Unsaturated Samples Research Articles

Thermal Conductivity of Standard Sands. Part III. Full Range of Saturation

The thermal conductivity $$(\lambda )$$ of three unsaturated standard quartz sands (Ottawa C-109 and C-190, and Toyoura) was measured by a transient thermal-conductivity probe, at room temperature of approximately $$25\,^{\circ }\text{ C }$$ and at loose and tight compactions. The measurements were carried out at different degrees of saturation $$(S_\mathrm{r})$$ from dryness to full saturation. In general, a sharp $$\lambda $$ increase was observed at low $$S_\mathrm{r}$$ , followed by a moderate rise until full saturation. However, experiments on loosely compacted C-190 samples revealed $$\lambda $$ deviation from a general trend ( $$\lambda $$ vs $$S_\mathrm{r})$$ caused by water percolation. Alternatively, successful experiments were carried out on loosely packed unsaturated C-190 samples using 1 % agar gel. For loosely compacted C-109 and Toyoura, $$\lambda $$ data obtained from 1 % agar gel closely agreed with $$\lambda $$ data for water as a saturation medium. The measured data were used to verify a model by de Vries for unsaturated soils. The model largely underestimates experimental data at $$S_\mathrm{r}<0.5$$ and produces an overall root-mean-square error of about $$0.2\, \text{ W }~{\cdot }~\text{ m }^{-1}~{\cdot }~\text{ K }^{-1}$$ . Measured $$\lambda $$ data agreed with data by a steady-state technique (a guarded hot-plate apparatus) at dryness and full saturation and exceeded the steady-state data in the unsaturated region. However, TCP data can be considered more reliable due to a lower temperature increase during $$\lambda $$ measurements and a shorter testing time. Consequently, in the case of unsaturated soils, evaporation and migration of water and steam can be avoided.

Hydrogen absorption cracking of zirconium alloy in the application of nuclear industry

The hydrogen absorption cracking behavior of Zr-4 has been investigated based on the microstructure, hydrogen absorption amount as well as residual stress. The results show that the grain size has a pronounced effect on the hydrogen absorption cracking, with the increase of grain size from 30 μm to 500 μm, the cracks vary from small cracks of independence to large cracks that connect with each other along the radial direction. The unsaturated hydrogen absorption samples which consist of γ- and δ-hydrides present a crack-free surface while the saturated hydrogen absorption samples which consist of ɛ-hydride exhibit not only large cracks but also bulges on the surface. The hydride decomposition temperatures of ɛ → δ and δ → α during dehydriding are determined to be about 600 °C and 700 °C respectively. In the unsaturated hydrogen absorption samples, both the thickness expansion and radial residual stress present a positive liner correlation with the hydrogen absorption amount. Based on the experimental results a mechanism of hydrogen absorption cracking is proposed in zirconium alloys.

Comparación Entre La Composición Química Y Las Propiedades Antiinflamatorias Del Sebo De Carnero De Origen Cubano Y Del Sahara

Según CLAUS y TYLER, 1998, el sebo de carnero, corresponde a la grasa interna del abdomen de la oveja Ovisaries L (Fam. Bóvidae, purificada por fusión y filtrado que contiene entre 70-80 % de la mezcla de ácido esteárico y ácido palmítico y 20-30 % de ácido oleico con propiedades emolientes y uso como base para ungüentos que necesitan más consistencia que la obtenida con otros ingredientes utilizados con estos fines. En Cuba, se utiliza en fricciones para aliviar procesos inflamatorios según la medicina tradicional, por lo que se decidió realizar una comparación entre el sebo procedente de Cuba con el sebo obtenido de la región del Sahara donde tiene el mismo uso popular y evaluar en ambos su composición química así como el efecto antiinflamatorio popularmente descrito para los mismos. En el presente trabajo se realiza un análisis por CG-EM de las muestras transmetiladas. El sebo procedente de Cuba tiene un 49,8 % de ácidos grasos saturados frente a 59,3 % el del Sahara y 36,1 % y 27,7 % de ácidos grasos insaturados respectivamente. Comparando con la indometacina, utilizada como control positivo, en el ensayo de la inducción de la inflamación por carragenina, se encontró que el sebo procedente de Cuba tiene aproximadamente 40 % menos de actividad antiinflamatoria que el procedente del Sahara e igual resultado que la indometacina utilizada como control positivo.

