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The Saint-Fabien landslide occurred in December 1976, 270 km northeast of Quebec City, Canada. The landslide took place in a valley filled with glaciomarine sensitive clay covered by peat bog deposits and presenting an upwards hydraulic gradient. Unique features of this event are the ground surface and the failure surface that are both close to the horizontal. In addition, passive and active failure zones were observed in the debris after the landslide, indicating a possible downward progressive failure mechanism, rarely observed in Eastern Canadian clays. Possible triggers of the event are: the continuous exploitation of the peat downslope and (or) the roadworks going on along Road 132 at the time of the event, which is crossing the landslide area upslope. Conventional stability analysis for the site gives a factor of safety of 1.43, indicating that limit equilibrium analysis cannot explain the formation of the failure surface observed at Saint-Fabien. The initiation and the propagation of the failure were analysed through 1D numerical modelling using the concept of progressive failure. The methodology consists of two steps: first the calculation of the initial stresses in the slope with the finite element software PLAXIS 2D; and second, the modelling of initiation and propagation of the progressive failure along the potential failure surface with the finite element code BIFURC, developed at the Norwegian Geotechnical Institute. Results from the modelling with BIFURC show that the concept of progressive failure is able to explain the extent of the landslide observed at Saint-Fabien with parameter values based on what was measured in situ. Key words: sensitive clay, progressive failure, large retrogressive landslide, downward translational landslide Le glissement de terrain de Saint-Fabien s'est produit le 16 decembre 1976, 270 km au nord-est de la ville de Quebec, Canada. Ce dernier a pris place dans une vallee remplie d'argile sensible glaciomarine recouverte de depots de tourbe et presentant un gradient hydraulique ascendant. La surface du sol et la surface de rupture sont pratiquement horizontales, ce qui est particulier a ce glissement. Aussi, une zone passive et une zone active ont ete observees dans les debris apres le glissement, indiquant un possible mouvement translationnel progressif vers le bas, rarement observe dans les argiles de l'est du Canada. L'exploitation de la tourbe en pied de pente ainsi que les travaux en cours le long de la route 132 a cette epoque sont de possibles elements declencheurs de ce glissement. L'analyse de stabilite conventionnelle a donne un coefficient de securite de 1,43. La methode a l'equilibre limite ne permet donc pas d'expliquer la formation de la surface de rupture observee a Saint- Fabien. L'initiation et la propagation de la rupture ont ete analysees avec la modelisation numerique en 1D en utilisant le concept de la rupture progressive. Les deux etapes de cette analyse sont : premierement de calculer les contraintes initiales dans la pente avec le logiciel d'elements finis PLAXIS 2D; et deuxiemement, de modeliser la propagation de la rupture progressive le long d'une surface de rupture potentielle avec le code d'elements finis BIFURC, developpe a l'Institut Norvegien de Geotechnique. Les resultats obtenus de la modelisation numerique avec BIFURC ont montre que le concept de rupture progressive permet d'expliquer l'etendue de la rupture observee a Saint-Fabien, avec des valeurs de parametres bases sur ce qui a ete mesure sur le terrain. Mots-cles : argile sensible, rupture progressive, glissement de terrain fortement retrogressif, glissement de terrain translationnel vers le bas, 1. Introduction On 16 December 1976, a landslide occurred near the municipality of Saint-Fabien, 270 km northeast of Quebec City, Canada, along Road 132 (Fig. 1). This landslide was first [...]

Soil-vegetation-atmosphere interaction has long been known to induce significant pore pressure variations at shallow depths and associated superficial slope movements. Recent findings suggest that the effect of this interaction may also extend to large depths in natural clay slopes. Multiple examples of weather-induced deep landslide mechanisms can be found in the Southern Apennines (Italy), where slopes are often formed of fissured clays. The relationship between the activity of these landslides and the hydro-mechanical processes due to soil-vegetation- atmosphere interaction was investigated herein by means of a two-dimensional coupled hydro-mechanical finite element analysis. A constitutive model capable of simulating the behaviour of highly overconsolidated clays, in both saturated and unsaturated states, was adopted in the analysis, in conjunction with a boundary condition capable of reproducing the combined effects of rainfall infiltration, evapo-transpiration, and run-off. The results of the analysis corroborate the connection between weather conditions, pore pressure variations, and slope movements in natural clay slopes. The importance of adequately reproducing the geological history of a natural slope to define its current state is also demonstrated. Key words: numerical modelling, finite element analysis, soil-vegetation- atmosphere interaction, natural slopes, landslides, fissured clays. L'interaction sol-vegetation-atmosphere est connue depuis longtemps pour induire d'importantes variations de pression interstitielle a faible profondeur et des mouvements de pente superficiels associes. Des resultats recents suggerent que l'effet de cette interaction peut egalement s'etendre a de grandes profondeurs dans les pentes argileuses naturelles. De multiples exemples de mecanismes de glissement de terrain profond induits par les conditions meteorologiques peuvent etre trouves dans les Apennins meridionaux (Italie), ou les pentes sont souvent formees d'argiles fissurees. La relation entre l'activite de ces glissements de terrain et les processus hydromecaniques dus a l'interaction sol-vegetation-atmosphere a ete etudiee ici au moyen d'une analyse bidimensionnelle couplee hydro-mecanique par elements finis. Un modele constitutif capable de simuler le comportement des argiles fortement surconsolidees, a la fois dans les etats satures et non satures, a ete adopte dans l'analyse, en conjonction avec une condition limite capable de reproduire les effets combines de l'infiltration des pluies, de l'evapotranspiration et du ruissellement. Les resultats de l'analyse corroborent le lien entre les conditions meteorologiques, les variations de pression interstitielle et les mouvements de pente dans les pentes argileuses naturelles. L'importance de reproduire adequatement l'histoire geologique d'un versant naturel afin de definir son etat actuel est egalement demontree. [Traduit par la Redaction] Mots-cles : modelisation numerique, analyse par elements finis, interaction sol- vegetation-atmosphere, pentes naturelles, glissements de terrain, argiles fissurees., Introduction Soil-atmosphere interaction has been extensively investigated in the laboratory and in the field (e.g., Blight 1997; Toll et al. 2011; Smethurst et al. 2012; Pirone et al. 2015; Askarinejad [...]

