bluuebunny/crossref_metadata_2025 huggingface dataset:
Paleobiology and Paleoecology of Palaeoaplysina and Eopalaeoaplysina New Genus in Arctic Canada
Authors: Anderson Kaylee D. , Beauchamp Benoit
Published: October 2014

Palaeoaplysina is an enigmatic platy macrofossil with a cellular skeleton and internal canal system common to upper Carboniferous–lower Permian reefs of the northern hemisphere. Its rapid flourishing from the Moscovian and subsequent extinction near the end of the Sakmarian, as well as its unique combination of physical features, are poorly understood. In addition to Palaeoaplysina reefs forming major petroleum exploration targets in Russia, Palaeoaplysina is abundant and well preserved in the Sverdrup Basin in the Canadian Arctic Archipelago. A new genus of Palaeoaplysinaceae, Eopalaeoaplysina n. gen., is also widespread in the Sverdrup Basin and identified based on a simple morphology with broad canals distributed in roughly even rows. The distribution of paleoaplysinids in strata from the Moscovian to the Sakmarian in the Sverdrup Basin reveals Eopalaeoaplysina and Palaeoaplysina represent two distinct reef-building forms with an increase in complexity over time. The aragonitic composition of Palaeoaplysina, in addition to its distribution within the photic zone and differentiated cellular skeleton, suggests paleoaplysinids were ancestral red algae. Palaeoaplysina occurs in both low-energy back-reef and higher-energy reef front facies. Preserved thin edges of Palaeoaplysina plates indicate it was encrusting, at least in low-energy conditions. The exclusion of Palaeoaplysina from the late Paleozoic tropics and the southern hemisphere, its rapid appearance and proliferation, and its eventual extinction may point towards an evolutionary niche optimized for warm-water conditions at unusually high latitudes along the western margin of Pangea.
Early Middle Cambrian Trilobites from La Laja Formation, Cerro El Molle, Precordillera of Western Argentina
Authors: Pratt Brian R. , Bordonaro Osvaldo L.
Published: October 2014

A tectonically undeformed portion of the lower part of La Laja Formation is exposed at Cerro El Molle near San Juan, Precordillera of western Argentina. It consists of shallow-water, variably argillaceous lime mudstone and sporadically interbedded bioclastic grainstone deposited in an inner shelf setting. The El Estero Member and the basal 0.2 m of the Soldano Member contain a trilobite fauna of olenelloids and ‘simple’ ptychoparioids indicative of the early Cambrian (series 2, stage 4; Dyeran stage of Laurentia). The succeeding 50 m of the lower Soldano Member yield trilobites characteristic of the early middle Cambrian (series 3, stage 5; Delamaran stage of Laurentia). In ascending order of occurrence,Amecephalus arrojosensis,Kochiella maxeyiandEokochaspis nodosa, along with several other taxa, includingPtychobaban. gen. (type speciesPtychoparella buttsi), belong to the traditional lowerPlagiura–PoliellaBiozone. However, while this fauna is similar to that of the Great Basin, the nominative species of theEokochaspsis nodosaand overlyingAmecephalus arrojosensisbiozones recognized in southern Nevada occur in reverse order in the Soldano Member. This suggests that the ranges of these species overlap, thereby reducing the temporal resolution in the Precordillera into a combinedAmecephalus arrojosensis–Eokochaspis nodosaBiozone. Argillaceous lime mudstones at the top yieldMexicella mexicana, indicative of theMexicella mexicanaBiozone recognized in the Great Basin, which is equivalent to the traditionalAlbertellaBiozone of Laurentia. Because corynexochids are almost absent, the low-diversity ‘kochaspid’-dominated biofacies appears to typify the platform interior. The fauna is entirely Laurentian in composition, reinforcing notions of a close proximity of Cuyania to Laurentia during the Cambrian that enabled faunal migration and interchange. The absence of a late early Cambrian to early middle Cambrian hiatus correlative with the Hawke Bay Event, however, suggests no close affinity to the Iapetus-facing margin of eastern Laurentia.
Mississippian Rugose Corals from Alabama: A Review
Authors: Rodríguez Sergio , Kopaska-Merkel David C.
Published: October 2014

The Mississippian rugose corals from Alabama housed in several museums in that state are revised on the basis of current knowledge of this subclass. Fifteen species belonging to 10 genera have been identified; three species are new, including Zaphrentites lacefieldi, Palastraea cullmanense, and Siphonophyllia alabamaense. Four coral assemblages characterize four stratigraphic subdivisions of the Mississippian in Alabama: Osagean, Meramecian, lower Chesterian, and upper Chesterian. Corals are abundant in some units but diversity is quite low in all assemblages. The level of endemism is very high, except for the lower Chesterian assemblage, which contains some western Paleotethyan forms. Two possible coral evolutionary lineages have been identified.
Early Ordovician Trilobites from the Nazareno Area, Northwestern Argentina
Authors: Tortello M. Franco , Esteban Susana B.
Published: October 2014

