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A formulation is proposed for reproducing the hydro-mechanical behaviour of compacted bentonites as interaggregate porosity becomes negligible. In that case, the model assumes the bentonite deformability to be controlled only by the microstructural modelling level in a double porosity approach. Hence, the bulk stiffness of the system is defined by the relationship between the microstructural void ratio and the thermodynamic swelling pressure, requiring no additional parameters to simulate the overall behaviour. An experimental study has been conducted to check the conceptual consistency of the formulation, with favourable results. The quantitative potential of the model has also been satisfactorily verified by numerical simulation of the tests carried out in this study. A displacement-based finite-element model developed for double porosity systems has been modified to run the simulations. The proposed formulation has been implemented using a simple strategy that can be easily replicated for similar numerical models. Both the simulation capabilities and the computational cost efficiency of the proposed formulation confirm its practical interest., Se propone una formulación para reproducir el comportamiento hidromecánico de las bentonitas compactadas a medida que la porosidad entre los agregados se vuelve despreciable. En ese caso, el modelo asume que la deformabilidad de la bentonita está controlada solo por el nivel de modelado microestructural en un enfoque de doble porosidad. Por lo tanto, la rigidez aparente del sistema se define por la relación entre la relación de vacíos microestructurales y la presión de expansión termodinámica, lo que no requiere parámetros adicionales para simular el comportamiento general. Se ha realizado un estudio experimental para comprobar la consistencia conceptual de la formulación, con resultados favorables. El potencial cuantitativo del modelo también ha sido verificado satisfactoriamente mediante la simulación numérica de las pruebas realizadas en este estudio. Se ha modificado un modelo de elementos finitos basado en el desplazamiento desarrollado para sistemas de doble porosidad para ejecutar las simulaciones. La formulación propuesta se ha implementado utilizando una estrategia simple que puede replicarse fácilmente para modelos numéricos similares. Tanto las capacidades de simulación como la rentabilidad computacional de la formulación propuesta confirman su interés práctico.

This paper presents a database of thermo-hydro-chemo-mechanical tests on bentonites, which has been named “Bento_DB4THCM”. 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 artículo se presenta una base de datos de ensayos termo-hidro-quimio-mecánicos sobre bentonitas, a la que se ha denominado “Bento_DB4THCM”. Después de una revisión exhaustiva de la literatura, se ha compilado un conjunto de pruebas experimentales. Los datos experimentales se utilizan para realizar ejercicios de validación de códigos numéricos para simular el comportamiento termohidromecánico y geoquímico acoplado de las bentonitas. La base de datos contiene la información requerida para la simulación de cada prueba experimental que resuelve un problema de valor límite. Los ejercicios de validación cubren una amplia gama de arcillas, incluidas las bentonitas más conocidas (MX-80, FEBEX, GMZ) entre otras. Los resultados recopilados en esta base de datos provienen de pruebas de hinchamiento libre, hinchamiento bajo carga, presión de hinchamiento y compresión. La base de datos se adjunta como material complementario.

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 macroscópico basado en un enfoque de doble porosidad para simular el hinchamiento causado por la subdivisión de partículas 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 móvil (asociada a la macroestructura), su contribución a las variaciones en la energía del sistema es similar a la provocada por el agua inmóvil que ocupa la microestructura Suponiendo condiciones isotérmicas, una relación funcional entre el aumento de la relación de vacíosy la disminución de la energía interna se definió a partir de la ecuación de Clausius-Duhem. A partir de esta relación funcional, se derivó un modelo constitutivo macroscópico para determinar el hinchamiento macroestructural en función de la disminución de la tensión efectiva microestructural. El modelo se aplicó para simular tanto ensayos con una gran relación de vacíos (hasta 50) como procesos con una notable variación de salinidad (desde agua desionizada hasta solución 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 límites hidroquímicos-mecánicos a escala de ingeniería y, por lo tanto, es de interés práctico directo.

In this paper, a simple precomputing procedure is proposed to improve the numerical performance of the technological application of critical state soil models. In these models, if associated plasticity is assumed, the normalization of the stress space allows both the yield surface and the plastic components of the elastoplastic matrix to be defined as a function of a single variable. This approach facilitates their parameterization and precomputation, preventing the repetition of calculations when the boundary value problems appear at the yield surface with the calculation of plastic strain. To illustrate the scope of the procedure, its application on a modified Cam Clay model is analysed, which shows that the method allows a significant reduction of about 50% (as compared with the conventional explicit integration algorithm) in the computational time without reducing the precision. Although it is intended for critical state models in soils, the approach can be applied to other materials and types of constitutive models provided that parameterization is possible. It is therefore a methodology of practical interest, especially when a large volume of calculations is required, for example when studying large-scale engineering systems, performing sensitivity analysis, or solving optimization problems.