Dynamically installed anchor (DIA) for deepwater mooring is an innovative and cost-effective technology in offshore foundation engineering; however, research on the effects of fin configuration of DIAs is limited. This study therefore systematically examines the effects of fin length-width ratio, fin surface area, fin position, and fin shape on the embedment depth and time-dependent holding capacity of DIAs by experimental and theoretical approaches. First, a series of centrifuge tests was performed on four DIA models with an identical fin surface area, but different fin configurations. It is found that the DIA model with short-wide-rectangular fins that are installed at the rear of the shaft achieves deeper embedment depth and higher holding capacity; whereas, the rectangular- and elliptical-shaped DIA models are similar in terms of embedment and capacity. This motivates the proposal for another nine types of finned DIAs in a more systematic manner. Furthermore, the performance of embedment depth and time-dependent holding capacity for these nine DIAs was theoretically assessed using the well-established theoretical methods. In this study, two scenarios with identical impact velocity or embedment depth were examined; wherein the variation of holding capacity with reconsolidation time was explicitly accounted for. Based on the findings, practical implications of fin configurations were reached that may benefit the design of finned DIAs in practice. Key words: dynamically installed anchor (DIA), fin configuration, centrifuge modelling, theoretical approach, clays, design. L'ancrage installe dynamiquement (<< DIA >>) pour l'amarrage en eau profonde est une technologie innovante et rentable dans l'ingenierie des fondations offshore; cependant, la recherche sur les effets de la configuration des ailettes des DIA est limitee. Cette etude examine donc systematiquement les effets du rapport longueur-largeur des ailettes, de la surface des ailettes, de leur position et de leur forme sur la profondeur d'enfouissement et la capacite de retention des DIA en fonction du temps, par des approches experimentales et theoriques. Tout d'abord, une serie d'essais de centrifugation a ete realisee sur quatre modeles de DIA ayant une surface d'ailettes identique mais des configurations d'ailettes differentes. Il s'avere que le modele DIA avec des ailettes rectangulaires courtes et larges qui sont installees a l'arriere de la tige permet d'obtenir une profondeur d'enfouissement plus importante et une capacite de retention plus elevee; considerant que les modeles DIA de forme rectangulaire et elliptique sont similaires en termes d'enfouissement et de capacite. C'est ce qui motive la proposition de neuf autres types de DIA a ailettes de maniere plus systematique. En outre, la performance de la profondeur d'enfouissement et de la capacite de retention en fonction du temps pour ces neuf DIA a ete evaluee theoriquement en utilisant les methodes theoriques bien etablies. Dans cette etude, deux scenarios avec une vitesse d'impact ou une profondeur d'enfouissement identique ont ete examines; ou la variation de la capacite de retention en fonction du temps de reconsolidation a ete explicitement prise en compte. Sur la base des resultats obtenus, on a pu determiner les implications pratiques des configurations d'ailettes qui pourraient etre utiles pour la conception des DIA a ailettes dans la pratique. [Traduit par la Redaction] Mots-cles: ancre installee dynamiquement (<< DIA >>), configuration des ailettes, modelisation de la centrifugeuse, approche theorique, argiles, conception., Introduction The concept of a dynamically installed anchor (DIA) for deepwater mooring is an innovative and cost-effective offshore technology whereby an anchoring foundation is installed through its free drop. Compared [...]

Richardson's ground squirrel (Urocitellus richardsonii (Sabine, 1822)) is a widespread burrowing mammal on the northern Great Plains. This species is a prominent prey item for a variety of predators and its burrows provide important habitat for other wildlife; however, Richardson's ground squirrel is also considered an economically damaging agricultural pest. Despite the ecological importance of Richardson's ground squirrels and their status as pests, there are gaps in our knowledge about large-scale habitat associations for this species. In 2011 and 2012, we conducted 1840 roadside surveys in a 130 000 [km.sup.2] area of southern Saskatchewan, Canada, to understand which habitat features are associated with Richardson's ground squirrel occurrence. Ground squirrels were observed on 8% of the surveys. Probability of ground squirrel occurrence was highest in areas with moderate amounts of grassland (approximately 30%), areas that were developed by humans (>30%), and had a high proportion of clay loam soils, presumably for burrowing. Our study highlights the importance of heterogeneous landscapes and that areas disturbed by humans may provide suitable vegetation structure for ground squirrels. This information can help to identify important habitat for species that rely on Richardson's ground squirrels and identify areas where Richardson's ground squirrels could come into conflict with agriculture. Key words: burrowing mammal, cropland, grassland, habitat use, prairie, Richardson's ground squirrel, Urocitellus richardsonii. Le spermophile de Richardson (Urocitellus richardsonii (Sabine, 1822)) est un animal fouisseur répandu dans les grandes plaines du Nord. Si l'espèce est une proie de premier plan pour différents prédateurs et que ses terriers fournissent d'importants habitats pour d'autres animaux, le spermophile de Richardson est toutefois aussi considéré comme un ravageur causant des pertes économiques en agriculture. Malgré l'importance écologique des spermophiles de Richardson et leur statut de ravageurs, il existe des lacunes dans les connaissances sur les associations d'habitats à grande échelle pour cette espèce. En 2011 et 2012, nous avons réalisé 1840 relevés en bordure de route dans un secteur de 130 000 [km.sup.2] du sud de la Saskatchewan (Canada), afin de mieux comprendre quelles caractéristiques des habitats sont associées à la présence de spermophiles de Richardson. Des spermophiles ont été observés dans 8% des relevés. La probabilité de présence de spermophiles était la plus grande dans les secteurs présentant des proportions modérées de prairie (environ 30%), à aménagements anthropiques (>30%) et qui présentaient une forte proportion de sols à loam argileux, possiblement pour le fouissage. L'étude fait ressortir l'importance des paysages hétérogènes et le fait que les secteurs perturbés par l'activité humaine pourraient fournir une structure de végétation convenant aux spermophiles. Cette information peut aider à cerner des habitats importants pour les espèces qui dépendent des spermophiles de Richardson et des secteurs où ces derniers peuvent entrer en conflit avec des activités agricoles. [Traduit par la Rédaction] Mots-clés : mammifère fouisseur, terre cultivée, prairie, utilisation des habitats, spermophile de Richardson, Urocitellus richardsonii., Introduction Burrowing mammals play important roles in grassland ecosystems (Benedict et al. 1996). Disturbances by burrowing mammals create a heterogeneous landscape that can provide suitable above- and below-ground habitat for [...]

Developing strategies to sequester carbon (C) in soils requires an understanding of the key factors that influence C stabilisation. Although fine mineral particles, especially clay, play a key role in stabilising soil organic matter (SOM), the relationship between SOM and texture is often not strong. We examined the role of the fine mineral fraction in C storage in sedimentary soils in New Zealand. Soils, representing two soil Orders (Brown and Recent) and different land use histories (total of 58 soils; 0-15 cm depth) were sampled. The concentration of C (and N) in four particle size fractions (50 µm) was determined (soils fractionated after dispersion by sonication). The soils had a wide range of textures and SOM; the mass proportion of clay (0.05) between the C concentration in whole soil and clay content. The concentration of C in the clay fraction, which varied over a wide range (35 to 135 g [kg.sup.-1] clay), decreased as the mass proportion of clay increased. A similar trend in C concentration was observed for the fine (5-20 µm) silt fraction. Because of this inverse relationship between the mass of the fine fractions and their C concentration, there was little change in amount of stable C (defined as C in the Additional keywords: C stabilisation by mineral particles, extractable Al & Fe, organic matter fractions., Introduction Soils play an important role in the global C cycle. Management practices that enhance soil C storage are frequently advocated as possible mitigation options to offset C[O.sub.2] emissions from [...]