A new physical model for the pressure sensitivity of unconsolidated sands

Knowledge of the pressure dependencies of rock properties in unconsolidated sands is important for accurate time-lapse feasibility studies, pore pressure prediction, and reservoir characterization. A key problem that arises in determining such pressure dependencies is an accurate model at low effective stress. We propose a double exponential model to describe the pressure sensitivity of the bulk modulus (K) or shear modulus (G) for unconsolidated sands. The physical basis for our model relies on observed porosity-depth trends in unconsolidated sands, and the concept of critical porosity. Our new model matches laboratory measurements on unsaturated sand samples that have a range of grain size distributions and compositions. Grain size distribution data is first used to estimate critical porosity, which is then used as a zero effective pressure constraint in the data fitting process. We show that our new model more accurately predicts pressure sensitivity near zero-effective pressure compared to current methods, and is thus more accurate for situations in which core measurements at low effective stresses are not available.

Dynamic characteristics of lime-treated expansive soil under cyclic loading

To better understand the dynamic properties of expansive clay treated with lime, a series of laboratory tests were conducted using a dynamic triaxial test system. The influential factors, including moisture content, confining pressure, vibration frequency, consolidation ratio, and cycle number on the dynamic characteristics were discussed. Experimental results indicate that specimens at low moisture contents tend to damage along the 30° shear plane and they present brittle failure, while saturated specimens show swelling phenomenon and plastic failure. A reduction in cohesion has been observed for unsaturated samples at large number of cycles, while it is opposite for the internal friction angle. For the saturated specimens, both the cohesion and internal friction angle decrease with increasing number of cycles.

Estimation of the hydraulic parameters of unsaturated samples by electrical resistivity tomography

In situ and laboratory experiments have shown that electrical resistivity tomography (ERT) is an effective tool to image transient phenomena in soils. However, its application in quantifying soil hydraulic parameters has been limited. In this study, experiments of water inflow in unsaturated soil samples were conducted in an oedometer equipped to perform three-dimensional electrical measurements. Reconstructions of the electrical conductivity at different times confirmed the usefulness of ERT for monitoring the evolution of water content. The tomographic reconstructions were subsequently used in conjunction with a finite-element simulation to infer the water retention curve and the unsaturated hydraulic conductivity. The parameters estimated with ERT agree satisfactorily with those determined using established techniques, hence the proposed approach shows good potential for relatively fast characterisations. Similar experiments could be carried out on site to study the hydraulic behaviour of the entire soil deposit.

On-sample water content measurement for a complete local monitoring in triaxial testing of unsaturated soils

To provide a complete local monitoring of the state of an unsaturated soil sample during triaxial testing, a local water content measurement device was adapted to a triaxial device comprising the measurement of local displacements (Hall effect transducers) and suction (high-capacity transducer). Water content was locally monitored by means of a resistivity probe. The water content/resistivity calibration curves of an intact, natural, unsaturated loess from northern France extracted by block sampling at two depths (1 and 3·3 m) were carefully determined, showing good accuracy and repeatability. The validity of two models giving the resistivity of unsaturated soils with respect to their water content was examined. The first triaxial tests carried out with this device in the range of in situ stresses gave satisfactory results, but with some effects of the applied cell stress on the water content measurements. Some preliminary behaviour characteristics of the natural unsaturated loess, a material rarely tested up to now in the literature, were evidenced. Also, the yield stresses appeared significantly higher than the in situ stresses, confirming the combined effect of partial saturation and bonding.

Determination of the Shear Strength of Unsaturated Loess Based on the Fractal Model Theory of Unsaturated Soils

The shear strength value of unsaturated loess is required in the design in geotechnical engineering in the North and the North West of China. In 2004, a new method, that is the fractal model theory, was proposed for determining the shear strength of unsaturated soil. Based upon the fractal model theory, the surface fractal dimension DS and the air entry value of two unsaturated loess samples are obtained from their soil-water characteristic curve (SWCC), the shear strength contribution due to matric suction of the two loess samples is determined, a new approach for determination of the shear strength of unsaturated loess with its SWCC is presented. By comparing results of this paper with those of the laboratory tests, the relationship between the SWCC and the shear strength of unsaturated loess is discussed and the validity of the fractal model theory for unsaturated loess is explained.

