Geotechnical Analysis of Contaminated Sand by Light Non-Aquous Phase Liquids

Contaminated soil reuse was investigated, with higher profusion, throughout the early 90’s, coinciding with the 1991 Gulf War, when efforts to amend large crude oil releases began in geotechnical assessment of contaminated soils. Isolated works referring to geotechnical testing with hydrocarbon ground contaminants are described in the state-of-the-art, which have been extended to other type of contaminated soil references. Contaminated soils by light non-aquous phase liquids (LNAPL) bearing capacity reduction has been previously investigated from a forensic point of view. To date, all the research works have been published based on the assumption of constant contaminant saturation for the entire soil mass. In contrast, the actual LNAPLs distribution plumes exhibit complex flow patterns which are subject to physical and chemical changes with time and distance travelled from the release source. This aspect has been considered along the present text. A typical Madrid arkosic soil formation is commonly known as Miga sand. Geotechnical tests have been carried out, with Miga sand specimens, in incremental series of LNAPL concentrations in order to observe the soil engineering properties variation due to a contamination increase. Results are discussed in relation with previous studies and as a matter of fact, soil mechanics parameters change in the presence of LNAPL, showing different tendencies according to each test and depending on the LNAPL content, as well as to the specimen’s initially planned relative density, dense or loose. Geotechnical practical implications are also commented on and analyzed. Variation on geotechnical properties may occur only within the external contour of contamination distribution plume. This scope has motivated the author to develop a physical model based on transparent soil technology. The model aims to reproduce the distribution of LNAPL into the ground due to an accidental release from a storage facility. Preliminary results indicate that the model is a potentially complementary tool for hydrogeological applications, site-characterization and remediation treatment testing within the framework of soil pollution events. A description of the test setup of an innovative three dimensional physical model for the flow of two or more phases, in porous media, is presented herein, along with a summary of the advantages, limitations and future applications for modeling with transparent material. En los primeros años de la década de los años 90, del siglo pasado, coincidiendo con la Guerra del Golfo en 1991, se investigó intensamente sobre la reutilización de suelos afectados por grandes volúmenes de vertidos de crudo, fomentándose la evaluación geotécnica de los suelos contaminados. Se describen, en el estado del arte de esta tésis, una serie de trabajos aislados en relación con la caracterización geotécnica de suelos contaminados con hidrocarburos, descripción ampliada mediante referencias relacionadas con otros tipos de contaminación de suelos. Existen estudios previos de patología de cimentaciones que analizan la reducción de la capacidad portante de suelos contaminados por hidrocarburos líquidos ligeros en fase no acuosa (acrónimo en inglés: LNAPL de “Liquid Non-Aquous Phase Liquid”). A fecha de redacción de la tesis, todas las publicaciones anteriores estaban basadas en la consideración de una saturación del contaminante constante en toda la extensión del terreno de cimentación. La distribución real de las plumas de contaminante muestra, por el contrario, complejas trayectorias de flujo que están sujetas a cambios físico-químicos en función del tiempo y la distancia recorrida desde su origen de vertido. Éste aspecto ha sido considerado y tratado en el presente texto. La arena de Miga es una formación geológica típica de Madrid. En el ámbito de esta tesis se han desarrollado ensayos geotécnicos con series de muestras de arena de Miga contaminadas con distintas concentraciones de LNAPL con el objeto de estimar la variación de sus propiedades geotécnicas debido a un incremento de contaminación. Se ha realizado una evaluación de resultados de los ensayos en comparación con otros estudios previamente analizados, resultando que las propiedades mecánicas del suelo, efectivamente, varían en función del contenido de LNAPL y de la densidad relativa con la que se prepare la muestra, densa o floja. Se analizan y comentan las implicaciones de carácter práctico que supone la mencionada variación de propiedades geotécnicas. El autor ha desarrollado un modelo físico basado en la tecnología de suelos transparentes, considerando que las variaciones de propiedades geotécnicas únicamente deben producirse en el ámbito interior del contorno de la pluma contaminante. El objeto del modelo es el de reproducir la distribución de un LNAPL en un terreno dado, causada por el vertido accidental de una instalación de almecenamiento de combustible. Los resultados preliminares indican que el modelo podría emplearse como una herramienta complementaria para el estudio de eventos contaminantes, permitiendo el desarrollo de aplicaciones de carácter hidrogeológico, caracterización de suelos contaminados y experimentación de tratamientos de remediación. Como aportación de carácter innovadora, se presenta y describe un modelo físico tridimensional de flujo de dos o más fases a través de un medio poroso transparente, analizándose sus ventajas e inconvenientes así como sus limitaciones y futuras aplicaciones.

