Most Cited Geotextiles and Geomembranes Articles
The most cited articles published since 2010, extracted from Scopus.
Volume 28, Issue 2, April 2010, Pages 149-162
Charles D. Shackelford | Gerald W. Sevick | Gerald R. Eykholt
The results of a comprehensive testing program conducted to evaluate the hydraulic conductivity (k) of two geosynthetic clay liners (GCLs) considered as a liner component for a tailings impoundment at a proposed zinc and copper mine are reported. The two GCLs were permeated with a relatively low ionic-strength ground water (GW) from the mine site and two electrolyte solutions, a process water (PW) and a simulated leachate (SL), with chemical compositions consistent with those expected during operation of the impoundment. A total of 22 flexible-wall tests were performed to determine the effects of prehydration with the GW, type of GCL, type of permeant liquid, and duration of the back-pressure stage of the test. The k values for both GCLs permeated with the GW were 1.7 × 10 -9 cm/s, which is within the range 1-3 × 10 -9 cm/s typically reported for GCLs permeated with low ionic-strength liquids, such as deionized water. However, the mean values of k based on permeation of duplicate specimens of both types of GCL with either PW or SL relative to the values of k based on permeation with GW, or k/k w, ranged from a factor of 200 (2.3 orders of magnitude) to a factor of 7600 (3.9 orders of magnitude). Thus, both tailings impoundment solutions had significant adverse impacts on the hydraulic performance of both GCLs. Given the overall range of k/k w values, factors such as prehydration, type of GCL, type of permeant liquid, and duration of back pressure, were relatively insignificant. The results of this study serve to emphasize the need to perform hydraulic conductivity testing using site specific materials. © 2009 Elsevier Ltd. All rights reserved.
Volume 28, Issue 3, June 2010, Pages 238-250
A. Diambra | E. Ibraim | D. Muir Wood | A. R. Russell
Sand reinforced with short polypropylene fibres has been tested in conventional triaxial compression and extension. The contribution of fibres to the strength was remarkable in compression while limited in extension confirming that it depends primarily on their orientation with respect to tensile strains. A modelling approach is proposed for coupling the effects of fibres with the stress-strain behaviour of unreinforced soil. It is necessary to define a fibre stiffness matrix and in this investigation it is assumed that fibres are working in their elastic domain. Any distribution of fibre orientations can be accounted for. The sand stiffness matrix is based on the Mohr Coulomb model although more elaborate models could be used. The constitutive model for the fibre-sand composite is calibrated against the results of drained triaxial compression and extension tests. Despite the simplistic nature of the Mohr-Coulomb assumptions for the sand matrix, simulations show how the influence of fibre orientation with respect to the strain conditions is captured and provide good agreement with experimental data. © 2009 Elsevier Ltd.
Investigation of factors influencing behavior of single geocell-reinforced bases under static loading
Volume 28, Issue 6, December 2010, Pages 570-578
Sanat K. Pokharel | Jie Han | Dov Leshchinsky | Robert L. Parsons | Izhar Halahmi
Geocell, one type of geosynthetics manufactured in the form of three-dimensional interconnected cells, can be used as a reinforcement to improve the behavior of base courses by providing lateral confinement to increase their stiffness and strength and reduce surface permanent-deformation. However, the use of geocells for base reinforcement is hindered by the existing gap between applications and theories. This study experimentally investigated the factors influencing the behavior (stiffness and bearing capacity) of single geocell-reinforced bases including shape, type, embedment, height of geocells, and quality of infill materials. Three of the four types of geocells investigated in this study were made of novel polymeric alloys using a new manufacturing technology. Repeatability and potential scale effects on test results were examined. The test results showed that the geocell placed in a circular shape had a higher stiffness and bearing capacity than that placed in an elliptical shape. The performance of the geocell-reinforced base depended on the elastic modulus of the geocell sheet. The unconfined geocell had a lower stiffness but a higher ultimate load capacity than the confined geocell. The benefit of the geocell was minimized when the infill material, quarry waste with apparent cohesion, was used as compared with the Kansas River sand without apparent cohesion. The single geocell-reinforced base had a lower stiffness and bearing capacity than the multiple geocell-reinforced base. © 2010 Elsevier Ltd.
