bluuebunny/crossref_metadata_2025 huggingface dataset:
Walls Reinforced with Fiber Reinforced Plastic Geogrids in Japan
Authors: Miyata K.
Published: October 2014

This paper deals with geosynthetic reinforced soil (GRS) retaining walls reinforced with high tensile strength and stiffness fiber reinforced plastic (FRP) geogrids. The geogrid properties are described and full-scale field tests using three different wall facings are presented. The performance of the test walls is compared with the results of finite element method analyses which were used to simulate the construction and loading of the field tests. The analyses indicate that geosynthetic stiffness affects wall face deformation. A case history which describes the construction of a GRS retaining wall is also presented.
Design and Construction of Geotextile Reinforced Soil Structures for Road Earthworks in Japan
Authors: Naemura S. , Miki H.
Published: October 2014

The application of geotextiles as reinforcement in embankments and retaining walls for permanent and temporary roads has recently gained popularity in Japan particularly since the publication of “Design and Construction Manual for Reinforced Soil using Geotextiles”. This manual sets the technical standard in Japan for the design and construction of earthworks involving geosynthetic reinforced embankments and walls. This paper describes the design of reinforced embankments using clayey soil fills with high water contents and the design of reinforced soil walls. A construction example, along with instrumentation results, is given for each case.
A Performance Test for Assessment of Long-Term Creep Behavior of Soil-Geosynthetic Composites
Authors: Wu J.T.H. , Helwany S.M.B.
Published: October 2014

A simple laboratory performance test was devised for the assessment of long-term creep behavior of geosynthetic reinforcement due to soil-geosynthetic interaction. In the test, the geosynthetic reinforcement and the confining soil deformed in an interactive manner under a sustained surcharge that was applied to the soil over a long period of time. Two long-term performance tests were conducted with different confining soils: a clean sand, and a kaolin clay. The tests clearly indicate that the long-term creep deformation of the geotextile reinforcement was significantly affected by the time-dependent deformation characteristics of the confining soils. It can be misleading to evaluate the long-term creep potential of a soil-geosynthetic composite based solely on the results of geosynthetic element creep tests such as constant load strip tensile tests and, confined creep tests which do not account for time-dependent deformation of the confining soil.
Strain-Softening Behavior of Waste Containment System Interfaces
Authors: Gilbert R.B. , Byrne R.J.
Published: October 2014

Laboratory test results indicate that many geosynthetic interfaces in liners and covers for waste containment exhibit strain-softening behavior. A peak shear strength is mobilized at small displacements, but post-peak strength reductions occur with increasing displacement. Mechanisms that contribute to strain-softening include clay particle reorientation, geosynthetic polishing, and geosynthetic failure. Test results obtained from direct shear and torsional ring shear devices are summarized to illustrate these mechanisms. The design implications of strain-softening behavior are then investigated using analytical and numerical models. Deformations in the waste under gravity are sufficient in many cases to limit the available shear resistance along an interface to less than the peak strength. It is recommended that a factor of safety greater than one be achieved in all containment system slope designs, assuming that residual strengths are mobilized along the base of the entire containment system.
Geotextile Reinforced Lime Treated Cohesive Soil Retaining Walls
Authors: Porbaha A.
Published: October 2014

The behavior of geotextile reinforced retaining walls backfilled with lime treated cohesive soil was investigated using reduced-scale physical models tested to failure under self-weight in a geotechnical centrifuge. The following three modes of failure were identified in this study for untreated and lime treated cohesive soil walls: overturning, rotational sliding, and planar sliding. The addition of 2% lime to the backfill significantly improved the prototype equivalent failure height, and it influenced the position of the failure surface by moving the slip surface toward the front of the wall. The lime treated backfill models collapsed suddenly along a bilinear slip surface in a brittle type of failure with little prefailure deformation, while the untreated clay backfill models collapsed gradually along a curvilinear slip surface and withstood large deformations prior to failure. A limit equilibrium analysis incorporating the horizontal and tangential effects of geotextile reinforcement was found to be a good predictor of wall behavior.
Full Scale Highway Load Test of Flexible Pavement Systems with Geogrid Reinforced Base Courses
Authors: Collin J.G. , Kinney T.C. , Fu X.
Published: October 2014

The use of geosynthetics to improve the performance of flexible pavements has increased significantly over the last decade. This paper describes a full scale testing research program that used a 20 kN moving wheel load to determine the benefit of using a stiff biaxial geogrid between the base and subgrade of a flexible pavement system. The traffic benefit ratio (TBR) was defined as the ratio of the number of load cycles of a stiff geogrid reinforced section, to the number of load cycles of an unreinforced section for a given level of performance. The TBR values ranged from 2 to over 10 for the conditions tested. Traffic benefit ratio values between 2 and 4 appear to be reasonable for use in pavement design.
Water Diffusion Through Geomembranes Under Hydraulic Pressure
Authors: Eloy-Giorni C. , Pelte T. , Pierson P. , Margrita R.
Published: October 2014