Modelling of chloride transport in non-saturated concrete : from microscale to macroscale

Corrosion of steel bars embedded in concrete has a great influence on structural performance and durability of reinforced concrete. Chloride penetration is considered to be a primary cause of concrete deterioration in a vast majority of structures. Therefore, modelling of chloride penetration into concrete has become an area of great interest. The present work focuses on modelling of chloride transport in concrete. The differential macroscopic equations which govern the problem were derived from the equations at the microscopic scale by comparing the porous network with a single equivalent pore whose properties are the same as the average properties of the real porous network. The resulting transport model, which accounts for diffusion, migration, advection, chloride binding and chloride precipitation, consists of three coupled differential equations. The first equation models the transport of chloride ions, while the other two model the flow of the pore water and the heat transfer. In order to calibrate the model, the material parameters to determine experimentally were identified. The differential equations were solved by means of the finite element method. The classical Galerkin method was employed for the pore solution flow and the heat transfer equations, while the streamline upwind Petrov Galerkin method was adopted for the transport equation in order to avoid spatial instabilities for advection dominated problems. The finite element codes are implemented in Matlab® . To retrieve a good understanding of the influence of each variable and parameter, a detailed sensitivity analysis of the model was carried out. In order to determine the diffusive and hygroscopic properties of the studied concretes, as well as their chloride binding capacity, an experimental analysis was performed. The model was successfully compared with experimental data obtained from an offshore oil platform located in Brazil. Moreover, apart from the main objectives, numerous results were obtained throughout this work. For instance, several diffusion coefficients and the relation between them are discussed. It is shown how the electric field set up between the ionic species depends on the gradient of the species’ concentrations. Furthermore, the capillary hysteresis effects are illustrated by a proposed model, which leads to the determination of several microstructure properties, such as the pore size distribution and the tortuosity-connectivity of the porous network. El fenómeno de corrosión del acero de refuerzo embebido en el hormigón ha tenido gran influencia en estructuras de hormigón armado, tanto en su funcionalidad estructural como en aspectos de durabilidad. La penetración de cloruros en el interior del hormigón esta considerada como el factor principal en el deterioro de la gran mayoría de estructuras. Por lo tanto, la modelización numérica de dicho fenómeno ha generado gran interés. El presente trabajo de investigación se centra en la modelización del transporte de cloruros en el interior del hormigón. Las ecuaciones diferenciales que gobiernan los fenómenos a nivel macroscópico se deducen de ecuaciones planteadas a nivel microscópico. Esto se obtiene comparando la red porosa con un poro equivalente, el cual mantiene las mismas propiedades de la red porosa real. El modelo está constituido por tres ecuaciones diferenciales acopladas que consideran el transporte de cloruros, el flujo de la solución de poro y la transferencia de calor. Con estas ecuaciones se tienen en cuenta los fenómenos de difusión, migración, advección, combinación y precipitación de cloruros. El análisis llevado a cabo en este trabajo ha definido los parámetros necesarios para calibrar el modelo. De acuerdo con ellas, se seleccionaron los ensayos experimentales a realizar. Las ecuaciones diferenciales se resolvieron mediante el método de elementos finitos. El método clásico de Galerkin se empleó para solucionar las ecuaciones de flujo de la solución de poro y de la transferencia de calor, mientras que el método streamline upwind Petrov-Galerkin se utilizó para resolver la ecuación de transporte de cloruros con la finalidad de evitar inestabilidades espaciales en problemas con advección dominante. El código de elementos finitos está implementado en Matlab® . Con el objetivo de facilitar la comprensión del grado de influencia de cada variable y parámetro, se realizó un análisis de sensibilidad detallado del modelo. Se llevó a cabo una campaña experimental sobre los hormigones estudiados, con el objeto de obtener sus propiedades difusivas, químicas e higroscópicas. El modelo se contrastó con datos experimentales obtenidos en una plataforma petrolera localizada en Brasil. Las simulaciones numéricas corroboraron los datos experimentales. Además, durante el desarrollo de la investigación se obtuvieron resultados paralelos a los planteados inicialmente. Por ejemplo, el análisis de diferentes coeficientes de difusión y la relación entre ellos. Así como también se observó que el campo eléctrico establecido entre las especies iónicas disueltas en la solución de poro depende del gradiente de concentración de las mismas. Los efectos de histéresis capilar son expresados por el modelo propuesto, el cual conduce a la determinación de una serie de propiedades microscópicas, tales como la distribución del tamaño de poro, además de la tortuosidad y conectividad de la red porosa.