Volume 29, Issue 6, December 2011, Pages 525-533
M. T. Rayhani | R. K. Rowe | R. W I Brachman | W. A. Take | G. Siemens
The hydration of different GCLs from the pore water of the underlying foundation soil is investigated for isothermal conditions at room temperature. Results are reported for three different reinforced (needle punched) GCL products. Both a silty sand (SM) and sand (SP) foundation soil are examined. GCL hydration is shown to be highly dependant on the initial moisture content of the foundation soil. GCLs on a foundation soil with a moisture content close to field capacity hydrated to a moisture content essentially the same as if immersed in water while those on soil at an initial moisture content close to residual only hydrated to a gravimetric moisture content of 30-35%. The method of GCL manufacture is shown to have an effect on the rate of hydration and the final moisture content. The presence or absence of a small (2 kPa) seating pressure is shown to affect the rate of hydration but not the final moisture content. The GCL hydration did not change significantly irrespective of whether a nonwoven cover or woven carrier GCL rested on the foundation soil. © 2011 Elsevier Ltd.
Volume 28, Issue 1, February 2010, Pages 54-62
Chao Sheng Tang | Bin Shi | Li Zheng Zhao
The interfacial mechanical interaction between the reinforcement and soil matrix is a key factor in controlling the engineering properties of reinforced soil. To evaluate the factors affecting the interfacial strength properties of polypropylene fiber (PP-fiber) reinforced soil, single fiber pull-out tests were performed by using a modified special apparatus. It has been found that the designed pull-out test is an efficient method to qualitatively obtain the interfacial peak strength (IPS) and interfacial residual strength (IRS) of fiber/soil. Both the IPS and IRS decrease with water content increase, while increase with increasing soil dry density. The cement inclusions dramatically improve the interfacial shear strength of fiber/soil, and the IPS and IRS increase with an increase in additives content and curing time. Finally, by using scanning electron microscopy (SEM), the micromechanical interaction behavior between soil particles and fiber reinforcement were discussed. The interfacial shear resistance of fiber/soil depends primarily on the rearrangement resistance of soil particles, effective interface contact area, fiber surface roughness and soil compositions, etc. © 2009 Elsevier Ltd. All rights reserved.
Measured and predicted performance of prefabricated vertical drains (PVDs) with and without vacuum preloading
Volume 28, Issue 1, February 2010, Pages 1-11
J. Saowapakpiboon | D. T. Bergado | S. Youwai | J. C. Chai | P. Wanthong | P. Voottipruex
This paper presents the effectiveness of vacuum preloading in accelerating the consolidation of PVD improved soft Bangkok clay by comparing with the corresponding results without vacuum preloading. Laboratory tests were conducted using a large scale consolidometer having diameter of 300 mm and height of 500 mm with reconstituted specimens installed with prefabricated vertical drains (PVD) with and without vacuum preloading. In addition, field data were collected from Second Bangkok International Airport (SBIA) site improved by PVD with and without vacuum pressures. Analyses were carried out to compare the compressibility parameters (Ch and kh/ks) by back-calculation of laboratory and field settlements using Hansbo (1979) method. From the laboratory tests, the horizontal coefficient of consolidation (Ch) values from reconstituted specimens were 1.08 and 1.87 m2/yr for PVD without and with vacuum pressure, respectively and the kh/ks values were 2.7 for PVD only and 2.5 for vacuum-PVD. After the improvement, the water contents of the soft clay were reduced, thereby, increasing its undrained shear strengths. Similarly, the field data analysis based on the back-calculated results showed that the kh/ks were 7.2 and 6.6 for PVD without and with vacuum, respectively. The Ch values increased slightly from 2.17 m2/yr for PVD only to 3.51 m2/yr for vacuum-PVD. The time to reach 90% degree of consolidation for soils with vacuum-PVD was one-third shorter than that for soils with PVD only because of higher Ch values. Thus, the addition of vacuum pressure leads to increase horizontal coefficient of consolidation which shortened the time of preloading. The PVDCON software was found to be useful to predict the settlements of the PVD improved ground with and without vacuum preloading. © 2009 Elsevier Ltd. All rights reserved.
