bluuebunny/crossref_metadata_2025 huggingface dataset:
Puncture Protection of Geomembranes Part I: Theory
Authors: Wilson-Fahmy R.F. , Narejo D. , Koerner R.M.
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. This paper, Part I, focuses on theory, Part II focuses on experiments and Part III focuses on design examples. The theoretical approach presented in this paper proposes an idealized geometry and then derives the necessary equations using tensioned membrane theory. Theoretical solutions for geomembranes with and without protection geotextiles are presented, and the necessity of using a protection material is evidenced. Also, the characteristics of the protruding object and the protection material are quantitatively defined. Graphs of the results obtained from several parametric evaluations of geomembranes with and without protection are presented.
Puncture Protection of Geomembranes Part III: Examples
Authors: Koerner R.M. , Wilson-Fahmy R.F. , Narejo D.
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, Part II focuses on experiments, and this paper, Part III, focuses on design examples and presents a comparison of results presented in Parts I and II. The design developed in Part II is used in this paper to provide several numerical examples that highlight the different strategies used in Germany and in the USA for the selection of protection geotextiles. This paper also includes a number of design charts for a wide variety of practical situations. Finally, puncture resistance results for a geomembrane with different types of protection materials (other than virgin polymer nonwoven needle punched geotextiles) are presented in the Appendix. The design procedures presented result in a site specific and material specific factor of safety.
Limit Analysis of Geosynthetic-Reinforced Soil Slopes
Authors: Zhao A.
Published: October 2014

A kinematic solution of the plasticity theory applied to the stability of geosynthetic-reinforced soil slopes is presented in this paper. Translational and rotational failure mechanisms are considered and rigorously compared. For slopes heavily reinforced with geosynthetics, the limit loads obtained using a translational failure mechanism are smaller than those obtained using a rotational failure mechanism, while for slopes with a reduced amount of geosynthetic reinforcement, the latter yields better results. A rotational failure mechanism consistently yields lower stability factor values for load-free geosynthetic reinforced slopes. Limit analysis method solutions are compared to solutions obtained using limit equilibrium and slip-line methods.
Rate of Leachate Migration Through a Defect in a Geomembrane Underlain by a Saturated Permeable Medium
Authors: Giroud J.P. , Khire M.V. , McKelvey J.A.
Published: October 2014

The leakage collection layer located beneath a geomembrane liner in a landfill may not have enough flow capacity to convey the leachate migrating through a geomembrane defect without becoming filled with leachate in a certain area around the defect. The presence of leachate in the leakage collection layer at the location of the geomembrane defect reduces the head loss through the defect and, consequently, reduces the rate of leachate migration through the defect. This paper presents an equation to evaluate this effect. The equation depends on the size of the defect in the geomembrane and the characteristics of the leakage collection layer: hydraulic conductivity, thickness and slope. Numerical applications show that the reduction of the leachate migration rate is generally negligible in the case of gravel leakage collection layers because they are thick and highly permeable. In contrast, with geonet and sand leakage collection layers, there are cases where the reduction is not negligible.
A Synthesis and Evaluation of Geosynthetic-Reinforced Base Layers in Flexible Pavements- Part I
Authors: Perkins S.W. , Ismeik M.
Published: October 2014

In recent years, geosynthetics have been proposed and used as reinforcement in the base course layer of flexible pavements for the purpose of improving performance and/or to allow for the reduction of base course thickness. Much of the pioneering work with geosynthetic-reinforced unpaved roads on very soft subgrades has indicated that appreciable deformation of the roadway surface is necessary before the reinforcement qualities of the geosynthetic can be realized. It may be expected that this same condition is necessary in a paved road, thereby obviating the practical use of geosynthetics as reinforcement. It appears that this view has gained acceptance in the research and practice oriented engineering communities. The purpose of this paper is to provide a synthesis and evaluation of the literature focusing on this application. The paper focuses on studies involving laboratory-scale experiments using stationary cyclic loads or moving wheel loads and field studies using controlled vehicle loads or random traffic loads. The majority of the studies reviewed indicate that appreciable improvement can be realized by proper placement of a geosynthetic in the base course of a flexible pavement and that improvement is seen over the entire service life of the pavement and not only for conditions of excessive surface deformation.
A Synthesis and Evaluation of Geosynthetic-Reinforced Base Layers in Flexible Pavements- Part II
Authors: Perkins S.W. , Ismeik M.
Published: October 2014