The reactive transport framework ORCHESTRA was used to implement a dual porosity reactive transport system that accounts for mechanical processes relevant for confined swelling clays at full saturation. The new implementations are based on water retention data generated by molecular dynamics simulations, and on fundamental mechanical formulations. The code predicts and fully couples porewater chemistry, exchanger population, diffusive transport, mineral reactions, volume fractions of the free and Donnan porosity domains, and swelling pressure. The chemomechanical predictions were compared with experimental measurements of swelling pressure and d-value of the clay in different chemical environments. A simulation of bentonite in contact with a constant concentration reservoir demonstrates the performance of the new model approach. It can be used to model interactions of bentonite with different groundwaters or cement and steel., El marco de transporte reactivo ORCHESTRA se utilizó para implementar un sistema de transporte reactivo de porosidad dual que da cuenta de los procesos mecánicos relevantes para las arcillas expansivas confinadas en plena saturación. Las nuevas implementaciones se basan en datos de retención de agua generados por simulaciones de dinámica molecular y en formulaciones mecánicas fundamentales. El código predice y acopla completamente la química del agua intersticial , la población del intercambiador, el transporte difusivo , las reacciones minerales, las fracciones de volumen .de los dominios de porosidad libre y de Donnan, y la presión de hinchamiento. Las predicciones quimiomecánicas se compararon con mediciones experimentales de la presión de expansión y el valor d de la arcilla en diferentes entornos químicos. Una simulación de bentonita en contacto con un yacimiento de concentración constante demuestra el rendimiento del nuevo enfoque del modelo. Puede usarse para modelar interacciones de bentonita con diferentes aguas subterráneas o cemento y acero.

Electrokinetic techniques have attracted considerable attention due to their competitive advantage in enhancing transport phenomena and remediation of low permeability soils. However, many types of low-permeability porous media, such as active clays like bentonite, present a double porosity structure that strongly affects mass transfer processes. In this work, we develop a modeling approach to simulate electrokinetic transport in double porosity media. The proposed model is based on the previously released code M4EKR and explicitly considers the transport due to electromigration as well the effects of the electrical diffuse layer in charged porous media. For this purpose, two modeling levels have been established: one associated with the soil macrostructure (bulk water) and the other with the microstructure (diffuse layer). At the latter level, the effect of the electrostatic interactions imposed by the negative charge of the clay particles is modeled with a Donnan approach. The comparison of the results between synthetic cases in single and double porosity systems shows the fundamental role of the microstructural modeling level. High enrichment of cations and, therefore, high cationic fluxes are produced in such microstructural level. These mechanisms significantly modify the extent of cation transport by electromigration and, thus, directly influence the transport of other species determined by the electrostatic interactions.

This work presents a study of the dissolution-precipitation processes of calcite in soil undergoing electrokinetic remediation processes. For this purpose, a numerical inspection of one of these processes in a calcareous soil (10% calcite content) contaminated with an of the organochlorine acid herbicide (3,6-dichloro-2-pyridinecarboxylic acid) was carried out. The numerical tool used to perform this analysis was the Multiphysics for EKR (M4EKR), a module programmed by the authors in the COMSOL Multiphysics platform. A detailed analysis of the pH, the distribution of species that have a significant influence on soil buffering capacity (carbonates and calcite), as well as the pollutant, has been performed. In this way, the kinetics of the calcite dissolution-precipitation processes have been analysed in order to determine the pH of the water in the pores and, therefore, how it directly affects the effectiveness of the treatment. Additionally, a sensitivity analysis of the selected EKR process has been carried out at different values of the rate of calcite dissolution due to the uncertainty associated with the reactive surface area parameter.

The deep geological repository concept for spent nuclear fuel considers many safety elements. Among them, compacted bentonite has been selected as the primary engineering barrier between the encapsulated radioactive waste and the host rock. Thermo-hydro-mechanical behaviour of this material has been studied in detail from an experimental and numerical point of view. Furthermore, the study of chemical behaviour has become very important, both for the evaluation of the transport of species through the clay matrix and for the evaluation of their coupling to other physico-chemical phenomena.Generally, to conduct these types of studies, infiltration tests through compacted bentonite columns are carried out using an experimental setup composed of common parts: (i) porewater and infiltration water reservoirs, (ii) pumping devices and (iii) a confined sample of bentonite. The infiltration/output solutions are injected/extracted through filters positioned in the top/bottom of the sample. The results obtained in these tests are strongly influenced by the properties of these filters. For this reason, it is very important how the chemical species and the fluid are transported in the filters to correctly interpret the experimental observations. The study presented in this work is framed in this context, in which a numerical sensitivity analysis of the transport properties and size of the filters has been conducted. For this purpose, a reactive transport model for bentonites (assuming this material as a double porosity media) formulated by the authors and fully implemented in the multiphysics platform, COMSOL, has been used to simulate a cation exchange-infiltration test in MX-80 bentonite defined in the “Chemical session” of the Task Force on Engineered Barrier Systems (EBS) organised by SKB AB. The results obtained depend on the tortuosity, porosity and thickness of the filters. These parameters have been estimated for the correct interpretation of the selected test.