Cyclic behaviour of saturated sands subject to previous horizontal shear stresses

The dynamic behaviour of saturated sands has been studied from different perspectives. However, most experimental research on this field does not take into account the shear stress conditions existing prior to the application of dynamic loads; i.e., a null initial static shear stress (τo = 0) is assumed. The main objective of this work is to report on the influence that static shear stresses (τo) have on the behaviour of saturated sands under cyclic shear loads. This article presents the results and analysis of part of a wider experimental programme involving 30 monotonic and 26 cyclic simple shear tests for different combinations of static shear stress (τo) and cyclic shear stress (τc) (all undrained), besides identification and classification tests. The tested samples have been taken from the area of the North Entrance Mouth at the Port of Barcelona (Spain).

Modelling of chloride penetration into non-saturated concrete: Case study application for real marine off shore structures

The aim of this paper is to explain the chloride concentration profiles obtained experimentally from control samples of an offshore platform after 25 years of service life. The platform is located 12 km off the coast of the Brazilian province Rio Grande do Norte, in the north-east of Brazil. The samples were extracted at different orientations and heights above mean sea level. A simple model based on Fick’s second law is considered and compared with a finite element model which takes into account transport of chloride ions by diffusion and convection. Results show that convective flows significantly affect the studied chloride penetrations. The convection velocity is obtained by fitting the finite element solution to the experimental data and seems to be directly proportional to the height above mean sea level and also seems to depend on the orientation of the face of the platform. This work shows that considering solely diffusion as transport mechanism does not allow a good prediction of the chloride profiles. Accounting for capillary suction due to moisture gradients permits a better interpretation of the material’s behaviour.

Amazonian white-sand forest: a black future?

Los bosques sobre arena blanca amazónicos son un tipo singular y frágil de bosque tropical húmedo de selva de zonas bajas, que aparecen dispersos sobre teselas de suelo muy oligotrófico y albergan un alto porcentaje de endemismos. No son susceptibles de aprovechamiento maderero ni de uso agrícola, pero su madera redonda de pequeño diámetro (5-15 cm) posee gran durabilidad y es un recurso extraído tradicionalmente por los pobladores locales para construir sus viviendas. A pesar de ello, este aprovechamiento local permanece invisible para la reglamentación forestal, lo que puede perjudicar el futuro de estos bosques sobre arena blanca. Este trabajo tiene por objetivo aportar conocimientos básicos sobre la estructura forestal y la composición florística de estos bosques, lo que es esencial para poder planificar un gestión sustentable. Los resultados muestran que, a pesar de su fragilidad, los bosques sobre arena blanca también presentan ciertas ventajas en vista de sus posibilidades de gestión sustentable en comparación con otro tipo de bosques tropicales húmedos: debido a un alto porcentaje de especies comerciales (26 %), a la clara dominancia de un pequeño grupo de especies, la mayoría de ellas (67%) con interés comercial y al hecho de que los fustes potencialmente aprovechables sólo suponen el 17% del área basimétrica total, resulta que en la situación actual, no es necesario aplicar técnicas de aprovechamiento de impacto reducido, puesto que los pies aprovechados son de pequeño diámetro, que no se utiliza maquinaria y que el transporte se realiza únicamente a hombros y/o por flotación

Modelling of chloride transport in non-saturated concrete : from microscale to macroscale

A model for chloride transport in concrete is proposed. The model accounts for transport several transport mechanisms such as diffusion, advection, migration, etc. This work shows the chloride transport equations at the macroscopic scale in non-saturated concrete. The equations involve diffusion, migration, capillary suction, chloride combination and precipitation mechanisms. The material is assumed to be infinitely rigid, though the porosity can change under influence of chloride binding and precipitation. The involved microscopic and macroscopic properties of the materials are measured by standardized methods. The variables which must be imposed on the boundaries are temperature, relative humidity and chloride concentration. The output data of the model are the free, bound, precipitated and total chloride ion concentrations, as well as the pore solution content and the porosity. The proposed equations are solved by means of the finite element method (FEM) implemented in MATLAB (classical Galerkin formulation and the streamline upwind Petrov-Galerkin (SUPG) method to avoid spatial instabilities for advection dominated flows).