In this and a companion paper, studies related to the use of geosynthetics in the base course layer of flexible pavements for the purpose of reinforcement are examined. The purpose of these papers is to provide a synthesis and evaluation of the literature focusing on this application. The companion paper is a review of studies involving physical experiments of reinforced roadways. The majority of the reviewed studies conclude that appreciable improvement can be realized by proper placement of a geosynthetic in the base course of a flexible pavement and that improvement is seen over the entire service life of the pavement and not only for conditions of excessive surface deformation. The companion paper demonstrates that these experimental results taken by themselves are insufficient for the development of an accepted design procedure due to the many dependent variables impacting the problem. It is concluded in the companion paper that the development of a comprehensive analytical model is a necessary step to reach the goal of providing a methodology for the design of such roadways. The purpose of this paper (Part II) is to review existing design techniques developed for this application. Analytical studies using finite element techniques to predict roadway response and to illustrate reinforcement mechanisms are summarized. A brief description of selected on-going research is also included in this paper.
Shaking Table Tests and Analyses of Geosynthetic-Reinforced Soil Retaining Walls
Authors: Matsuo O. , Yokoyama K. , Saito Y.
Published: October 2014

Shaking table tests were performed on six geosynthetic-reinforced soil retaining wall (GRS-RWs) models. The geogrid reinforcement length, wall height, wall facing type, wall slope, and input acceleration waveform were varied in order to observe the behavior and the reinforcement mechanisms that occur in GRS-RWs. The test results were compared with the results of a pseudo-static seismic stability analysis that is adopted in the current design method in Japan. The analysis showed that this design method provides a margin of safety against the failure of reinforced soil walls. Permanent displacement computations based on the cumulative damage concept and the simplified sliding block method were performed for the tested model walls. The results showed that the sliding block method has the potential to estimate the permanent displacement of GRS-RWs.
A Methodology for the Evaluation of Geotextile Pore Opening Sizes Under Confining Pressure
Authors: Palmeira E.M. , Fannin R.J.
Published: October 2014

This paper presents a methodology used to evaluate the pore opening sizes of a needle-punched, nonwoven polyester geotextile under pressure, using a permeameter subject to vibration. Particles passing through the geotextiles were collected and analysed to establish a particle size distribution curve. Preliminary results obtained under no confining pressure compare well with a standard test method based on hydrodynamic sieving. Confining pressures up to 25 kPa appeared to exert some influence on the pore opening size of relatively thin geotextiles. However, for pressures greater than 25 kPa, the variation of geotextile pore opening size is small. The tests results and microscopic observations suggest that needle-punching during the geotextile manufacturing process has a significant influence on the geotextile pore structure. Regardless of the limited amount of data available, the methodology described may provide a useful tool for the study of geotextile pore opening sizes under confining pressure.
Pull-Out Resistance of Polyester Straps at Low Overburden Stress
Authors: Lo S.C.R.
Published: October 2014

The pull-out resistance of a high tenacity polyester strap at a low overburden stress of less than 100 kPa was studied with a large-scale pull-out box. Three different types of soil hauled from active construction sites were used. The test results indicated that the friction factor, as defined by the ratio of the average failure shear stress to average normal stress, increased with a reduction in the overburden stress. This increase was observed to be more significant for the soil with a high dilatancy. The difference in the friction factor between the Grade 20 and 30 straps was slight. These observations can be consistently explained by the constrained dilatancy hypothesis.
Hydraulically-Filled Geomembrane Bags for Land Reclamation
Authors: Bridle R.J. , Barr B.I.G. , John Mr. S.
Published: October 2014

A method of constructing a berm in water using geomembrane bags filled with dredged marine soil or sand, instead of expensive rockfill, is described. The design and construction methodology for this structure is presented. Other potential applications of this construction method are discussed.
Dynamic and Static Characterization of Polypropylene Fiber-Reinforced Dune Sand
Authors: Al-Refeai T. , Al-Suhaibani A.
Published: October 2014

Dune sands characterized by a susceptibility to large deformations can be a useful pavement construction material if reinforced or treated with cement. Sand can be easily reinforced with synthetic fibers to increase its stiffness and load-carrying capacity. This study was undertaken to investigate the resilient behavior of polypropylene fiber-reinforced sand. Triaxial, California bearing ratio (CBR), and resilient modulus tests were conducted on fiber-reinforced sand as well as unreinforced sand, and the results compared. The optimum fiber content was found to be 0.4% by weight. The triaxial shear strength of the fiber-reinforced sand specimens revealed that there were two modes of failure, fiber-sand bond failure and fiber failure, and the internal friction angle depended on the mode of failure. Synthetic fiber-reinforced sand has greater CBR values than those of unreinforced sand. The effect of fiber reinforcement on the resilient modulus, MR, values was investigated in terms of resilient modulus model parameters. In general, the model parameters revealed a decreasing effect of both the deviator and confining stresses on the MR values up to 0.2 to 0.4% fiber content. The permanent deformation of sand specimens was reduced by the addition of fibers, and the permanent deformation decreased as fiber content increased.
A Comparison of the Response of Geosynthetics in the Multi-Axial and Uniaxial Test Devices
Authors: Bray J.D. , Merry S.M.
Published: October 2014