In this chapter, the importance of mathematical models to analyze the electrokinetic remediation process is highlighted. Due to the amount of coupled physicochemical, electrochemical, and electrokinetic phenomena that take place in this soil treatment, it is necessary to develop conceptual models and numerical tools that, combined with experimental information, improve the global understanding of these processes.

Soil is a natural porous material with fluids in its voids. The distribution of the space occupied by solid particles, water, and gases is fundamental to understanding soil behavior under the influence of external actions. The mineralogical and geochemical composition of the system and the characteristics of solid–liquid–gas complex under different fluxes of matter and energy also play determining roles in soil behavior. Changes in the boundary conditions of a soil generate these fluxes, some of which may be of interest for the eventual decontamination of a site. In the specific case of electrokinetic soil remediation, the application of a direct electric current generates a flow of water and solutes and, at the same time, induces other thermal, hydraulic, mechanical, and chemical phenomena, which may favor or hinder the remediation process. To better understand and optimize electrokinetic remediation processes, the soil complexity should be analyzed prior to a more in-depth study of the electrokinetic treatment.

The water retention curve deduced with low water content data allows the modelling of the bentonite void ratio associated with the pores located inside the clay aggregates, or micropores. However, if both the water content and the microporosity continue to increase, the latter can no longer be directly obtained from the former, because, in that case, the presence of water in the pores existing between the aggregates (macropores) may not be negligible. Therefore, it is not easy to obtain experimental evidence that allows to contrast whether the model's extrapolation of the microstructural void ratio obtained under dry conditions is valid for higher water contents. This work analyses the use of data obtained from molecular dynamics models to assess the validity of such extrapolations, and defines the variables needed to compare the results from molecular dynamics and laboratory experiments. The encouraging agreement obtained contributed to the confidence in the proposed procedure, which enabled a new strategy that uses molecular dynamics data to model the macroscopic behaviour of compacted sodium bentonites.

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. © 2019 Elsevier Ltd

The increasing needs for modelling of reactive transport phenomena in different areas of environmental modelling have led to the development of many numerical codes. However, many of them suffer from a lack of flexibility, which hinders the adaptation of the codes to new problems. Moreover, in many cases, changes can be done by a very reduced group of people, and often by a single person, the main developer. Implementation platforms based on multiphysics modelling removes these barriers, although until now within that programming environments has been only possible the coupling of geochemical codes to transport equations using operator splitting techniques. This paper presents the EE4MGM tool, a MS Excel worksheet, provided in supplementary material, for the edition and complete implementation of reactive transport models in COMSOL. The tool automatically generates the code needed to solve the desired reactive transport problem by selecting only which species make up the geochemical system. This way, the numerical model will be completely adapted to the idealisation to be applied, being able to choose easily and effortlessly from a wide range of different levels of conceptual complexity. The organization of data input and the equation libraries obtained for the implementation in the multiphysics COMSOL environment are first described. Afterwards, two examples, in one and two-dimensional domains, to check the utility of the tool are presented.

Electroosmotic permeability is a soil parameter that is fundamental for designing and implementing environmental remediation, dewatering, or soil stabilization processes. It presents a narrow range of variation compared to hydraulic permeability, so that in many occasions no experimental tests are carried out to determine it. Traditionally, the Helmholtz–Smoluchowski equation has been used to estimate electroosmotic permeability, despite having several drawbacks that make it difficult to apply, as it was deduced for large capillaries (unusual in clays) and its dependence on the zeta potential of the soil, difficult to measure and dependent on a wide variety of factors. The present work describes a semi-empirical formulation that allows the estimation of the electroosmotic permeability as a function of the specific surface area and the total void ratio and is based on the Donnan equilibrium and the ion hydration models. The parameters for modeling are calibrated and validated with experimental data, obtaining better results than those given by the Helmholtz–Smoluchowski model. In addition, the expected trends in the behavior of clays that can be found in the literature are obtained in a quantitative and consistent manner for different types of clays with variable water content and pore water salinity.

This work analyses the characterization of the hygric behaviour of a stone heritage material by solving the inverse problem using experimental data obtained from a water absorption by capillarity test (EN 15801). This common test is undemanding and requires relatively simple equipment as compared to other hygric characterization tests. For the solution of the direct problem of transient flow in partially saturated porous media, a computational module was developed in COMSOL Multiphysics that includes the conceptual model from the standard EN 15026. The selected material was the heritage stone of the Cuenca Cathedral, differentiating between two characteristic lithotypes: one with greater porosity and another that is more resistant, with more reduced porosity. Based on the experimental results, the intrinsic permeability and the parameters of the moisture storage function are estimated for the two lithotypes. Similarly, contrast tests were conducted to quantify the estimation error. A stochastic analysis was performed to assess if the estimated hygric parameters satisfactorily characterize the behaviour of the studied stone.