This study addresses the use of an industry by-product, carbide slag (CS), to activate another industry by-product, ground granulated blastfurnace slag (GGBS), for soft clay stabilization in comparison to Portland cement (PC). The properties of CS-GGBS stabilized clays were investigated through unconfined compressive strength (UCS) test, mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results indicated that the optimum CS content for the CS-GGBS stabilized clay to yield the highest UCS was 4%-6%, varying slightly with curing age and GGBS content. The UCS of the optimum CS-GGBS stabilized clays was more than twice that of the corresponding PC stabilized clays. The main hydration products detected for the CS-GGBS stabilized clays included calcium silicate hydrates (CSH), calcium aluminate hydrates (CAH), and alumino-ferrite monosulfate (AFm). Key words: carbide slag, ground granulated blastfurnace slag, soft clay stabilization, unconfined compressive strength, microstructure. La presente etude traite de l'utilisation d'un sous-produit de l'industrie, les scories de carbure (SC) pour activer un autre sous-produit de l'industrie, le laitier granule broye de haut-fourneau (LGBH), en vue de la stabilisation de l'argile plastique, en comparaison avec l'emploi de ciment Portland (CP). Les proprietes d'argiles stabilisees par des SC et du LGBH ont ete analysees par le biais d'essais de resistance a la compression non confinee (RCNC) et par porosimetrie au mercure (PM), diffractometrie de rayons X (DRX) et microscopie electronique a balayage (MEB). Les resultats ont montre que la teneur optimale en SC permettant a l'argile stabilisee par les SC et le LGBH d'offrir une RCNC maximale etait comprise entre 4 et 6 %, intervalle qui varie legerement selon le niveau de cure et la teneur en LGBH. La RCNC des meilleures argiles stabilisees par des SC et du LGBH represente plus du double de celle des argiles stabilisees par le CP. Les principaux produits d'hydratation detectes dans les argiles stabilisees par des SC et du LGBH sont notamment les hydrates de silicate de calcium (HSC), les hydrates d'aluminates de calcium (HAC) et le monosulfate d'aluminoferrite (AFm). [Traduit par la Redaction] Mots-cles: scories de carbure, laitier granule broye de haut-fourneau, stabilisation de l'argile plastique, resistance a la compression non confinee, microstructure., Introduction The cement dry jet mixing method is commonly used for soft clay treatment, which introduces powdered Portland cement (PC) into the ground and mixes it with in situ clay [...]

The mechanical behavior of clay subjected to cyclic loading is important to consider in the design of the foundations of many types of structures that must resist cyclic loading, such as subgrades and offshore foundations, because clay undergoes greater settlement under cyclic loading than under static loading. The difference in settlement between these two loading patterns due to creep behavior is affected by the cyclic frequency and the cyclic stress ratio. This study investigated the effects of the frequency and cyclic stress ratio of cyclic loading on the creep behavior of a natural clay in China using stress-controlled triaxial tests. The assessed the following parameters: three frequencies, four cyclic stress ratios, and six vertical stresses. The test results indicate that the soft clay displays accelerated creep behavior under dynamic loads. A specific “limit frequency” (in this case, 0.2 Hz) and a “safe load” at which the strain of the soft clay increases very slowly were observed. The effect of the effective axial stress on the creep behavior increases with the increase in the cyclic stress ratio. Based on the tests, the critical cyclic stress ratio is 0.267 at a certain effective axial stress and frequency. [ABSTRACT FROM AUTHOR]

Phosphate processing plants produce an excessive amount of phosphatic clay. This clay represents a serious environmental problem due to their disposal in huge ponds. Finding a feasible method to reduce the clay disposal area is needed. Although the flocculation process, in the presence of fibrous material, seems to be a good dewatering process for phosphatic clay wastes, the maximum solid percentage of flocculated clay does not exceed 18% (starting from 3 to 4%). Recently, the microwave proved a better performance in several research areas as compared to the conventional drying. In this study, clay dewatering by microwave was investigated. Several factors affecting the dewatering process were studied such as heating time, microwave power efficiency, and fiber percentage. Using the microwave, the solid content significantly increases in a reasonably short time. The time and power are the most significant among the studied factors. In addition, sand–clay mix was tested to improve the solid percentage to be used as a filling material. The results showed that the presence of sand enhances the clay drying due to the transparency of sand to the microwave irradiation as well as increasing the clay bed porosity, which facilitates migration of liquid water and/or water vapor toward the surface of dried material. [ABSTRACT FROM PUBLISHER]

Natural antibacterial clays can inhibit growth of human pathogens; therefore, understanding the antibacterial mode of action may lead to new applications for health. The antibacterial modes of action have shown differences based on mineralogical constraints. Here we investigate a natural clay from the Colombian Amazon (AMZ) known to the Uitoto natives as a healing clay. The physical and chemical properties of the AMZ clay were compared to standard reference materials: smectite (SWy-1) and kaolinite (API #5) that represent the major minerals in AMZ. We tested model Gram-negative ( Escherichia coli ATCC #25922) and Gram-positive ( Bacillus subtilis ATCC #6633) bacteria to assess the clay's antibacterial effectiveness against different bacterial types. The chemical and physical changes in the microbes were examined using bioimaging and mass spectrometry of clay digests and aqueous leachates. Results indicate that a single dose of AMZ clay (250 mg/mL) induced a 4-6 order of magnitude reduction in cell viability, unlike the reference clays that did not impact bacterial survival. AMZ clay possesses a relatively high specific surface area (51.23 m/g) and much higher total surface area (278.82 m/g) than the reference clays. In aqueous suspensions (50 mg clay/mL water), soluble metals are released and the minerals buffer fluid pH between 4.1 and 4.5. We propose that the clay facilitates chemical interactions detrimental to bacteria by absorbing nutrients (e.g., Mg, P) and potentially supplying metals (e.g., Al) toxic to bacteria. This study demonstrates that native traditional knowledge can direct scientific studies. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to investigate the effect of clay mineralogy on aggregate stability under the consideration of soil particle surface electric field in electrolyte solution. Materials and methods: Aggregates of montmorillonite, kaolinite, and their compounds in different mass ratio were used as experimental materials. The degree to which the aggregates broke down under different electrolyte concentrations was evaluated both qualitatively and quantitatively. The aggregate breakdown process was observed with a video microscope. Furthermore, the percentage of particles (micro-aggregates and single particles) in diameter of <10, <5, and <2 μm to the total sample mass were measured based on Stokes equation. Results and discussion: Different electrolyte concentrations correspond to different surface potential values around the particle surface. (1) The amount of released small particles for aggregate of clay compounds was several times higher than that for montmorillonite aggregate after breakdown. (2) Under high surface potential conditions, aggregate breakdown in a way of explosion was observed, and the critical surface potential values for the explosion increased with the increase of kaolinite content in aggregates. (3) The content of released particles for clay compound aggregates with high kaolinite content was much higher than that for aggregates with low kaolinite content under high surface potential values. Conclusions: The coupling effects of electric field and clay mineralogy determined the aggregate stability of montmorillonite and clay compounds. This indicated that soil aggregates with relatively high silt content would be less stable than those with relatively high clay content under heavy rainfall; the most erosive soil might not be clay soils, but the silt soils, especially those under sudden storm after long-time drought. [ABSTRACT FROM AUTHOR]

This note revisits the benchmark problem involving a spherical failure surface in clay, gives an integral expression for the safety factor defined in terms of moments, and points out the mistakes in the solution of Silvestri. An integral expression for the safety factor of three-dimensional simplified Janbu's method is also presented to facilitate the validation of three-dimensional limit equilibrium methods that satisfy force equilibrium conditions. Key words: three-dimensional slope stability analysis, safety factor, limit equilibrium methods, slopes, landslides. Cette note se penche sur le probleme classique impliquant une surface de rupture spherique dans l'argile, donne une expression integrate pour le facteur de securite defini selon les moments et souligne les erreurs dans la solution de Silvestri. L'expression integrale pour le facteur de securite de la methode en trois dimensions simplifiee de Janbu est aussi presentee afin de faciliter la validation des methodes tridimensionnelles d'equilibre limite qui repondent aux conditions de l'equilibre des forces. Mots-cles : analyses de stabilite de pente en trois dimensions, facteur de securite, methodes d'equilibre limite, pentes, glissements de terrain. [Traduit par la Redaction], Introduction The stability of slopes has commonly been evaluated using two-dimensional limit equilibrium methods, assuming that the slope is infinitely long in the direction perpendicular to the plane of interest. [...]