The wide strip tension test imposes boundary conditions that vary from a uniaxial stress state near the middle of the specimen to a plane-strain, biaxial stress state at the clamps. The multi-axial tension test imposes boundary conditions that vary from a plane-strain, biaxial stress state at the restraining ring to a nearly isotropic, biaxial stress state at the center. To evaluate the influence of the stress state induced during testing on the stress-strain response of geomembranes, strain-controlled multi-axial and wide strip tests were performed on specimens of elastic latex, polyvinyl chloride (PVC), and high density polyethylene (HDPE). The ratio of the secant Young's modulus in the multi-axial test to that in the wide strip uniaxial test was approximately 1.2 for the nearly linear, elastic latex membrane, which is substantially less than the theoretically derived value of 2.0. This ratio was approximately 1.4 and 1.9 for PVC and HDPE geomembranes at 1% strain, respectively, indicating greater differences between measured multi-axial and uniaxial responses with materials exhibiting more nonlinearity. Strength values measured in the tests were similar, but the uniaxial test overestimated the ductility (i.e. failure strain) of the HDPE geomembrane. Wider use of the multi-axial test device is recommended for cases where the geomembrane deforms in a biaxial stress state, and material ductility and stiffness are important.
Comparative Model Study of Geosynthetic Pull-Out Response
Authors: Gurung N. , Iwao Y.
Published: October 2014

This technical note describes the analysis of reinforcement pull-out tests using a shear model that incorporates a hyperbolic shear stress-displacement relation for the soil-reinforcement interface. Numerical studies of pull-out tests were performed for small to large strains in inextensible and extensible reinforcements. Predictions based upon a hyperbolic model of shear mobilisation are compared with a theoretical bilinear model presented by Madhav et al. in 1998. Comparative parametric studies using both models were carried out for ranges of relative stiffness and bond resistance values. Normalised load-displacement relations and the variations of pull-out force and displacements with distance, are presented for comparative evaluation. The finite difference equations of the hyperbolic model result in a faster convergence than the bilinear model. The incorporated hyperbolic model estimates the pre- and post-yield deformations, and shear stress and tensile force variations along the length of the reinforcement. Predictions of laboratory and field pull-out results from the available theoretical and experimental tests for inextensible steel straps, and extensible geotextiles, polymers, and nylon geosynthetics are also presented.
Dynamic Properties of EPS Geofoam: An Experimental Investigation
Authors: Athanasopoulos G.A. , Pelekis P.C. , Xenaki V.C.
Published: October 2014

This paper presents the results of an experimental investigation of the dynamic properties of two expanded polystyrene (EPS) geofoam materials. Torsional resonant column tests and cyclic uniaxial tests were conducted on block-molded EPS geofoam specimens with mean densities of 12.4 and 17.1 kg/m3, under zero confining pressure. The estimated dynamic moduli values (shear modulus and modulus of elasticity) and damping ratio values are presented as functions of cyclic strain amplitude and loading frequency. The geofoam behavior for strains ranging from 5 × 10-4 to 8.0% was studied by combining the results of the two types of tests. It was found that EPS geofoam behaves linearly for strain values of up to 0.1%; however, a strong nonlinearity develops for strains greater than 1%. The geofoam density significantly affected the dynamic moduli values (the moduli increase with increasing density) whereas no appreciable effect on damping ratio values was found. The damping ratio values were very low (∼1%) for strains less than 0.1% and gradually increased to 10% for strains greater than 1%. The test results also indicated that frequency of loading does not significantly affect the moduli values, whereas the damping ratio values decreased with increasing frequency values. Based on the test results, shear modulus, G/G0, versus cyclic shear strain amplitude, ξc, and damping ratio, D versus ξc, curves are proposed to describe the EPS geofoam nonlinear properties.
Mechanisms of Pumping at the Subgrade-Subbase Interface of Highway Pavements
Authors: Alobaidi I. , Hoare D.J.
Published: October 2014

Research into the mechanisms of pumping of fines at the subgrade-subbase interface of highway pavements is presented and discussed with respect to the behaviour of the subgrade-subbase system without a geotextile/transition layer and with a geotextile/transition layer at the interface. When no geotextile layer is used, softening of the subgrade soil occurs both outside the subbase particle-subgrade areas of contact due to swelling, and under the subbase particle-subgrade areas of contact due to cyclic loading. This softening causes the penetration of the subbase particles into the subgrade soil with consequent reduction of subbase layer thickness. When a geotextile layer is placed between the subbase and subgrade layers, it acts as a separator and, thus, prevents the intermixing of the two layers. However, the geotextile allows for rapid dissipation of the cyclic pore pressures under areas of contact and this causes erosion (pumping) of the subgrade surface. The geotextile layer reduces the static stress under areas of contact, but has a less significant effect on reducing the cyclic stress. Thus, the net effect is to cause an increase in the amount of pumping of fines. Geocomposites, which have a high compression modulus, high in-plane extensibility, low flexural stiffness, and ability to spread point loads from a subbase onto the subgrade, are more effective in reducing pumping. An anti-pumping geocomposite should also have a low short-term permeability to reduce the rapid dissipation of pore pressures during a loading cycle and sufficient permeability to dissipate pore pressures in the long term.
Design of Geomembrane Anchorage Against Wind Action
Authors: Giroud J.P. , Gleason M.H. , Zornberg J.G.
Published: October 2014

