bluuebunny/crossref_metadata_2025 huggingface dataset:
Caracterização das ações motoras de crianças com baixa visão e visão normal durante o brincar: cubos com e sem estímulo luminoso ou alto contraste
Authors: Schmitt Beatriz Dittrich , Pereira Karina
Published: October 2014

O brincar de crianças com baixa visão deve ser estimulado a fim de aprimorar os sentidos, adquirir habilidades com uso das mãos/corpo, reconhecer as características dos objetos e explorar o ambiente. O objetivo desse estudo foi identificar e descrever as ações motoras de crianças com baixa visão e visão normal durante o brincar com cubos com e sem estímulo luminoso ou alto contraste. Foram avaliadas seis crianças com baixa visão (43 meses; ±2) e sete com visão normal (42,3 meses; ±2,9). Para a avaliação, utilizaram-se quatro cubos: luminoso, alto contraste, transparente e preto. Cada avaliação foi filmada para possibilitar a identificação e descrição das ações motoras realizadas. Cada cubo foi apresentado à criança por 1 minuto, com intervalo de 15 segundos entre eles. A ordem de entrega dos cubos foi randomizada. As ações motoras identificadas foram: alcance (unimanual, bimanual ou com os pés), deslizar as mãos/dedos, afastar o cubo, bater no cubo, bater com o cubo, girar, agitar, aproximar os olhos e jogar o cubo para cima. As duas últimas ações foram realizadas somente por crianças com baixa visão. Essas realizaram 11 ações motoras nos cubos sem estímulo visual e nove nos cubos com estímulo visual. As crianças com visão normal realizaram oito ações motoras nos cubos de alto contraste, transparente e preto. Concluiu-se que crianças com baixa visão realizam maior variedade de ações motoras em todos os cubos do que crianças com visão normal, em especial nos cubos sem estímulo visual.
SEASONAL ASSESSMENT OF HYDROGRAPHIC VARIABLES AND PHYTOPLANKTON COMMUNITY IN THE ARABIAN SEA WATERS OF KERALA, SOUTHWEST COAST OF INDIA
Authors: Rai Sushanth Vishwanath , Rajashekhar Madaiah
Published: October 2014

The seasonal variation of the hydrographic variables and phytoplankton species in the Arabian Sea waters of the Kerala coast, Southern India was investigated during different seasons. The variables such as pH, temperature, salinity, turbidity and chlorophyll-a contents of water were found to be high during pre-monsoon season and the dissolved oxygen content was minimal. The concentration of nutrients viz., nitrate, phosphate, silicate varied independently. In the study a total of 53 species of phytoplankton were recorded. Their density was higher during the post-monsoon season than during other seasons and the diatoms were found to be the dominant species. The major phytoplankton in terms of frequency and abundance were the species namely, Biddulphia mobiliensis, Chaetoceros curvisetus, Licmophora abbreviata, Skeletonema costatum, Prorocentrum micans and Oscillatoria sp. They showed significant positive correlation with pH, temperature, salinity, nitrate, phosphate and chlorophyll-a contents, whereas turbidity, dissolved oxygen and silicate exhibited significant negative correlation. The Principal Component Analysis (PCA) developed two principal components with 84.74% of total variability in the water quality which separated pre- and post-monsoon periods from the monsoon season on axis I, and pre-monsoon and monsoon periods from post-monsoon on axis II.
FEEDING AND REPRODUCTIVE ACTIVITY OF THE COPEPODS Drepanopus forcipatus AND Calanus australis DURING LATE SUMMER ON THE SOUTHERN PATAGONIAN SHELF (ARGENTINA, 47°-55°S)
Authors: Antacli Julieta Carolina , Sabatini Marina E. , Silva Ricardo I. , Hernández Daniel R. , Jaureguizar Andrés J. , Akselman Rut
Published: October 2014

Drepanopus forcipatus and Calanus australis are key planktonic copepods on the southern Patagonian shelf. Their feeding and reproductive patterns and population status were investigated during late summer, when environmental conditions may be critical. The presence of food in the gut and food-pellet length were recorded in adult females and the most abundant copepodite stages. Diet composition was also studied in adult females. Female reproductive status was evaluated by gonad staging. Despite generally low feeding conditions and decreasing seasonal temperature, both copepods fed to some degree. The most numerous copepodites and adult females of both species showed similarly low feeding activity. About half of the adult females of the two species and C5s of C. australis contained food in their guts, but the proportion of fed C4-females of D. forcipatus was much lower. All copepods were generally feeding at low or intermediate levels. Gonad stage distribution and population structure showed low but still ongoing reproduction in both species. Gut content findings suggest a preference for smaller nanoplanktonic particles, especially dinoflagellates by D. forcipatus, and for autotrophic prey, particularly large diatoms by C. australis. The feeding and reproduction patterns of the two copepods were likely influenced by the distributions of potential food resources and temperature.
GROWTH OF Litopenaeus schmitti (BURKENROAD, 1936) AND Farfantepenaeus paulensis (PEREZ-FARFANTE, 1967) SHRIMP REARED IN RECIRCULATION CULTURE SYSTEM
Authors: Henriques Marcelo Barbosa , Alves Pedro Mestre Ferreira , Barreto Oscar José Sallée , Souza Marcelo Ricardo de
Published: October 2014