A theoretical analysis of fluid transport mechanisms through geomembranes is presented. Diffusion and permeation tests that use a volumetric and radioactive tracer method to measure the amount of water flow through geomembrane specimens give an understanding of the mechanism of water transport through the following different types of geomembranes: high density polyethylene (HDPE), polyvinyl chloride (PVC), and bituminous geomembranes. The use of the hydraulic permeation test and hydraulic conductivity (as defined by Darcy's law) to characterize geomembrane permeability are discussed. It appears that the transport of water through the tested geomembranes is mainly a function of the hydrophobic behavior of the geomembranes but not of the pressure gradient. Therefore, hydraulic conductivity as defined by Darcy's law is unable to describe water transport through geomembranes.
Designing to Residual Strength of Geosynthetics Instead of Stress Rupture
Authors: Greenwood J.H.
Published: October 2014

The tensile design strength of geosynthetic reinforcement may be governed by strain or load and, in the latter case, some design codes base the design strength on stress-rupture. However, when a factor of safety is applied, this approach can be over-conservative. By considering the residual or available strength, it is possible to define a more realistic procedure that can be integrated with the effects of environmental degradation and mechanical damage.
Strength and Deformation Properties of Soils Reinforced With Fibrillated Fibers
Authors: Nataraj M.S. , McManis K.L.
Published: October 2014

The results of preliminary laboratory tests on a clay and a sand reinforced with randomly distributed fibrillated fibers are presented. The results of compaction, direct shear, unconfined compression and California Bearing Ratio (CBR) tests are described. The influence of test parameters such as normal stress, the amount of reinforcement, specimen size, and moisture content is addressed. The tests show that fibers significantly increase the peak compressive strength of clay and sand. The addition of fiber reinforcement in the sand and clay specimens resulted in substantial increases in the peak friction angle and cohesion values. The increase in strength is a function of fiber content and moisture content. The Mohr-Coulomb failure envelopes for the clay specimens are described by a combination of curvilinear and linear sections. The CBR values for the clay and sand specimens were also significantly improved using fiber reinforcement. This preliminary study suggests that for the soils tested and reinforced with 25 mm long polypropylene fibrillated fibers, the optimum fiber content is approximately 0.3% of the dry unit weight of the soil.
Geosynthetic-Reinforced Soil Retaining Walls as Important Permanent Structures 1996 - 1997 Mercer Lecture
Authors: Tatsuoka F. , Tateyama M. , Uchimura T. , Koseki J.
Published: October 2014

During the past decade, more than 26 km of geosynthetic-reinforced soil retaining walls (GRS-RWs) with full-height rigid (FHR) facings were constructed in Japan as important permanent structures mainly for railways and occasionally for highways. These include retaining walls for embankments, bridge abutments, a wall backfilled with a nearly saturated clay constructed on a thick soft clay deposit, a wall that survived a very severe earthquake, and walls constructed to support bullet train tracks. The full-height rigid facings are cast in place using staged construction procedures. A new method of stiffening reinforced soil by vertical preloading and prestressing is also described.
Leachate Flow in Leakage Collection Layers Due to Defects in Geomembrane Liners
Authors: Giroud J.P. , Gross B.A. , Bonaparte R. , McKelvey J.A.
Published: October 2014

This paper provides analytical and graphical solutions related to the flow of leachate in a leakage collection layer due to defects in the overlying liner (i.e. the primary liner of a double liner system). The defects are assumed to be small (e.g. holes in geomembrane liners). It is shown that leachate flows in a zone of the leakage collection layer (the wetted zone) that is limited by a parabola. A simple relationship is established between the rate of leachate migration through the defect and the maximum thickness of leachate in the leakage collection layer; this relationship depends on the hydraulic conductivity (but not on the slope) of the leakage collection layer. Equations are provided to calculate the average head of leachate on top of the liner underlying the leakage collection layer (i.e. the secondary liner of a double liner system), which is useful for calculating the rate of leachate migration through that liner. Finally, the case of several leaks randomly distributed is considered, and equations for the surface area of the wetted zone and the average head are given for this case. Parametric analyses and design examples provide useful comparisons between the three types of materials used in leakage collection layers: gravel, sand and geonets.
Equations for Calculating the Rate of Liquid Migration Through Composite Liners Due to Geomembrane Defects
Authors: Giroud J.P.
Published: October 2014