Comparison of bearing capacity of a strip footing on sand with geocell and with planar forms of geotextile reinforcement
Volume 28, Issue 1, February 2010, Pages 72-84
S. N Moghaddas Tafreshi | A. R. Dawson
Comprehensive results from laboratory model tests on strip footings supported on the geocell and planar reinforced sand beds with the same characteristics of geotextile are presented. The various parameters studied in this testing program include the reinforcement width, the number of planar layers of geotextile and height of the geocell below the footing base. Contrary to other researches, the performance of the geocell and planar reinforcement is investigated at the range of low to medium settlement level, similar to those of interest in practice. The results show that the efficiency of reinforcement was decreased by increasing the number of the planar reinforcement layers, the height of the geocell reinforcement and the reinforcement width. For the same mass of geotextile material used in the tests at the settlement level of 4%, the maximum improvement in bearing capacity (IF) and percentage reduction in footing settlement (PRS) were obtained as 2.73 and 63% with the provision of geocell, respectively, while these values compare with 1.88 and 47% for the equivalent planar reinforcement. On the whole, the results indicate that, for the same quantity of geotextile material, the geocell reinforcement system behaves much stiffer and carries greater loading and settles less than does the equivalent planar reinforcement system. Therefore, a specified improvement in bearing pressure and footing settlement can be achieved using a lesser quantity of geocell material compared to planar geotextile. © 2009 Elsevier Ltd.
Volume 28, Issue 3, June 2010, Pages 292-302
S. R. Lo | R. Zhang | J. Mak
This paper presents the findings of a series of numerical studies on the contribution of geosynthetic encasement in enhancing the performance of stone columns in very soft clay deposits. In this study, the imposed loading is from a fill embankment, and the stone columns act like reinforcements. Observed settlement of a trial embankment built on very soft clay strengthened with stone columns indicated that the stone columns alone were not adequately effective in reducing settlement because the very softy clay could not provide adequate confining stress to the stones. An alternative system utilizing geosynthetic encasement was examined numerically. As the primary issue is the development of settlement with time after the completion of stone column installation, a fully coupled analysis was performed. To reduce the computational effort, a unit cell idealization was adopted. This study showed that the use of geosynthetic encasement has the potential of significantly enhancing the effectiveness of stone columns in very soft clay and the simplified analysis presented in earlier work is valid. Furthermore, the predicted performance was found to be insensitive to assumed stiffness parameters of the compacted stone. However, it was found to be dependent on the locked-in stress in the geosynthetic encasement induced during installation. © 2009 Elsevier Ltd.
Volume 28, Issue 2, April 2010, Pages 206-218
C. H. Benson | A. H. Ören | W. P. Gates
GCLs containing powdered Na-bentonite treated with different dosages of a proprietary additive intended to reduce the impacts of chemical interactions were permeated with three solutions: a hyperalkaline solution (1 M NaOH and 1.3 mM CsCl) having similar pH to aluminum refining leachate, a 1.3 mM CsCl solution (no NaOH), and DI water. For a given permeant solution, the hydraulic conductivity of both GCLs was similar. Thus, the higher additive dosage had no measureable impact on hydraulic conductivity. Hydraulic conductivity of both GCLs decreased by a factor of approximately 1.5-1.8 during permeation with CsCl in response to osmotic swelling induced by the low ionic strength of the CsCl solution entering the pore space. In contrast, permeation with the NaOH-CsCl solution caused the hydraulic conductivity of both GCLs to increase modestly (<50 times the hydraulic conductivity to DI water), and then level out (or decrease slightly) as a result of reduced osmotic swelling in the interlayer combined with dissolution of the mineral. For the tests conducted with CsCl solution, nearly all of the Cs was adsorbed by the bentonite. In contrast, Cs broke through readily when the NaOH-CsCl solution was used as the permeant solution. Permeation with the NaOH-CsCl solution also increased the sodicity of the bentonite by replacing bound K, Ca, and Mg on the mineral surface. © 2009 Elsevier Ltd. All rights reserved.