The upper part of the Santa Rosita Formation (Ordovician, Tremadocian) in the Nazareno area, Cordillera Oriental, northwestern Argentina, records the vertical passage of high-energy, shallow water platform environments to offshore settings. Eighteen trilobite species are described from this locality for the first time. Although the taxa from the lower part of the succession (Leptoplastidessp.,Asaphellussp.) are scarce and non-age diagnostic, those from the upper part include diverse assemblages partially assigned to the late TremadocianNotopeltis orthometopaZone. Systematic descriptions of several species (Geragnostus nesossiiHarrington and Leanza,G. callaveiformisHarrington and Leanza,Asaphellus jujuanusHarrington,Notopeltis orthometopa[Harrington],Mekynophrys nannaHarrington,Ceratopyge forficuloidesHarrington and Leanza,Apatokephalus tibicenPřibyl and Vanĕk) are improved, the genusNileusDalman (includingN. australisn. sp.) is first reported from the Tremadocian of western Gondwana, and new species ofAsaphellusCallaway (A. nazarenensisn. sp.),ConophrysCallaway, andApatokephalusBrøgger are described. The trilobites have their closest affinities with faunas from Norway and Sweden.Notopeltis orthometopaandMekynophrys nannaare restricted to the uppermost part of the succession, well above the first records of most other trilobites recognized.
Anthracotheres from Wadi Moghra, Early Miocene, Egypt
Authors: Miller Ellen R. , Gunnell Gregg F. , Gawad Mohamed Abdel , Hamdan Mohamed , El-Barkooky Ahmed N. , Clementz Mark T. , Hassan Safiya M.
Published: October 2014

The early Miocene site of Wadi Moghra, Qattara Depression, Egypt, is important for interpreting anthracothere (Mammalia, Artiodactyla) evolution, because the Moghra sediments preserve a higher diversity of anthracotheres than any other pene-contemporaneous site. New specimens from Moghra are described and form the basis for the systematic revision of Moghra anthracotheres provided here. Among the important discoveries recently made at Moghra is the first complete skull ofSivameryx moneyi. Other new specimens described here include two new species ofAfromeryx, and a new genus and species, all of which are unique to Moghra. A review of biogeographic information supports the conclusion that three of the Moghra anthracotheres (Brachyodus depereti, B. mogharensis,andJaggermeryx naida, n. gen. n. sp.) are members of late surviving lineages with a long history in Africa, while three other species (Afromeryx grex, n. sp., A. palustris, n. sp., andSivameryx moneyi) represent more recent immigrants from Eurasia.
Morphometrics Indicates Giant Ordovician Macluritid Gastropods Switched Life Habit During Ontogeny
Authors: Novack-Gottshall Philip M. , Burton Keoki
Published: October 2014

Paleontologists have long speculated that the bizarre, giant Ordovician gastropods Maclurites Le Sueur, 1818 and Maclurina Ulrich and Scofield, 1897 lived more like suspension-feeding oysters than typical algivorous snails. Geometric and eigenshape morphometrics demonstrate the plausibility of this lifestyle, but with a twist. The apertures of these gastropods were small ellipsoids when young, transitioning rapidly to polygonal morphologies at maturity, with angulations (sinuses) occurring in regions associated with development of mature ctenidia (gills) and enhanced stability on the seafloor. Combined with knowledge of extant suspension-feeding gastropods and functional and phylogenetic analysis of the anatomy of other fossil relatives, this ontogenetic pattern suggests these snails began life as typical mobile algae-grazers, but switched to sedentary suspension-feeders as they aged.
Remarks on the Cortical Structure of Late Paleozoic “Phylloid Algae”
Authors: Corrochano Diego , Vachard Daniel
Published: October 2014

The cortical structure of the green anchicodiacean alga Anchicodium in the Pennsylvanian Dueñas Formation of the Cantabrian Zone (northwestern Spain) is described and illustrated. Anchicodium is characterized by a broad phylloid or leaflike calcified thallus, consisting of a bilateral cortex and a poorly calcified central medulla. The organization and morphology of the cortical system have been revealed with great detail using cathodoluminescence microscopy. Anchicodium cortex is composed of up to three (four?) orders of dichotomized branched cortical siphons that are usually swollen at the center; primary siphons are bulbous and are followed by elongate cylindrical siphons. Cortical siphons are preserved as dull-bright luminescent molds filled with micrite or microsparite, and contrast sharply with the surrounding non-luminescent calcite infilling the intersiphonal spaces, originally occupied by aragonite. Anchicodium in the Dueñas Formation exhibits a variety of preservational stages. Through a compilation of the taxonomic nomenclature and morphologic re-interpretations, it is concluded that some late Paleozoic anchicodiacean algae might represent diagenetic stages of Anchicodium or Eugonophyllum without any taxonomic significance. This conclusion is suggested particularly for the taphotaxon Ivanovia.
Relationship Between Geomembrane Density and Carbon Black Content
Authors: Giroud J.P.
Published: October 2014