Use of clayey soil has been explored in the laboratory scale experiment as a low cost adsorbent for the removal of copper from wastewater. The influence of metal ion concentration, weight of adsorbent, stirring rates, influence of temperature, pH are also evaluated and the results are fitted using adsorption isotherm models. From the experimental results it is observed that almost 90-99% copper can be removed from the solution using clay at optimized pH 5.5. Langmuir adsorption isotherm, Freundlich isotherm and Tempkin isotherm model have been used to describe the distribution of copper between the liquid and solid phases in batch studies and it has been observed that Langmuir isotherm better represents the phenomenon. From the experimental results rate constant, activation energy, Gibbs free energy, enthalpy, and entropy of the reaction are calculated to determine the mechanism of the sorption process. Thomas, Adams-Bohart, and Yoon-Nelson models are applied to the experimental data to determine the characteristic parameters of the column for process design. DOI: 10.1061/(ASCE)EE.1943-7870.0000289 CE Database subject headings: Adsorption; Kinetics; Copper; Errors; Mathematical models; Clays; Wastewater management. Author keywords: Adsorption isotherm models; Adsorption kinetics; Copper; Error analysis; Mathematical modeling.

The containment function of clay barriers used for waste containment applications (e.g., landfills) can be enhanced if such clays exhibit membrane behavior or the ability to restrict the migration of solutes (e.g., contaminants). [n this regard, compacted specimens of a locally available natural clay known as Nelson Farm Clay (NFC), as well as NFC amended with 5% (dry weight) sodium bentonite, were evaluated for hydraulic conductivity, k, and the potential for membrane behavior. The membrane efficiencies of specimens of both soils compacted such that k was less than [10.sup.-7] cm/s were measured by establishing steady salt (KCl) concentration differences, -[DELTA][C.sub.o], ranging from 3.9 to 47 mM across the specimens in a flexible-wall cell under closed-system boundary conditions. The measured membrane efficiency for the unamended NFC was negligible (i.e., [less than or equal to] 1.4%), even though the k was suitably low (i.e., k < [10.sup.-7] cm/s). In contrast, compacted specimens of the bentonite amended NFC exhibited not only lower k but also significant membrane behavior, with membrane efficiencies as high as 97.3% for -[DELTA][C.sub.0], of 3.9-mM KCl. The results suggest that natural clays typically suitable for use as compacted clay liners (CCLs) are not likely to behave as semipermeable membranes unless the clay is amended with bentonite or the clay is inherently rich in high swelling clay minerals (e.g., sodium smectite). The potential benefit resulting from membrane behavior in a CCL constructed with the bentonite amended NFC is illustrated analytically in terms of liquid flux. DOI: 10.1061/(ASCE)GT.1943-5606.0000358 CE Database subject headings: Bentonite; Clay liners; Compacted soils; Seepage. Author keywords: Bentonite; Chemico-osmosis; Clay liners; Clay membranes; Compacted soils; Seepage.

Adding anionic polyacrylamide (PAM) to soils stabilizes existing aggregates and improves bonding between and aggregation of soil particles. However, the dependence of PAM efficacy as an aggregate stabilizing agent with soils having different clay mineralogy has not been studied. Sixteen soil samples (loam or clay) with predominantly smectitic, illitic, or kaolinitic clay mineralogy were studied. We measured aggregate sensitivity to slaking in soils that were untreated or treated with an anionic high-molecular-weight PAM using the high energy moisture characteristic (HEMC) method and deionized water. The index for aggregate susceptibility to slaking, termed stability ratio (SR), was obtained from quantifying differences in the water retention curves at a matric potential range of 0 to-5.0 J [kg.sup.1] for the treatments studied. For the untreated soils, the SR ranged widely from 0.24 to 0.80 and generally SR of kaolinitic > illitic > smectitic softs. The SR of PAM-treated aggregates exhibited a narrow range from 0.70 to 0.94. The efficiency of PAM in improving aggregate and structural stability relative to untreated soils ranged from 1.01 to 3.90 and the relative SR of kaolinitic < illitic < smectitic samples. These results suggest that the less stable the aggregates the greater the effectiveness of PAM in increasing aggregates stability (i.e., smectitic vs. kaolinitic samples). 7he effectiveness of PAM in improving structure and aggregate stability was directly related to clay activity and to soil conditions affecting PAM adsorption (e.g., electrolyte resources, pH, and exchangeable cations) to the soil particles and inversely to the inherent aggregate stability. doi: 10.2136/sssaj2009.0279

The consolidation behavior of a geosynthetic clay liner (GCL) was evaluated by consolidating duplicate specimens of the GCL in a flexible-wall cell to a final effective stress, [sigma]', of 241 kPa (35.0 psi). The hydraulic conductivity, k, also was measured at the end of each loading increment. The results indicated that the GCL was normally consolidated for values of [sigma]' greater than 34.5 kPa (5.0 psi), which correlates well with limited consolidation data reported in the literature for GCLs based on confined compression using oedometers. Values of the coefficient of consolidation, [c.sub.v], for the GCL ranged from 5.2 x [l0.sup.-10] [m.sup.2]/s to 2.1 X [10.sup.-9] [m.sup.2]/s, and generally decreased with increasing [sigma]', albeit only slightly. Values of the measured k, [k.sub.measured], for the GCL were low ([less than or equal to] DOI: 10.1061/(ASCE)GT.1943-5606.0000181 CE Database subject headings: Soil compression; Soil consolidation; Geosynthetics; Clay liners; Hydraulic conductivity. Author keywords: Compressibility; Consolidation; Geosynthetic clay liner; Hydraulic conductivity.

This paper presents the results and analysis of a laboratory investigation of the behavior of lightly overconsolidated compressible Chicago glacial clays over a wide strain range. Each specimen was trimmed from high quality block samples taken from an excavation in Evanston, Illinois. Specimens were instrumented with three sets of bender elements and local LVDTs. After [K.sub.0] consolidation to the in situ vertical effective stress of the block, drained stress probe tests were conducted. Results of bender elements tests obtained prior to stress probing show that compressible Chicago glacial clay initially is cross anisotropic. Propagation velocities measured by bender elements in axial direction after [K.sub.0] reconsolidation and drained creep agrees well with the in situ shear wave velocity measured by seismic cone penetration tests. Results of drained stress probe tests are analyzed in terms of shear, volumetric and coupled stiffness, stiffness degradation, and direction of loading. The significant variability of shear, bulk and cross-coupling response depending on stress path direction and strain level provide experimental evidence that the Chicago clays are incrementally nonlinear at the strain levels investigated. DOI: 10.1061/(ASCE)GT.1943-5606.0000186 CE Database subject headings: Clays; Anisotropy; Stiffness; Limit state; Experimentation; Stress strain relations; Sampling. Author keywords: Chicago clay; Cross anisotropy; Stiffness; Limit state; Bender element; Experiments.

