11 research outputs found

    Two-Dimensional Modelling Approach for Electrokinetic Water Transport in Unsaturated Kaolinite

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    Although electrokinetic treatments for soil remediation and ground improvement have gradually undergone significant experimental development, one of the most important physical phenomena has received very little attention in recent years. Electroosmotic flow, especially in unsaturated conditions, has not been simulated in domains of more than one dimension. In the present work, a modification of the M4EKR code was used to study water movement in partially saturated soils under electrokinetic treatments. Two different configurations were studied: electrodes placed in electrolyte wells and electrodes directly inserted into the soil, and the treatment was started under unsaturated conditions for both. Due to the unrestricted availability of fluid in the first case, soil saturation is inevitable, but in the second case, only a spatial redistribution of water content can be observed. A detailed analysis of a variety of configurations involving several electrolyte wells showed that the number of electrodes, the distance between them and, above all, the ratio between the two magnitudes determines the efficiency of soil saturation and the energy consumed in the process.Aunque los tratamientos electrocin茅ticos para la recuperaci贸n y mejora de suelos han experimentado gradualmente un importante desarrollo experimental, uno de los fen贸menos f铆sicos m谩s importantes ha recibido muy poca atenci贸n en los 煤ltimos a帽os. El flujo electroosm贸tico, especialmente en condiciones no saturadas, no ha sido simulado en dominios de m谩s de una dimensi贸n. En el presente trabajo se ha utilizado una modificaci贸n del c贸digo M4EKR para estudiar el movimiento del agua en suelos parcialmente saturados bajo tratamientos electrocin茅ticos. Se estudiaron dos configuraciones diferentes: electrodos colocados en pozos electrol铆ticos y electrodos insertados directamente en el suelo, y el tratamiento se inici贸 en condiciones no saturadas para ambos. Debido a la disponibilidad ilimitada de fluido en el primer caso, la saturaci贸n del suelo es inevitable, pero en el segundo s贸lo se observa una redistribuci贸n espacial del contenido de agua. Un an谩lisis detallado de diversas configuraciones con varios pozos electrol铆ticos demostr贸 que el n煤mero de electrodos, la distancia entre ellos y, sobre todo, la relaci贸n entre ambas magnitudes determinan la eficacia de la saturaci贸n del suelo y la energ铆a consumida en el proceso

    Database for validation of thermo-hydro-chemo-mechanical behaviour in bentonites

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    This paper presents a database of thermo-hydro-chemo-mechanical tests on bentonites, which has been named 鈥淏ento_DB4THCM鈥. After a comprehensive literature review, a set of experimental tests have been compiled. The experimental data are used to perform validation exercises for numerical codes to simulate the coupled thermo-hydro-mechanical and geochemical behaviour of bentonites. The database contains the information required for the simulation of each experimental test solving a boundary value problem. The validation exercises cover a wide range of clays, including the best-known bentonites (MX-80, FEBEX, GMZ) as well as others. The results collected in this database are from free swelling, swelling under load, swelling pressure and squeezing tests. The database is attached as Supplementary material.En este art铆culo se presenta una base de datos de ensayos termo-hidro-quimio-mec谩nicos sobre bentonitas, a la que se ha denominado 鈥淏ento_DB4THCM鈥. Despu茅s de una revisi贸n exhaustiva de la literatura, se ha compilado un conjunto de pruebas experimentales. Los datos experimentales se utilizan para realizar ejercicios de validaci贸n de c贸digos num茅ricos para simular el comportamiento termohidromec谩nico y geoqu铆mico acoplado de las bentonitas. La base de datos contiene la informaci贸n requerida para la simulaci贸n de cada prueba experimental que resuelve un problema de valor l铆mite. Los ejercicios de validaci贸n cubren una amplia gama de arcillas, incluidas las bentonitas m谩s conocidas (MX-80, FEBEX, GMZ) entre otras. Los resultados recopilados en esta base de datos provienen de pruebas de hinchamiento libre, hinchamiento bajo carga, presi贸n de hinchamiento y compresi贸n. La base de datos se adjunta como material complementario