A theoretical relationship is established between the density of a polymeric geomembrane, the density of the polymer, the density of carbon black, and the carbon black content. Then an approximate relationship is established for polyethylene geomembranes. For the usual range of parameters, the approximate relationship is in close agreement with the rigorous relationship.
Manufacturing Quality Control and Certification of Geotextiles
Authors: Sprague C.J.
Published: October 2014

Accurate reporting of characteristic geotextile properties in brochures, certifications, or trade journals requires a comprehensive quality control and certification program which includes systematic sampling and testing as well as proper management of test data and a knowledge of the required level of confidence required by the user. If any of these elements are missing, then the reported properties will be cloaked with uncertainty at best and, at worst, may be false and misleading. Therefore, to ensure accuracy, users must request a specific confidence level when requesting “minimum” values. In addition, manufacturers must establish a comprehensive database developed from a systematic sampling and testing program to ensure correct documentation of the characteristic properties of their products. This paper presents a comprehensive manufacturing quality control and certification protocol for geotextiles which, if followed by all manufacturers of geotextiles, would ensure statistical accuracy and uniformity in the reporting of the characteristic properties of geotextiles. Additionally, guidance is given to geotextile specifiers for the proper definition of “minimum”, so that geotextiles can be supplied which provide the desired level of confidence required by the specifier.
Geosynthetic-Reinforced Soils Under Repeated Loading: A Review and Comparative Design Study
Authors: Ashmawy A.K. , Bourdeau P.L.
Published: October 2014

Many types of geosynthetic-reinforced soil are subjected to repeated or cyclic loading. In transportation infrastructures such loading conditions occur in pavements supported by reinforced soil retaining walls, reinforced soil bridge abutments, reinforced roadways, or railway foundations. Insufficient knowledge on the mid- and long-term performance of geosynthetics and on soil-reinforcement interaction under such conditions might be considered a hurdle to their use as reinforcement in permanent earth structures. In this paper, information on the performance of geosynthetic-reinforced soil structures and the durability of geosynthetic materials under repeated or cyclic loading is summarized. Semi-empirical methods are currently available to design geosynthetic-reinforced unpaved roads under traffic loading. A spreadsheet program was used in order to perform sensitivity analyses on three widely used design methods for unpaved roads. Based on the analytical results, the limitations of the currently available experimental database are discussed and research needs identified.
An Integrated Approach to Evaluating Single-Layer Reinforced Soils
Authors: Espinoza R.D. , Bray J.D.
Published: October 2014

A new procedure for evaluating the load capacity of single-layer reinforced soils is presented. Slippage between the reinforcement and the granular fill is considered in the analysis. This procedure incorporates two important membrane support contributions, namely normal stress membrane support and interfacial shear stress membrane support. The improved subgrade capacity due to the membrane-induced reduction in shear stresses at the top of the subgrade is also captured. Using this procedure, it is demonstrated that a significant membrane contribution can be developed even for cases in which proper anchorage is not provided. The derived expression satisfies both vertical and horizontal force equilibrium along the reinforcement. The proposed analytical procedure was validated by comparing the analytical results to the results from small-scale model tests performed by others. The potential usefulness of the proposed procedure is illustrated by using the resulting equations to evaluate the performance of an embankment supported on a soft foundation overlain by a reinforcing layer.
Graphical Solutions for Determining Geosynthetic Tension in Cover Systems
Authors: Long J.H.
Published: October 2014

Graphical solutions are provided for determining the geosynthetic tensile force required for the stability of cover systems. The graphs are based on force equilibrium solutions and are presented using dimensionless axes and parameters. Solutions are provided that allow upper-bound and lower-bound estimates to be made for the tensile force in the geosynthetics required for stability of cover systems.
Stability of Geosynthetic-Soil Layered Systems on Slopes
Authors: Giroud J.P. , Williams N.D. , Pelte T. , Beech J.F.
Published: October 2014

This paper presents a method based on limit equilibrium to evaluate the stability of geosynthetic-soil layered systems on slopes. Examples of geosynthetic-soil layered systems constructed on slopes include liner systems used in landfills, liquid impoundments, dams and canals, and cover systems used on landfills and sludge ponds. The method, which is applicable whether the thickness of the layered system is uniform or not, takes into account all mechanisms that contribute to the stability of the layered system: the interface shear strength along the slip surface, the toe buttressing effect that results from the internal shear strength of the soil components of the layered system located above the slip surface, and the reinforcement provided by all geosynthetics located above the slip surface. The factor of safety against sliding is expressed by an equation as the sum of five terms, making it possible to readily identify the contribution of each term to the factor of safety. A parametric study shows that the factor of safety calculated with this method is very close to the factor of safety obtained using a rigorous method, which consists of defining the factor of safety as the ratio between the assumed and mobilized values of the strength parameters. Furthermore, factor of safety calculations using the proposed method are much easier than with the rigorous method.
Bearing Capacity of Geosynthetic Clay Liners for Cover Soils of Varying Particle Size
Authors: Fox P.J. , De Battista D.J. , Chen S.H.
Published: October 2014