This paper provides a method for designing anchor benches and trenches used to secure geomembranes exposed to wind action. Only the cases where anchorage is provided by gravity (i.e. by the weight of the material in the bench or trench) are considered. Anchorage by tensile members is not considered. Three potential failure mechanisms are identified for the case of anchor benches: (i) sliding of the anchor bench in the downslope direction; (ii) sliding of the anchor bench in the upslope direction; and (iii) uplifting of the anchor bench. It is shown that the first mechanism is the most likely and that the third mechanism is the least likely. Criteria are provided to determine the governing potential failure mechanism as a function of the geometry of the slope on which the geomembrane is resting and the geomembrane tensions induced by wind action. Equations are provided to calculate the required size of anchor benches for each of the three identified potential failure mechanisms. It is shown that the usual method, which consists of only checking the resistance of anchor benches against uplifting, is unconservative because, in the case of anchor benches, lateral sliding is more likely to occur than uplifting. The use of the proposed method as a conservative approach for the design of anchor trenches is discussed. Practical recommendations are made and design examples are provided.
Design of Liquid Collection Layers With Radial Flow
Authors: Giroud J.P. , Zhao A.
Published: October 2014

The present paper provides equations for the design of liquid collection layers sloping radially toward a sump located in a corner of the liquid collection layer. It is pointed out that an equation currently used by some design engineers is not correct because it corresponds to the case of confined flow, which is not the type of flow that should take place in a liquid collection layer; this equation leads to grossly underestimated values of the required thickness and hydraulic transmissivity of liquid collection layers. A detailed discussion of the difference between confined and unconfined flow is presented. Design examples are provided.
Criterion for Acceptable Bentonite Loss From a GCL Incorporated Into a Liner System
Authors: Giroud J.P. , Soderman K.L.
Published: October 2014

The following case is considered in the present paper: a geosynthetic clay liner (GCL) used in the composite primary liner of a double-lined landfill is overlain by a geomembrane and underlain by the secondary leachate collection layer, which consists of a geonet. If bentonite particles migrate downward out of the GCL, through the geotextile(s) that separate(s) the bentonite layer from the geonet, they penetrate into the secondary leachate collection layer. Depending on the amount of bentonite particles migrating from the GCL, these particles may decrease the hydraulic transmissivity of the secondary leachate collection layer. Also, the loss of bentonite particles from the GCL may decrease the performance of the composite liner. The present paper provides theoretical analyses of these detrimental effects of bentonite particle loss, which lead to an acceptance criterion that can be used to evaluate the results of tests performed to determine if the geotextile(s) that separate(s) the bentonite from the geonet is (are) suitable or if another (or additional) geotextile is necessary.
Liquid Flow Through Composite Liners due to Geomembrane Defects: Nonuniform Hydraulic Transmissivity at the Liner Interface
Authors: Touze-Foltz N. , Rowe R.K. , Navarro N.
Published: October 2014

Rates of liquid flow through composite liners are intimately linked with the existence of a transmissive layer between the soil liner and the geomembrane. The aim of this paper is to propose analytical solutions for estimating the rate of liquid flow through composite liners for the case where two zones of different hydraulic transmissivities coexist in the transmissive layer. Solutions are given for both the axi-symmetric and two-dimensional cases. The development of these analytical solutions is directly based on solutions that have been proposed previously for uniform hydraulic transmissivity. Results tend to show, for the simple cases evaluated, that, in situations where there is variable hydraulic transmissivity, neglecting the variability can result in a significant overestimation of the rate of liquid flow. This preliminary approach shows the importance of taking into account a realistic distribution of hydraulic transmissivity in attempts to estimate the rate of liquid flow through composite liners and highlights the need for more research in this area.
Elastic Analysis of Soil-Geosynthetic Interaction
Authors: Zhan C. , Yin J.H.
Published: October 2014

A two-dimensional analytical model based on elasticity theory is developed for modeling soil-geosynthetic interaction for a geosynthetic layer of finite length embedded horizontally between granular fill and soft ground under a foundation loading. The soil-geosynthetic interaction is analyzed in both the vertical and horizontal directions. The vertical soil-geosynthetic interaction is modeled using Winkler springs. The horizontal soil-geosynthetic interaction is simulated using horizontal shear springs. The geosynthetic reinforcement is assumed to be elastic and only experiences tension without bending and shearing resistance. The soil mass is treated as an isotropic homogeneous elastic material. The proposed analytical model can be used to obtain the two-dimensional deformation and stress field in the soil mass and reinforcement. The results from the proposed model are compared with rigorous two-dimensional finite difference modeling results. Material and geometry parametric analyses are carried out using the proposed model to investigate the effectiveness of soft ground improvement.
Investigation and Modeling of Two Composite Landfill Covers
Authors: Finley C.A. , Holtz R.D.
Published: October 2014

