Geotechnical and Structures Laboratory

Drain wells have been used to accelerate the consolidation of fine-grained compressible soils subjected to new loads. However, mathematical analyses of such wells have become available only recently, and are confined to wells having infinitely pervious well backfill and no peripheral smear. Complete formulas for consolidation by vertical and radial flow to wells, for cases with or without peripheral smear and drain well resistance, are presented in this paper; necessary derivations are given in Appendix II. Because soils are not homogeneous, and because of incomplete knowledge of stress-strain consolidation characteristics of soils, these solutions should be regarded as approximate when applied to practical problems.

Polychlorinated biphenyls (PCBs) as environmental contaminants often cannot be adequately described by reference to Aroclors or to total PCBs. Although there are 209 possible PCB configurations (congeners), perhaps half that number account for nearly all of the environmental contamination attributable to PCBs. Still fewer congeners are both prevalent and either demonstrably or potentially toxic. If potential toxicity, environmental prevalence, and relative abundance in animal tissues are used as criteria, the number of environmentally threatening PCB congeners reduces to about thirty-six. Twenty-five of these account for 50 to 75% of total PCBs in tissue samples of fish, invertebrates, birds, and mammals. A few PCB congeners that are sterically similar to 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) are directly toxic. Other PCB congeners, as well as those that are directly toxic, may also be involved in toxicity indirectly by stimulating the production of (inducing) bioactivating enzyme systems. The most consequential of these have the ability to induce aryl hydrocarbon metabolizing mixed-function oxidases (MFOs). A result can be an increased capacity for bioactivation of otherwise nontoxic foreign compounds such as certain polynuclear aromatic hydrocarbons (PAH) to cytotoxic or genotoxic metabolites. The effectiveness of specific PCB congeners as inducers of different types of cytochrome P-450-dependent MFO systems is determined by their stereochemistry. Although MFO induction is not a proximate cause, it is a strong correlate of certain kinds of toxicities. Structural patterns can thus be used to discriminate among PCB congeners on the basis of toxic potential, if not entirely on toxicity per se. Congeners that demonstrate 3-methylcholanthrene-type (3-MC-type) and mixed-type MFO induction have the greatest toxic potential. These congeners most closely resemble 2,3,7,8-TCDD in their structures and in their toxic effects. The larger group of phenobarbital-type (PB-type) inducers have considerably less potential for contributing to toxic effects. Weak inducers and noninducing congeners have the least potential for toxicity. Using the rationale described in this paper, we assigned the most evironmentally threatening PCB congeners to four groups. Congeners assigned to Group 1 are considered most likely to contribute to adverse biological effects attributable to PCBs in an environmental sample. Group 1A contains the three most potent (pure 3-MC-type inducer) congeners, IUPAC numbers 77, 126, and 169. Six congeners, numbers 105, 118, 128, 138, 156, and 170, are assigned to Group 1B. These congeners are mixed-type inducers that have been reported frequently in environmental samples.(ABSTRACT TRUNCATED AT 400 WORDS)

Crystals of earth-abundant tin disulfide exhibit high-surface-area platelet formation with ideal photocatalytic properties for water splitting in their ground state.

Physical processes constituting fine, cohesive sediment transport in estuarial waters are described. These processes, which include settling and deposition, consolidation, erosion and transport in suspension, are typically interlinked by the cyclic nature of the tide dominated environment. Complexities in process characterization arise as a consequence of the dual dependence of sediment aggregate properties on the physico‐chemical properties of the sediment‐water mixture as well as the turbulent flow field. Present day knowledge of the processes enables reliable predictions of rates of sedimentation and erosion in navigable channels, waterways and harbors through numerical modeling. Further research is required for improving procedures for measuring settling velocities, identification of depth at which a definable bed is encountered, and the behavior of near‐bed high density suspensions.

SUMMARY. The mobilization of sediment phosphorus (P) by three submersed freshwater macrophyte species was investigated on five different sediments. The study was conducted under controlled environmental conditions in lucite columns that enabled the separation of sediment and plant roots from the overlying P‐free ‘complete’ nutrient solution. The species investigated ( Egeria densa, Hydrilla verticillata , and Myriophyllum spicatum ) had minor root systems (on a biomass basis), but were demonstrated to be fully capable of deriving their P nutrition exclusively from the sediments. Phosphorus absorption and translocation into shoots (i.e., mobilization) was substantial, and in some cases suggested a greater than 1000‐fold turnover of interstitial water PO 4 ‐P over a 3‐month period. Sediment P mobilization, a function of both plant growth and tissue P concentration, differed considerably among plant species and sediments. Phosphorus release from the species investigated appears to be primarily dependent upon tissue decay rather than excretory processes. The mobilization of sediment P by submersed macrophytes represents an important aspect of the P cycle, and may affect the overall metabolism of lacustrine systems.