A study of the correlation between electrical resistivity and matric suction for unsaturated ash-fall pyroclastic soils in the Campania region (southern Italy)

In the territory of the Campania region (southern Italy), critical rainfall events periodically trigger dangerous fast slope movements involving ashy and pyroclastic soils originated by the explosive phases of the Mt. Somma-Vesuvius volcano and deposited along the surrounding mountain ranges. In this paper, an integration of engineering-geological and geophysical measurements is presented to characterize unsaturated pyroclastic samples collected in a test area on the Sarno Mountains (Salerno and Avellino provinces, Campania region). The laboratory analyses were aimed at defining both soil water retention and electrical resistivity curves versus water content. From the matching of the experimental data, a direct relationship between electrical resistivity and matric suction is retrieved for the investigated soil horizons typical of an ash-fall pyroclastic succession. The obtained relation turns out to be helpful in characterizing soils up to close saturation, which is a critical condition for the trigger of slope failure. In such a regime, the water content and the matric suction have small variations, while electrical resistivity variations can be appreciated in a larger range of values. For this reason, besides suction measurements on very small soil volumes through classical tensiometers, our analyses suggest the direct monitoring of in situ electrical resistivity values as an effective tool to recognise the hydrological state of larger and more representative soil volumes and to improve early warning of dangerous slope movements.

Towards a Tensiometer Based Suction Control System for Laboratory Testing of Unsaturated Soils

Abstract This paper presents the development of an automated tensiometer based suction control system for testing unsaturated soil samples. The system is able to dry and wet soil, while measuring suction (pore water pressure – air pressure) and water content. The system uses air circulation within a closed loop to dry the soil, or water injection to wet the soil, to achieve the required pore water pressure while the air pressure is kept atmospheric. Pore water pressure is controlled by using a feedback computer system that dries or wets soil samples according to measurements obtained from sample-mounted high suction tensiometers. Excess moisture in the air circulation loop is captured by an in-line moisture trap consisting of a sealed cell containing a desiccant (silica gel), which is placed on an electronic balance to give continuous measurements of retained water. Changes of the sample water content are measured as the difference between the amount of water injected and that retained by the moisture trap. The system is fully automated and runs controlled by software with minimum assistance. The proposed suction control system presents advantages over the conventional axis translation technique as it avoids the need for elevated pore air pressures and hence better replicates the natural processes of wetting and drying of soils. The system was developed for use in a triaxial cell, but could also be used with other instruments and for the determination of water retention curves.

Swelling kinetics of unsaturated polyester and their montmorillonite filled nanocomposite synthesized from glycolyzed PET

The solvent resistance properties of the unsaturated polyster and their montmorillonite filled nanocomposites are studied in acetic through equilibrium swelling method at different temperatures. The kinetics of sorption is studied by using the equation of transport phenomena. The values of ‘n’ in solvent transport equation are found to be below ‘0.5’, showing the non-Fickian or pseudo-Fickian transport in the polymer. The dependence of diffusion coefficient on composition and temperature has been studied for all polymeric samples. The diffusion coefficient of unsaturated polyester samples decreases with an increase in unsaturated acid content. The nanocomposite samples show low diffusion coefficient than corresponding pristine polymers. The diffusion coefficient, sorption coefficient and permeation coefficient increase with an increase in temperature for all samples. The crosslink density for neat polymer with varied unsaturated acid content ranges from 2.98 to 3.52 ×105mol/cm3. For the nanocomposite samples it ranges from 3.70 to 5.72 × 105 mol/cm3.