The Litopenaeus schmitti and Farfantepenaeus paulensis shrimp captured in estuaries are marketed as live bait for recreational fishing. As an alternative to shrimp extractive activities, the authors evaluated the rearing of these species in a recirculation culture system. For each species, the grow-out study was carried out in two 120-day production cycles, using 3,300 juveniles of an average length of 25 mm and weight of 0.9 grams in each, distributed in 12 tanks of 1,500 liters and 1.32 m2, at a population density of 208.3 shrimp per m2. The growth parameters were obtained using the von Bertalanffy model based on the length (mm) and age (weeks) data. The adjustments were made in the R environment of the non-linear least-square method. The von Bertalanffy growth model showed a proper fit, with determination coefficients of 0.900 for L. schmitti and 0.841 for F. paulensis. The values of L∞ and k were 172.66 and 0.027 mm for L. schmitti and 110.13 mm and 0.050 for F. paulensis, respectively. In the current study, L. schmitti showed negative allometric growth (p=4,314x10-18) and F. paulensis isometric growth (p=0.267). The growth of shrimp obtained in the proposed recirculation system can supply live bait for the sport fishing market.
Conversion of land use and cover in northwest Amazon (Brazil)
Authors: Silva Junior Carlos Antonio da , Nanni Marcos Rafael , Silva Anderson Antonio da , Cezar Everson , Romagnoli Franciele
Published: October 2014

The increasing use of natural resources in a disorderly way has been demanding constant monitoring and ecological-economic zoning. The knowledge on land use and cover allows that measures that guarantee the preservation, maintenance of the environment and space management be appropriate to the reality, since through these factors it is possible to follow the probable environmental impacts and the socioeconomic development of a place in several contexts. The Geographical Information System (GIS) and remote sensing techniques have been applied to land use and land cover mapping. This study aimed to analyze the conversion of land use from different perspectives, concerning geoprocessing techniques, in the southeastern of Roraima State, Brazil, in two distinct periods. In order to verify the land use and cover, two analyses were conducted, using the Spring and TerraView softwares. Great part of the cultivated areas was converted into capoeira, what probably denotes an ending of profitable agriculture, as well as its abandonment caused by the nutritional deficiency of the soil, that became inappropriate for cultivation in the subsequent years. A fuzzy logic would possibly fit well to the types of data analyzed, because the attribute query is overly complex.
Characterization of Geosynthetic Load-Strain Behavior After Installation Damage
Authors: Allen T.M. , Bathurst R.J.
Published: October 2014

Installation damage can be expected to modify the mechanical properties of geosynthetics in reinforcement applications. The paper reviews data from controlled installation damage trials reported in the literature and other sources. Geosynthetic properties taken from the results of index tensile tests are reviewed and the peak strength, strain at failure, and modulus of control and damaged specimens compared. The results of this interpretation of test data are grouped according to reinforcement type and constituent polymer. The data reveals that there are critical levels of reinforcement damage described as percent of peak strength retained that identify the onset of degradation in modulus and/or strain at rupture for each reinforcement classification. The interpretation of the test data presented in the paper illustrates that the current interpretation of installation damage based on peak strength retained is conservative for some types of geosynthetic materials. For these materials, the percentage of modulus retained is a more rational quantitative measure of resistance to site installation damage.
Strain Behaviour of Polymeric Geogrids Subjected to Sustained and Repeated Loading in Air and in Soil
Authors: McGown A. , Yogarajah I. , Andrawes K.Z. , Saad M.A.
Published: October 2014

The stress transfer mechanism in uniaxially and biaxially stretched polymeric geogrids are largely dependent on the interlocking mechanism between the soil and reinforcement. Over the years, this mechanism which may be termed the static interlock mechanism, has been researched and gained wide recognition. When pre-stretched polymeric geogrids are subjected to repeated loading cycles such as compaction forces, a second mechanism which may be termed the dynamic interlock mechanism is developed. In this paper, the existence of this mechanism is established through a series of in-air and in-soil static and dynamic tensile load tests using uniaxially pre-stretched HDPE geogrid specimens. The series of tests also identifies the importance of proper positioning of strain measuring instruments along reinforcements used in reinforced soil structures.
Geotextile Filtration Tests on Two Brazilian Soils and Current Filter Criteria
Authors: Almeida M.S.S , Spada J. , Ehrlich M.
Published: October 2014

This paper presents results of filtration tests with geotextiles in combination with a uniform fine sand and a clayey fine sand. The tests with the clayey sand were long term tests during which the pH, electrical conductivity and turbidity of the percolation water were monitored with time. These observations, together with a detailed measurement of permeability values, indicate that the three geotextiles performed adequately with regard to drainage and soil particle retention. It is shown that current geotextile filter design criteria are conservative and only one among six criteria was able to predict the behavior of all the geotextiles tested.
Geotextile Filters for Internally Stable/Unstable Soils
Authors: Bhatia S.K. , Huang Q.
Published: October 2014