Geosynthetic clay liners (GCLs) are covered with soil after installation to protect them from stress concentrations due to construction activities and permanent structural loads. In this study, laboratory cover soil penetration tests (i.e. bearing capacity tests) were used to investigate the potential for lateral bentonite displacement within hydrated GCLs under concentrated loads. A greater cover thickness is required to adequately protect a GCL as the mean particle size of the cover soil increases. A ratio of cover soil thickness to breadth of loading area (H/B) between 1.0 and 1.5 is satisfactory for soils composed of sand and fine gravel. A larger H/B ratio is required for GCLs covered with clean medium-sized gravel. As compared to needle-punched products, adhesive-bonded and stitch-bonded GCLs show a greater tendency for lateral bentonite displacement under concentrated loads. If a hydrated GCL is protected by a suitably thick layer of cover soil, the results of this study show that the GCL will be undamaged by concentrated loads applied to the surface of the cover.
Geomembrane Response in the Wide Strip Tension Test
Authors: Merry S.M. , Bray J.D.
Published: October 2014

The geomembrane wide strip tension test is a performance test that provides test data from which the stress-strain response of a geomembrane may be calculated. However, the volumetric response of the geomembrane must be accounted for when processing the test data to obtain the geomembrane stress-strain properties. This paper presents the results of strain controlled, uniaxial tension tests performed on two common polymeric geomembranes. During the tests, measurements were taken at specific locations on the geomembrane specimen. These measurements, combined with results from photographic analyses, allowed the specimen width and thickness to be determined during the tests. The measured values corresponded well with the theoretical values, assuming that the geomembrane is incompressible. The test results were not sensitive to the aspect ratio of the test specimen. The wide strip tension test should be considered a uniaxial (not a plane strain) tension test. It was also shown that modeling the stress-strain response of polymeric geomembranes with a constant cross sectional area instead of a constant volume significantly underestimates the actual stress-strain response of the geomembrane, particularly at large strains.
An Interface Pullout Formula for Extensible Sheet Reinforcement
Authors: Sobhi S. , Wu J.T.H.
Published: October 2014

Pullout tests have been widely used to evaluate soil reinforcement interface properties for the design and analysis of reinforced soil structures. However, there are difficulties interpreting pullout test results particularly when extensible materials, such as geotextiles, are used as reinforcement. In this study, an analytical model (an “interface pullout formula”) is presented for predicting and interpreting pullout test results in a unified and consistent manner. The model is based on three postulates that were deduced from the measured behavior of laboratory pullout tests and numerical results from finite element analyses. A number of applications of the interface pullout formula for predicting and interpreting the results of pullout tests are presented, including: how to predict the active length at a given applied pullout force; how to predict the pullout failure force for reinforcement of a given length; how to determine the coefficient of friction from results of a pullout test; and, how to predict the displacement at any point along the reinforcement for a given applied pullout force. Results using the interface pullout formula are shown to be in good agreement with the results of an instrumented pullout test and finite element analyses.
Stability Analysis of Reinforced and Unreinforced Embankments on Soft Ground
Authors: Long P.V. , Bergado D.T. , Balasubramaniam A.S.
Published: October 2014

General solutions are developed for the rotational stability analysis of an embankment with and without reinforcement constructed on soft ground that has an undrained shear strength varying with depth. The general cases of an embankment having a berm, dry or wet tensile cracks, and multiple layers of reinforcement are considered. The additional friction caused by the reinforcement force normal to the slip plane is incorporated into the solution. The solutions are presented in the form of simple equations. The relationship between the critical slip circles through the embankment with and without reinforcement is expressed explicitly. The analysis procedures and supporting graphs allow the user to obtain the solutions using hand computations. A simple computer program in the form of a worksheet was developed to quickly obtain the final results. Applications and illustrative examples of embankments with one and two step berms, and distributed loads are given. The results obtained using the approach presented in this paper compare very well to the solutions obtained from the method of slices using the computer programs SB SLOPE and PC STABL6.
Puncture Protection of Geomembranes Part II: Experimental
Authors: Narejo D. , Koerner R.M. , Wilson-Fahmy R.F.
Published: October 2014

Geomembrane protection materials should be considered in design if geomembranes are to properly serve the role of barrier materials. The type, thickness and properties of the required protection material are in significant need of a rational design method. This series of three papers provides a design method for the inclusion of geomembrane protection materials, geotextiles in particular. Part I focuses on theory, this paper, Part II, focuses on experiments, and Part III focuses on design examples. In this paper, truncated cone and stone puncture test results for both short and long term durations are presented. A 1.5 mm thick high density polyethylene (HDPE) geomembrane, and various nonwoven needle punched geotextiles with varying masses per unit area made from virgin polyester and polypropylene continuous and staple fibers were tested. Using the results of this testing program, a design methodology was developed for calculating the required mass per unit area of a puncture protection material for a given factor of safety. Conversely, the design can be used to determine the unknown factor of safety for a given type of protection material.
Finite Element Modelling of Inelastic Deformation of Ductile Polymers
Authors: Zhang C. , Moore I.D.
Published: October 2014