The performance of two municipal solid waste landfill final covers was investigated. A field investigation of each landfill was performed, with test pits excavated and soil and geotextile samples collected. The investigation and analysis showed that the cover components were generally in good condition and performing their intended function in the field. Differential settlements that had occurred at both landfills were modeled with a finite difference code. The model results were used to calculate geomembrane strains and relate them to surface settlement characteristics. Using this method, two areas of differential settlement at one of the landfills were evaluated, and the geomembrane strains were found to be well below yield strains. In addition, a general design method for composite landfill covers spanning voids was developed with the finite difference model.
Influence of Creep and Stress-Relaxation of Geosynthetic Reinforcement on Embankment Behaviour
Authors: Li A.L. , Rowe R.K.
Published: October 2014

The effects of viscous behaviour of geosynthetic reinforcement on both the short-term and long-term performance of basally reinforced embankments over inviscous soft foundations are investigated. The construction of embankments reinforced with both viscous reinforcement and inviscous reinforcement is numerically simulated to identify the magnitude of creep and stress-relaxation of reinforcement under both limit-state and working stress conditions and the consequent effects on the stability and deformations of the system. The effects of viscoelastic properties of four reinforcement products made of polyester, polypropylene, and polyethylene are examined. It is shown that the viscous behavior of geosynthetic reinforcement can decrease the short-term stability, and the creep of geosynthetic reinforcement can significantly magnify the long-term shear deformations of the foundation soil. The isochronous stiffness can reasonably represent the mobilized reinforcement stiffness at the end of construction. The mobilized reinforcement stiffness and force are examined and the design considerations are discussed.
Consolidation Efficiency of Natural and Plastic Geosynthetic Band Drains
Authors: Jang Y.S. , Kim Y.W. , Park J.Y.
Published: October 2014

Consolidation efficiency of natural and plastic geosynthetic band drains is examined using laboratory tests and a three-dimensional numerical flow model. The numerical model is first validated by comparing its results with the laboratory consolidation data and then the influence of the drain installation depth on the consolidation time is estimated. The drains used in the analysis are circular and band-shaped natural drains and a band-shaped plastic drain. The results of discharge capacity tests show that the discharge capacity of the plastic drain is larger than those of the natural drains. Despite the difference in discharge capacity of the plastic and natural geosynthetic drains, the degree of consolidation versus time relationships obtained from laboratory consolidation tests were similar and the numerical model predicted the consolidation behavior quite well. The numerical simulation results of the effect of installation depth showed that the degree of consolidation versus time relationship for the circular-shaped natural and plastic geosynthetic drains was not significantly influenced by increases in installation depth. However, the consolidation-time relationship for the band-shaped natural geosynthetic drain, having a smaller discharge capacity, was influenced by well resistance with increased installation depth.
Shear Behaviour of Geosynthetics in the Inclined Plane Test – Influence of Soil Particle Size and Geosynthetic Structure
Authors: Lopes P.C. , Lopes M.L. , Lopes M.P.
Published: October 2014

This paper reports the investigation of the shear behaviour of six geosynthetics with two granular soils. The test equipment, soils, and geosynthetics properties are described and the soil-geosynthetic interaction behaviour is studied. The influence of soil particle size, geosynthetic structure, and test method are discussed by analysing the results of inclined plane tests. The main conclusions of the study are as follows: geosynthetic structure has an important influence on the soil-geosynthetic interface friction angle; higher soil-geosynthetic interface friction angles are measured when the geosynthetic surface has significantly sized apertures (e.g., geogrids) or allows the penetration of soil particles into the geosynthetic (e.g., nonwoven, spun-bonded geotextiles); geosynthetic surface roughness (e.g., geomembranes) is associated with higher soil-geosynthetic interface friction angles; soil particle size has an important influence on the soil-geosynthetic interface friction angle; broadly graded soils with large average soil particle sizes allow an increase in the soil-geosynthetic interface resistance; the method of test does not significantly influence the soil-geomembrane or soil-geotextile interface friction angles (geosynthetics with continuous surfaces); and the validity of evaluating the soil-geogrid interface resistance using a rigid support (Test method 1) depends on the structure of the geogrid. It is suggested that site conditions is the greatest factor to consider when selecting the most appropriate test method.
Field Performance of a 17 m-High Reinforced Soil Retaining Wall
Authors: Runser D.J. , Fox P.J. , Bourdeau P.L.
Published: October 2014