A series of filtration tests were performed to examine geotextile filters and internally unstable soils (broad and gap-graded soils) under non-steady state hydraulic conditions. Eight different nonwoven geotextiles with four model soils and one natural soil were tested. It was observed that for broad and gap-graded soils the internal stability can be characterized by the coefficient of curvature, Cc, of the soil, and that these soils have a strong effect on the filtration performance of the soil/geotextile system. Soil piping failure was measured for some filtration systems for soils with a Cc greater than seven. The instantaneous application of a high hydraulic gradient only has a short-term influence on the filtration performance. Digital image analyses were performed on the soil/geotextile interfaces after the filtration tests. These digital images have shown that the vaults or arches formed by soil particles at the soil/geotextile interface occurred only for internally stable soil structures and were altered by sudden changes in hydraulic gradient. Based on this study, a new retention criteria is proposed, which accounts for the internal stability of the soils.
Modelling of Geosynthetic-Reinforced Engineered Granular Fill on Soft Soil
Authors: Shukla S.K , Chandra S.
Published: October 2014

A ground improvement technique to improve the load-settlement behaviour of a soft foundation soil involves placing a geosynthetic-reinforced engineered granular fill over the foundation. In this paper, a mechanical foundation model for the analysis of such a reinforced soil system is proposed by representing the geosynthetic reinforcement, the granular fill, and the soft foundation soil by a stretched rough elastic membrane, a Pasternak shear layer, and Winkler springs, respectively. This model incorporates the effect of compaction of the granular fill by considering an appropriate shear stress transfer mechanism at the fill-geosynthetic interface. The results obtained using a wide range of parameter values have been compared with those computed using two other existing mechanical models of geosynthetic-reinforced granular fill-soft soil systems. It was observed from this study that the compaction of granular fill by a load higher than the working load results in a reduction of both the settlement of the reinforced foundation soil and the mobilized tension in the reinforcement. Additionally, the effect of compaction is reduced when the geosynthetic reinforcement is pretensioned.
Pullout Interaction Mechanism of Geogrid Strip Reinforcement
Authors: Alfaro M.C. , Hayashi S. , Miura N. , Watanabe K.
Published: October 2014

Soil-reinforcement interaction parameters used in the design of reinforced soil systems are typically evaluated by measuring pullout resistance. A combined two-dimensional and three-dimensional interaction mechanism is proposed to evaluate the pullout resistance of geogrid strip reinforcement embedded in dense granular soil. Pullout tests were conducted using uniaxial geogrid reinforcement of various specimen widths. Results from the pullout tests confirmed that a three-dimensional interaction mechanism had developed at both edges of the strip reinforcement. This interaction mechanism is caused by a confinement of the dilating zone of soil around the reinforcement as described by Schlosser and Elias (1978). For the type of geogrid reinforcement and backfill material used in this investigation, the combined interaction mechanism is applicable for a strip reinforcement width, B, greater than 20 cm. For strip reinforcement with B less than 20 cm, the influence of restrained soil dilatancy results in the development of a purely three-dimensional interaction mechanism across the strip reinforcement width.
Pseudo-Static Seismic Analysis Of Geosynthetic-Reinforced Segmental Retaining Walls
Authors: Bathurst R.J. , Cai Z.
Published: October 2014

The paper examines seismic stability analyses of geosynthetic-reinforced segmental retaining walls (modular block walls). Stability analyses are developed within the framework of a pseudo-static approach that gives factors of safety against collapse mechanisms or rupture of component materials. The Mononobe-Okabe method is used to estimate dynamic earth pressures. Parametric analyses of forces and factors of safety related to external, internal and facing failure modes for walls constructed on competent foundations are presented. Shear interfaces between facing units are considered as possible planes of failure in facing stability analyses. The potential for local toppling of the facing column is also investigated. The results of analyses demonstrate that there is a limiting value of the horizontal seismic coefficient above which the margin of safety against base sliding and overturning may be unacceptably low during a seismic event for segmental retaining walls designed to just satisfy minimum factors of safety under static loading conditions. Pseudo-static seismic analyses of the performance of two geosynthetic-reinforced segmental walls during the Northridge Earthquake in Los Angeles in 1994 are demonstrated to be consistent with visual observation of tension cracks in the soil backfill. Limitations of pseudo-static methods are discussed and recommendations for further research are made.
Compatibility of Geosynthetic Clay Liners with Three Pennsylvania Municipal Solid Waste Leachates
Authors: Narejo D.B. , Memon G.Q.
Published: October 2014

The free swell of three commercially available geosynthetic clay liners is evaluated using the Geosynthetic Research Institute test method GCL 1. Leachate from three Pennsylvania municipal solid waste landfills is used in the test procedure. It is seen that the swelling of all three geosynthetic clay liners is significantly affected by the composition of the landfill leachates; however, the magnitude of the decrease in swelling varies with each leachate. Since the permeability of clays is inversely related to their swell potential, a significant drop in free swell may indicate an increase in permeability. Therefore, a significant drop in free swell as compared to de-ionized water may indicate incompatibility of a geosynthetic clay liner with the service environment in question.
Comparison of Geomembranes Subjected to Differential Settlement
Authors: Giroud J.P. , Soderman K.L.
Published: October 2014