Equations available to date for calculating the rate of liquid migration through a composite liner due to geomembrane defects require the use of graphs to obtain the value of one of the terms of the equations for the case where the liquid head is larger than the thickness of the low-permeability soil component of the composite liner. In this paper, it is shown that the terms that require graphs can be expressed analytically, which leads to a new set of equations that provides an entirely analytical means of calculating the rate of liquid migration through composite liners. This new set of equations is particularly useful when the liquid head is large compared to the thickness of the low-permeability soil component of the composite liner, which is often the case when the low-permeability soil associated with the geomembrane to form a composite liner is a geosynthetic clay liner. A numerical example is given.
Rate of Liquid Migration Through Defects in a Geomembrane Placed on a Semi-Permeable Medium
Authors: Giroud J.P. , Khire M.V. , King T.D. , Sanglerat T.R. , Hadj-Hamou T.
Published: October 2014

This paper provides an equation for calculating the rate of liquid migration through a defect in a geomembrane underlain by a semi-permeable medium. In the context of this paper, a semi-permeable medium is a medium that has a hydraulic conductivity greater than k G and smaller than k B , where k G is the hydraulic conductivity above which Giroud's equation is not valid and k B the hydraulic conductivity below which Bernoulli's equation is not valid. Giroud's equation is an equation that gives the rate of liquid migration through a defect in a geomembrane underlain by a low-permeability medium, and Bernoulli's equation is the equation that gives the rate of free flow through an orifice and which is used to calculate the rate of liquid migration through a defect in a geomembrane underlain by a very permeable medium. The equation for semi-permeable media presented in this paper was obtained by interpolation between Giroud's equation and Bernoulli's equation.
Comparison of Leachate Flow Through Compacted Clay Liners in Landfill Liner Systems
Authors: Giroud J.P. , Badu-Tweneboah K. , Soderman K.L.
Published: October 2014

The purpose of this paper is to provide an approach for comparing the effectiveness of geosynthetic clay liners (GCLs) and compacted clay liners (CCLs) used in association with geomembranes to form composite liners. Comparing the effectiveness of these two types of composite liners is required in “equivalency demonstrations” intended to demonstrate that a geomembrane-GCL composite liner is equivalent to a conventional geomembrane-CCL liner prescribed by a regulation. In the first part of the paper, the contribution of the geomembrane is ignored and the paper presents analytical evaluations of advective leachate flow through GCLs, low-permeability soil layers (such as CCLs), and two-layer systems including a GCL and a low-permeability soil layer. The analyses presented explain why some calculations typically performed for landfill liner system design or for equivalency demonstrations lead to the paradoxical result that the advective flow of leachate is greater when a GCL is placed on a layer of low-permeability soil than when the GCL is placed on a layer of high-permeability soil. The second part of the paper presents an analytical method for comparing the effectiveness of a composite liner including a GCL and a composite liner including a CCL. This analytical method enables design engineers to compare the effectiveness of various composite liners without neglecting the beneficial effect of the geomembrane. A parametric study presented in the paper shows that neglecting the geomembrane liner in equivalency demonstrations (which is frequently done in the current state of practice) penalizes composite liners that incorporate a GCL.
Interaction Between Tire Shreds, Rubber-Sand and Geosynthetics
Authors: Bernal A. , Salgado R. , Swan R.H. , Lovell C.W.
Published: October 2014

Waste tires can be shredded (tire shreds) and re-used as fill material. The fill material may be comprised solely of tire shreds or mixed with sand (rubber-sand). If geosynthetics are to be used with fills containing tire shreds, it is necessary to understand the physical interaction between tire shreds, or rubber-sand, and the geosynthetic of interest. A laboratory testing program consisting of direct shear tests, interface direct shear tests, and geosynthetic pullout tests was conducted to determine the interaction properties of tire shreds and rubber-sand fills with three different flexible geogrids and a woven geotextile. Direct shear and interface direct shear tests were conducted using a large direct shear box with dimensions of 300 mm by 300 mm and a total depth of 230 mm. Pullout tests were carried out in a large pullout box with dimensions of 1.2 m in length by 0.9 m in width and a total depth of 0.5 m. The details of the testing program, the test results, and conclusions based on the test results are presented in this paper.
Shaking and Tilt Table Tests of Geosynthetic-Reinforced Soil and Conventional-Type Retaining Walls
Authors: Koseki J. , Munaf Y. , Sato T. , Tatsuoka F. , Tateyama M. , Kojima K.
Published: October 2014

A series of shaking table tests was performed on relatively small-scale models of a geosynthetic-reinforced soil retaining wall with a full-height rigid facing and conventional type (gravity-type, leaning-type, and cantilever-type) retaining walls. Tilt table tests were also conducted on the geosynthetic-reinforced soil retaining wall and the leaning-type model walls. The seismic stability of these different types of walls are evaluated by both shaking and tilt table test methods and compared with each other. The observed critical seismic acceleration coefficients are compared with the values predicted by the conventional pseudo-static approach. Similarly, the observed failure plane angles in the backfill are compared with the predicted values. The effects of simple shear deformation of the reinforced backfill for the reinforced-type walls and the effects of post-peak reduction of shear resistance along the failure plane are also discussed.
A Nonlinear Model for the Seismic Response of Geosynthetic-Reinforced Soil Structures
Authors: Carotti A. , Rimoldi P.
Published: October 2014