A 17 m-high steel strip reinforced soil retaining wall was instrumented to compare field measurements with predictions given by the design guidelines of the American Association of State Highway and Transportation Officials (AASHTO) 1996 Standard Specifications and the AASHTO 1999 Interim Revisions. The AASHTO models were conservative with respect to external lateral earth pressures and lateral earth pressures on the facing panels. On average, the AASHTO 1996 and 1999 models overestimated lateral pressure at the facing by 94 and 142%, respectively. Measured values of foundation bearing stress were generally in good agreement with values calculated using soil unit weight and depth, except that the average force from the facing panels on the leveling pad was twice that of the weight of the panels themselves. This discrepancy is attributed to shear stress on the back of the facing panels and vertical loads transferred to the panels through the strip connection clips. The location of the zone of maximum strip tension was in good agreement with the assumed failure surface. On average, the AASHTO 1996 and 1999 models underestimated maximum strip tensions by 17 and 8% and overestimated strip connection tensions by 127 and 154%, respectively. Finally, the apparent soil-reinforcement friction coefficient for the ribbed steel strips exceeded values specified in the AASHTO models by an average of 132%.
Effects of Preloading and Prestressing on the Strength and Stiffness of Geosynthetic Reinforced Clay in Plane Strain Compression
Authors: Roh H.S. , Tatsuoka F.
Published: October 2014

A series of plane strain compression (PSC) tests was performed to evaluate effects of preloading and prestressing on the stress-strain properties of reinforced saturated relatively soft clay. Saturated specimens of compacted clay, either unreinforced or reinforced with two horizontal layers of a composite consisting of woven and nonwoven geotextiles, were consolidated anisotropically simulating typical field stress conditions. Without drained preloading, the undrained strength of reinforced clay specimens did not noticeably increase when compared to unreinforced specimens, because a high positive excess water pressure developed in the reinforced clay due to the original high contractibility of the clay, which was not eliminated by reinforcement alone. The drained compressive strength increased substantially with reinforcement, while the peak strength was attained only at a large strain and the initial stiffness did not increase. By drained preloading to a load level that was much higher than the drained strength of unreinforced clay, the overall pre-peak stiffness, yield strength, and peak strength of reinforced clay under undrained conditions became substantially larger than those of unreinforced clay that had not been preloaded. The initial stiffness of preloaded clay at small strains became larger with increases in the prestress level as long as the prestress level was not too close to the preload level.
Analytical Equations for Predicting Concentration and Mass Flux from Composite Liners
Authors: Foose G.J. , Benson C.H. , Edil T.B.
Published: October 2014

Composite liners, consisting of a geomembrane overlying a soil liner, are often required as bottom liners for waste containment systems. In many applications, regulations prescribe the type of liner that must be installed. However, regulations often have provisions that permit an alternative liner design, provided that the alternative liner is equivalent to, or as effective as, the prescriptive liner. The current approach for demonstrating equivalency is based on comparing leakage rates for the alternative and prescriptive liners. This approach is too simplistic because leakage rate is not always indicative of the mass of contaminants discharged from the liner. In this paper, practical equations are presented for predicting the discharge of contaminants from composite liners and for designing alternative liners. The equations can be implemented using hand-held calculators or computer spreadsheet applications. Some of these equations are shown to provide predictions of mass flux and contaminant breakthrough that are similar to predictions made with more complex one- and three-dimensional numerical models for composite liners having perfect contact, circular defects, a constant source concentration, and relatively simple boundary conditions.
Instruments Measuring Perceived Racism/Racial Discrimination: Review and Critique of Factor Analytic Techniques
Authors: Atkins Rahshida
Published: October 2014

Several compendiums of instruments that measure perceived racism and/or discrimination are present in the literature. Other works have reviewed the psychometric properties of these instruments in terms of validity and reliability and have indicated if the instrument was factor analyzed. However, little attention has been given to the quality of the factor analysis performed. The aim of this study was to evaluate the exploratory factor analyses done on instruments measuring perceived racism/racial discrimination using guidelines from experts in psychometric theory. The techniques used for factor analysis were reviewed and critiqued and the adequacy of reporting was evaluated. Internet search engines and four electronic abstract databases were used to identify 16 relevant instruments that met the inclusion/exclusion criteria. Principal component analysis was the most frequent method of extraction (81%). Sample sizes were adequate for factor analysis in 81 percent of studies. The majority of studies reported appropriate criteria for the acceptance of un-rotated factors (81%) and justified the rotation method (75%). Exactly 94 percent of studies reported partially acceptable criteria for the acceptance of rotated factors. The majority of articles (69%) reported adequate coefficient alphas for the resultant subscales. In 81 percent of the studies, the conceptualized dimensions were supported by factor analysis.
Ovarian Cancer: Diagnostic, Biological and Prognostic Aspects
Authors: Davidson Ben , Tropé Claes G
Published: October 2014

Ovarian cancer remains the most lethal gynecologic malignancy, owing to late detection, intrinsic and acquired chemoresistance and remarkable heterogeneity. Despite optimization of surgical and chemotherapy protocols and initiation of clinical trials incorporating targeted therapy, only modest gains have been achieved in prolonging survival in this cancer. This review provides an update of recent developments in our understanding of the etiology, origin, diagnosis, progression and treatment of this malignancy, with emphasis on clinically relevant genetic classification approaches. In the authors' opinion, focused effort directed at understanding the molecular make-up of recurrent and metastatic ovarian cancer, while keeping in mind the unique molecular character of each of its histological types, is central to our effort to improve patient outcome in this cancer.
The question is whether hemiparesis is more common in unilateral than bilateral chronic subdural hematoma
Authors: Jukovic Mirela , Petrovic Kosta , Till Viktor
Published: October 2014