Two uniaxial constitutive models, a nonlinear viscoelastic (NVE) model and a viscoplastic (VP) model, have recently been developed for time dependent inelastic analysis of ductile polymers. This study extends these models to provide a multiaxial formulation. The new multiaxial models are implemented in a general purpose finite element program, together with a conventional treatment of geometrical nonlinearity. The solution procedure is based on a simple explicit integration method that is suitable for the new material models and is easy to implement. Two example problems are studied to evaluate the performance of the new finite element procedure. Finite element simulations of a perforated high density polyethylene (HDPE) plate under remote uniaxial loading are performed, and finite element model simulations of an HDPE pipe section under parallel plate loading are also performed. The finite element modelling results are then compared with the measured experimental results. It is found that the finite element model provides good predictions of the inelastic deformation of HDPE under various loading histories, including cases that involve a highly nonlinear material and geometrical response.
Optimal Configuration of a Double Liner System Including a Geomembrane Liner and a Composite Liner
Authors: Giroud J.P. , Soderman K.L. , Badu-Tweneboah K.
Published: October 2014

A number of landfills are designed with a double liner system that includes a geomembrane liner and a composite liner. The design engineer must select which of these two liners should be the primary liner. A comparative study is presented in this paper to help determine which configuration is preferable. The comparative study consists of comparing the rate of leachate migration through two double liner systems having the following inverse configurations: (i) a double liner system where the primary liner is a geomembrane liner and the secondary liner is a composite liner; and (ii) a double liner system where the primary liner is a composite liner and the secondary liner is a geomembrane liner. The composite liner considered in the study consists of a geomembrane on a geosynthetic clay liner (GCL). The comparison between the two liner systems is based only on advective flow through geomembrane defects (i.e. defects in the geomembrane liner as well as defects in the geomembrane component of the composite liner). Other factors that may have an impact on the selection of a liner configuration, such as diffusive flux and construction issues, are not considered in the comparison. The study shows that, from the viewpoint of minimizing the advective flow of leachate through geomembrane defects, it is preferable to use the configuration where the primary liner is a composite liner.
Evaluation of the Surface Area of A GCL Hydrated by Leachate Migrating Through Geomembrane Defects
Authors: Giroud J.P. , Rad N.S. , McKelvey J.A.
Published: October 2014

When a geosynthetic clay liner (GCL) is used in a composite liner, the bentonite of the GCL may be hydrated by moisture from the underlying medium and by leachate migrating through defects in the overlying geomembrane. When hydration caused by the underlying medium is negligible, the GCL is hydrated only in areas associated with geomembrane defects. This paper provides a method to evaluate the fraction of the GCL surface area that is hydrated by leachate migrating through geomembrane defects. Results presented in this paper show that, in most usual cases, the GCL is hydrated only in a small fraction of its surface area when the only cause of hydration is leachate migrating through defects in the overlying geomembrane. The method presented in this paper is not applicable when a GCL is placed in contact with a soil that retains water by capillarity, since this water may migrate into the GCL; the method is essentially applicable to GCLs placed on top of a relatively dry and highly permeable leakage collection layer (gravel or geonet). The study presented in this paper also shows that hydration of the bentonite by leachate migrating through defects in the overlying geomembrane takes only days. From this it is concluded that the size of the hydrated area located around each geomembrane defect is governed by the largest leachate head in the history of the liner.
Mechanical Behavior of Sand Reinforced With Mesh Elements
Authors: Morel J.C. , Gourc J.P.
Published: October 2014

This paper presents a study of the shear strength of sand reinforced with randomly-oriented and vertically-aligned polypropylene mesh elements. A biaxial apparatus was designed to load specimens under plane strain conditions, and photogrammetry was used to measure the strain field within the specimens during loading. The biaxial test results obtained for sand specimens reinforced with randomly-oriented mesh elements illustrate the effect of reinforcement content on specimen strength. Strain localization was observed for both reinforced and unreinforced sand specimens; however, for the reinforced sand specimens, the strain localization phenomenon was not accompanied by a drop in strength. Further testing was performed using a large shear box to impose a fixed shear plane in the reinforced specimens. Sand specimens with randomly-oriented mesh elements, as well as sand reinforced with vertically-aligned mesh elements were tested in the large shear box.
A Nonlinear Model of Geosynthetic-Reinforced Granular Fill Over Soft Soil
Authors: Yin J.H.
Published: October 2014

This paper extends a recently developed one-dimensional foundation model for geosynthetic-reinforced granular fills over soft soil using a nonlinear constitutive model for the granular fill and a nonlinear spring model for soft soil. The mathematical form of the soil and spring models is a hyperbolic function that represents the nonlinear shear stress-shear strain behaviour of the granular fill and the nonlinear reaction of the soft soil. The foundation model is derived using the nonlinear soil and spring models, and the iterative finite difference scheme that is used to solve the nonlinear equations of the foundation model is presented. Parametric analyses of the nonlinear parameters are performed to study the effect on the foundation settlement and the mobilised tension in a geosynthetic layer. The computed results are presented and discussed.
Water Retention Functions of Four Nonwoven Polypropylene Geotextiles
Authors: Stormont J.C. , Henry K.S. , Evans T.M.
Published: October 2014