This paper proposes a mathematical model for the dynamic response of geogrid-reinforced soil under horizontal base excitation. First, a linear model of the soil without reinforcement is introduced, followed by a Newtonian nonlinear model for the dynamic response of soil with layers of geosynthetic reinforcement. The proposed model considers the following three effects of geogrid reinforcement on soil structures: (i) an increase of interlayer soil stiffness as a consequence of soil-geogrid interaction; (ii) an increase in the viscous damping as a consequence of the soil-geogrid interaction; and (iii) a further increase of the interlayer viscous damping, as a consequence of the geogrid-soil Coulomb friction. The proposed theory has been used to simulate the seismic response of two actual soil structures: a reduced-scale model of a soil retaining wall; and full-scale railway track retaining walls under a Kobe, Japan earthquake record. The results are encouraging and suggest directions for further refinement of the numerical model. Finally, a linearization of the Coulomb-type nonlinear model is proposed: an approximate viscous-equivalent model is presented, which provides a simple tool for performing a preliminary assessment of the order of magnitude of seismic effects.
Performance of Protective Cover Systems for Landfill Geomembrane Liners Under Long-Term MSW Loading
Authors: Reddy K.R. , Saichek R.E.
Published: October 2014

This paper presents the results of large-scale laboratory simulation tests conducted to evaluate the relative performance of different cover systems, consisting of a granular soil layer (i.e. a drainage layer) both with and without the presence of a needle-punched nonwoven geotextile, to protect a 1.5 mm thick smooth HDPE geomembrane liner under long-term municipal solid waste (MSW) loading conditions. Five different granular soils that range from a coarse gravel to a medium sand were used in the testing program. The protective cover system and the geomembrane liner were subjected to incremental loading to a maximum pressure of 1.4 MPa. The effect of long-term loading on the characteristics of the cover soils was assessed by performing particle size analyses, and the physical damage that occurred to the geomembrane liner was visually assessed in addition to performing multi-axial tension, wide strip tension, and water vapor transmission tests. The test results revealed that the degree of geomembrane liner protection decreases as the soil mean particle size increases and as the soil particle sphericity decreases. This study demonstrates that a 300 mm thick granular soil layer consisting of particles with a mean size less than 30 mm and a sphericity greater than 0.8, combined with a 270 g/m2 nonwoven geotextile provides adequate protection for a 1.5 mm thick HDPE geomembrane liner from MSW loading.
The Clogging of Nonwoven Geotextiles With Cattle Manure Slurries
Authors: Barrington S.F. , El Moueddeb K. , Jazestani J. , Dussault M.
Published: October 2014

Three different types of heat-bonded, needle-punched, nonwoven polyester geotextile specimens with similar hydraulic conductivities, but with different O 90 values and average pore opening sizes, were exposed to a 3.6 m head of cattle manure slurry containing 7.5% total solids (TS) in laboratory columns to test the effect of pore opening size on geotextile specimen clogging. Geotextile specimens, with the smallest pore openings, were also exposed to 1, 2, and 4% TS cattle manure slurries to test the sealing effect of the TS. After 100 days of exposure to the slurries, geotextile specimen clogging was verified by measuring the geotextile specimen hydraulic conductivity using 0.9 and 3.65 m falling water head tests after removing all of the manure liquids and solids. The lowest volumetric infiltration rate, 1.1 L/m2/day, was obtained for geotextile specimens with the smallest pore opening size after 80 days of exposure to the 7.5% TS cattle manure slurry. Geotextile specimen infiltration rates were exponentially related to the amount of TS in the manure slurries. The geotextile specimen hydraulic conductivity values (for water), after the removal of the cattle manure slurries and all surface solids, was 105 times smaller that that measured before testing. This indicates that geotextile specimen clogging did occur while in contact with the cattle manure slurries.
Modelling of Geosynthetic Reinforcement in Soil Retaining Walls
Authors: Sawicki A.
Published: October 2014

The paper is focused on the behaviour of geosynthetic reinforcement layers in the active and anchorage zones of soil retaining walls. Differential equations that describe the reinforcement layer force/stress distribution, while embedded in soil, are derived for both elastic and visco-elastic reinforcement layers. The solutions to these differential equations provide a simple method of analysing the following phenomena: reinforcement pull-out, the influence of wall facing flexibility on the distribution of forces in the reinforcement, and stress relaxation in reinforcement layers that exhibit creep behaviour. Practical examples are used to illustrate the influence of parameter values on model predictions.
Geotextile-Reinforced Embankments on Soft Clays - Effects of a Foundation Soil Crust Strengthened by Lime Diffusion
Authors: Edinçliler A. , Güler E.
Published: October 2014