This paper presents a user-friendly tool&mdash, FLoW1D (One-Dimensional Water Flow)&mdash, for 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&copy, 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).

The proposed use of active clays for the isolation of radioactive wastes in deep geological repositories has been followed by a deeper understanding of this type of soils. This increased knowledge has led to the need for both conceptual and numerical models capable of capturing the main trends in behaviour and the different couplings between different physical-chemical phenomena. In addition, the model must have a high degree of flexibility that enables it to accommodate future developments or new relevant phenomena. This work presents a numerical THMC code developed entirely on the COMSOL Multiphysics numerical implementation platform, which provides the required adaptability. This model includes, for the first time in this environment, a reactive transport model in unsaturated porous media for a relevant geochemical system (consistent with the MX-80 bentonite) together with a THM model based on a double porosity approach. The chemical potentials of water and solutes are used for the definition of thermodynamic equilibria between both porosity levels. Trends in the behaviour of a bentonite sample under oedometric conditions are satisfactorily simulated in response to a process of saturation and change in salinity conditions. Variations in swelling pressure, porosity distribution or dissolution/precipitation of the main accessory minerals are analysed and explained by means of the proposed conceptual model.

The erosion behaviour of bentonites is influenced by the ions concentration to which they are exposed, which could lead to link the erodibility of bentonite to salinity. However, changes in salinity produce further changes in bentonite hydration and swelling that are not always considered. The aim of this work is to apply a numerical model to inspect the influence of salinity in the erosion behaviour of MX-80 bentonite, analysing the effect of swelling on erosion. To this end, a coupled hydro-chemo-mechanical and erosion model, which considers the expansive behaviour of bentonite as a function of salinity, and a hydro-mechanical model with a salinity-dependent erodibility coefficient are used to simulate pinhole erosion laboratory tests with saline waters. The results of the simulations illustrate that the influence of ion species concentration in the erosion behaviour of bentonites does not need a change in erodibility to be reproduced. On the contrary, they show that hydro-chemo-mechanical effects, and especially the changes that salinity induces in the swelling behaviour of bentonite, play a key role in erosion. Taking them into account leads to a more consistent formulation approach that can explain the observed behaviour, and, for that reason, such an approach is strongly recommended to analyse bentonite erosion processes.

This article presents a numerical study of the transport phenomena involved in the electrokinetic remediation of soils polluted with polar pesticides. 2,4-Dichlorophenoxyacetic acid is used as a representative of this pesticide type. A one-dimensional configuration with two facing electrodes placed in electrolyte compartments and a cathodic overflow pollutant extraction system has been used for that purpose. The conventional electrokinetic remediation process is evaluated by keeping the electrode polarity constant, and to obtain acceptable yields, it is necessary to extend the treatment for more than 250 days. The application of periodic polarity reversals is proposed to improve these results. This strategy maximises the pesticide concentration in the cathodic compartment, thus maximising the pollutant extraction rate. The results show that by applying polarity reversals over 6-h periods, it is possible to accelerate the treatment, thus improving its overall efficiency up to 94.5% compared with the treatment using a constant electrode polarity.

A simple procedure is proposed to simulate a smooth transition from elastic to elastoplastic behaviour in Cam-Clay models. The procedure consists of the definition of an external constitutive surface where full yield is assumed, and an internal one that allows the definition of the position in which plastic strains start to appear before the external yield surface is reached. The comparison of the model results with different laboratory tests shows the validity of the procedure. The method considers one additional parameter with regard to a “standard” critical state model, and it can easily be implemented in existing integration modules.

A simple procedure is proposed to reduce the error in the calculation of the stresses when simulating stress paths applying explicit stress integration schemes in Cam-Clay models with an associated flow rule. The procedure consists of defining the value of the preconsolidation stress (the hardening parameter of a Cam-Clay model) so that the drift of the yield surface is zero at each calculation step. The results demonstrate the efficiency of the proposed procedure, especially along softening paths. The method can easily be implemented in existing explicit integration modules, which facilitates its practical application.

This study focuses on the evaluation of the electrokinetic soil flushing (EKSF) strategy to remediate soil following a simulated spill of the herbicide oxyfluorfen. EKSF is attained by placing (in the soil mockup) two rows of electrodes of different polarity facing each other. The results are compared with those obtained in a reference experiment in which the same spill was simulated and no remediation actions were taken. In addition to the daily monitoring of the most important parameters in the flows, after the remediation test, a post-mortem analysis was performed to obtain a 3-D map of the pollutant distribution. Those results demonstrate that despite the hydrophobic character of oxyfluorfen, it can be efficiently transported by EKSF. Hence, after 34 days of treatment, a 26.8% improvement in the removal of oxyfluorfen was achieved (explained in terms of the effect of the electric field on the pollutant) compared with the reference experiment in which only volatilization can explain the removal of the herbicide. Comparison of the removal of oxyfluorfen by EKSF with that of 2,4-D (studied in a previous study) demonstrates that comparable dragging to the cathode and volatilization are obtained. However, the lower efficiency of the transport of oxyfluorfen by gravity fluxes and electromigration (explained because it is contained as micelles) yielded worse performance of EKSF for this water-insoluble pesticide and hence less efficient remediation. This contradictory result reveals the importance of tests at large-scale facilities such as that used in this work to predict the performance of real systems in future full-scale applications.