Volume 29, Issue 3, June 2011, Pages 345-359
S. J M van Eekelen | A. Bezuijen | A. F. van Tol
The piled embankment is an increasingly popular construction method. The Dutch Design Guideline for piled embankments (CUR 226) was published in the first half of 2010. Several existing models have been analysed to determine the calculation rules used in the Dutch Guideline. The British Standard BS8006 sometimes calculates tensile forces in the geosynthetic reinforcement that differ considerably from other models. For quite thin embankments in particular, BS8006 designs a relatively strong and thus expensive geosynthetic (basal) reinforcement in comparison with other design models. These differences are not always fully understood, leading to uncertainty. This paper analyses BS8006 and demonstrates why it behaves differently from other models. It also examines why this behaviour is different than would be expected. For example, it is shown that calculations using BS8006 are based on a higher load than the actual load. A modification to BS8006 is proposed, which is shown to give comparable results to the German Standard EBGEO for situations where there is no subsoil support. The results of BS8006, Modified BS8006, and the German/Dutch guideline are compared with finite element calculations and field measurements. It is concluded that the results given by the Modified BS8006 are more accurate to those using BS8006. © 2011 Elsevier Ltd.
Volume 28, Issue 1, February 2010, Pages 93-99
Fauziah Ahmad | Farshid Bateni | Mastura Azmi
Triaxial compression tests were conducted to evaluate the response of randomly distributed fibre on the strength of reinforced silty sand. In this study, oil palm empty fruit bunch (OPEFB) fibre was mixed with silty sand soil to investigate the increase of shear strength during triaxial compression. The specimens were tested under drained and undrained conditions with 0.25% and 0.5% content of OPEFB fibres of different lengths (i.e. 15 mm, 30 mm and 45 mm). In addition, OPEFB fibres coated with acrylic butadiene styrene thermoplastic were tested to determine the effect of coating on reinforcement. Inclusion of randomly distributed discrete fibres significantly improved the shear strength of silty sand. Coated OPEFB fibres increased the shear strength of silty sand much more compared to uncoated fibres. Coating fibres increases interface friction between fibre and soil particles by increasing the surface area. Reinforced silty sand containing 0.5% coated fibres of 30 mm length exhibited approximately 25% increase in friction angle and 35% in cohesion under undrained loading conditions compared to those of unreinforced silty sand. The results indicate that the shear strength parameters of the soil-fibre mixture (i.e. Φ′ and c′) can be improved significantly. © 2009 Elsevier Ltd. All rights reserved.
Volume 28, Issue 5, October 2010, Pages 475-482
Ling Zhang | Minghua Zhao | Caijun Shi | Heng Zhao
Soil reinforcement using geocells has been utilized in many areas of geotechnical engineering. In this paper, a model and a simple bearing capacity calculation method for the geocell-supported embankment on the soft subgrade were proposed based on the study of the reinforcement functions of a geocell layer in a road embankment. The model and calculation procedures considered both the " vertical stress dispersion effect" and " membrane effect" of geocell reinforcement. They were verified by a laboratory experiment and compared with Koerner's method. The results indicated that the calculated results obtained from the present method were much closer to the experimental results than those from Koerner's method when the foundation settlement is large. The study also indicated that the installation of the geocell onto the crushed stone cushion significantly increased the bearing capacity of the soft subgrade. © 2009 Elsevier Ltd.
Volume 29, Issue 1, February 2011, Pages 29-39
Boštjan Pulko | Bojan Majes | Janko Logar
This paper presents a newly developed design method for non-encased and encased stone columns. The developed analytical closed-form solution is based on previous solutions, initially developed for non-encased columns and for non-dilating rigid-plastic column material. In the present method, the initial stresses in the soil/column are taken into account, with the column considered as an elasto-plastic material with constant dilatancy, the soil as an elastic material and the geosynthetic encasement as a linear-elastic material. To check the validity of the assumptions and the ability of the method to give reasonable predictions of settlements, stresses and encasement forces, comparative elasto-plastic finite element analyses have been performed. The agreement between the two methods is very good, which was the reason that the new method was used to generate a parametric study in order to investigate various parameters, such as soil/column parameters, replacement ratio, load level and geosynthetic encasement stiffness on the behaviour of the improved ground. The results of this study show the influence of key parameters and provide a basis for the rational predictions of settlement response for various encasement stiffnesses, column arrangements and load levels. The practical use of the method is illustrated through the design chart, which enables preliminary selection of column spacing and encasement stiffness to achieve the desired settlement reduction for the selected set of the soil/column parameters. © 2010 Elsevier Ltd.