Mitigation of spudcan punch-through is one of the principal aspects for inclusion in the ISO standard 19905-1. This paper investigates the potential for using skirted foundations as an alternative to spudcans in an attempt to mitigate punch-through failure of jack-up rigs during installation and preloading in sand-over-clay deposits. A series of centrifuge model tests is undertaken on a spudcan and two skirted foundations, varying the length of the skirt relative to the foundation diameter. The thickness of the sand layer is also varied to cover a range of practical interest. The results from this study confirm that the use of skirted foundations as an alternative to spudcans can eliminate the potential of punch-through failure on sand-over-clay deposits. The degree of post-peak bearing reduction, one of the key measures of the severity of punch-through failure, is shown to be linked directly to the effective sand layer thickness beneath the foundations. Skirted foundations assist in mitigating the severity of punch-through failure by reducing the effective sand layer thickness. [ABSTRACT FROM AUTHOR]

Natural cores from the crust that is found over deep-ocean sediments off the west coast of Africa have been tested in direct shear following one-dimensional consolidation under normal stresses relevant to pipelines. Shearing tests were conducted at different speeds of 0·5, 0·05, 0·005 and 0·0005 mm/s, both within the soil and against interfaces of different roughness. The behaviour in these tests is observed to be strongly influenced by the structure of the natural soil, which contains abundant faecal pellets. The data of shear tests, especially when conducted at faster speeds, display significant randomness, which is attributed to the random location of pellets and their associated macro-voids. Nevertheless, certain trends are evident. Two key observations are made. The first is that the interface friction factor when shearing against a smooth interface can be greater than that of a rough interface. The second is that the rate of shearing has a strong influence on the residual interface-friction value when shearing against a rough interface. When shearing at 0·5 mm/s, the apparent friction factor on a rough interface was observed to drop to zero, whereas the apparent friction factor of a smooth interface tended to be larger. This is attributed to excess pore pressures created by damage to the natural structure of the soil. Slow shearing at 0·005 mm/s produced higher apparent friction factors in the range 0·15-0·30, although excess pore pressures may still be present. It is concluded that the testing of natural cores is essential for a complete understanding of the behaviour of hot-oil pipelines that are subject to pipe walking and buckling. If designers rely instead on tests that have been conducted on reconstituted soils, pipelines may misbehave. [ABSTRACT FROM AUTHOR]

Aggregation of microbes with particles can reduce the effectiveness of ultraviolet (UV) disinfection. This study evaluated the comparative impact of dispersed spores, dispersed spores mixed with clay particles (nonaggregated), spore--spore aggregates, and spore-clay aggregates on UV disinfection performance in simulated drinking waters. Aggregates were induced by flocculation with alum and characterized by particle size analysis (count, volume, and surface area) of dispersed and aggregated systems, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. It was concluded that spores within aggregates of the spore--clay system were protected from UV irradiation compared to nonaggregated spores and the difference between these systems was found to be statistically significant throughout the UV range tested. In addition SEM-EDX analysis suggested that aggregate composition is nonhomogeneous with respect to the ratio of spores and clay particles among aggregates. It was estimated that 30--50% of the spores in the aggregates tested were protected from UV irradiation. DOI: 10.1061/(ASCE)0733-9372(2006)132:6(596) CE Database subject headings: Microbes; Disinfection; Aggregates; Clays; Ultraviolet radiation; Water treatment.

Individual rainfall events are recorded as thin clay bands in annually laminated, freshwater-carbonate tufa. Runoff from rainfall events entrains clay that then adheres to the tufa surface. A specimen collected from southwest Japan exhibits >100 clay bands formed during a 15 yr period from 1988 to 2002. The chronology of the clay bands was determined by using the temperature-dependent cycle of oxygen isotope ratios in the carbonate, and the clay content was quantified by electron-probe microanalysis Si X-ray strength. The obtained Si X-ray strength curve and actual rainfall record follow a nearly identical pattern. The clay content of each band correlates with rainfall amount. Rainfall of >50 mm/week produced sufficient amounts of suspended cave clay to produce clay bands in the tufa. Because the clay bands survive postdepositional alteration, this new method can be applied to ancient tufa deposits and has great potential as a high-resolution rainfall record for use in climate studies. Keywords: tufas, travertines, high-resolution record, rainfall, paleoclimatology.

The influence of amorphous clay-size materials on geotechnical engineering properties is recognized only for soils developed from volcanic ash under extremely wet, alumina-rich soil environments (called Andisols). The objective of this study was to quantify the amorphous clay-size materials in less weathered volcanic soils that are rich in silica, and to determine the influence of the amorphous materials on plasticity and shrink-swell behavior of these soils. Soil and weathered rock samples were taken from a slow-moving landslide site in Honolulu. Quantification of amorphous and crystalline clay content was performed with x-ray diffraction and the Rietveld method. Atterberg limits and shrink-swell potential of the soil samples were determined. The results showed that clay-size fraction in both soil and weathered rock samples were predominantly amorphous (55-74% in soil and 48-63% in weathered rock). Smectite and halloysite were the primary crystalline clay minerals, constituting about 15-30% of the clay fraction in soils. Atterberg limits of the soil ranged from 65 to 135 for liquid limit, from 30 to 40 for plastic limit, and 9 to 25 for shrinkage limit. Volumetric free swell ranged from 2 to 21%. The plasticity and shrink-swell potential increased with increasing the content of amorphous clay-size materials in the soil. Air drying and oven drying did not significantly change the plasticity. The study concluded that silica-rich amorphous materials dominate the clay mineralogy of the soils studied, resulting in the plasticity and shrink-swell behavior similar to that of smectite-rich soils and distinct from that of Andisols. CE Database keywords: Plasticity; Clays; Soils; Expansion; Shrinkage.

The modern view of colloidal particle behavior in water is based on the DLVO (Derjaguin-Landau-Verwey-Overbeek) theory, which hypothesizes strictly repulsive long-range interactions among charged particles. However, numerous phenomena of colloidal behavior, some recently discovered, cannot be explained quantitatively or qualitatively by this theory. An alternative description of the fundamental forces involved in the formation of dispersions and gels was outlined in 1938 by Langmuir, and further developed theoretically by Sogami, Ise, and Smalley. This model, unlike DLVO, hypothesizes a long-range Coulombic attractive force countering osmotic repulsion, which may explain experimentally confirmed multiparticle phenomena such as long-range attraction and transitions among ordered (liquid crystalline) and disordered phases of colloidal suspensions. The key concepts of Sogami-Ise theory and its experimental support are reviewed in the present article. This review begins with an analysis of the extent to which dynamic (Brownian) motion and interparticle steric hindrance influence the macroscopic properties of clay dispersions and gels. It is shown that the covolume theory of Onsager in some cases could explain the existence of apparent long-range interparticle interactions, and phase transitions between ordered and disordered states in colloidal dispersions, without invoking long-range forces. Nevertheless, in situations where the composition of the electrolyte solution influences the observed interparticle interactions, the experimental evidence for long-range attraction among charged colloidal spheres points to a force that is fundamentally electrostatic in nature, of the type envisioned by Langmuir. After consideration of all experimental and theoretical results to date, it is concluded that the DLVO theory adequately describes the repulsive interaction between isolated like-charged particles, whereas a long-range attractive force is needed to explain multi-particle interactions in suspensions under conditions of low electrolyte concentration and high particle charge.