The water retention functions of four nonwoven polypropylene geotextiles were measured. Each of the four geotextile types were tested in two conditions: new and cleaned. The water retention functions of each geotextile specimen were found to be hysteretic. The new geotextile specimens always contained more water at comparable suction heads than the cleaned geotextile specimens. At zero suction head, the new specimens approached saturation, whereas the cleaned specimens were less than 20% saturated.
Seismic Response Analysis of a Geosynthetic-Reinforced Soil Retaining Wall
Authors: Bathurst R.J. , Hatami K.
Published: October 2014

The paper reports results from numerical experiments that were carried out to investigate the influence of reinforcement stiffness, reinforcement length, and base boundary condition on the seismic response of an idealized 6 m high geosynthetic-reinforced soil retaining wall constructed with a very stiff continuous facing panel. The numerical models were excited at the foundation elevation by a variable-amplitude harmonic motion with a frequency close to the fundamental frequency of the reference structure. The two-dimensional, explicit dynamic finite difference program Fast Lagrangian Analysis of Continua (FLAC) was used to carry out the numerical experiments. Numerical results illustrate that the seismic response of the wall is very different when constructed with a base that allows the wall and soil to slide freely and when the wall is constrained to rotate only about the toe. Parametric analyses were also carried out to investigate the quantitative influence of the damping ratio magnitude used in numerical simulations and the effects of distance and type of far-end truncated boundary. The response of the same wall excited by a scaled earthquake record was demonstrated to preserve qualitative features of wall displacement and reinforcement load distribution as that generated using the reference harmonic ground motion applied at 3 Hz. The lessons learned in this study are of value to researchers using dynamic numerical modeling techniques to gain insight into the seismic response of reinforced wall structures.
Interpretation of Transmissivity Test Data for Geonets
Authors: Fannin R.J. , Choy H.W.
Published: October 2014

Transmissivity tests were performed on a geonet confined between a pair of geomembranes under five increments of compressive stress ranging from 25 to 400 kPa. Each successive increment of stress was applied for 24 hours. In total, four geonets and seven geomembranes were evaluated in the test program. Measurements of flow rate per unit width through the geonet taken at five hydraulic gradients between the values of 0.02 and 0.10 indicate that the flow regime is semi-turbulent. Interpretation of the data addresses a comparison of flow behaviour in the geonet with that of fine gravel. A relative permeability factor is used to quantify the flow capacity in the semi-turbulent regime. The relationship between the relative permeability factor and the hydraulic gradient offers a useful approach for the estimation of flow capacity at gradients for which test data are not available. In contrast to the behaviour of gravels, a stress dependency of the curves may be expected at magnitudes of confining stress that result in a compression of the geonet and/or intrusion of the geomembrane into the apertures of the geonet.
Leachate Flow Mound Equations for Steady-State Flow Over a Landfill Geosynthetic Bottom Liner
Authors: Masada T.
Published: October 2014

A simple approach, using Darcy’s law, is taken to derive a set of equations to estimate the shape of the leachate flow mound over a landfill geosynthetic bottom liner. Steady-state flow conditions through a homogeneous porous media, over a sloping impervious base, are assumed. The derivation is extended to analyze the leachate flow mounding in a two-layer drainage system. The two-layer model may be particularly suited for analyzing leachate flow over a landfill geosynthetic bottom liner system that incorporates a geonet. The results of parametric analyses of the derived leachate flow mound equations and several other flow mound equations found in the literature are compared. Finally, based on the performance of the new leachate flow mound equations, recommendations are made concerning an often overlooked aspect of the leachate collection and removal system (LCRS) design.
Creep and Stress Relaxation of Geotextile-Reinforced Soils
Authors: Helwany S.M.B. , Shih S.
Published: October 2014

Creep and stress relaxation phenomena occur simultaneously in a geosynthetic-reinforced soil (GRS) structure. Therefore, the simultaneous measurement of creep and stress relaxation occurring in a soil-geosynthetic composite during long-term laboratory interaction tests is essential. This paper describes a new test apparatus that measures creep and stress relaxation simultaneously in soil-geotextile composites, which is essential for understanding the long-term interactive behavior between geosynthetic reinforcement layers and the confining soil.
A Basis for Modelling Creep and Stress Relaxation Behaviour of Geogrids
Authors: Sawicki A.
Published: October 2014

Based on the test data published in 1997 by Leshchinsky et al., analytical models of the creep and stress relaxation of some geogrids are presented. It is shown that in the case of Geogrid C2 (high density polyethylene) a standard rheological model describes the experimental data in the low stress level range. In other cases, new rheological models can be developed, such as the new model proposed for Geogrid A1 (polyester). The models are defined by differential constitutive equations whose solutions are presented for creep at constant stress and stress relaxation at constant strain. Model parameters are also determined.
Bearing Capacity Failure of a Trapezoidal, Geosynthetic-Reinforced Soil Wall
Authors: Lo S.C.R. , Bosler J. , Gopalan M.
Published: October 2014