An approach is proposed for simulating the coupled processes of swelling and mechanical erosion of compacted MX-80 bentonites. The loss of mass at the water–soil interface is described by means of a simplified erosion model, assuming the “instantaneous” activation of erosion. A double-porosity formulation was adopted based on the Barcelona Expansive Model to describe the deformability of the bentonite. In addition, a state surface was introduced to describe the increase in macrostructural porosity caused by the swelling and destructuration of the aggregates. This formulation was implemented in the multiphysics partial differential equation solver Comsol Multiphysics (CM), which was adapted to incorporate a mixed method and a Lagrangian formulation. The “Deformed Geometry” module of the CM solver allowed for the smooth and continuous updating of the active material domain to the bentonite mass loss defined in the erosion model. Satisfactory data fits were obtained by simulating a variety of pinhole tests on MX-80 samples of various configurations. Thus, although more experimental validation is needed, and the approach could be further improved (introducing, e.g., the effect of water salinity), the obtained results indicate that this method is a useful starting point for describing and quantifying the coupled erosion and swelling of MX-80 bentonites.

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−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 aplicación de tecnologías de lavado electrocinético del suelo (EKSF) para remediar el suelo contaminado con ácido 2,4-diclorofenoxiacético (2,4-D). Este compuesto fue seleccionado como un ejemplo de herbicidas polares que pueden causar la filtración del suelo y la contaminación de las aguas subterráneas debido a su alta solubilidad en agua, vida útil y movilidad. Para evaluar esta tecnología, se realizó una prueba de 40 días en un banco de pruebas (175 dm 3 de capacidad) totalmente automatizado y operando en modo potenciostático (1 V cm −1). La corriente eléctrica, la temperatura, el pH, la humedad y la concentración de contaminantes en los pozos de electrolitos fueron monitoreados diariamente y al final de las pruebas, se realizó una caracterización post-análisis de la sección del suelo para obtener gráficas tridimensionales de los cambios en cada uno de ellos. parámetro. Simultáneamente, se realizó una prueba en blanco (sin aplicación de campo eléctrico) para determinar la dispersión del contaminante en el suelo que no experimentó campo eléctrico. Los resultados indican que el 2,4-D es transportado a los pozos anódicos por electromigración (la especie primaria es un anión bajo el pH del tratamiento) y a los pozos catódicos por arrastre electroosmótico, aunque se obtiene una menor concentración debido a un gran volumen de el agua es movilizada. después de 40 días del tratamiento con EKSF, se eliminó el 50 % del 2,4-D inicial que se filtró al suelo, el 25 % permaneció en el suelo y el 25 % restante se volatilizó.

Soils polluted with 2,4-D (model of ionic herbicide) can be remediated using a fence of alternating anodes and cathodes surrounding the main contamination point. This works reports results obtained in case study consisting of a 175 dm 3 pilot plant, in which a soil polluted with an average concentration of 20 mg kg −1 of 2,4-D (spread by simulating an accidental spill) undergoes electroremediation for two months with an electric field of 1.0 VDC cm −1 (between consecutive electrodes). Intensity, temperature, pH, moisture and pollutant concentration in electrolyte wells were daily monitored, and at the end of the experiments, an in-depth post-mortem analysis was carried out. In less than two months, the remediation technology attains a transport of more than 22% of the 2,4-D contained in the soil to the flushing fluids. However, the main mechanism for the removal of 2,4-D was found to be volatilization (which totalizes up to 57% of removal of 2,4-D). The significance of this mechanism was confirmed with the comparison of the results obtained in the remediation test with the results obtained in a reference test consisting of the monitoring of the dispersion of the 2,4-D pollutant in a soil which does no undergo electroremediation treatment. These results are of a great importance for future scaling-up of the technology.

The good knowledge of the moisture transfer in materials used in the construction of architectonic cultural heritage is a key issue to define conservation and restoration actions. In recent years, numerical models are used in this field to improve the hygrothermal characterization of these materials. However, the structure of state functions involved in the modelization is not standardised, and they present a highly empirical parametrization . For this reason, the main objective of this work is to review the structure of the state functions corresponding to moisture transport (moisture content, liquid and vapour water permeabilities) and to suggest more compact functional structures that allow reducing the number of parameters. Two conventional tests used to characterize the hygrothermal behaviour of heritage elements, (i) water absorption by capillary test (EN 15801) and (ii) water vapour permeability test (EN 15803) have been simulated to check the capacity and quality of the moisture transfer simulation with the new functions. These numerical exercises were carried out using a moisture transport module implemented in COMSOL Multiphysics. The material selected was the limestone used in the construction of the Cathedral of Santa Maria and San Julian (Cuenca, Spain). The satisfactory results obtained demonstrate the utility of the functions proposed to model the hydraulic conductivity and diffusion resistance factor. A significant reduction in the number of material parameters is achieved without compromising the simulation capacity.