A three-story school supported by shallow foundations was affected by an adjacent 12.2-m-deep excavation in soft clay in which the excavation support system was a 0.9-m-wide secant pile wall braced by both cross-lot struts and tiebacks. The school is a reinforced concrete frame structure with exterior reinforced concrete foundation walls. This paper summarizes the conditions at the site and presents correlations among construction activities, measured deformations and distortions, and attendant damage in the school. The lateral ground movements associated with the excavation were monitored with four inclinometers placed around the school. The building movements were monitored with optical survey points established on interior columns, exterior walls and on the roof, and with tiltmeters installed on the exterior foundation walls. The damage to the school mainly consisted of 300 to 500-mm-long hairline cracks in nonload bearing walls. Only a few cracks had widths greater than 6 mm. The school deformed such that the portion closest to the excavation sagged and the remainder hogged. Damage was first observed in the area of sagging when angular distortions reached 1/940 and the excavation was approximately 5.5-m deep. Angular distortions as large as 1/300 were observed at the end of the project. The data suggest that angular distortions had to be less than 1/1000 to preclude any damage to the school. DOI: 10.1061/(ASCE)0887-3828(2002)16:1(10) CE Database keywords: Soft clay; Excavation; Shallow foundations; Distortion; Foundation settlement.

Polyacrylamide (PAM) is a long-chain synthetic polymer that acts as a strengthening agent, binding clay particles together. The interaction between anionic PAM and clay particles is not well understood yet. This interaction was evaluated by rheological measurements for Na-montmorillonite suspensions. Three anionic PAMs of three molecular weights (MWs) (3.5 x [10.sup.3], 2 x [10.sup.5], and 8 x [10.sup.6] g [mol.sup.-1]) at similar hydrolysis levels (>85%) and three anionic PA Ms at various degrees of hydorlysis (DH) (15, 33, and 92%) of similar MW were studied. In an electrolyte-free clay suspension at DH >85%, only the polymers with high MWs (2 x [10.sup.5], and 8 x [10.sup.6]) could form a three-dimensional structure of clay platelets. The smallest polymer molecule size (3.5 x [10.sup.3]) was too short for bonding two adjacent platelets. At similar MW, the effect of the polymers increased with DH. At NaCl concentration of 10 [mmol.sub.c] [L.sup.-1], at which the attractive forces between clay platelets were weak, the polymers had a significant impact on flow behavior. The effectiveness of the polymers increased with increasing MW and DH. At NaCl concentration of 100 [mmol.sub.c] [L.sup.-1], the three polymers of DH > 85% stabilized flocs that already existed in the clay suspension. The effectiveness of the polymers in bridging adjacent clay flocs increased as their DH decreased. The polymer conformation factor has a greater impact on clay structure stabilization in suspension than the electrostatic repulsion effect. The clay structure stability was increased with increasing polymer electrostatic negative charge for similar molecular weights.

In this work, catalysts were synthesized based on chemically modified clays through pillaring process with Al (III) and Fe (III) using commercial bentonite and acidtreated montomorillonite like KSF montmorillonite and K10 montmorillonite from Aldrich, as raw materials. The raw materials and chemically modified clays were characterized by: BET (Brunauer-Emmet-Teller) method and XRD (X-ray diffraction). Afterwards these catalysts were tested during wet oxidation with peroxides using phenol as target compound. Experimental results show that chemically modified clays with Fe(III) presented a higher catalytic activity in Fenton like processes than Al-Fe clays. [ABSTRACT FROM AUTHOR]

Purpose: The objective of this research was to apply the same immobilization (stabilization/solidification) clay-based treatments to sediment contaminated with different metals (Pb, Cd, Ni, Zn, Cu, Cr) with different distributions and availabilities in sediment. We also examined the possibility of using clay as an immobilization agent without the application of thermal treatment, in order to reduce the economic cost of this expensive remediation procedure. Materials and methods: Clay from a canal in Vojvodina, Republic of Serbia, was used as the immobilization agent in a stabilization/solidification treatment to remediate metal-contaminated sediment. Semi-dynamic and toxicity characteristic leaching tests were conducted to assess the effectiveness of the nonthermal and thermal immobilization treatments with clay, and the long-term leaching behavior of these metals was determined using the following parameters: cumulative percentage of metals leached; diffusion coefficients; leachability indices; and toxicity characteristic leaching test concentration. Results and discussion: Based on these parameters, both clay-based treatments were effective in immobilizing metals in the contaminated sediment. Results suggest that both heating temperature and clay proportion in the sediment-clay mixture impact the degree of metal immobilization. Conclusions: Clay-based products are potentially good immobilization materials for metal-contaminated sediments, with the distribution of metals in the original sediment not influencing the efficacy of the treatments. Even without the thermal treatment, the metals were effectively immobilized. The leaching of metals was largely inside the regulatory limits and the treated samples can be regarded as nonhazardous materials. This justifies the choice of not applying the more expensive thermal treatment during remediation, especially when treating sediments containing a mixture of pollutants. [ABSTRACT FROM AUTHOR]

Introduction: The removal of heavy metals by natural adsorbent has become one of the most attractive solutions for environmental remediation. Natural clay collected from the Late Cretaceous Aleg formation, Tunisia was used as a natural adsorbent for the removal of Hg(II) in aqueous system. Methods: Physicochemical characterization of the adsorbent was carried out with the aid of various techniques, including chemical analysis, X-ray diffraction, Fourier transform infrared and scanning electron micrograph. Batch sorption technique was selected as an appropriate technique in the current study. Method parameters, including pH, temperature, initial metal concentration and contact time, were varied in order to quantitatively evaluate their effects on Hg(II) adsorption onto the original and pillared clay samples. Adsorption kinetic was studied by fitting the experimental results to the pseudo-first-order and pseudo-second-order kinetic models. The adsorption data were also simulated with Langmuir, Freundlich and Temkin isotherms. Results: Results showed that the natural clay samples are mainly composed of silica, alumina, iron, calcium and magnesium oxides. The sorbents are mainly mesoporous materials with specific surface area of <250 m g. From the adsorption of Hg(II) studies, experimental data demonstrated a high degree of fitness to the pseudo-second-order kinetics with an equilibration time of 240 min. The equilibrium data showed the best model fit to Langmuir model with the maximum adsorption capacities of 9.70 and 49.75 mg g for the original and aluminium pillared clays, respectively. The maximum adsorption of Hg(II) on the aluminium pillared clay was observed to occur at pH 3.2. The calculated thermodynamic parameters (∆ G°, ∆ H° and ∆ S°) showed an exothermic adsorption process. The entropy values varied between 60.77 and 117.59 J mol K, and those of enthalpy ranged from 16.31 to 30.77 kJ mol. The equilibrium parameter ( R) indicated that the adsorption of Hg(II) on Tunisian smectitic clays was favourable under the experimental conditions of this study. Conclusion: The clay of the Aleg formation, Tunisia was found to be an efficient adsorbent for Hg(II) removal in aqueous systems. [ABSTRACT FROM AUTHOR]