    A new double-porosity macroscopic model of bentonite free swelling

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    A macroscopic model based on a double-porosity approach is proposed to simulate the swelling caused by the subdivision of particles and aggregates that occurs when bentonites are hydrated under a high water content and low confinement. In the model, it is assumed that although the water that occupies this new porous structure can be considered mobile (associated with the macrostructure), its contribution to variations in the energy of the system is similar to that caused by the immobile water that occupies the microstructure. Assuming isothermal conditions, a functional relationship between the increase in the void ratio and the decrease in internal energy was defined from the Clausius-Duhem equation. From this functional relationship, a macroscopic constitutive model was derived to determine the macrostructural swelling as a function of the decrease in the microstructural effective stress. The model was applied to simulate both tests with a large void ratio (up to 50) and processes with a notable variation in salinity (from deionized water to 1 M solution), and satisfactory results were obtained in all cases. This study proposes a simple strategy to incorporate the model into the equations generally used to solve hydro-chemical-mechanical boundary problems at the engineering scale and is thus of direct practical interest.Se propone un modelo macrosc贸pico basado en un enfoque de doble porosidad para simular el hinchamiento causado por la subdivisi贸n de part铆culas y agregados que ocurre cuando las bentonitas se hidratan bajo un alto contenido de agua y bajo confinamiento. En el modelo se asume que si bien el agua que ocupa esta nueva estructura porosa puede considerarse m贸vil (asociada a la macroestructura), su contribuci贸n a las variaciones en la energ铆a del sistema es similar a la provocada por el agua inm贸vil que ocupa la microestructura Suponiendo condiciones isot茅rmicas, una relaci贸n funcional entre el aumento de la relaci贸n de vac铆osy la disminuci贸n de la energ铆a interna se defini贸 a partir de la ecuaci贸n de Clausius-Duhem. A partir de esta relaci贸n funcional, se deriv贸 un modelo constitutivo macrosc贸pico para determinar el hinchamiento macroestructural en funci贸n de la disminuci贸n de la tensi贸n efectiva microestructural. El modelo se aplic贸 para simular tanto ensayos con una gran relaci贸n de vac铆os (hasta 50) como procesos con una notable variaci贸n de salinidad (desde agua desionizada hasta soluci贸n 1 M), y se obtuvieron resultados satisfactorios en todos los casos. Este estudio propone una estrategia simple para incorporar el modelo en las ecuaciones generalmente utilizadas para resolver problemas de l铆mites hidroqu铆micos-mec谩nicos a escala de ingenier铆a y, por lo tanto, es de inter茅s pr谩ctico directo

    A numerical inspection on the squeezing test in active clays

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    Squeezing tests are performed to obtain liquid samples from soil to characterise the chemical composition of the aqueous saline solution in its pores. However, the representativeness of the extract obtained from active clays has been debated, as a mixture of macrostructural and microstructural solutions is likely to be obtained. To analyse this question, given the complexity and the strong hydro-chemo-mechanical coupling of the processes that occur during a squeezing test, it is of interest to simulate the test using a conceptual model able to characterise the processes involved in active clays. This type of simulation is performed in this study, showing that the chemo-mechanical interaction between macrostructure and microstructure is unavoidable. However, in saturated soils with low dry densities, most of the extracted water is directly obtained from the macrostructure, and the extract can be considered representative of the macrostructural solution. With increasing dry density, the mixing increases, and the representativeness of the extract may be compromised. In unsaturated soil with a low water content and high dry density, an important mass exchange occurs between the macrostructure and microstructure. If the test is viable (i.e., sufficient solution volume can be obtained), the representativeness of the extract must be carefully evaluate

    Long-term monitoring of the distribution of a building's settlements: Sectorization and study of the underlying factors

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    The monitoring of the structural behaviour of singular buildings and the environmental variables that affect them is an upward trend on a global scale. This paper presents a monitoring project of the building of the Institute of Technology (IT) of the University of Castilla-La Mancha in Cuenca, Spain. Different monitoring actions were carried out, specifically there were installed 27 measuring points of the soil water content (both outside and under the building), 4 clinometers with thermometers, a weather station, and 22 points for topographical levelling, thirteen of which are located on the footings of the building. Although 3 of the clinometers recorded data marked almost entirely by the evolution of the interior temperature, the one located in Module 4 showed a more complex behaviour. In order to determine the possible underlying causes of this behaviour, the footings were grouped according to the evolution of the settlements obtained by differential levelling. For this purpose, a novel clustering technique based on the calculation of the Jeffreys distance has been used instead of other more common dissimilarity measures. The analysis revealed a potential cause of the anomalous behaviour of a group of footings and permitted the study of the influence of temperature and other environmental and operative variables on this behaviour, allowing the detection of anomalies in the future