Bearing capacity failure of geosynthetic-reinforced soil walls with a trapezoidal reinforced zone was studied analytically by a series of finite difference stress analyses. Non-associated flow rules and modelling of both construction and the path to collapse were adopted in the analyses. A range of factors, including wall height, soil parameters, and path to failure were studied. For each trapezoidal reinforced soil wall, its equivalent rectangular reinforced wall was also analysed in order to provide a benchmark for evaluation of simplified design models. The results of the analysis were used to calibrate three possible simplified design methods. The performances of these design models were evaluated by the margin of conservatism relative to their equivalent rectangular wall.
Behaviour of EPS Geofoam as Flexible Pavement Subgrade Material in Model Tests
Authors: Zou Y. , Leo C.J. , Small J.C.
Published: October 2014

The behavior of expanded polystyrene (EPS) geofoam used as subgrade and fill material under flexible pavement was investigated by carrying out a series of tests in a model pavement testing facility. In the experimental setup, pavement test sections that consisted of a wearing course, a gravel base layer, and a sand subbase were placed on EPS blocks inside a test tank. Traffic loading on the test pavement was simulated using a loaded wheel running on an oval-shaped test track. The investigation studied the effects of repeated traffic loading on the performance of the EPS geofoam, the influence of the EPS block size, and the presence or lack of lateral restraint. For comparison purposes, a pavement section using sand fill instead of EPS geofoam was also constructed and tested and is considered as the baseline case. The performance of the EPS geofoam was benchmarked against the baseline case to analyze its performance and to determine possible problems that may occur when used in full-scale pavement sections. Implications for pavement design are also discussed.
Permeability of Damaged Geosynthetic Clay Liners
Authors: Mazzieri F. , Pasqualini E.
Published: October 2014

The results of an experimental test program for the permeability of a damaged, adhesive-bonded, geosynthetic clay liner (GCL) are presented. GCL specimens were damaged to simulate damage occurring during handling or installation. Either a portion of the GCL was removed to simulate tearing with bentonite loss, or the GCL was punctured with a metal object to simulate damage without bentonite loss. In general, positive results were obtained for the case of damage with bentonite loss: holes up to 3 cm in diameter self-healed with only a slight increase in hydraulic conductivity compared to an intact GCL. However, the self-healing process can be compromised if torn GCLs with bentonite loss are placed on a coarse subgrade with large pore openings, which allows the bentonite to migrate from the puncture in the GCL. Damage without bentonite loss was simulated for both hydrated and unhydrated GCL specimens. Complete self-healing of punctures was generally obtained, but it was also shown that the conversion of sodium bentonite to calcium bentonite causes a drastic reduction of the self-healing capacity of the GCL, confirming that ion exchange is particularly harmful to the overall performance of GCLs.
Effect of the Foundation Quality on a Geotextile-Reinforced, Brick-Faced Soil Retaining Wall
Authors: Pinto M.I.M. , Cousens T.W.
Published: October 2014

This paper describes a study carried out on geotextile-reinforced, brick-faced retaining walls built with different foundation conditions and reinforcement geometry in order to examine the effect of foundation quality. A total of five different foundations were tested in order to investigate if either a good foundation or a large and expensive wall-face footing might be necessary to ensure good performance of rigid-faced walls with short reinforcement layers. The results show that the foundation quality is indeed a very important factor in determining the behaviour of the walls. However, walls built on compressible foundations, with footings three times the width of the wall, show a behaviour similar to walls built on strong foundations (simulated in this study by the base of a steel test tank).
The Myth of Hydraulic Transmissivity Equivalency Between Geosynthetic and Granular Liquid Collection Layers
Authors: Giroud J.P. , Zhao A. , Bonaparte R.
Published: October 2014

Design engineers often assume that a geosynthetic liquid collection layer and a granular liquid collection layer having the same hydraulic transmissivity are equivalent. In the United States, such equivalency is often mandated by regulations for leachate collection layers and leakage detection and collection layers used in landfills. This approach is based on the assumption that two liquid collection layers having the same hydraulic transmissivity have the same flow capacity. As shown in the present paper, this is true only in the case of confined flow. A theoretical analysis described in the present paper shows that, in the case of unconfined flow (which is the usual design case), two liquid collection layers that have different thicknesses and hydraulic conductivities (such as granular and geosynthetic liquid collection layers) cannot have the same flow capacity (i.e. cannot be equivalent) if they have the same hydraulic transmissivity. To be equivalent, the thinner liquid collection layer (generally, the geosynthetic liquid collection layer) should have a greater hydraulic transmissivity than the thicker liquid collection layer (generally, the granular liquid collection layer).
Nonwoven Geotextile-Sabkha and -Sand Interface Friction Characteristics Using Pull-Out Tests
Authors: Aiban S.A. , Ali S.M.
Published: October 2014