Introduction. Chronic subdural hematoma is an intracranial hemorrhagic lesion
that illustrates various expressions in clinical and radiological practice.
The aim of this study was to emphasize the correlation between the brain site
of chronic subdural hematoma and clinical symptoms/signs of disease.
Furthermore, the study denotes the significance of hemiparesis occurrence in
the patients with unilateral chronic subdural hematomas more than in those
with bilateral ones, associated with time required to diagnose hematoma.
Material and Methods: A three-year study included 72 patients with chronic
subdural hematoma. According to their clinical and neurological symptoms on
hospital admission, all patients underwent non-contrast brain computed
tomography scan, which confirmed the diagnosis. The radiological parameters,
inlcuding the site of chronic subdural hematoma, a hematoma width and midline
shift were recorded to give precise data about the correlation with
neurological symptoms. A special focus was put on the lag time between the
onset of symptoms and signs to diagnosis of chronic subdural hematoma.
Results. The study proved that the patients with unilateral chronic subdural
hematoma had more frequent occurrence of hemiparesis than the patients with
bilateral chronic subdural hematoma. It took the left-sided chronic subdural
hematomas less time (about 200 hours earlier) than the rightsided ones to
present its symptoms although the average hematoma diameter value was almost
the same. Conclusion. The site and the form of intracranial lesion-chronic
subdural hematoma could have a great influence on neurological and functional
condition in a patient. Although the length of time required for making
diagnosis as well as clinical symptoms greatly differ and the latter are not
always so clear, physicians should maintain a high level of suspicion for
this disease and thus contribute to prompt diagnosis and better clinical
outcome of patients.
Thyroid-stimulation hormone - receptor antibodies as a predictor of thyrosuppressive drug therapy outcome in Graves’ disease patients
Authors: Aleksic Aleksandar , Aleksic Zeljka , Manic Saska , Mitov Vladimir , Jolic Aleksandar
Published: October 2014

Introduction. Graves? disease is autoimmune hyperthyroidism caused by
pathological stimulation of thyroid-stimulation hormone - receptor
antibodies. The decision on changing the therapy can be made on time by
determining the prognostic factors of thyrosuppressive drug therapy outcome.
The aim of the study was to determine the significance of thyroid-stimulation
hormone-receptor antibodies level on the prediction of therapy outcome.
Material and Methods. The study was prospective and involved 106 drug-treated
patients with newly diagnosed Graves? disease. Thyroid- stimulation hormone -
receptor antibodies level was measured at the beginning of therapy, during
therapy and 12 months after it had been introduced. Results. No statistically
significant difference in the level of thyroid-stimulation hormone - receptor
antibodies was found at the beginning of disease and 12 months after the
introduction of thyrosuppressive drug therapy among the patients who had been
in remission and those who had not. Regardless of the outcome,
thyroid-stimulation hormone - receptor antibodies level significantly
decreased in all patients 12 months after the therapy had been introduced.
Conclusion. The level of thyroid-stimulation hormone - receptor antibodies at
the beginning of disease and 12 months after the introduction of therapy
cannot predict the outcome of thyrosuppressive drug therapy.
Modulatory role of nitric oxide in cardiac performance
Authors: Smiljic Sonja , Nestorovic Vojkan , Savic Sladjana
Published: October 2014

Nitric oxide is produced by almost all cardiac cells, endothelial cells,
cardiomyocytes and nerve fibers. It is synthesized by an enzyme, a nitric
oxide synthase, which occurs in endothelial, neural and inducible form. The
distribution of nitric oxide synthase in the heart is characterized by a
pronounced non-uniformity. Nitric oxide exerts its effects in physiological
and pathophysiological conditions. The physiological effects of low
concentrations of nitric oxide, which is released in the normal conditions
under the influence of constituent enzymes, occur via cyclic guanosine
monophosphate. The synthesized nitric oxide exhibits its effect in the cells
where it is produced, in an autocrine manner, or by diffusing into the
neighboring cells, in a paracrine manner. Nitric oxide acts by regulating the
coronary vessel tonus, affecting the contractility of cardiomyocytes,
generating an inotropic effect in a dose-dependent manner and controlling the
cellular respiration. Other effects of nitric oxide in the cardiovascular
system include the hyperpolarization of the smooth muscle cells in blood
vessels, the inhibition of the monocyte adhesion, the inhibition of platelet
migration, adhesion and aggregation and the proliferation of smooth muscle
cells and fibroblasts. The anti-atherosclerotic effects of nitric oxide are
based on these effects. Nitric oxide is a weak free radical in gaseous state,
and the cytotoxic and/or the cytoprotective effects of the higher
concentrations of nitric oxide are related to the chemical structure of
nitric oxide as a free radical. The excessive production of nitric oxide by
the activation of inducible nitric oxide synthase can lead to major
irregularities in the function of cardiomyocytes and cardiac insufficiency.
Understanding the nitric oxide molecular mechanisms of signaling pathways in
the heart can provide a new strategic approach to prevention and treatment of
cardiovascular diseases.
Are Sulfonylurea and Insulin Therapies Associated With a Larger Risk of Cancer Than Metformin Therapy? A Retrospective Database Analysis
Authors: Kowall Bernd , Rathmann Wolfgang , Kostev Karel
Published: October 2014