This paper presents a simplified method for the study of the soil-structure interaction problem for isolated footings on soils subjected to water content-related volume changes. The method is based on the 2D modelling of thermo-hydro-mechanical processes occurring in the soil and the soil–atmosphere interface, the calculation of the soil-footing system stiffness and the modelling of the structure. The idealization of soil-structure interaction from an equivalent springs model, obtained from the above characteristics, allows the movements changes in time of the foundations to be obtained. These in turn can be used for evaluation of building damage related to angular distortion among foundations.

In the treatment of a polluted soil, the pH has a strong impact on the development of different physicochemical processes as precipitation/dissolution, adsorption/desorption or ionic exchange. In addition, the pH determines the chemical speciation of the compounds present in the system and, consequently, it conditions the transport processes by which those compounds will move. This question has aroused great interest in the development of pH control technologies coupled to soil remediation processes. In electrokinetic remediation processes, pH has usually been controlled by catholyte pH conditioning with acid solutions, applied to cases of heavy metals pollution. However, this method is not effective with pollutants that can be dissociated in anionic species. In this context, this paper presents a study of the electrokinetic remediation of soils polluted with 2,4-Dichlorophenoxyacetic acid, a common polar pesticide, enhanced with an anolyte pH conditioning strategy. A numerical study is proposed to evaluate the effectiveness of the strategy. Several numerical tests have been carried out for NaOH solutions with different concentrations as pH conditioning fluid. The results show that the anolyte pH conditioning strategy makes it possible to control the pH of the soil and, consequently, the chemical speciation of pollutant species. Thus, it is possible to achieve an important flux of pesticide into the anolyte compartment (electro-migration of anionic species and diffusive transport of acid species). This way, it possible to maximise the pesticide accumulation in this compartment, allowing a much more effective removal of pollutants from the soil than without the anolyte pH conditioning strategy.

Traditionally, Spanish schools of civil engineering provide their students a class on “Technical English” in order to develop their language skills. However, this class does not cover all the skills that the student would need in the labor market and mainly focuses in the reading and writing skills, and in a lower degree in the speaking and listening ones. This paper proposes a series of innovative and informal training activities, such as cine-forum on technical civil engineering topics and role playing on real professional situations, that allow Spanish civil engineering students to develop English skills, that can rarely be worked in the classroom (i. e. speaking, negotiating and conversing), which encourage debate, participation, and foster their self-confidence to speak about technical-English topics in public. Although the students’ level of English is much lower than expected, they all agree on the importance of technical English for their future career. The results also show the students’ lack in skills that are difficult to train in regular classes (speaking and talking). Consequently, this situation would require to provide complementary activities like the ones suggested in this project in order to develop these skills and increase the students’ demand for engineering classes taught in English. Традиционно для студентов испанских строительных университетов проводятся курсы технического английского языка для повышения их уровня владения языком. Однако эти курсы ориентированы на чтение и письмо, в меньшей степени — на навыки разговорного языка и не охватывают всех компетенций, требующихся на рынке труда. В этой статье предлагается ряд новых и неформальных учебных методов (использование кинокамер при изучении вопросов гражданского строительства и ролевой игры в реальных профессиональных ситуациях), которые позволяют испанским студентам-строителям развивать навыки английского языка, которые трудно получить в обычном классе, что развивает уверенность, позволяет студентам овладевать навыками ведения переговоров, бесед, участвовать в дискуссиях. Хотя уровень владения английским языком испанских студентов намного ниже, чем ожидалось, все они согласны с важностью овладения техническим английским для дальнейшей карьеры. Результаты опросов также показывают отсутствие у студентов навыков, которые трудно тренировать в обычных классах (речь и разговоры). Таким образом, для развития навыков владения английским языком для студентов‑строителей требуются дополнительные методики, которые предлагаются в этом проекте.

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 × 10 −4 , 2 × 10 −3 , 0.11 and 21.76 m 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.