Experimental investigation of the delayed behavior of unsaturated argillaceous rocks by means of Digital Image Correlation techniques

We present an experimental study on the delayed behavior of unsaturated argillaceous rocks, including shrinkage, swelling, and creep, by means of Digital Image Correlation (DIC) techniques. In order to measure the very low strain rate of the argillaceous rocks at various scales (100 μm–cm) under uniaxial compression and various environmental conditions, a specific optimized optical setup was used. The natural argillaceous rocks were hydrated or dehydrated by controlling the ambient humidity around the samples, and the obtained unsaturated samples were then subjected to creep tests at different stress levels. The mechanical response to hydration and dehydration strongly depended on the mechanical loading, which induced an additional deformation. During creep, the strain rate increased when the moisture or the applied stress increased. The strain rate at a relative humidity of 75% was about one order of magnitude larger than at a dried state (relative humidity = 25%). The anisotropy of the strain induced by the moisture and mechanical loading was enhanced over time. The time dependent behavior as observed at different scales (100 μm–cm) is discussed.

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

A 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.

Knudsen and Molecular Diffusion Coefficients for Gas Transport in Unconsolidated Porous Media

This study was an assessment of the Knudsen and molecular diffusion coefficients in relation to gas‐phase permeability and air‐filled porosity, respectively, for gas transport in unconsolidated porous media. Single gas flow experiments at various gas pore pressures and equimolar binary experiments were conducted to determine apparent, effective gas permeabilities as well as the Knudsen and molecular diffusion coefficients. Experimental results integrated with data from previous studies showed that for dry porous media, the Knudsen diffusion coefficient value for kaolin with total porosity ranging from 0.675 to 0.85 is on the order of 10−4 m2, while it is at least one order of magnitude greater for sea sand and one order less for silica flour. Additionally, the existing correlations of the Knudsen diffusion coefficient can give lower and upper limits to the order of this coefficient value for porous media with effective gas permeabilities in the order of 10−14 to 10−16 m2 The gas‐phase molecular diffusion coefficient for an unsaturated silica flour sample with total porosity of 0.386 and water saturation levels &gt;50% was measured to be one order of magnitude less than those for the other samples with total porosities ranging from 0.402 to 0.417 at similar air‐filled porosities. The former also had lower gas diffusivity under rewetting than under desaturation conditions. The diffusivity factor values obtained from all of the unsaturated silica flour samples were far less than the predictions from other commonly used diffusivity relationships.

Experimental and Numerical Study of the Effect of an Oversize Particle on the Shear Strength of Mined-Rock Pile Material

AbstractDuring in situ direct shear testing on the Questa mined-rock pile material, oversize rock fragments were encountered in the shear box. To study the effect of an oversize particle on the measured friction angles and cohesions, both laboratory and numerical direct shear tests were conducted on unsaturated samples of the rock pile material. In the numerical simulation, a hybrid discrete-finite element method was implemented in which the rock pile material was modeled with discrete particles while the shear box was modeled with finite elements. Both the numerical and physical tests suggest an increase in the measured shear strength of the material due to the presence of an oversize particle in the box. More specifically, the presence of an oversize particle causes an increase in friction angle while cohesion in most situations decreases. The location of the oversize particle along the shear plane was found to be important, as it can modify the failure mechanism.

Effect of microabsorption heterogeneity in the X-ray fluorescence analysis of ultrafine particles

The dependence of the intensity (I i ) of X-ray fluorescence on the size (D) of finely ground particles was studied for saturated and unsaturated samples. It was found that even at the wet grinding (addition of ethanol) of powders with D < 10 μm, the aggregation and covering of larger grains (α) with smaller grains of different compositions occur, which changes the character of the dependence I i = f(D), particularly, if fluorescence is emitted by the grains α. The nature of the observed effects is proved by the results of granulometric analysis and by electron probe X-ray analysis. In the transition from saturated to unsaturated samples, the discussed effects are enhanced.