    A User-Friendly Tool to Characterize the Moisture Transfer in Porous Building Materials: FLoW1D

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    This paper presents a user-friendly tool鈥擣LoW1D (One-Dimensional Water Flow)鈥攆or the estimation of parameters that characterize the unsaturated moisture transfer in porous building materials. FLoW1D has been developed in Visual Basic for Applications and implemented as a function of the well-known Microsoft Excel漏 spreadsheet application. The aim of our work is to provide a simple and useful tool to improve the analysis and interpretation of conventional tests for the characterization of the hygric behavior of porous building materials. FLoW1D embraces the conceptual model described in EN 15026 for moisture transfer in building elements, and its implementation has been verified and validated correctly. In order to show the scope of the code, an example of an application has been presented. The hygric characterization of the limestone that is mostly employed in the Cathedral of Santa Maria and San Julian in Cuenca (Spain) was conducted based on an analysis of the conventional water absorption by capillarity tests (EN 15801)

    Remediation of soils polluted with 2,4-D by electrokinetic soil flushing with facing rows of electrodes: A case study in a pilot plant

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    This study focuses on evaluating the application of electrokinetic soil flushing (EKSF) technologies to remediate soil polluted with 2,4-dichlorophenoxyacetic acid (2,4-D). This compound was selected as an example of polar herbicides that may cause soil percolation and groundwater contamination due to its high water solubility, lifetime and mobility. To evaluate this technology, a 40-day test was conducted on a bench-scale set-up (175 dm3 of capacity) that was fully automated and operating under potentiostatic mode (1 V cm鈭1). The electrical current, temperature, pH, humidity and pollutant concentration in the electrolyte wells were monitored daily, and at the end of the tests, a post-analysis characterization of the soil section was performed to obtain 3-D plots of the changes in each parameter. Simultaneously, a blank test was carried out (without applying an electric field) to determine spreading of the pollutant in the soil that did not experience an electric field. The results indicate that the 2,4-D is transported to the anode wells by electromigration (the primary species is an anion under the treatment pH) and the cathode wells by electroosmotic drag, even though a lower concentration is obtained because a large volume of water is mobilized. After 40 days of the EKSF treatment, 50% of the initial 2,4-D leaked into the soil was eliminated, 25% remained in the soil, and the remaining 25% was volatilized.Este estudio se enfoca en evaluar la aplicaci贸n de tecnolog铆as de lavado electrocin茅tico del suelo (EKSF) para remediar el suelo contaminado con 谩cido 2,4-diclorofenoxiac茅tico (2,4-D). Este compuesto fue seleccionado como un ejemplo de herbicidas polares que pueden causar la filtraci贸n del suelo y la contaminaci贸n de las aguas subterr谩neas debido a su alta solubilidad en agua, vida 煤til y movilidad. Para evaluar esta tecnolog铆a, se realiz贸 una prueba de 40 d铆as en un banco de pruebas (175 dm 3 de capacidad) totalmente automatizado y operando en modo potenciost谩tico (1 V cm 鈭1). La corriente el茅ctrica, la temperatura, el pH, la humedad y la concentraci贸n de contaminantes en los pozos de electrolitos fueron monitoreados diariamente y al final de las pruebas, se realiz贸 una caracterizaci贸n post-an谩lisis de la secci贸n del suelo para obtener gr谩ficas tridimensionales de los cambios en cada uno de ellos. par谩metro. Simult谩neamente, se realiz贸 una prueba en blanco (sin aplicaci贸n de campo el茅ctrico) para determinar la dispersi贸n del contaminante en el suelo que no experiment贸 campo el茅ctrico. Los resultados indican que el 2,4-D es transportado a los pozos an贸dicos por electromigraci贸n (la especie primaria es un ani贸n bajo el pH del tratamiento) y a los pozos cat贸dicos por arrastre electroosm贸tico, aunque se obtiene una menor concentraci贸n debido a un gran volumen de el agua es movilizada. despu茅s de 40 d铆as del tratamiento con EKSF, se elimin贸 el 50 % del 2,4-D inicial que se filtr贸 al suelo, el 25 % permaneci贸 en el suelo y el 25 % restante se volatiliz贸