Behaviour of footings on reinforced sand subjected to repeated loading - Comparing use of 3D and planar geotextile
Volume 28, Issue 5, October 2010, Pages 434-447
S. N Moghaddas Tafreshi | A. R. Dawson
This paper describes a series of laboratory model tests performed on strip footings supported on 3D and planar geotextile-reinforced sand beds under a combination of static and repeated loads. Footing settlement due to initial static applied load and up to 20,000 subsequent load repetitions was recorded, until its value becomes stable or failure occurred due to excessive settlement. The response under the first few cycles was found to be a significant behavioral characteristic of footings under repeated loads. The influence of various amplitudes of repeated load on foundations containing different numbers of planar geotextile layers and different heights of the 3D geotextile reinforcement were investigated. Most of the observed responses show plastic shakedown developing - that is a stable, resilient response is observed once incremental plastic strains under each load repetition have ceased to accumulate. The results show that the maximum footing settlement due to repeated loading is comparable for either planar- or 3D-reinforced sand and much improved over the settlement of unreinforced sand. The efficiency of reinforcement in reducing the maximum footing settlement was decreased by increasing the mass of reinforcement in the sand. On the whole, the results indicate that, for the same mass of geotextile material used in the tests, the 3D geotextile reinforcement system behaves more effectively than planar reinforcement as a retardant for the effects of dynamic loading. Thus, a specific improvement in footing settlement can be achieved using a lesser quantity of 3D geotextile material compared to planar geotextile. © 2009 Elsevier Ltd.
Volume 28, Issue 2, April 2010, Pages 219-225
W. P. Gates | A. Bouazza
Strongly alkaline solution pH causes changes to the mineralogy of bentonites which might impact on their performance as environmental barriers. The long term effect of solution pH on the performance of bentonite barriers such as in Geosynthetic Clay Liners needs to be studied from the viewpoint of solubility and stability of the mineral phases present at extreme pH values. Changes to bentonite mineralogy brought about by extended reaction with 1 M sodium hydroxide solutions at 20-25 °C reveal that certain components of bentonites, namely smectite, opaline silica and quartz, are subject to dissolution in alkaline solution. Associated with dissolution is the formation of hydrous hydroxy-aluminosilicate as well as hydrous carbonate mineral phases. It is postulated that these precipitates, formed from reaction of bentonite with alkaline leachates can result in pore filling, which is responsible for recently measured lower hydraulic conductivity of some bentonites to high pH leachates. © 2009 Elsevier Ltd. All rights reserved.
Volume 28, Issue 2, April 2010, Pages 199-205
K. Lange | R. K. Rowe | H. Jamieson
Combined passive treatment technologies have been used to treat acidic rock drainage (ARD), the well-known acute and costly environmental problem facing the mining industry. It is shown that geosynthetic clay liners (GCLs) were able to attenuate metals from lime treated ARD water, and maintain a neutral pH and low hydraulic conductivity (less than 4.0 × 10-11 m/s) after 16 pore volumes of permeation; this implies their usefulness as a potentially significant component in combined passive treatment systems. Presented are laboratory breakthrough data for Cu, Cd, Ni, Mn, and Zn from the permeation of GCLs with 16 pore volumes of ARD, treated ARD (TARD), and a landfill leachate. Metal retention occurred in all solutions, but was greatest for the TARD, producing removal efficiencies of greater than 80%. © 2009 Elsevier Ltd. All rights reserved.