This paper presents the results of a study of the effects of a lime crust in the foundation soil, obtained by lime diffusion, on the performance of nonwoven geotextile-reinforced embankments. The study consists of laboratory model tests to simulate failure mechanisms during the construction and lifetime of embankments. A 1/100-scale model of the embankment was constructed. Lime was spread over the foundation soils to increase the shear strength of the soil through lime diffusion. In the laboratory experiments, vertical and horizontal deformations of the geotextile were recorded. Spreading of lime reduced the water content of the clay in the crust layer. It was observed that crust formation using lime diffusion increased the shear strength of the foundation soil thereby allowing the soil to carry larger loads. The soil was capable of carrying loads up to five times greater than that of the untreated soil. It was found that the shear strength increase is dependent on the quantity of lime added, temperature, and curing time.
Soil-Geosynthetic Interface Strength and Stiffness Relationships From Pullout Tests
Authors: Perkins S.W. , Cuelho E.V.
Published: October 2014

Pullout tests are commonly used to describe the ultimate shearing resistance developed along the interface between the confining soil and the geosynthetic as a function of normal stress confinement. Pullout tests can also be used to define the complete soil-geosynthetic interface relationship between shear stress and shear displacement interaction. Such a description of interface strength and stiffness characteristics is needed in analytical models used to predict a displacement response of geosynthetic-reinforced soil structures. Due to the extensibility of geosynthetics, data from pullout tests cannot be used directly to calculate strength and stiffness interface properties. The pullout test must be analyzed as a boundary-value problem with appropriate assumptions made regarding the constitutive relationship of the geosynthetic itself and for the interface interaction. An analytical method is presented that allows for the relationship between shear stress and shear displacement to be back-calculated from pullout test data. This method is used to evaluate interface shear stiffness and shear strength for a geogrid and geotextile product for three normal stress confinement levels. The significance of material models used in the formulation is examined.
Mechanical Response of Geosynthetic-Reinforced Flexible Pavements
Authors: Perkins S.W.
Published: October 2014

Laboratory-based, large-scale experiments are reported on pavement test sections with aggregate base layers containing a layer of geosynthetic reinforcement. The tests involved comparative reinforced and unreinforced test sections with pavement layer materials and thicknesses commonly encountered in the field. Pavement load was provided by a nontranslating, cyclic load applied to a plate resting on the pavement surface. The test sections contained an extensive array of sensors to measure pavement load, surface deformation, stress in the base and subgrade layers, and strain in the asphalt concrete, base, subgrade, and geosynthetic layers. Test section variables include geosynthetic type, geosynthetic placement position within the base, and base layer thickness. The test results show a significant improvement in the permanent deformation behavior of the pavement system due to geosynthetic reinforcement for the variables examined. Stress and strain measurements illustrate reinforcement mechanisms pertinent to paved roadways, which include a reduction of radial strain developed in the bottom of the base, an improved vertical stress distribution on the top of the subgrade, and a reduction of shear deformation in the top of the subgrade. These mechanisms result in lower vertical strain in the base and subgrade layers. A comparison of benefits due to reinforcement and those realized by the addition of aggregate base shows that geosynthetic reinforcement and additional base aggregate provide similar structural enhancements to the pavement system.
Modelling a Geotextile-Reinforced, Brick-Faced Soil Retaining Wall
Authors: Pinto M.I.M. , Cousens T.W.
Published: October 2014

Scale models are a powerful means of studying engineering problems; they are versatile because it is easier to make alterations, relatively inexpensive because less space is required, as well as requiring less time for construction, instrumentation, and testing. This paper describes the work carried out in an experimental study on the behaviour of geotextile-reinforced, brick-faced soil retaining walls by means of one-fifth (1/5) scale models under normal gravity (1g) and compares the model results with data from a previous research programme on prototype-scale walls. The modelling was based on the principles of similarity and dimensional analysis. An experimental apparatus was designed and suitable materials were selected taking into account the modelling requirements. Comparisons between the model results and those obtained in previous prototype-scale tests were undertaken. An acceptable degree of agreement was achieved.
Comparison of Geotextile Durability to Outdoor Exposure Conditions in the Peruvian Andes and the Southeastern USA
Authors: Grubb D.G. , Diesing W.E. , Cheng S.C.J. , Sabanas R.M.
Published: October 2014