Sabkha soil is abundant along the Arabian Gulf and Red Sea coasts and is a problematic soil due to its acute water sensitivity and chemical aggressiveness. In many situations, it is required to improve the load carrying capacity of sabkha, and the use of geotextiles was found appropriate. The objectives of this research were to study frictional characteristics of sand-geotextile-sand and sabkha-geotextile-sand interfaces and to compare the pull-out resistance of locally available nonwoven geotextiles taking into account different test parameters. An experimental setup was developed to conduct the pull-out tests. These test results have indicated the existence of three stages of deformation in the geotextile under pull-out testing, which ultimately lead to the slippage of the entire geotextile strip. The use of the pull-out plate reduces the effects of the lateral earth pressure developed on the front wall of the pull-out box and ensures that the free geotextile is kept within the box and, thus, under the required confinement throughout the test. The pull-out tests results indicated that high tensile strength geotextiles require a large pull-out force in the case of the sand-geotextiles and interface, whereas the least extensible geotextile requires the maximum pull-out force in the case of the sabkha-geotextile-sand interface. It was also found that the geotextile surface texture and extensibility are the two main factors, in addition to the mass per unit area of the geotextile, in the case of sabkha-geotextile-sand interface.
Domestic Violence and Treatment Seeking: A Longitudinal Study of Low-Income Women and Mental Health/Substance Abuse Care
Authors: Cheng Tyrone C. , Lo Celia C.
Published: October 2014

A study with 591 low-income women examined domestic violence's role in treatment seeking for mental health or substance abuse problems. (The women resided in one of two California counties.) Following Aday's behavioral model of health services utilization, the secondary data analysis considered the women's need, enabling, and predisposing factors. Generalized estimating equations analyzed the women's longitudinal records of treatment seeking. Results showed that those in the sample who were likely to seek treatment had experienced three or more controlling behaviors and only one abusive behavior. Multivariate data analysis showed treatment-seeking women were likely to be white and older; responsible for few dependent children; not graduates of high school; employed; not participating in Medicaid; diagnosed; and perceiving a need for treatment. The implications of these results for services and policies are discussed.
Factors Associated with Job Satisfaction among Public-Sector Physicians in Belo Horizonte, Brazil
Authors: Ribeiro Rafael Brito Nery , Assunção Ada Ávila , de Araújo Tânia Maria
Published: October 2014

Evidence indicates an association between job satisfaction and illness among physicians. There are also negative consequences of physician dissatisfaction on the quality of medical services. With this in view, a cross-sectional study of a stratified random sample of physicians (n = 266) was conducted in the municipal public health care system in Belo Horizonte, Brazil. Participants answered a questionnaire about job satisfaction, sociodemographic and lifestyle characteristics, work and employment conditions, and health status. Of the 232 respondents, 150 (64.94%) declared themselves satisfied with the work, with no significant difference between male and female physicians (66.4% vs. 64.2%; p = 0.74). The number of physicians satisfied with their work was significantly higher among those who experienced a high level of social support at work ( p < 0.01) and was significantly lower among those working under high-strain conditions ( p = 0.01) and those who screened positive for the presence of common mental disorders ( p < 0.01). These findings suggest that policies to promote social support and mental health in the workplace, as well as the implementation of strategies to increase physicians' control over their work activities, can have a positive effect on the job satisfaction of these professionals.
Revisiting the Schism
Authors: Litsios Socrates
Published: October 2014

The schism between medicine and public health has deep historical roots. The Rockefeller Foundation's Clinical Epidemiology program, initiated in the late 1970s, was seen by Kerr White, its director, as the means to heal the schism. This article revisits the role that the Foundation played in creating that schism before reviewing post-World War II efforts on the part of both the Foundation and the World Health Organization to incorporate the teaching of preventive medicine in medical education curricula. White labeled these efforts as failures, but a closer look at the history raises questions concerning what evidence he used to make this judgment and whether clinical epidemiology has not instead widened the gap between cure and prevention.
Glossary of Access to Health Care and Related Concepts for Low- and Middle-Income Countries (LMICs): A Critical Review of International Literature
Authors: Cabieses Baltica , Bird Philippa
Published: October 2014

Access to health care is a multidimensional and complex concept. Achieving equitable access to care is an important goal for all countries, but particularly challenging in Low- and Middle-Income Countries (LMICs). Despite wide use of the concept of access, it continues to be defined and measured in very different ways. This glossary is a structured overview of key definitions for concepts related to access to health care, with special focus on the interpretation for LMICs. It aims to help people with interest in health service delivery to draw an overview and provide some pointers for further reading in both conceptual and empirical advances in access to health care in LMICs. This document is structured in five sections. The first introduces a general description of the concept of access to health care and its relevance to LMICs, the second displays the search conducted on access to health care for LMICs and the framework used for presentation of glossary terms, the third describes theoretical models most frequently used in the past when looking at access to health care in LMICs, the fourth is the list of terms, and the final section is a discussion of the most salient aspects of this critical review.