OBJECTIVE

Several meta-analyses of observational studies suggested that metformin use reduces cancer risk in type 2 diabetes. However, this result was not confirmed by the few available randomized controlled trials (RCTs), and many observational studies on metformin and cancer were potentially afflicted with time-related bias. We aimed to avoid this bias when comparing cancer incidence in users of sulfonylurea, insulin, and other diabetes medications, respectively, with cancer incidence in metformin users.

RESEARCH DESIGN AND METHODS

In a retrospective observational study, we used the German Disease Analyzer database with patient data from general practices throughout Germany. The study sample included 22,556 patients diagnosed with type 2 diabetes. During the median follow-up time of 4.8 years, 1,446 (6.4%) patients developed any cancer. In Cox regression analyses with either monotherapies or first diabetes medications as drug exposure, users of sulfonylurea (or insulin or other antidiabetes medications) were compared with metformin users.

RESULTS

In multivariable adjusted models, hazard ratios were 1.09 (95% CI 0.87–1.36) for sulfonylurea monotherapy, 1.14 (95% CI 0.85–1.55) for insulin monotherapy, and 0.94 (95% CI 0.67–1.33) for other diabetes medications compared with metformin monotherapy. Results were similar for comparison of first diabetes medications.

CONCLUSIONS

In a retrospective database analysis, taking into account potential time-related biases, no reduced cancer risk was found in metformin users. To clarify the association between diabetes medication and cancer risk, further well-designed observational studies and RCTs are needed.
Smoking and Long-Term Risk of Type 2 Diabetes: The EPIC-InterAct Study in European Populations
Authors:   The InterAct Consortium, Spijkerman Annemieke M.W. , van der A Daphne L. , Nilsson Peter M. , Ardanaz Eva , Gavrila Diana , Agudo Antonio , Arriola Larraitz , Balkau Beverley , Beulens Joline W. , Boeing Heiner , de Lauzon-Guillain Blandine , Fagherazzi Guy , Feskens Edith J.M. , Franks Paul W. , Grioni Sara , Huerta José María , Kaaks Rudolf , Key Timothy J. , Overvad Kim , Palli Domenico , Panico Salvatore , Redondo M. Luisa , Rolandsson Olov , Roswall Nina , Sacerdote Carlotta , Sánchez María-José , Schulze Matthias B. , Slimani Nadia , Teucher Birgit , Tjonneland Anne , Tumino Rosario , van der Schouw Yvonne T. , Langenberg Claudia , Sharp Stephen J. , Forouhi Nita G. , Riboli Elio , Wareham Nicholas J.
Published: October 2014

OBJECTIVE

The aims of this study were to investigate the association between smoking and incident type 2 diabetes, accounting for a large number of potential confounding factors, and to explore potential effect modifiers and intermediate factors.

RESEARCH DESIGN AND METHODS

The European Prospective Investigation into Cancer and Nutrition (EPIC)-InterAct is a prospective case-cohort study within eight European countries, including 12,403 cases of incident type 2 diabetes and a random subcohort of 16,835 individuals. After exclusion of individuals with missing data, the analyses included 10,327 cases and 13,863 subcohort individuals. Smoking status was used (never, former, current), with never smokers as the reference. Country-specific Prentice-weighted Cox regression models and random-effects meta-analysis were used to estimate hazard ratios (HRs) for type 2 diabetes.

RESULTS

In men, the HRs (95% CI) of type 2 diabetes were 1.40 (1.26, 1.55) for former smokers and 1.43 (1.27, 1.61) for current smokers, independent of age, education, center, physical activity, and alcohol, coffee, and meat consumption. In women, associations were weaker, with HRs (95% CI) of 1.18 (1.07, 1.30) and 1.13 (1.03, 1.25) for former and current smokers, respectively. There was some evidence of effect modification by BMI. The association tended to be slightly stronger in normal weight men compared with those with overall adiposity.

CONCLUSIONS

Former and current smoking was associated with a higher risk of incident type 2 diabetes compared with never smoking in men and women, independent of educational level, physical activity, alcohol consumption, and diet. Smoking may be regarded as a modifiable risk factor for type 2 diabetes, and smoking cessation should be encouraged for diabetes prevention.