Outdoor exposure tests were completed on two woven slit-film polypropylene geotextiles with carbon black and two nonwoven needle-punched polyester geotextiles in Huaron (∼11°S; 4,600 m elevation) and Vijus (∼7°45′S; 1,250 m elevation), Peru, and Atlanta, Georgia, USA (∼33°46′N, 315 m elevation), for a period of 12 months. The retained strength values of the polypropylene geotextiles deployed in Vijus ranged from approximately 64 to 95% and 49 to 122% for the 180 and 260 g/m2 mass per unit area geotextiles, respectively, compared to unexposed specimens. Likewise, the retained strength values of the polyester geotextiles deployed in Vijus ranged from approximately 64 to 82% and 70 to 98% for the 420 and 550 g/m2 geotextiles, respectively. Higher retained strength values (10 to 15%) were obtained for the geotextiles exposed to outdoor conditions in Huaron and Atlanta. The role of latitude and altitude in the strength loss of geotextiles was not clear; the strongest observed trend was that the highest strength losses appeared to be more closely correlated with the highest maximum and minimum temperatures.
Finite Element Study of a Geosynthetic-Reinforced Soil Retaining Wall With Concrete Block Facing
Authors: Ling H.I. , Cardany C.P. , Sun L-X. , Hashimoto H.
Published: October 2014

This paper focuses on the results of finite element modeling of a full-scale, concrete-block, geosynthetic-reinforced soil retaining wall constructed at the Public Works Research Institute in Japan. A nonlinear hyperbolic geosynthetic model was incorporated into a computer program that is capable of simulating soil-structure interaction behavior. The soil was simulated using a hyperbolic model while the block-block and soil-block interactions were simulated using interface elements. Comparison of numerical and measured experimental results indicated that the finite element model is capable of simulating the construction behavior of concrete-block geosynthetic-reinforced soil structures.
Effect of Prefabricated Vertical Drain Clogging on the Rate of Consolidation: A Numerical Study
Authors: Basu D. , Madhav M.R.
Published: October 2014

Ground treatment of soft soil deposits by prefabricated vertical drains (PVDs) is a common practice in geotechnical engineering. The PVDs accelerate the consolidation process and help to rapidly increase the strength and stiffness of soil. Certain operational problems, such as clogging, are inherent to PVDs. The fine particles in the soil may become entrapped within the fibers of the filter, i.e. the geotextile, surrounding the PVD. If the pores of the filter sleeve are clogged, the discharge capacity of the PVD reduces and, consequently, the consolidation process is impeded. In this paper, a numerical study is carried out to investigate the effect of PVD geotextile filter clogging on the rate of soil consolidation. The rate of consolidation decreases with increasing clogging and is a function of the location of the clogged area in the PVD. In the parametric study, the PVD was sequentially clogged and its effect studied. The effect of smear was also included in the analysis.
Shear-Induced Changes in Smooth HDPE Geomembrane Surface Topography
Authors: Zettler T.E. , Frost J.D. , DeJong J.T.
Published: October 2014

The shear strength of particulate material-“smooth” high density polyethylene (HDPE) geomembrane interfaces results predominantly from plowing and/or sliding of the particles at the interface. The relative contribution of particle sliding and plowing for a given “smooth” geomembrane surface is principally a function of the relative material hardness, the particle size and angularity, the normal stress, and the soil density. When plowing occurs, the geomembrane surface wears, resulting in altered surface roughness and changed interface strength. This paper summarizes the results of a study that quantified changes in surface roughness as a function of shearing displacement, normal stress, and soil particle shape. Increased particle angularity significantly increased both the geomembrane surface wear and the interface strength. Change in surface topography occurred relatively early in the shearing process with continued displacement inducing additional wear, but not substantially altering the surface roughness further. This study provides quantitative insight into the wear mechanisms of smooth geomembranes during interface shearing.
Hydraulic Design of Geosynthetic and Granular Liquid Collection Layers
Authors: Giroud J.P. , Zornberg J.G. , Zhao A.
Published: October 2014

The present paper provides equations for the hydraulic design of liquid collection layers. A first series of equations gives the maximum thickness of the liquid collected in a liquid collection layer. These equations are used in design to check that the maximum liquid thickness is less than an allowable thickness. Some of the equations make it possible to rigorously calculate the liquid thickness, whereas other equations, which are simpler, give an approximate value of the liquid thickness. A second series of equations makes it possible to calculate the required hydraulic conductivity of the liquid collection layer material and the required hydraulic transmissivity of the liquid collection layer. These equations are useful for selecting the material used to construct the liquid collection layer. The equations provided in the present paper include reduction factors to quantify the decrease in flow capacity of liquid collection layers due to thickness reduction (caused by the applied stresses) and hydraulic conductivity reduction (caused by clogging). Practical recommendations and design examples are presented for both geosynthetic and granular liquid collection layers.
Effect of Thickness Reduction on Geosynthetic Hydraulic Transmissivity
Authors: Giroud J.P. , Zhao A. , Richardson G.N.
Published: October 2014

A new theoretical relationship that quantifies the reduction in hydraulic transmissivity resulting from a reduction in geosynthetic thickness is presented. It is shown that the proposed relationship is in good agreement with experimental data on geotextiles and geonets. This relationship is useful to predict hydraulic transmissivity reduction from the results of compression tests on geosynthetics. This is particularly useful when the thickness reduction is due to creep, because it is impractical to conduct hydraulic transmissivity tests over a long period of time.
Calculation of Flow Velocity in Pipes as a Function of Flow Rate
Authors: Giroud J.P. , Palmer B. , Dove J.E.
Published: October 2014