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 evaluated

The volumetric deformability of the microstructure of compacted active clays is linked to the water mass exchange with the macrostructural void space. Given that this exchange is determined by the difference in the chemical potential of water in these two structural levels, this work proposes to define a microstructural effective stress (understood as the magnitude controlling microstructural strains) from this difference in chemical potentials, identifying the microstructural effective stress with the thermodynamic swelling pressure. To assess the scope of this definition, an inspection exercise has been conducted, examining the important functional dependence on the microstructural void ratio for different loads, water content and environmental salinity conditions. For the compacted active clays analysed, the thermodynamic swelling pressure is a robust and consistent definition of the microstructural effective stress. © 2017 Elsevier Ltd

In the treatment of a polluted soil, the pH has a strong impact on the development of different physicochemical processes as precipitation/dissolution, adsorption/desorption or ionic exchange. In addition, the pH determines the chemical speciation of the compounds present in the system and, consequently, it conditions the transport processes by which those compounds will move. This question has aroused great interest in the development of pH control technologies coupled to soil remediation processes. In electrokinetic remediation processes, pH has usually been controlled by catholyte pH conditioning with acid solutions, applied to cases of heavy metals pollution. However, this method is not effective with pollutants that can be dissociated in anionic species. In this context, this paper presents a study of the electrokinetic remediation of soils polluted with 2,4-Dichlorophenoxyacetic acid, a common polar pesticide, enhanced with an anolyte pH conditioning strategy. A numerical study is proposed to evaluate the effectiveness of the strategy. Several numerical tests have been carried out for NaOH solutions with different concentrations as pH conditioning fluid. The results show that the anolyte pH conditioning strategy makes it possible to control the pH of the soil and, consequently, the chemical speciation of pollutant species. Thus, it is possible to achieve an important flux of pesticide into the anolyte compartment (electro-migration of anionic species and diffusive transport of acid species). This way, it possible to maximise the pesticide accumulation in this compartment, allowing a much more effective removal of pollutants from the soil than without the anolyte pH conditioning strategy.

This paper proposes a calculation procedure to estimate the swelling pressure of bentonites. The experimental information needed to obtain the estimations can be obtained from relatively conventional tests, including the determination of the water retention curve, and swelling pressure tests using oedometric sample holders. This allows to obtain physically based predictions of the changes in swelling pressure with environment salinity. To facilitate the calculations, an open access spreadsheet in which the proposed approach has been implemented is attached as Supplementary material. A set of significant swelling pressure tests are modelled, obtaining very good fits. The fits not only build confidence in the proposed methodology, but also improve the validation of the hydro-chemo-mechanical formulation on which the proposed procedure is based.

This article describes the multicriteria Monitoring and Alert System designed to allow safe access to Santos Morcillo Lake (located in Ruidera Lakes Natural Park, Central Spain). In the spring of 2007, two families of cracks were observed on both banks of the lake, located near the barrage separating it from the downstream Batana Lake. A sinkhole was also detected. This raised great community alarm, since it was feared that the barrage would collapse. A geoelectric and geotechnical survey was carried out to monitor the crack aperture, the barrage movements and the evolution of the lake water level. On the basis of the information obtained, a model was designed that was able to offer a simple and consistent explanation of the system’s behaviour. Therefore, the model was used as a basis to define the safety assessment system proposed here. The system is based on the data from previously installed monitoring devices that would be processed daily by the Technical Staff of the Park. In the event that a warning should be triggered, an integrated analysis of all the information must be conducted, and an alert would be activated. The alert level will depend on how reliable the mobilisation hypothesis is, and different degrees of restricted access to Santos Morcillo, Batana and Colgada Lakes will take effect.

Traditionally, Spanish schools of civil engineering provide their students a class on “Technical English” in order to develop their language skills. However, this class does not cover all the skills that the student would need in the labor market and mainly focuses in the reading and writing skills, and in a lower degree in the speaking and listening ones. This paper proposes a series of innovative and informal training activities (cine-forum on technical civil engineering topics and role playing on real professional situations) that allow Spanish civil engineering students to develop English skills that can rarely be worked in the classroom (i.e. speaking, negotiating and conversing), encouraging debate, participation, and fostering their self-confidence to speak about technical-English topics in public. Although the students’ level of English is much lower than expected, they all agree on the importance of technical English for their future career. The results also show the students’ lack in skills that are difficult to train in regular classes (speaking and talking). Consequently, this situation would require to provide complementary activities like the ones suggested in this project in order to develop these skills and increase the students’ demand for engineering classes taught in English.

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's 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. © 2017 Elsevier B.V.

This work evaluated water transport that occurs in a partially saturated soil of low hydraulic permeability when undergoing an electrokinetic remediation process. The soil used was a compacted kaolinite. To evaluate a wide range of possible conditions, soil with three different initial water contents (10, 15 and 20%) was used, obtaining a range of dry densities of 1300–1600 kg m−3. The tests were performed using a lab-scale setup with a soil capacity of 675 cm3 and applying different electrical potential gradients (0.5, 1, 1.5 and 2 V cm−1). The experimental results obtained were used to validate a conceptual model implemented in COMSOL. The validated model was used to conduct a detailed interpretation of the observed water transport processes and to perform a study of the hydraulic behaviour of the soil as a function of the initial conditions of compaction, water saturation and applied electrical potential gradient.