Dry sand as a specialized layer to improve the acoustic insulation between rooms one above another = La arena como capa intermedia especializada para la mejora del aislamiento acústico entre recintos superpuestos

Se comprueba la mejora en el aislamiento acústico entre recintos de la colocación de una capa de arean entre el solado y el forjado

The sand hill [Material gráfico] : engraved from an original painting of D. Teniers...

Inscripción en ángulo inf. derech.: "Nº 23"

Modelling of chloride penetration into non-saturated concrete: case study application for real marine offshore structures

The aim of this paper is to explain the chloride concentration profiles obtained experimentally from control samples of an offshore platform after 25 years of service life. The platform is located 12 km off the coast of the Brazilian province Rio Grande do Norte, in the north-east of Brazil. The samples were extracted at different orientations and heights above mean sea level. A simple model based on Fick’s second law is considered and compared with a finite element model which takes into account transport of chloride ions by diffusion and convection. Results show that convective flows significantly affect the studied chloride penetrations. The convection velocity is obtained by fitting the finite element solution to the experimental data and seems to be directly proportional to the height above mean sea level and also seems to depend on the orientation of the face of the platform. This work shows that considering solely diffusion as transport mechanism does not allow a good prediction of the chloride profiles. Accounting for capillary suction due to moisture gradients permits a better interpretation of the material’s behaviour

Estudio sobre la durabilidad de los nuevos tipos de cemento para la evaluación del comportamiento de morteros y hormigones frente a la agresión química de los sulfatos y del agua de mar