There are many design situations where the rate of flow in a pipe is known and the average velocity of the liquid in the pipe must be calculated. The classical method to determine the average velocity of flow in pipes as a function of the flow rate is based on Manning's equations. This method requires an iterative process or the use of cumbersome tables or graphs. A direct relationship between the average velocity of flow and the rate of flow in pipes is proposed. To the best of the authors' knowledge, this is the first time that such a direct relationship is proposed. The derivation of the relationship and its practical use are presented. Comparisons of the flow velocities calculated using the proposed relationship and flow velocities rigorously calculated using the iterative process show that a great degree of precision is obtained even when the flow rate is very small compared to the maximum flow capacity of the pipe. This is important because the traditional method is not precise when the flow rate is small, and there are many applications (such as pipes used in leakage collection systems beneath a landfill liner) where liquid flows in a pipe that is almost empty. The proposed method is explicitly analytical and can easily be programmed on a pocket calculator.
Long-Term Variations of Force and Strain in a Steep Geogrid-Reinforced Soil Slope
Authors: Fannin R.J.
Published: October 2014

Instrumentation was used to measure soil temperature and, independently, the force and strain in a steep geogrid-reinforced soil slope. The monitoring period extends to 10 years after construction. A nonlinear increase of force occurs with time that is described by a hyperbolic representation. The elapsed time to achieve force equilibrium was approximately 2.5 × 104 hours (approximately three years). The time-dependent increase of reinforcement force is attributed to deformation of the structure resulting from creep of the backfill sand. Strain in the reinforcement exhibits a complex variation with time. The long-term variation of strain is attributed primarily to: (i) the nonlinear increase of force; and (ii) creep of the geogrid reinforcement. Seasonal temperature fluctuations in the backfill sand may induce additional variations in strain.
Shear Strength Characteristics of PVC Geomembrane-Geosynthetic Interfaces
Authors: Hillman R.P. , Stark T.D.
Published: October 2014

Torsional ring shear and large-scale direct shear tests were conducted to investigate the shear behavior of polyvinyl chloride (PVC) geomembrane-geosynthetic interfaces. Specifically, the smooth and faille-finished sides of a 0.75 mm-thick PVC geomembrane were sheared against five different nonwoven geotextiles, a drainage composite, a geonet, and an unreinforced geosynthetic clay liner (GCL). Test results indicate that the smooth side of the PVC geomembrane yields a higher interface shear resistance than the faille-finished side due to the larger contact area and higher pliability of the smooth side. The interface shear behavior of the PVC geomembrane is compared to that of a high density polyethylene (HDPE) geomembrane and two very flexible polyethylene (VFPE) geomembranes. Faille-finished PVC geomembrane-nonwoven geotextile interfaces experience a post-peak strength loss of less than 25% at normal stresses between 100 and 400 kPa and no post-peak strength loss at normal stresses of 50 kPa and below. This behavior is attributed to the pliability of the PVC geomembrane, which enables (i) the geomembrane surface to be roughened, (ii) the other interface component to embed into the geomembrane as shearing progresses, and (iii) no texturing to be used that can damage the overlying geosynthetic. The effects of nonwoven geotextile fiber type, mass per unit area, and calendering on PVC geomembrane-nonwoven geotextile interface strength are also investigated.
Self-Healing Properties of Geosynthetic Clay Liners
Authors: Sivakumar Babu G.L. , Sporer H. , Zanzinger H. , Gartung E.
Published: October 2014

The sealing effect and containment of moisture in landfill covers and liners containing geosynthetic clay liners (GCLs) are largely influenced by moisture retention, swelling, and the self-healing behaviour of bentonite used in GCLs. The method of binding of GCLs also significantly affects the behaviour. To examine these aspects, percent swell and swell pressure tests under different effective pressures were conducted on two sodium-based GCLs. Permittivity tests were performed on GCL specimens with different hole diameters and also on specimens dried at 20 and 60°C. The test results are presented and discussed. The study shows that the GCLs considered have a good self-healing capacity for the case of desiccation cracks or punctures. In addition, the method of binding the GCL components, i.e., stitch-bonded or needle-punched, has a significant influence.
Measuring the plastic limit of fine soils: an experimental study
Authors: Sivakumar Vinayagamoorthy , O'Kelly Brendan C. , Henderson Laura , Moorhead Catherine , Chow Shiao Huey
Published: October 2014