This technical paper presents a theoretical analysis of the mechanism of deformation of a geomembrane supported by a soil dike and subjected to differential settlement at its connection to a rigid structure. The analysis leads to the development of a new concept, the “co-energy” of the geomembrane tension-strain curve. It is shown that an appropriate way to evaluate and compare the abilities of geomembranes to withstand differential settlement is through the co-energy concept. The use of the co-energy concept is illustrated with a numerical example comparing the abilities of several common geomembrane types to withstand differential settlement.
Filtration Criteria for Prefabricated Vertical Drain Geotextile Filter Jackets in Soft Bangkok Clay
Authors: Bergado D.T. , Manivannan R. , Balasubramaniam A.S.
Published: October 2014

Filtration tests on soil-geotextile filter systems were conducted in the laboratory in order to evaluate the filtration and clogging performance of prefabricated vertical drain (PVD) geotextile filter jackets in soft Bangkok clay. Initially, the flow was very slow for all types of PVD geotextile filter jackets and the soil permeability characteristics controlled the flow behavior. Subsequently, flow increased with time followed by a loss of fine particles. Finally, flow decreased and reached an equilibrium stage. As a result of the laboratory filtration tests, filtration and clogging criteria are proposed for geotextile filter jackets on PVDs in soft Bangkok clay.
Geotextile Characterization and Pore-Size Distribution: Part II. A Review of Test Methods and Results
Authors: Bhatia S.K. , Smith J.L.
Published: October 2014

Six of the most commonly used methods for evaluating the pore-size distribution of geotextiles in the United States and Europe are reviewed: dry sieving, hydrodynamic sieving, wet sieving, bubble point method, mercury intrusion porosimetry, and image analysis. In this study, these methods were used to evaluate pore-size distribution characteristics of over 580 specimens from 28 different geotextiles. The results are presented in this paper. In general, the sieving and image analysis techniques required greater amounts of time to perform than the bubble point and mercury intrusion porosimetry tests. The bubble point and mercury intrusion porosimetry tests required extensive preliminary study of testing parameters and test equipment, however, they were fairly simple and rapid to perform. Typical results are given for each method and confirm that there are fundamental differences between the methods. Before any test method is used and applied to the design of geotextiles as filters, it is imperative that the mechanisms of the test and the factors which may influence the test results are understood.
Influence of Strain Rate, Specimen Length and Confinement on Measured Geotextile Properties
Authors: Boyle S.R. , Gallagher M. , Holtz R.D.
Published: October 2014

In-isolation and in-soil tests were performed on four woven and two nonwoven geotextiles to investigate the effect of strain rate, specimen length, and confinement in soil on the measured strength characteristics. It was determined that woven geotextiles are affected by strain rate but not by confinement. Nonwoven geotextiles were found to be influenced by both confinement and specimen gauge length. It was concluded that different manufacturing techniques influence measured strength properties, and a standardized wide-width strip tensile test, such as ASTM D 4595, may not be an appropriate method for all types of geosynthetic reinforcement products.
Interface Shear Behavior of Landfill Composite Liner Systems: A Finite Element Analysis
Authors: Reddy K.R. , Kosgi S. , Motan E.S.
Published: October 2014

The use of various types of geosynthetics to construct landfill composite liner systems results in interfaces between different geosynthetics, and between geosynthetics and compacted cohesive soil liners/subgrade soil. These interfaces are potentially critical for stability due to their in-plane shear behavior. Conventional limit equilibrium analyses can provide an overall assessment of composite liner system stability; however, they lack the capability to compute displacements along the critical shear plane, and the resulting strain levels within the composite liner systems. In this study, the shear displacements of typical landfill composite liner system interfaces in response to municipal solid waste loads were evaluated using a finite element analysis. The interface shear-displacement parameters determined from available laboratory direct shear test data were used for the analysis. A parametric study was performed for soft, intermediate and stiff municipal solid waste conditions to evaluate the effect of different types of municipal solid waste on composite liner behavior.
Combined Allowable Strength Reduction Factor for Geosynthetic Creep and Installation Damage
Authors: Allen T.M. , Bathurst R.J.
Published: October 2014

The current practice to determine the combined geosynthetic strength reduction due to installation damage and creep is to multiply the individual strength reduction factors for damage and creep together. However, it is difficult to know if this procedure results in conservative design, nonconservative design, or is sufficiently accurate for practical purposes. The effect of synergism on the combined effect of polymeric creep and installation damage is explored in the paper by reviewing published and unpublished constant load (creep) data for both undamaged and installation-damaged geosynthetic specimens. A methodology is developed that uses data from both constant load (creep) tests and index tests to reconstruct installation-damaged isochronous creep curves. Based on the limited data available and the interpretation of reconstructed isochronous curves, it is shown that multiplication of creep reduction and installation damage factors may be conservative and hence results in errors on the safe side for design.
Response of a Woven and a Nonwoven geotextile to Monotonic and Cyclic Simple Tension
Authors: Ashmawy A.K. , Bourdeau P.L.
Published: October 2014

