional oven drying. It indicates that the proposed method can be used to obtain the distribution of water content on the soil surface and may provide a new idea for the future research on the spatio-temporal evolution characteristics of in-situ soil under climate change and provide a new choice for leakage detection of structures like dams, tunnels, etc. 

Chao-Sheng Tang

Papers

A New Apparatus for the Measurement of Swelling Pressure Under Constant Volume Condition

Influence of Stress-Strain Boundary Conditions on the Swelling Behavior of Bentonite

Modeling of Drying‐Induced Soil Curling Phenomenon

An efficient microbial sealing of rock weathering cracks using bio-carbonation of reactive magnesia cement

Measurement of water content at bare soil surface with infrared thermal imaging technology