Esta investigación ha sido desarrollada para analizar la influencia de las características específicas de los nuevos cementos en el comportamiento expansivo originado durante cinco años por el ataque externo por sulfatos o agua de mar, y para estudiar la validez de diversos métodos de ensayo aplicables para evaluar la resistencia de los conglomerantes a los sulfatos o al agua de mar. Se han determinado las características químicas y mecánicas de los quince cementos seleccionados en el estudio (su contenido de yeso, tipo y cantidad de adiciones, contenidos de C3A y C4AF) para examinar la relación entre estos parámetros y su durabilidad frente al ataque por sulfatos. Se han llevado a cabo ensayos para evaluar la resistencia a sulfatos sobre probetas de mortero fabricadas con los quince cementos comunes seleccionados de muy distintos tipos, la mayoría de ellos resistentes a sulfatos conforme a la norma UNE-EN 197-1. Por cada tipo de cemento se fabricaron probetas de mortero para la realización de ensayos acelerados usando Na2SO4 como medio agresivo según la norma ASTM C 1012 manteniendo esas condiciones de exposición durante dos años. En paralelo se fabricaron otras series de probetas idénticas, que fueron conservadas en agua de mar y en agua saturada en cal (como patrón de un medio no agresivo) durante el mismo plazo. Adicionalmente estos cementos fueron evaluados conforme a los procedimientos de ensayo acelerado de la norma ASTM C 452 y del ensayo de Koch y Steinegger. También se fabricaron otras series de probetas de 40x40x160 mm (adoptando una relación a/c=0,5 y la composición arena:cemento definida en la norma UNE-EN 196-1). Durante cinco años de exposición en las tres condiciones de conservación establecidas (sulfatos, agua de mar y agua patrón) se han efectuado ensayos para determinar la resistencia a compresión y el deterioro superficial de las probetas de mortero. Ninguno de los conglomerantes fue mezclado inicialmente con yeso para acelerar el ataque ni se establecieron otras condiciones no realísticas en la fabricación de los morteros Se ha analizado el comportamiento durable de los cementos tanto frente al ataque por sulfatos como por agua de mar. Para la evaluación se han tomado en consideración las variaciones de contenido en C3A, los tipos y proporciones de los constituyentes (adiciones puzolánicas, escorias de horno alto, caliza …) con el mismo tipo de clínker en algunos casos. Se ha procedido a evaluar la validez de los límites de aceptación establecidos en cada uno de los ensayos acelerados para determinar la resistencia a sulfatos y valorar su idoneidad en los nuevos cementos, y se ha propuesto un método de ensayo acelerado recomendable para discriminar cementos resistentes y no resistentes a sulfatos. A la edad final de los tres tipos de exposición han sido correlacionados los parámetros relativos a la degradación superficial, pérdida de resistencia y expansión lineal de las probetas con las características de los cementos y los productos expansivos analizados mediante difracción de rayos X, con objeto de poder redefinir las características recomendables exigibles a los cementos resistentes a sulfatos o al agua de mar. Experimental research has been performed to relate specific cement characteristics to expansion due to sulfate or sea water attack during five years, and to study different test methods suitability for sulfate and marine resistance. Chemical and mechanical characteristics were studied to determine the variation in properties of selected cements (SO3 content, type and amount of additions, C3A, and C4AF content) and examine relationships between these characteristics and the results of sulfate resistance. Sulfate resistance testing have been performed on mortar specimens prepared from fifteen cement types of statistically diverse chemical composition, most of them with sulfate resistant properties according to European standard EN 197-1 Mortar specimens testing using Na2SO4 as the aggressive medium according to ASTM C 1012 was performed using each cement; identical specimens were also stored in sea water, and in lime saturated water (blank condition), up to two years age. Additionally these cements were tested conforming to ASTM C 452 and Koch and Steinegger test. Mortar specimens of 40x40x160 mm were also moulded (with w/c ratio and cement:sand composition of EN 196-1). Compressive strength of these mortar specimens have been tested during five years of immersion in a sulfate solution and also in seawater (and in lime saturated water, as a blank condition), and external damage and have been analyzed. None of the prepared mortars was blended with gypsum or any other nonrealistic condition. Durability behaviour in sulfate resistant common cements conforming to EN 197-1 exposed to sulfate attack was evaluated, and also the correlation between sulfate resistance and seawater resistance has been studied. Different C3A contents, variable types and proportioning of constituents (limestone, pozzolanic additions, blastfurnace slag ...) with or without the same clinker type were investigated. Recommended acceptance limits for sulfate resistance of cements concerning to each used test method were evaluated in order to explore their suitability. A new accelerated method has been recommended to provide a meaningful discrimination between sulfate resistant or non-sulfate resistant cements. Relationships between cement characteristics, degradation, expansive products obtained by X-ray diffraction techniques, strength loss and maximum expansion after applied storage treatments, were correlated at final age, to redefine cement characteristics for sulfate resistant and marine resistant Portland cement.

Toward an understanding of the biochemical and pharmacological complexity of the saliva of a hematophagous sand fly Lutzomyia longipalpis

The saliva of blood-sucking arthropods contains powerful pharmacologically active substances and may be a vaccine target against some vector-borne diseases. Subtractive cloning combined with biochemical approaches was used to discover activities in the salivary glands of the hematophagous fly Lutzomyia longipalpis. Sequences of nine full-length cDNA clones were obtained, five of which are possibly associated with blood-meal acquisition, each having cDNA similarity to: (i) the bed bug Cimex lectularius apyrase, (ii) a 5′-nucleotidase/phosphodiesterase, (iii) a hyaluronidase, (iv) a protein containing a carbohydrate-recognition domain (CRD), and (v) a RGD-containing peptide with no significant matches to known proteins in the blast databases. Following these findings, we observed that the salivary apyrase activity of L. longipalpis is indeed similar to that of Cimex apyrase in its metal requirements. The predicted isoelectric point of the putative apyrase matches the value found for Lutzomyia salivary apyrase. A 5′-nucleotidase, as well as hyaluronidase activity, was found in the salivary glands, and the CRD-containing cDNA matches the N-terminal sequence of the HPLC-purified salivary anticlotting protein. A cDNA similar to α-amylase was discovered and salivary enzymatic activity demonstrated for the first time in a blood-sucking arthropod. Full-length clones were also found coding for three proteins of unknown function matching, respectively, the N-terminal sequence of an abundant salivary protein, having similarity to the CAP superfamily of proteins and the Drosophila yellow protein. Finally, two partial sequences are reported that match possible housekeeping genes. Subtractive cloning will considerably enhance efforts to unravel the salivary pharmacopeia of blood-sucking arthropods.