Simple tension tests were performed to investigate the load-elongation behavior of two geotextiles, a woven polyester and a nonwoven polypropylene, under monotonic and cyclic loading conditions. Creep tests under constant load were also performed in order to examine the time-dependent properties of both geotextiles. A wide difference in behavior was observed between the geotextiles due to different structures, manufacturing processes and polymer types. Visual inspection showed that progressive breakage of bonds between the fibers, and reorientation of the fibers were the main mechanisms controlling failure of the nonwoven geotextile. The behavior of the woven geotextile was mainly affected by polymer characteristics and exhibited nearly linear behavior under monotonic and cyclic loading, up to failure. A simple model was formulated to relate the monotonic and cyclic load to the number of load cycles. The model can be used to predict the permanent deformation as a function of the cyclic loading level and number of load cycles, or to establish fatigue criteria for design.
Role of Specimen Geometry, Soil Height, and Sleeve Length on the Pull-Out Behaviour of Geogrids
Authors: Lopes M.L. , Ladeira M.
Published: October 2014

This paper examines pull-out test results of geogrid specimens embedded in a granular soil. The influence of specimen geometry, soil height and sleeve length on the pull-out force of the geogrid specimen is discussed and the results of nine pull-out tests are analysed. Soil and geogrid properties are also fully described and the soil-geogrid interaction behaviour is studied. The conclusions of this study are as follows: the pull-out tests are reproducible; the influence of the geogrid specimen length on the geogrid specimen pull-out response is a function of the density of the granular soil; the influence of the geogrid specimen width on the pull-out response of the geogrid specimens tested is minimal; the effect of the soil height above and below the geogrid specimen on the soil-geogrid interface shear resistance is minimal for the two soil heights tested; and, the placement of a 0.20 m long steel sleeve in the front wall of the pull-out box reduces the magnitude of back calculated soil-geogrid interface shear resistance because it minimizes the effects of friction that are caused by the roughness of the front wall.
In-Isolation Strain Measurement of Geosynthetics in Wide-Width Strip Tension Test
Authors: Perkins S.W. , Lapeyre J.A.
Published: October 2014

Field and laboratory scale studies of geosynthetic behavior typically require an assessment of strain across a region of the geosynthetic material. Measurements of strain, or displacement, are typically provided by attaching electronic sensors directly to the geosynthetic specimen. Of interest and concern, is the comparison between the measured strain and the true (global) strain experienced by the geosynthetic. The measured strain, is influenced by the structure of the geosynthetic, the size of the sensor, the attachment technique used for the sensor and the type of load applied. A large wide-width strip tension apparatus was constructed to assess the differences between the global and measured strain for four types of strain sensors attached to geogrid and geotextile specimens. The four sensors used were vibrating wire displacement gages, vibrating wire strain gages, linear variable differential transformers, and bonded resistance foil strain gages. The results indicate differences between the measured and global strain response with the magnitude of these differences being dependent on the sensor, the geosynthetic material, and the type of load applied. Calibration factors are developed and applied to the results to achieve a match between the measured and global strains.
Creep and Stress Relaxation of Geogrids
Authors: Leshchinsky D. , Dechasakulsom M. , Kaliakin V.N. , Ling H.I.
Published: October 2014

Most research on the long term behavior of geosynthetics has focused on creep; very little data is available on the stress relaxation behavior of geogrids. Consideration of both creep and stress relaxation in design may ultimately produce a more efficient structure while allowing for the use of a smaller creep reduction factor. The results of an initial effort to experimentally identify the stress relaxation behavior of nine typical geogrids used to reinforce soil structures is presented. A simple test method that directly measures the stress relaxation of geogrids was developed. The geogrids were subject to initial loads of 40, 60, and 80% of their ultimate short term strengths. Each test was carried out for a period of one month, or until creep rupture occurred, whichever was shortest. The maximum potential stress relaxation was approximately 30% of the initial load for polyester geogrids, and 50% for polyethylene geogrids.
Shear Behavior of an Unreinforced Geosynthetic Clay Liner
Authors: Eid H.T. , Stark T.D.
Published: October 2014