Due to the existence of physicochemical effects, the pore fluid type generally has a significant influence on the geotechnical behavior of clays. The present paper focuses on the stress-strain and shear-strength behavior of kaolinite in various pore fluids. Kaolinite specimens, initially prepared by 1D consolidation of kaolinite/water slurries, were isotropically consolidated in a triaxial cell to the desired consolidation pressure. The specimens were then leached with the desired fluid and sheared under undrained condition to failure. Six different fluids including water, formamide, ethanol, acetic acid, triethylamine, and heptane were used. It was observed that leaching with certain fluids converts the otherwise normally consolidated specimens into over-consolidated specimens with respect to the stress-strain behavior of the soil. As a result of the apparent over-consolidation, the shear strength of the triaxial specimens increases. The results are discussed in relation to the change in physicochemical factors. A possible cause of apparent overconsolidation is presented, with some supporting physicochemical analyses.

Sediment amendments provide promising strategies of enhancing sequestration of heavy metals and degradation of organic contaminants. The impacts of sediment amendments for metal and organic remediation including apatite, organoclay (and apatite and organoclay in geotextile mats), acetate, and chitin on environmental microbial communities in overlying water and sediment profiles are reported here. These experiments were performed concurrent with an ecotoxicity evaluation (data submitted in companion paper) and X-ray absorption spectroscopy of zinc speciation post apatite amendments. X-ray absorption spectra showed that a modest modification of zinc speciation occurred in amended treatments. Significant changes in both bacterial cell densities and populations were observed in response to amendments of apatite+organoclay, chitin, and acetate. The enriched bacteria and breakdown of these amendments were likely attributed to water quality degradation (e.g. ammonia and dissolved oxygen). Molecular fingerprints of bacterial communities by denaturant gradient gel electrophoresis (DGGE) showed that distinct bacterial populations occurred in overlying waters from different amendments: apatite+organoclay led to the dominance of Gammaproteobacteria, acetate enriched Alphaproteobacteria, and chitin treatment led to a dominance of Bacteroidetes and Alphaproteobacteria. In amended sediments, Firmicutes, Bacteroidetes, and Deltaproteobacteria (Desulfovibrio) were commonly found with chitin and apatite+chitin treatments. Finally, sulfate-reducing bacteria (e.g. Desulfovibrio) and metal-reducing bacteria were also recovered with most probable number (MPN) analyses in treatments with acetate, chitin, and apatite+chitin. These geochemically important bacteria were stimulated by amendments and may play critical functional roles in the metal and organic contaminant remediation process for future investigations of contaminated sediments. [Copyright &y& Elsevier]

Experimental materials currently being investigated for use as amendments for the in situ remediation of contaminated sediments were assessed for their potential impacts on marine benthos. Laboratory toxicity tests involving lethal and sublethal endpoints were conducted on sediments amended with apatite, organoclay, chitin, or acetate, with the polychaete Neanthes arenaceodentata, the amphipod Eohaustorius estuarius, and the larval sheepshead minnow Cyprinodon variegatus. Amendments were mixed loosely into uncontaminated or metal-contaminated sediments, and also added inside experimental geotextile mats, at sediment dry weight (dw) concentrations ranging from 0.5% to 10%. The geotextile mats, containing apatite (5 or 10% dw), and/or organoclay (5%) did not result in adverse effects on any of the test organisms. Chitin and acetate, however, repetitively resulted in adverse effects on survival and/or adverse or positive effects on organism growth at concentrations of ≤2.5% dw. The adverse effects were attributed to water quality degradation in the exposure vessels (notably ammonia and dissolved oxygen concentration, for chitin and acetate, respectively) as a result of the microbial breakdown of the amendments. For N. arenaceodentata, growth was enhanced in the presence of chitin at concentrations as low as 0.5% sediment dw, which stimulated bacterial growth that may have provided an additional food source for the polychaete. Sediment chitin concentrations of 0.5% resulted in a statistically significant reduction in N. arenaceodentata body burdens of 61%, 29%, and 54%, relative to unamended contaminated sediment, for Cu, Zn, and Cd, respectively. The studies suggest a lack of inherent toxicity of these materials on the experimental organisms, as the adverse or positive responses observed are likely related to artifacts associated with laboratory exposure. Assessments in field settings are needed to verify this conclusion. [Copyright &y& Elsevier]

Copyright of Revista Brasileira de Engenharia Agricola e Ambiental - Agriambi is the property of Revista Brasileira de Engenharia Agricola e Ambiental and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The current study investigated the sorption of sulfadimethoxine (SMT), sulfamethoxazole (SMX), tetracycline (TET), and oxytetracycline (OTC) to Na-rich montmorillonite clay in synthetic effluent (SE) and field wastewater effluent (FE). Both SMT and SMX showed a low sorption capacity and are therefore likely to be highly mobile in the environment, while the sorption of TET to clay in environmental pH range (6.5–7.5) showed similarly high adsorption capacity. Differences in sorption capacities of TET and OTC to SE or FE were attributed to the various concentrations of divalent cations in the effluents. In addition, differences in sorption of OTC or TET to SE were attributed to their different molecular structure. Moreover, the adsorption of TET in SE and FE showed linear adsorption isotherms and fitted to Freundlich model. Further experiments showed that addition of humic acid or SE to TET sorbed to clay did not enhance or suppress the sorption of TET to clay. [ABSTRACT FROM AUTHOR]

The main objective of the present study was to assess the roles of various soil components in sorption of organic compounds differing in polarity. Removal of the whole soil organic matter decreased sorption by approximately 86% for nonpolar 1,3,5-trichlorobenzene (TCB), but only 34–54% for highly polar 1,3,5-trinitrobenzene (TNB); however, removal of the extractable humic/fulvic acids did not much affect sorption of the two sorbates. With normalization of solute hydrophobicity, TNB exhibits several orders of magnitude stronger sorption compared with TCB to maize burn residue (black carbon), extracted humic acid and Na+-saturated montmorillonite clay, suggesting specific sorptive interactions for TNB with the individual model soil components. It was proposed that sorption of TCB to the bulk soil was dominated by hydrophobic partition to the condensed, non-extractable fraction of organic matters (humin/kerogen and black carbon), while interactions with soil clay minerals were an important additional factor for sorption of TNB. [Copyright &y& Elsevier]