Cs2SnI6, a rarely studied perovskite variant material, is recently gaining a lot of interest in the field of photovoltaics owing to its nontoxicity, air-stability and promising photovoltaic properties. In this work, we report intrinsic defects in Cs2SnI6 using first-principles density functional theory calculations. It is revealed that iodine vacancy and tin interstitial are the dominant defects that are responsible for the intrinsic n-type conduction in Cs2SnI6. Tin vacancy has a very high formation energy (>3.6 eV) due to the strong covalency in the Sn-I bonds and is hardly generated for p-type doping. All the dominant defects in Cs2SnI6 have deep transition levels in the band gap. It is suggested that the formation of deep defects can be suppressed significantly by employing an I-rich synthesis condition, which is inevitable for photovoltaic and other semiconductor applications.

Tracer dispersion has been simulated in three-dimensional models of regular and random sphere packings for a range of Peclet numbers. A random-walk particle-tracking (PT) method was used to simulate tracer movement within pore-scale flow fields computed with the lattice-Boltzmann (LB) method. The simulation results illustrate the time evolution of dispersion, and they corroborate a number of theoretical and empirical results for the scaling of asymptotic longitudinal and transverse dispersion with Peclet number. Comparisons with nuclear magnetic resonance (NMR) spectroscopy experiments show agreement on transient, as well as asymptotic, dispersion rates. These results support both NMR findings that longitudinal dispersion rates are significantly lower than reported in earlier experimental literature, as well as the fact that asymptotic rates are observed in relatively short times by techniques that employ a uniform initial distribution of tracers, like NMR.

Damage detection in vibrating beams, or beam systems, is dealt with in this paper. Damage is represented by a more or less concentrated decrease in stiffness. A linear behavior is assumed before and after the damage. A peculiar aspect of damage detection, at times neglected, is that damage is frequently concentrated in a few zones, albeit unknown, so that only the modification in the characteristics of a few sections or elements needs to be determined. Attention is focused on the basic aspects of the problem, by discussing the amount of frequencies necessary to locate and quantify the damage uniquely. Two different procedures of damage identification are used, which mainly take advantage of the peculiar characteristics of the problem. Cases with pseudoexperimental and experimental frequencies are solved. A generalization of the procedure based on finite-element models, which makes possible the tackling complex structural cases, is illustrated and discussed with some examples.

Carbon nanotubes (NTs) may be among the most useful engineered nanomaterials for structural applications but could be difficult to study in ecotoxicological evaluations using existing tools relative to nanomaterials with a lower aspect ratio. Whereas the hydrophobicity and van der Waals interactions of NTs may suggest aggregation and sedimentation in aquatic systems, consideration regarding how engineered surface modifications influence their environmental fate and toxicology is needed. Surface modifications (e.g., functional groups and coatings) are intended to create conditions to make NTs dispersible in aqueous suspension, as required for some applications. In the present study, column stability and settling experiments indicated that raw, multiwalled NTs (MWNTs) settled more rapidly than carbon black and activated carbon particles, suggesting sediment as the ultimate repository. The presence of functional groups, however, slowed the settling of MWNTs (increasing order of stability: hydroxyl > carboxyl > raw), especially in combination with natural organic matter (NOM). Stabilized MWNTs in high concentrations of NOM provided relevance for water transport and toxicity studies. Aqueous exposures to raw MWNTs decreased Ceriodaphnia dubia viability, but such effects were not observed during exposure to functionalized MWNTs (> 80 mg/L). Sediment exposures of the amphipods Leptocheirus plumulosus and Hyalella azteca to different sizes of sediment-borne carbon particles at high concentration indicated mortality increased as particle size decreased, although raw MWNTs induced lower mortality (median lethal concentration [LC50], 50 to >264 g/kg) than carbon black (LC50, 18-40 g/kg) and activated carbon (LC50, 12-29 g/kg). Our findings stress that it may be inappropriate to classify all NTs into one category in terms of their environmental regulation.