Dry and hydrated specimens of an unreinforced geomembrane-backed geosynthetic clay liner (GCL) were sheared against a textured geomembrane using a torsional ring shear apparatus to study the shear behavior of geomembrane encapsulated bentonite. Shearing of the dry GCL against a textured geomembrane at high normal stresses resulted in failure occurring within the GCL adhesive that attaches the bentonite to the geomembrane backing and not the GCL bentonite/geomembrane interface. This type of failure occurred when both smooth and textured geomembranes were used as the GCL backing material. Conversely, shearing of the hydrated GCL against a textured geomembrane resulted in failure occurring at the GCL bentonite/textured geomembrane interface. The order of hydration and normal stress application was found to significantly affect the GCL/textured geomembrane interface shear strength. The mobilized shear strength of the GCL/textured geomembrane interface does not equal the drained shear strength of bentonite because of the effect of geomembrane texturing and the lack of drainage during dry and hydrated GCL testing, respectively. Finally, the hydrated GCL/textured geomembrane interface exhibits an increase in peak shear strength of approximately 13% per log cycle of the shear rate. Therefore, the selection of a shear displacement rate is important for unreinforced geomembrane-backed GCL/textured geomembrane interface shear tests.
Geosynthetic Interface Behavior Under Dynamic Loading
Authors: Yegian M.K. , Kadakal U.
Published: October 2014

The seismic stability of earth slopes, embankments, and landfills that incorporate geosynthetics has been receiving increased attention in geotechnical engineering practice. In the analysis of such structures, the dynamic interface shear properties play important role. The authors have been conducting research to understand the dynamic response of various geosynthetic-geosynthetic and geosynthetic-soil interfaces. This paper presents an overview of the research including: a description of the shaking table facility and the experimental setup developed; typical test results and discussions; and a description of a constitutive model for a geosynthetic-geosynthetic interface that can be used in wave propagation analysis of soil and landfill liner systems that incorporate geosynthetics.
Newmark Seismic Deformation Analysis for Geosynthetic Covers
Authors: Matasovic N. , Kavazanjian E. , Giroud J.P.
Published: October 2014

This paper investigates the impact of the following five assumptions on the accuracy of Newmark seismic deformation analysis applied to geosynthetic cover systems: (i) the potential failure mass is noncompliant; (ii) the dynamic response of the potential failure mass is uncoupled from displacement (slip); (iii) permanent displacements accumulate in only one direction; (iv) vertical ground motions do not influence permanent displacement; and (v) the yield acceleration is constant. Information presented in the literature indicates the impact of the assumption of a noncompliant failure mass and the assumption of a seismic response uncoupled from displacement is insignificant for typical geosynthetic cover systems. The results of computer analyses indicate that the effects of two-way sliding and vertical ground motions can, in most practical cases, be neglected. However, the assumption of a constant yield acceleration, when based on residual (or la rge displacement) shear strength, may result in calculated displacements that are significantly larger than those calculated using a yield acceleration that degrades with accumulated displacement from a peak value to a residual, or large displacement, value. Overall, results of this investigation indicate that conventional Newmark analyses based upon residual shear strength yield conservative results when applied to geosynthetic cover systems.
Unreinforced Geosynthetic Clay Liner Case History
Authors: Stark T.D. , Arellano D. , Evans W.D. , Wilson V.L. , Gonda J.M.
Published: October 2014

This paper describes a slope failure involving an unreinforced geosynthetic clay liner (GCL) in a municipal solid waste (MSW) landfill liner system. The precise mechanism for the shear movement of the interim slope is not known. However, the significant damage observed in the upper components of the composite liner system suggests that the failure was translatory primarily along the interface between the recompacted soil liner and the overlying hydrated bentonite of the geomembrane-backed GCL. It also appears evident that the slope inclination, slope height, physical characteristics, e.g. high unit weight, of the waste, and possibly the overlying smooth geomembrane/geonet interface played a significant role in the movement. Design recommendations for interface strengths and stability analyses are also presented.
Design Methodology for a Gas Pressure Relief Layer Below a Geomembrane Landfill Cover to Improve Slope Stability
Authors: Thiel R.S.
Published: October 2014

Pore pressures generated by landfill gas underneath a final cover system that incorporates a geomembrane can significantly reduce the effective normal stress on the lower geomembrane interface to the point of creating cover veneer instability. To the author's knowledge, no design methodology has previously been published to address this issue. Recently, however, large-scale slope failures have been attributed to landfill gas pore pressures. Therefore, a need for a design methodology exists. An estimation of gas flux from a landfill surface can allow a gas-relief layer to be designed using Darcy's law for gas flow through a porous medium. The methodology incorporates knowledge of the gas transmissivity of a chosen medium to design a spacing for highly permeable strip drains. The strip drains in turn can discharge the gas either to vents or an active gas collection system. The gas-relief layer typically consists of sand or a geonet composite. Limited testing of nonwoven, needle-punched (NWNP) geotextiles indicates that these materials may also be acceptable for gas relief in some designs. However, more testing is recommended before using NWNP geotextiles alone in this application. The greatest assumption in the proposed methodology concerns the estimation of gas flux. More research is required in this regard; however, the basic concept of providing a gas-relief layer with intermittent highly permeable strip drains is recommended as a prudent engineering measure for landfill final cover systems incorporating geomembrane barriers.
The Role of Geotextile Reinforcement in the Control of Pumping at the Subgrade-Subbase Interface of Highway Pavements
Authors: Alobaidi I. , Hoare D.J.
Published: October 2014