Moisture Distribution in Partially Saturated Concrete Studied by Impedance Spectroscopy

The moisture content and its spatial distribution has a great influence on the durability properties of concrete structures. Several non-destructive techniques have been used for the determination of the total water content, but moisture distribution is difficult to determine. In this paper impedance spectroscopy is used to study the water distribution in concrete samples with controlled and homogeneously distributed moisture contents. The technique is suitable for the determination of water distribution inside the sample, using the appropriate equivalent circuits. It is shown that using the selected drying procedures there is no change in the solid phase of the samples, although the technique can only be used for the qualitative study of variations in the solid phase when samples are too thick. The results of this work show that for a wide range of concrete percentages of saturation, from full to 18 % saturation, practically all the pores keep at least a thin layer of electrolyte covering their walls, since the capacitance measurement results are practically independent of the saturation degree.

Fate and Transport of Naproxen in a Sandy Aquifer Material: Saturated Column Studies and Model Evaluation

Naproxen-C14H14O3 is a nonsteroidal anti-inflammatory drug which has been found at detectable concentrations in wastewater, surface water, and groundwater. Naproxen is relatively hydrophilic and is in anionic form at pH between 6 and 8. In this study, column experiments were performed using an unconsolidated aquifer material from an area near Barcelona (Spain) to assess transport and reaction mechanisms of Naproxen in the aquifer matrix under different pore water fluxes. Results were evaluated using HYDRUS-1D, which was used to estimate transport parameters. Batch sorption isotherms for Naproxen conformed with the linear model with a sorption coefficient of 0.42 (cm3 g−1), suggesting a low sorption affinity. Naproxen breakthrough curves (BTCs) measured in soil columns under steady-state, saturated water flow conditions displayed similar behavior, with no apparent hysteresis in sorption or dependence of retardation (R, 3.85-4.24) on pore water velocities. Soil sorption did not show any significant decrease for increasing flow rates, as observed from Naproxen recovery in the effluent. Sorption parameters estimated by the model suggest that Naproxen has a low sorption affinity to aquifer matrix. Most sorption of Naproxen occurred on the instantaneous sorption sites, with the kinetic sorption sites representing only about 10 to 40% of total sorption.

Morphological classification of microtidal sand and gravel beaches

A new classification of microtidal sand and gravel beaches with very different morphologies is presented below. In 557 studied transects, 14 variables were used. Among the variables to be emphasized is the depth of the Posidonia oceanica. The classification was performed for 9 types of beaches: Type 1: Sand and gravel beaches, Type 2: Sand and gravel separated beaches, Type 3: Gravel and sand beaches, Type 4: Gravel and sand separated beaches, Type 5: Pure gravel beaches, Type 6: Open sand beaches, Type 7: Supported sand beaches, Type 8: Bisupported sand beaches and Type 9: Enclosed beaches. For the classification, several tools were used: discriminant analysis, neural networks and Support Vector Machines (SVM), the results were then compared. As there is no theory for deciding which is the most convenient neural network architecture to deal with a particular data set, an experimental study was performed with different numbers of neuron in the hidden layer. Finally, an architecture with 30 neurons was chosen. Different kernels were employed for SVM (Linear, Polynomial, Radial basis function and Sigmoid). The results obtained for the discriminant analysis were not as good as those obtained for the other two methods (ANN and SVM) which showed similar success.

Castles in the sand: Mali and the demise of the EU’s Common Security and Defence Policy. CEPS Commentary, 28 January 2013

The threat posed by the crisis in Mali is direct, multidimensional and without regard to geographical proximity or historical and colonial heritage, writes Giovanni Faleg. France’s solitary intervention in Mali and the EU’s absence there raise two important questions for the future of the EU’s supposedly ‘Common’ Security and Defence Policy. The first has to do with the crisis itself; its nature and the threat posed by the terrorist groups and militias that are being countered by French armed forces. The second concerns the causes and implications of yet another example of the EU’s inability to take responsibility for security matters in its neighbourhood and beyond.