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Abstract Dredging can have significant impacts on aquatic environments, but the direct effects on fish have not been critically evaluated. Here, a meta‐analysis following a conservative approach is used to understand how dredging‐related stressors, including suspended sediment, contaminated sediment, hydraulic entrainment and underwater noise, directly influence the effect size and the response elicited in fish across all aquatic ecosystems and all life‐history stages. This is followed by an in‐depth review summarizing the effects of each dredging‐related stressor on fish. Across all dredging‐related stressors, studies that reported fish mortality had significantly higher effect sizes than those that describe physiological responses, although indicators of dredge impacts should endeavour to detect effects before excessive mortality occurs. Studies examining the effects of contaminated sediment also had significantly higher effect sizes than studies on clean sediment alone or noise, suggesting additive or synergistic impacts from dredging‐related stressors. The early life stages such as eggs and larvae were most likely to suffer lethal impacts, while behavioural effects were more likely to occur in adult catadromous fishes. Both suspended sediment concentration and duration of exposure greatly influenced the type of fish response observed, with both higher concentrations and longer exposure durations associated with fish mortality. The review highlights the need for in situ studies on the effects of dredging on fish which consider the interactive effects of multiple dredging‐related stressors and their impact on sensitive species of ecological and fisheries value. This information will improve the management of dredging projects and ultimately minimize their impacts on fish.

Abstract A dual interface shear apparatus (simple or direct) was developed to evaluate the distribution and magnitude of friction between granular materials and solid inextensible surfaces. Ideal and natural granular materials were sheared along controlled and random solid surface geometries. The test results were evaluated through a model describing the interface friction mechanism based on a micromechanical approach. The influence of boundary conditions and interfacial shear modes was examined and compared to the results obtained in a modified direct shear box. The test results show that the grain shape and the surface roughness, quantified with respect to the grain size, are the primary parameters controlling the interfacial shear strength at a given normal stress level. Three zones of normalized roughness associated with different shear strength levels were identified. These zones can be categorized into two possible shear mechanisms: interfacial and internal. The use of a small-size direct shear box (modified) to evaluate interfacial friction seems markedly influenced by the boundary conditions. The resulting interface friction angles exceed those that would develop along an unrestricted interface of soil and a solid surface, especially when shear takes place along the solid surface (e.g., smooth and intermediate normalized roughness). Erratum to this paper appears in 18(4).

This paper provides an overview of the Southeast Louisiana Flood and Hurricane Protection System that was in place at the time of Hurricane Katrina. Both geography and components of the system are described. A brief description of the development of the storm, the major damage caused, and lessons learned are discussed.

This paper deals with geosynthetic tubes that are made of several geosynthetic sheets sewn together to form a shell capable of confining pressurized slurry. The slurry is sufficiently fluid so that it is possible to hydraulically fill the tube. After pumping the slurry in, the geosynthetic shell acts as a “cheese cloth,” allowing seepage of liquid out and retaining the solid particles. The availability of a wide selection of geosynthetics in terms of strength, durability, and permeability enables the use of hydraulically filled tubes in many applications, some of which may be considered critical (e.g., encapsulate contaminated soil). This paper presents an overview of an analysis to calculate both stresses in the geosynthetic and geometry of the tube. It also verifies the correctness and validity of the results obtained from a computer program developed to solve the problem. An instructive parametric study implies that the most critical factor needed to assure successful construction is the pumping pressure; a slight accidental increase in this pressure may result in a very significant stress increase in the encapsulating geosynthetic. Pressure increase beyond a certain level, however, has little influence on the storage capacity of the tube. Guidance in selecting an adequate geosynthetic, including partial safety factors and filtration properties, is also presented. Design aspects associated with required spacing of inlets and head loss of the slurry as it flows through the tube are considered outside the scope of this paper.

An 11-mound site in Louisiana predates other known mound complexes with earthen enclosures in North America by 1900 years. Radiometric, luminescence, artifactual, geomorphic, and pedogenic data date the site to over 5000 calendar years before present. Evidence suggests that the site was occupied by hunter-gatherers who seasonally exploited aquatic resources and collected plant species that later became the first domesticates in eastern North America.

Abstract Special accurate and efficient hybrid elements were developed to account for notch‐tip singularities of type r γ , where γ can be complex. Proper normalization of the notch‐tip element size was used to minimize the oscillation of the assumed function around the boundaries of the element and to improve the accuracy of the solution. Examples of various notch angles and sizes are presented.