Based on observations of laboratory tests, this paper considers the role of geotextile reinforcement at the subgrade-subbase interface in controlling subgrade pumping of highway pavements. The four stages that develop during a pumping test are identified: (i) the development of tension under the subbase particles; (ii) the development of a gap under the subbase particles; (iii) the plastic flow of subgrade soil into the gap; and (iv) global separation in which a gap develops between the underside of the geotextile and the top of the subgrade. Two mechanisms of geotextile reinforcement are identified and their role in the development of pumping is considered. Global reinforcement concerns the whole area subjected to traffic loading, while local reinforcement considers the area of contact between a subbase particle, the subgrade surface, and the unloaded zone surrounding the subbase particle. Global separation occurs when the load carried by the geotextile becomes equal to the minimum total applied load, during the unloading stage of a load cycle. Calculation methods to assess the permanent deformation of the subgrade soil at which separation occurs both in small-scale laboratory tests and field tests are presented.
Bearing Capacity of a Geotextile-Reinforced Unpaved Road as a Function of Deformation: A Model Study
Authors: Som N. , Sahu R.B.
Published: October 2014

An experimental investigation has been carried out to study the bearing capacity of a geotextile-reinforced unpaved road as a function of its deformation. A number of model footing tests were performed on compacted granular fill overlying an artificially sedimented kaolinite layer. The test bed was instrumented to determine the vertical stresses at the fill-subgrade interface. The test results were used to estimate the bearing capacity factors of the foundation as a function of footing deformation. A load transfer mechanism has been proposed to explain the improvement in bearing capacity of the geotextile-reinforced soil models.
High Altitude Exposure Testing of Geotextiles in the Peruvian Andes
Authors: Grubb D.G. , Diesing W.E. , Cheng S.C.J.
Published: October 2014

The use of geotextiles in the Andean mining industry provides some unique challenges due to climate, altitude, latitude, and the pervasiveness of acid mine drainage (AMD) conditions. Two nonwoven needle-punched polyester geotextiles (420 and 550 g/m2) were deployed at an elevation of 3,675 m in Northern Peru for ultraviolet (UV) deterioration and chemical resistance testing over a 12-month period. The retained grab strength, trapezoidal tear, and index puncture resistance of the UV-exposed specimens ranged from approximately 68 to 124% and 90 to 101% for the 420 and 550 g/m2 specimens, respectively. The coefficient of variation on the measured strengths for the 420 g/m2 specimens showed an increasing trend after 30 days. Immersion in flowing AMD (average pH = 1.82; 5,600 mg/L total metals) did not reduce the retained strengths of the geotextiles below 70% after 180 days. Design challenges associated with reactive tailings particles, and drainage and filter criteria are briefly discussed.
Elastic Settlements of Circular Footings on Geosynthetic-Reinforced Soil
Authors: Pitchumani N.K. , Madhav M.R.
Published: October 2014

The interactions between soil and a buried circular geosynthetic reinforcement layer placed below a circular load are studied using elastic continuum theory with particular regard for the reinforcement effect in reducing surface settlements. To represent the displacement at the soil-inextensible geosynthetic reinforcement interface, the net radial displacements are equated to zero, and for the soil-extensible geosynthetic reinforcement interface, the net radial displacements are equated to the radial elongations assuming the reinforcement behaves as a thin membrane. A parametric study illustrates the effect of the reinforcement layer radius and depth on reducing surface settlements.
Effect of Shear Displacement Rate on Internal Shear Strength of a Reinforced Geosynthetic Clay Liner
Authors: Eid H.T. , Doerfler C.K.
Published: October 2014

Torsional ring shear tests were performed to evaluate the effect of shear displacement rate on the internal shear strength of a needle-punched geosynthetic clay liner (GCL) under different normal stresses. The test results suggest that the internal shear strength of the needle-punched GCL depends on the following three factors: (i) resistance against reinforcement fibers pulling out and/or tearing; (ii) amount of positive pore-water pressure induced during shear; and (iii) bentonite water content at the time of shearing. The laboratory tests indicate that the net effect of these three factors result in the peak internal shear strength being less sensitive to shear displacement rate at normal stresses between 200 and 400 kPa than at normal stresses less than 200 kPa. Shear displacement rate appears to have little influence on the residual internal shear strength regardless of normal stress. The amount of shear displacement required to reach the peak and residual internal shear strengths is dependent on the shearing normal stress, shear displacement rate, and quantity of needle-punched fibers.
Performance Testing of Landfill Geoprotectors: Background, Critique, Development, and Current UK Practice
Authors: Gallagher E.M. , Darbyshire W. , Warwick R.G.
Published: October 2014