The Casagrande thread-rolling method for determining the plastic limit of fine-grained soil is heavily dependent on operator judgement and can often give inconsistent or unreliable results. This paper presents an energy-based approach used in the development of an improved testing procedure for the plastic strength limit. A 0·727 kg cone is allowed to fall freely through 200 mm before contacting the surface of the test specimen, with the plastic strength limit determined for a cone penetration depth of 20 mm. For ten mineral clays of intermediate to very high plasticity tested, the plastic limits deduced using the cone were in good agreement with the measured Casagrande plastic limits. The values deduced using an 8 kg contacting cone were consistently lower than the Casagrande limits.
Chemo-hydro-mechanical behaviour of compacted Boom Clay: joint effects of osmotic and matric suctions
Authors: MOKNI N. , ROMERO E. , OLIVELLA S.
Published: October 2014

An experimental programme involving osmotic and matric suction controlled tests is carried out to investigate the effects of increasing pore fluid concentration, chemical cycling (salinisation/dilution) and matric suction on the liquid retention properties, shear strength and volume change behaviour of Boom Clay. This Tertiary Clay formation has been thoroughly investigated as a possible host material for the disposal of Eurobitum bituminised radioactive waste (BW) in Belgium. Within this context chemical impact and partially saturated conditions are studied in a combined way to cover a wide range of in-situ states induced by underground construction, ventilation and diffusion of a large amount of sodium nitrate (NaNO3) (contained in the bituminised waste). Statically compacted specimens are prepared at different sodium nitrate concentrations or are exposed, at constant vertical stress, to sodium nitrate salinisation or pore water dilution. An aggregated structure with a double porosity network is induced on salinisation and subsequent compaction even at high water contents. An increase in pore fluid concentration enhances the aggregation of the microstructure and reduces the liquid retention properties of the material. Results of oedometer tests performed under constant matric suction and increasing osmotic suction show shrinkage of the sample, a decrease of the compressibility and an increase in the preconsolidation stress. Shear strength results have been interpreted using a single constitutive stress (average skeleton stress) to take into account matric suction and chemical effects on degree of saturation and on microstructural changes. A unique linear shear strength failure envelope has been obtained for the tests performed at different osmotic and matric suctions. The modification of the liquid retention behaviour of the material induced by salinisation has proven to be a crucial aspect for the interpretation of the obtained results.
What Can the World Health Organization Learn from EU Lessons in Civil Society Engagement and Participation for Health?
Authors: Battams“ Samantha
Published: October 2014

This article explores challenges for and the development of civil society engagement and stakeholder representation, transparency, and accountability measures in the European Union, with a specific focus on health policy. The stance of the European Union on stakeholder participation within reform debates of the World Health Organization (WHO) is also considered, along with EU lessons for multi-stakeholders at the WHO. The European Commission has developed a number of measures for stakeholder engagement and transparency; however, the European Union has been prone to lobbying interests and has found difficulty in leading and making accountable the private sector when it comes to achieving its own health policy goals. The strong influence of corporate lobbyists on the European Union has come to light, with concerns about a lack of transparency and accountability in decision-making processes. While the WHO could learn from the European Union in terms of its strategies for stakeholder engagement, it could also heed some of the important lessons for the European Union when it comes to working with a broad range of stakeholders.
Exploring Textile Traditions, Gender Shifts, and Social Capital in the American Southwest
Authors: Jolie Ruth Burgett
Published: October 2014

Gender is fundamental to the organization of labor. Cross-culturally, women are often the producers of textile arts. Several researchers have argued that men take over the means of textile production when a society is dominated by a market economy. However, in non-state level societies lacking market economies there are cases where men assume the role of primary textile producer. Examining these gender shifts illuminates how gendered textile production affects the social status of men and women. Archaeological and ethnographic data suggest that in such contexts, as among middle-range societies in the American Southwest, weaving may have taken on ritual or symbolic significance that increased opportunities for the weaver to accumulate social capital that was more important than economic capital. In this article, connections between the gendered division of labor, textile traditions, and the accumulation of social capital within non-state societies are examined using Hopi peoples as a case study.
Human Chronic Gonadotropin Concentrations in Very Early Pregnancy and Subsequent Preeclampsia
Authors: Rabie Nader Z , Magann Everett F
Published: October 2014

Evaluation of: Asvold BO, Vatten LJ, Tanbo TG, Eskild A. Concentrations of human chorionic gonadotrophin in very early pregnancy and subsequent preeclampsia: a cohort study. Hum. Reprod. 29(6), 1153-1160 (2014). A total of 2405 consecutive singleton pregnancies were followed to determine if early HCG levels were associated with the development of preeclampsia. All pregnancies were conceived by in vitro fertilization, which allowed very accurate gestational age dating. HCG levels were obtained on day 12, and grouped into four categories (<50, 50-99, 100-149, >150). HCG levels less than 50 were associated with an odds ratio of 2.3 (95% CI: 1.2-4.7) for preeclampsia and and odds ratio of 4.2 (95% CI: 1.4-12.2) for severe preeclampsia. Early HCG levels may serve as a marker for the detection of preeclampsia.