A palygorskite unit was discovered in a road cut of undifferentiated Tertiary limestone between the villages of El Pariso and San Roman (18°49.309N, 88°37.861W) in the southeastern Yucatán Peninsula, Mexico. This is the southern most locality of a clay-rich sedimentary unit reported in the literature for the Tertiary carbonates of the Yucatán Peninsula. This occurrence indicates a much wider range of palygorskite-rich clay deposition than previously recognized. The lithology is 99% clay and 1% sand to silt size diagenetic quartz grains. The clay consists of approximately 85% palygorskite, 15% montmorillonite and trace amounts of titanium oxides. EDS analyses on palygorskite are largely consistent with sedimentary palygorskites from other coastal marine settings, however palygorskite has a low total Fe content (average = 0.40 wt% expressed as Fe2O3) compared to many other sedimentary palygorskites. Montmorillonite chemical compositions are typical and compared to the palygorskite have substantially higher Fe2O3 concentrations (average = 3.90 wt%). The low percentage of coarse grains in the lithology combined with a high proportion of palygorskite and lack of detrimental trace minerals suggest the deposit is of industrial grade; however, it has limited reserves (6,000 m3). The unit could be potentially used in a wide array of environmental applications which are needed in the region including liners for landfills and constructed wetlands. The unit is in a geographic location which would serve the expanding economy of the region. This resource has the potential to have great impact on the quality of the local environment and the economy of a region under great environmental threat. [ABSTRACT FROM AUTHOR]

The effects of pH, ionic strength, cadmium concentration, and chelating agents on the zeta potential of a natural clay of high acid/base buffer capacity from Shanghai, China were investigated in this study, with a view to enhancing the efficiency of electrokinetic remediation of the cadmium-contaminated clay. An increase in the ionic strength of the background solution or cadmium concentration increases the zeta potential on soil particle surfaces, i.e., less negative. CAIW increases the zeta potential slightly but the effects are not pronounced. EDTA and phosphonates decrease the zeta potentials of soil particle surfaces, thus enhancing forward electroosmotic flow. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Integrated Coastal Zone Management / Revista de Gestão Costeira Integrada is the property of Associacao Portuguesa dos Recursos Hidricos and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Dredged spoil (DS) was used as a silt and clay additive in the construction of artificial tidal flats from mountain sand (MS). As the ratio of DS in the sediment media increased, the number of emerging macrobenthos increased. The composition of the macrobenthic community was also affected by the addition of DS, and the changes might be dependent on the ratio of DS to MS. In addition, the macrobenthos in the artificial tidal flats was more abundant than that in the control tidal flat, which was constructed with natural tidal flat sediment. With a silt and clay content of 25%, polychaetes Ceratonereis erythraeensis and Capitella sp. and the gastropod Batillaria cumingii were dominant, whereas no bivalves were present. With less silt and clay (5% and 10%), the bivalves Ruditapes philippinarum and Musculista senhousia were observed in the artificial flats, while their numbers in the control tidal flat were lower. [Copyright &y& Elsevier]

Habitat assessments were conducted in an intermountain watershed at three spatial extents to explore ways to predict the presence of tubificid oligochaetes likely to support the parasite Myxobolus cerebralis, cause of salmonid whirling disease. Stream reaches with six different reach slope characteristics were selected using GIS. The aquatic habitat in 60 reaches selected at random was measured and classified into distinct habitat units. Within the habitat units, areas of microhabitat with depositional fine sediments were chosen, measured, and core samples were removed to characterize the sediments and benthic oligochaetes. Two tubificids, Tubifex spp. and Limnodrilus hoffmeisteri, were abundant and co-occurred in silt-clay and fine sand sediments in these habitats. Models were posed and tested to predict the presence and relative abundance of tubificids using habitat characteristics from the three spatial extents: reach, habitat unit, and microhabitat. At the reach extent, tubificids were associated with low-reach slope and with slow water habitats. Within habitat units, tubificids were associated with higher percentages of fine sediments and higher stream width:depth ratios. In microhabitat cores, the presence of silt-clay sediments was positively associated with higher average stream width:depth ratios. Since ecological relationships are often scale dependent and stream systems have a natural hierarchy, predictive habitat models such as these that use measures from several scales may help researchers and managers more efficiently identify and quantify aquatic communities at highest risk of infection by the M. cerebralis parasite. [ABSTRACT FROM AUTHOR]

Abstract: Thirteen soils collected from 11 provinces in eastern China were used to investigate the butachlor adsorption. The results indicated that the total organic carbon (TOC) content, clay content, amorphous Fe2O3 content, silt content, CEC, and pH had a combined effect on the butachlor sorption on soil. Combination of the data obtained from the 13 soils in the present study with other 23 soil samples reported by other researchers in the literature showed that would be a poor predictive parameter for butachlor adsorption on soils with TOC content higher than 4.0% and lower than 0.2%. The soils with the ratio of clay content to TOC content (RCO) values less than 60 adsorbed butachlor mainly by the partition into soil organic matter matrix. The soils with RCO values higher than 60 apparently adsorbed butachlor by the combination of the partition into soil organic matter matrix and adsorption on clay surface. [Copyright &y& Elsevier]

Abstract: An in situ trickling filter system, named Trickling Trench, is being used to treat biodegradable organic compounds at a site underlain by silt and clay. This method provides the containment advantages of pump-and-treat remediation with the low-cost benefits of in situ bioremediation. A design method is presented using a conventional trickling filter analytical model with kinetic coefficients for various organic compounds calculated from published data. Performance monitoring data obtained from the Trickling Trench bioreactor are compared to design predictions.

This paper presents graphical solution charts for 1D consolidation of a single homogeneous layer of normally consolidated clay under a surcharge load. Cast in dimensionless form, the charts include the effects of vertical strain, self-weight, and decreasing compressibility and hydraulic conductivity during the consolidation process. To estimate total settlement, the user must specify the initial layer thickness, compression index, initial void ratio at the midheight of the layer, and initial and final effective stress conditions at the top of the layer. To estimate the rate of settlement and distribution of excess pore pressure, boundary drainage conditions and the initial hydraulic conductivity at the midheight of the layer are also required. As a design tool, the charts can be used to make preliminary estimates of settlement and excess pore pressure with fewer restrictive assumptions than for conventional theory. The charts can also be used to verify solutions obtained from numerical analyses. Furthermore, the charts are educational in that they illustrate the effect of different variables on the consolidation process. Using the solution charts, estimated values for settlement are in good agreement with field measurements for a well-documented case study. Estimated and measured values for excess pore pressure are in reasonable agreement during the middle stages of consolidation but are in lesser agreement during the early and later stages.

The article discusses the leaching potential of the herbicide Pendimethalin and the effects of surfactant on sandy soils in the citrus groves of Florida. The distance moved through the Candler fine sands under different rainfall treatments of the herbicide (brand name Prowl®H2O) was determined. According to the authors, the mobility of Pendimethalin depends on the organic matter and clay content where it is absorbed. The herbicide had some leaching potential, with all rainfall treatments. Addition of surfactant significantly reduced leaching of Prowl®H2O under both simulated rainfall treatments.

The mineralization of phenanthrene in pure cultures of a Pseudomonas fluorescens strain was measured in the presence of soil humic fractions and montmorillonite. Phenanthrene is a polycyclic aromatic hydrocarbon that is usually found in contaminated soils. Results show that the acclimation phase is shortened by humic acid and clay, separately, or in combination. Higher mineralization results when humic acid reaches 100 microgram per milliliter. A concentration of 10 microgram per milliliter of humic acid degrades the phenanthrene only when 10 grams of clay per liter is present.