Geomembrane basal landfill liners are typically overlain by a stone drainage layer with a geoprotector layer placed between the drainage layer and the geomembrane to protect the geomembrane from environmental stress cracking caused by pressures transmitted through the stone drainage layer. The effectiveness of the geoprotector layer (which may be mineral or synthetic, or a combination of both) is demonstrated by means of a cylinder test using site specific materials. Current United Kingdom (UK) practice is to follow the Environment Agency (EA) method for this performance test, which evolved from guidelines produced in the early 1990s by the German “Quo Vadis Schutzlagen” working party. This paper reviews the background information for the test, in particular, the perceived deficiencies in the original German guidelines, and, hence, the need for the new EA methodology. A commentary on the new EA test method from the perspectives of regulator, designer, manufacturer, and test institution is included. The EA test standardises the apparatus, testing procedure, method of measuring deformations, and calculation of local strains.
Efficiency of Geosynthetic Protection Layers for Geomembrane Liners: Performance in a Large-Scale Model Test
Authors: Zanzinger H.
Published: October 2014

Geomembrane landfill basal liners must be protected from damage caused by overlying, large-particle leachate collection/drainage systems. Geosynthetics, such as geotextiles and geocomposites, are being used as protection layers for geomembrane liners. To date, there has been no systematic observation as to the efficiency of these protection layers in a landfill. Large-scale tests were carried out at LGA-Geotechnical Institute in Nuremberg, Germany to model field conditions at the base of a landfill. The geomembranes showed no signs of damage after long-term loads of approximately 800 kPa. For the large-scale tests, higher maximum local strain values were measured than in standard, small-scale protection efficiency laboratory tests. Although the maximum strain measured in the large-scale tests exceeded 0.25%, which is the limiting maximum strain value according to the German approval procedure, the protection layers performed satisfactorily.
Liquid Flow Through Composite Liners due to Geomembrane Defects: Analytical Solutions for Axi-Symmetric and Two-Dimensional Problems
Authors: Touze-Foltz N. , Rowe R.K. , Duquennoi C.
Published: October 2014

A general framework for calculating the rate of liquid flow through a composite liner (geomembrane plus soil liner) with holes is presented. Solutions given for a circular hole and a damaged wrinkle can be used for interpreting data from laboratory tests, modelling expected field conditions, and interpreting field leakage data. A number of existing solutions arise from the general solution as special cases. Finally, the paper is extended to consider the potential interaction between damaged wrinkles, and it is theoretically shown that while this may be an important issue for composite liners incorporating a compacted clay liner, it is far less likely to be significant for those incorporating a geosynthetic clay liner.
Using a Reduced Equivalent Diameter for a Prefabricated Vertical Drain to Account for Smear
Authors: Welker A.L. , Gilbert R.B. , Bowders J.J.
Published: October 2014

Many different formulations for converting a prefabricated vertical drain with a rectangular cross section to an equivalent diameter well have been developed. In addition to equivalent diameter, engineers must also consider the impact of smear when designing a system that utilizes prefabricated vertical drains. An experiment and mathematical modeling were used to study the validity of using a reduced equivalent diameter to account for smear. Mathematical modeling of the four most commonly used equivalent diameter formulations yielded nearly the same equipotentials. In addition, the equipotentials calculated for the equivalent diameter wells differed substantially from a prefabricated vertical drain modeled with and without smear. This indicates that equipotentials are not the best means to evaluate equivalent diameter formulations because the change in shape from a rectangle to a circle impacts the head values to such a degree that the equipotentials will never be similar, regardless of whether smear is included.
Investigation of the Isochrone Concept for Predicting Relaxation of Geogrids
Authors: Kaliakin V.N. , Dechasakulsom M. , Leshchinsky D.
Published: October 2014

Due to the perceived complexity of relaxation tests, the relaxation response of geosynthetics has, in the past, been predicted from isochronous curves generated from creep tests. However, the validity of such an approach has not been extensively investigated. Using experimental data from in-isolation creep and relaxation tests performed on eleven different geogrids, the validity and limitations of using creep isochronous curves to predict relaxation response of geogrids has been investigated. Acceptable agreement between predicted and experimental relaxation responses was rather limited, being observed for specimens tested at low initial load levels and for materials exhibiting relatively large creep strains. With minor exceptions, the experimentally measured force relaxation was under-predicted by using the isochrone approach. Nonetheless, it appears that for the geogrids tested, overall accurate relaxation response cannot be predicted from isochronous curves constructed using creep data.
A Theoretical Model for Anchored Geosynthetics in Pull-Out Tests
Authors: Gurung N.
Published: October 2014

A theoretical model is presented for the pull-out response of strip anchor reinforcement based on a nonlinear elastic (hyperbolic) shear stress-displacement relationship for the soil-reinforcement interface. The interface pull-out mechanism has been simplified by formulating the boundary conditions for the anchor section. Additional terms for the soil-reinforcement interaction, which incorporate the anchor section, are also introduced. A new concept of an anchorage factor (anchor-to-strip reinforcement capacities), the relative stiffness, and the displacement parameters are defined to explain the pull-out behaviour. A parametric study is carried out for a range of relative stiffness values, interface shear stresses, and anchorage factors. The normalised load-displacement relationship and the variations of pull-out force and displacements with distance along the reinforcement, at different anchorage factors, are presented. Experimental pull-out test results for planar reinforcements are also examined/compared with the model using a zero anchorage factor. The model helps to evaluate the pull-out displacements, stresses, and strains along the length of the strip anchor reinforcement.