    Enhancing soil vapor extraction with EKSF for the removal of HCHs

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    This paper evaluates the combination of electrokinetic soil flushing (EKSF) with soil vapor extraction (SVE) for the removal of four hexachlorocyclohexane (HCH) isomers contained in a real matrix. Results demonstrate that the combination of EKSF and SVE can be positive, but it is required the application of high electric fields (3 V cm鈭1) in order to promote a higher temperature in the system, which improves the volatilization of the HCH contained in the system. Electrokinetic transport is also enhanced with the application of higher electric gradients, but these transport processes are slower than the volatilization processes, which are the primary in this system. Hence collection of species in the electrolyte wells is negligible as compared to the compound dragged with air by the SVE but the temperature increase demonstrates a good performance. Combination of EKSF with SVE can efficiently exhaust the four HCH isomers reaching a removal of more than 90% after 15 days of treatment (20% more than values attained by SVE) but it is required the application of high electric fields to promote a higher temperature in the system (to improve the volatilization) and EK transport (to improve the dragging). 1-D transport model can be easily used to estimate the average pore water velocity and the effective diffusion of each compound under the different experimental conditions tested.Este art铆culo eval煤a la combinaci贸n de lavado electrocin茅tico del suelo (EKSF) con extracci贸n de vapor del suelo (SVE) para la eliminaci贸n de cuatro is贸meros de hexaclorociclohexano (HCH) contenidos en una matriz real. Los resultados demuestran que la combinaci贸n de EKSF y SVE puede ser positiva, pero se requiere la aplicaci贸n de campos el茅ctricos elevados (3 V cm 鈭1) con el fin de promover una mayor temperatura en el sistema, lo que mejora la volatilizaci贸n del HCH contenido en el sistema. El transporte electrocin茅tico tambi茅n mejora con la aplicaci贸n de gradientes el茅ctricos m谩s altos, pero estos procesos de transporte son m谩s lentos que los procesos de volatilizaci贸n, que son los principales en este sistema. Por lo tanto, la recolecci贸n de especies en los pozos de electrolito es insignificante en comparaci贸n con el compuesto arrastrado con aire por el SVE, pero el aumento de temperatura demuestra un buen desempe帽o. La combinaci贸n de EKSF con SVE puede agotar eficientemente los cuatro is贸meros de HCH alcanzando una eliminaci贸n de m谩s del 90 % despu茅s de 15 d铆as de tratamiento (20 % m谩s que los valores alcanzados por SVE) pero se requiere la aplicaci贸n de campos el茅ctricos elevados para promover una temperatura m谩s alta en el sistema (para mejorar la volatilizaci贸n) y transporte EK (para mejorar el arrastre). El modelo de transporte 1-D se puede usar f谩cilmente para estimar el promediola velocidad intersticial del agua y la difusi贸n efectiva de cada compuesto bajo las diferentes condiciones experimentales probadas

    Modelling of compacted bentonite swelling accounting for salinity effects

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    This paper presents a formulation to incorporate the influence of water salinity on the swelling behaviour of a MX-80 bentonite into previously developed hydro-mechanical models that can reproduce swelling under dilute conditions. The effects of salinity on macro- and microstructural water chemical potentials were introduced. In addition, a description of solute transport was included to characterise the evolution of the system鈥檚 salinity. A simplified geochemical model was adopted to idealise the geochemical complexity of bentonite. In addition, the modelling of the destructuration process that occurs during swelling was modified to account for the effect of salinity. The formulation was implemented in a multiphysics partial differential equation finite element solver, and the numerical model was used to simulate several vertical free swelling tests with feed water of different salt contents (deionised, 10, 35 and 70 g/L). The results demonstrate that even though the model can be developed further, it represents a significant improvement over models that do not account for the effects of salinity

    Techno-economic analysis of the scale-up process of electrochemically-assisted soil remediation

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    This work presents a techno-economic study of the scaling-up of the electrochemically-assisted soil remediation (EASR) process of polluted soil. Four scales have been selected for the study: laboratory, bench, pilot and prototype, with a capacity of treating a volume of soil of 1鈥椻10鈭4, 2鈥椻10鈭3, 0.11 and 21.76鈥痬3, respectively. This study analyses the technical information produced by studies carried out at each scale, and informs about the fixed costs (construction of the electrokinetic remediation reactor, installation of auxiliary services and purchase of analytical equipment) and variable costs (start-up, operation and dismantling of the test) derived from running a test at each of the evaluated scales. The information discussed in based on the experience gained with many evaluations carried out over the last decade at these scales. This information can provide useful guidance for developing a scaling-up of the EASR for many researchers starting on the evaluation of this important environmental remediation technology
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