Vertical small scale variations of sorption and mineralization of three herbicides in subsurface limestone and sandy aquifer

Vertical variation in sorption and mineralization potential of mecoprop (MCPP), isoproturon and acetochlor were investigated at low concentrations (μg-range) at the cm-scale in unsaturated sub-surface limestone samples and saturated sandy aquifer samples from an agricultural catchment in Brévilles, France. From two intact core drills, four heterogenic limestone sections were collected from 4.50 to 26.40 m below surface (mbs) and divided into 12 sub-samples of 8–25 cm length, and one sandy aquifer section from 19.20 to 19.53 m depth divided into 7 sub-samples of 4–5 cm length. In the sandy aquifer section acetochlor and isoproturon sorption increased substantially with depth; in average 78% (acetochlor) and 61% (isoproturon) per 5 cm. Also the number of acetochlor and isoproturon degraders (most-probable-number) was higher in the bottom half of the aquifer section (93–> 16 000/g) than in the upper half (4–71/g). One 50 cm long limestone section with a distinct shift in color showed a clear shift in mineralization, number of degraders and sorption: In the two brown, uppermost samples, up to 31% mecoprop and up to 9% isoproturon was mineralized during 231 days, the numbers of mecoprop and isoproturon degraders were 1300 to > 16 000/g, and the sorption of both isoproturon and acetochlor was more than three times higher, compared to the two deeper, grayish samples just below where mineralization (≤ 4%) and numbers of degraders (1–520/g) were low for all three herbicides. In both unsaturated limestone and sandy aquifer, variations and even distinct shifts in both mineralization, number of specific degraders and sorption were seen within just 4–15 cm of vertical distance. A simple conceptual model of herbicides leaching to groundwater through a 10 m unsaturated limestone was established, and calculations showed that a 30 cm active layer with the measured sorption and mineralization values hardly impacted the fate of the investigated herbicides, whereas a total thickness of layers of 1 m would substantially increase natural attenuation.

Experimental Study on Thermal Effect of Shear Strength of Cohesive Soil

The paper mainly studies the influence rules of temperature (10°C~60°C) and curing time on shear strength indexes of cohesive soil, such as cohesion and internal friction angle, which are very significant in civil engineering works as the temperature of the earth’s surface increases. Such influence plays an even more important role in the design of the ground source heat pump and the geological disposal of high-level radioactive wastes. In this paper, the triaxial unconsolidated-undrained tests on unsaturated cohesive soil samples have recently been performed. And the testing results show that the shear strength increase as temperature and curing time increase, which is a phenomenon that needs further researches. The cementation get reinforced and the change of the content of closed air caused by the temperature curing may be the key factors.

Development of a procedure for the determination of X-ray fluorescence of metals in aerosols

The precision of the determination of the of heavy metals in aerosols by X-ray fluorescence after their collection on a paper filter is evaluated depending on the chemical composition and weight of unsaturated samples. Recommendations on the choice of the optimal shape of the calibration function and on the conditions for the determination of its coefficients used for the X-ray analysis of unsaturated samples are formulated. A procedure for the X-ray determination of metals in aerosols collected on paper filters is developed; its performance characteristics are presented.

Differential scanning calorimetry thermal properties and oxidative stability indices of microwave heated extra virgin olive oils

The use of differential scanning calorimetry (DSC) for assessing the deterioration effect of microwave heating on vegetable oils, and on olive oils in particular, has been partially explored in literature. The aim of this work was to evaluate the potential of DSC to discriminate among microwaved extra virgin olive oils (EvOo from different olive cultivar and origin), according to changes on thermal properties (upon cooling and heating) and traditional oxidative stability indices (peroxide, p-anisidine and TOTOX values). An elevated value of lipid oxidation was reached by the most unsaturated EvOo sample (9.5% of linoleic acid) at 6 min of microwave treatment. Free acidity significantly increased (0.42%) only for the oil sample with the highest water content (874 mg kg(-1) oil) at the longest time of treatment. Crystallisation enthalpies significantly decreased and the major exothermic peak shifted towards lower temperature, leading to enlargement of the transition range in all samples due to the formation of weak and mixed crystals among triacylglycerols and lipid degradation products. On the contrary, thermal properties upon heating appeared to similarly vary among samples. The analysis of DSC thermal properties upon cooling seemed to clearly discriminate among different EvOo samples after microwaving. The relation between changes of thermal properties and oxidation parameters should be further studied using additional oxidative stability indices on a larger set of oil samples, due to the complexity of EvOo composition.