The distribution and abundance of fishes in submersed aquatic plants of three relative densities (no plants, intermediate plant density, high plant density) were estimated in the tidal Potomac River near Alexandria, Virginia. Fish were sampled with a boat-mounted electroshocker at night in May (when plants were emerging), August (peak plant densities), and November (plant senescence) of 1986. Mean densities of all plants ranged from 9 to 33 g/m2 (dry-weight basis) in May, and 400 to greater than 1,000 g/m2 in August and November. Hydrilla verticillata was usually the dominant aquatic plant. In May, overall mean fish abundance was highest in areas of high plant density (36 fish/5 min shocking), whereas in August and November fish abundance was highest in areas of intermediate plant densities (100 and 62 fish/5 min electroshocking, respectively). Areas without plants contained a relatively high number of filter-feeding fishes, including Atlantic menhaden Brevoortia tyrannus and blueback herring Alosa aestivalis. The fish assemblage in the vegetated sites comprised mainly brown bullhead Ictalurus nebulosus, banded killifish Fundulus diaphanus, pumpkinseed Lepomis gibbosus, largemouth bass Micropterus salmoides, and yellow perch Perca flavescens. The bay anchovy Anchoa mitchilli, white perch Morone americana, and inland silverside Menidia beryllina were distributed throughout all three sites during the study. Fish also were sampled with pop nets in aquatic plants and with seines between shore and the plant beds. More than five times more fish (9.8/m2) were collected with pop nets in areas with intermediate plant density, where there were several codominant plant species, than in areas with dense hydrilla (1.8 fish/m2). Shore-zone fish densities estimated with seine hauls were higher in areas adjacent to dense hydrilla beds (9 fish/m2) than in areas with no plants (1.5/m2) or near intermediate plant densities (3.3/m2), but the number of fish species was lowest near hydrilla.

This paper describes the potential suitability of a new family of concrete mixtures for use in protective structures. Two very‐high‐strength concrete mixtures are discussed and experimental results of penetration studies on one of these are presented. The results are compared to penetration‐study results of other, more conventional concrete mixtures, and the advantages of the very‐high‐strength mixtures are described.

Recent technological developments have made available efficient bender transducers based on the piezoelectric effect. In this paper an electrical circuit analog to the Timoshenko beam is synthesized using a Lagrangian method and by paralleling capacitive flux linkages to rotation and transverse displacement. A Piezo-ElectroMechanical (PEM) beam is conceived by uniformly distributing piezoelectric transducers on a beam and interconnecting their electric terminals via the found analog circuit, completed with suitable resistors. The high performance features of the synthesized novel circuit include the following. (i) The circuit topology is extremely reduced, the used components are all but one two-terminal elements, and the only two-port network needed is an ideal transformer. (ii) One and the same dissipative circuit ensures a multiresonance coupling with the vibrating beam and the optimal electrical dissipation of mechanical vibrations energy. (iii) For a prototype of a PEM beam, the design of the analog circuit is possible and the obtained nominal values of the circuital elements ensure that can be technically realized without any external feeding. The insertion of resistors in the analog circuit is determined according to two optimality criteria (namely minimization of strain energy time envelope and maximization of vibration time rate decay), based on specific engineering needs. The former seems to be suitable for applications in fatigue phenomena and the latter when the amplitude of vibrations must be rapidly decreased, independently of the initial conditions.

Barium titanate (BaTiO 3 ) powders were prepared by a polymerized complex method based on the Pechini‐type reaction route, wherein a mixed solution of citric acid (CA), ethylene glycol (EG), and barium and titanium ions, with a molar ratio of CA:EG:Ba:Ti = 10:40:1:1, was polymerized to form a transparent resin, which was used as a precursor for BaTiO 3 . Characterization of the initial precursor solution of EG, CA, and barium and titanium ions by Raman scattering and 13 C‐NMR spectroscopy indicated that barium and titanium ions were simultaneously stabilized with CA to form a barium‐titanium mixed‐metal CA complex with a stoichiometry similar to Ba:Ti:CA = 1:1:3. Raman and 13 C‐NMR spectra of the liquid mixture at various reaction stages indicated that the fundamental coordination structure of the mixed‐metal complex remained almost unchanged throughout the polymerization process. X‐ray diffractometry (XRD) measurements indicated formation of pseudo‐cubic BaTiO 3 free from BaCO 3 and TiO 2 when the barium‐titanium polymeric precursor was heat‐treated in air at 500°C for 8 h or at 600°C for 2 h. However, the Raman spectra of the same powders indicated the formation of tetragonal (rather than cubic) BaTiO 3 , with traces of high‐temperature hexagonal BaTiO 3 stabilized at room temperature. XRD of a pyrolyzed product at 500°C for 2 h revealed a simple mixture of BaTiO 3 and an intermediate phase, Ba 2 Ti 2 O 5 . CO 3 . A solid‐state reaction between BaCO 3 and TiO 2 was concluded as not being responsible for the BaTiO 3 formation; rather, BaTiO 3 formed directly by thermal decomposition of the intermediate Ba 2 Ti 2 O 5 . CO 3 phase at temperatures >500°C. In addition, by Raman scattering measurements, the intermediate Ba 2 Ti 2 O 5 . CO 3 phase was found to be unstable in ambient air, yielding BaCO 3 as one of the decomposed products.