This study compares the capabilities of two numerical models that simulate the behaviour of compacted saturated MX-80 bentonite exposed to different chemical environments. Both codes have different approaches: one of them is a reactive transport model, and the other is a hydrogeomechanical model. The study shows that the combined use of both approaches provides a useful basis for designing bentonite barriers in the geological disposal of high-level nuclear waste. Although, their application is now limited to simple geometries and boundary conditions, the proposed approaches are a first step towards a fully thermo-hydro-mechano-chemical model. It is also shown that there is a need for a greater understanding of the chemomechanical coupling that occurs at the microstructural scale to achieve this comprehensive model in the future.

This article proposes a new plastification mechanism to model bentonite free swelling processes by using an elastoplastic approach. The formulation is based on an interaction function that defines the plastic macrostructural strains induced by microstructural effects. This term is defined as a function of the microstructural void ratio, and it establishes a direct connection between the destructuration of the micro- and macrostructures of the bentonite during the free swelling processes. The formulation proposed also includes a new approach to the calculation of the microstructural void ratio as well as a new method to describe the kinetic mass exchange between micro- and macrostructural water, considering that there may not be equilibrium between the two types of water. The model was used to analyse several free swelling tests and was found to yield satisfactory results.

Using multiphysics computer codes has become a useful tool to solve systems of partial differential equations. However, these codes do not always allow for the free introduction of implicitly defined state functions when automatic differentiation is used to compute the iteration matrix. This makes it considerably more difficult to solve geomechanical problems using non-linear constitutive models. This paper proposes a method for overcoming this difficulty based on multiphysics capabilities. The implementation of the well-known Barcelona basic model is described to illustrate the application of the method. For this purpose, without including formulation details addressed by other authors, the fundamentals of its implementation in a finite element code are described. Examples that demonstrate the scope of the proposed methodology are also presented.

A constitutive model of the volumetric behaviour of bentonite aggregates is proposed. The model is based on a state function to define the inter-aggregate (microstructural) void ratio and on a mass transfer function to calculate the mass exchange between macrostructural and microstructural water. Although both functions have been used previously for clay soils, their application beyond the range for which they were derived is proposed. To evaluate whether this extrapolation is valid, data on the swelling of individual bentonite aggregates are analysed. This novel aspect of this study is significant because it is not common to analyse microstructural data directly without introducing any hypothesis about the behaviour of the macrostructure. Despite the lack of a more intensive validation, which will be conducted when more experimental data become available, the results obtained have been satisfactory.

The sustainability of groundwater resources has been a central issue in the Upper Guadiana Basin (Spain) since two of its primary aquifer units were declared overexploited at the end of the 1990s. Three hydrogeological aquifer units located to the north of the primary aquifers have rarely been studied because of their low economic value, despite a large part of the wetlands of La Mancha Humeda Biosphere Reserve overlying the Basin. This report presents the foundations upon which conceptual and numerical models of the Upper Guadiana Basin are based. An evaluation of the sustainability of the groundwater use in Upper Guadiana Basin has been also carried out. The effect of five management options and a simplified climatic-change scenario have been considered for the three northern aquifers. A decrease in the net recharge, a change in river–aquifer interactions, and the total abstraction volumes authorised have been identified as the main factors to address in management planning. In addition, the expected recovery in the primary Western Mancha aquifer is shown to have little correlation with the total volume abstracted from the three northern tributary aquifers.

Parameter identification is one of the key elements in the construction of models in geosciences. However, inherent difficulties such as the instability of ill-posed problems or the presence of multiple local optima may impede the execution of this task. Regularization methods and Bayesian formulations, such as the maximum a posteriori estimation approach, have been used to overcome those complications. Nevertheless, in some instances, a more in-depth analysis of the inverse problem is advisable before obtaining estimates of the optimal parameters. The Markov Chain Monte Carlo (MCMC) methods used in Bayesian inference have been applied in the last 10 years in several fields of geosciences such as hydrology, geophysics or reservoir engineering. In the present paper, a compilation of basic tools for inference and a case study illustrating the practical application of them are given. Firstly, an introduction to the Bayesian approach to the inverse problem is provided together with the most common sampling algorithms with MCMC chains. Secondly, a series of estimators for quantities of interest, such as the marginal densities or the normalization constant of the posterior distribution of the parameters, are reviewed. Those reduce the computational cost significantly, using only the time needed to obtain a sample of the posterior probability density function. The use of the information theory principles for the experimental design and for the ill-posedness diagnosis is also introduced. Finally, a case study based on a highly instrumented well test found in the literature is presented. The results obtained are compared with the ones computed by the maximum likelihood estimation approach.

This article discusses how sensitivity analysis is a sound assessment tool for selecting the most efficient stabilization method of slopes at failure. A discretized form of the variational approach is used not only for performing sensitivity analysis but to locate the critical slip surface, i.e., the sensitivity analysis is carried out in the same way as it is done in optimization problems. This method supplies a robust formulation and methodology for obtaining the sensitivities of the safety factor with respect to both the soil parameters and the slope profile, stating the slope stabilization design as a relatively simple minimization problem. Two well known examples, as the Selset landslide and the Sudbury Hill slip are used to illustrate the application of the method and to highlight both its capabilities and limitations.