Volume 28, Issue 2, April 2010, Pages 191-198
W. P. Hornsey | J. Scheirs | W. P. Gates | A. Bouazza
Mine owners and operators are presented today with a diverse range of geosynthetic products which all appear to provide similar benefits. Key factors in selecting geosynthetics for use in the mining industry include construction and operational durability issues such as slope stability, puncture resistance and resistance to weathering; but also their chemical resistance when they come into contact with the extreme liquors present on many mining operations and processes. The long-term performance of the geosynthetic depends largely on the type of polymer used in the manufacture, or in the case of geosynthetic clay liners (GCLs), also on the mineralogy and chemical make of the bentonite present in the GCL. This paper provides a guide to the characteristics of the leachates/liquors likely to be generated for a given mining process and the likely effect it will have on the performance of a given geosynthetic. © 2009 Elsevier Ltd. All rights reserved.
Investigation of geotextile-soil interaction under a cyclic vertical load using the discrete element method
Volume 28, Issue 1, February 2010, Pages 33-43
Anil Bhandari | Jie Han
Geotextiles are often used in roadway construction as separation, filtration, and reinforcement. Their performance as reinforcement in geotextile-reinforced bases depends on geotextile-soil interaction. This paper investigates the geotextile-soil interaction under a cyclic wheel load using the Discrete Element Method (DEM). In this study, soil was modeled as unbonded particles using the linear contact stiffness model, and the geotextile was modeled as bonded particles. The micro-parameters of the soil and the geotextile were determined using biaxial tests and a tensile test, respectively. The influence of the placement depth and the stiffness of the geotextile on the performance of the reinforced base was investigated. The DEM results show that the depth of the geotextile significantly affected the degree of interaction between the geotextile and the soil. Under the applied cyclic vertical load, the geotextile developed a low tensile strain. The effect of the stiffness of the geotextile on the deformation was more significant when the geotextile was placed at a shallower location than when placed at a deeper location. © 2009 Elsevier Ltd. All rights reserved.
Volume 28, Issue 4, August 2010, Pages 374-385
E. Ibraim | A. Diambra | D. Muir Wood | A. R. Russell
This paper explores the possibility of improving the monotonic undrained response of a loose clean sand which normally appears susceptible to the phenomenon of static liquefaction by mixing the sand with discrete flexible fibres. It is shown that the reinforcement inclusions reduce the potential for the occurrence of liquefaction in both compression and extension triaxial loadings and convert a strain softening response (typical for a loose unreinforced sand) into a strain hardening response. Fibre orientation distribution and the apparent sand matrix densification due to the presence of fibres in the voids appear important for the fibre reinforced soil behaviour. Normalisation of the effective stress paths with the mean effective stress at the end of consolidation shows a common path once the characteristic state is reached irrespective of the fibre concentration. The mobilised angles of friction coming from the slopes of the stress paths at large strains are very different for compression and extension and this is a consequence of the anisotropic nature of the distribution of fibre orientations. When full liquefaction of reinforced specimens is induced by strain reversal, the lateral spreading of soil seems to be prevented. Analytical developments including the key aspect of fibre orientation distribution, have shown that once the tensile contribution of fibres has been taken out of the composite stresses, the experimental data in the stress plane for all the tests at large shear strains nicely collapse onto a unique line corresponding very closely to the mobilised steady state or critical state angle of friction of the tested sand. © 2009 Elsevier Ltd.
Volume 28, Issue 6, December 2010, Pages 536-546
Craig H. Benson | I. Emre Kucukkirca | Joseph Scalia
Samples of geocomposite drain (GCD), geomembrane (GM), and geosynthetic clay liner (GCL) were exhumed from a final cover at a solid waste landfill to assess their condition after 4.7-5.8 yr of service. Permittivity of the GCD diminished by a factor of 3.9, but the transmissivity was higher than published by the manufacturer. Ply adhesion of the GCD diminished by a factor of 2.0. Geonet ribs in the geocomposite drain (GCD) contained a light coating of fines and plant roots, but there was no evidence of significant clogging. The geotextile on the upper surface of the GCD met the commonly used criterion for filtration (AOS < 0.6 mm for adjacent soil with <50% fines), indicating that this filtration criterion was satisfactory. Tensile yield strength of the GM diminished by a factor of 1.2, but the melt flow index was unchanged and the oxidation induction time exceeded the manufacturer's specification. GCD-geomembrane interface strength appeared unchanged. Four GCL samples had hydraulic conductivities 1000-10,000 times higher than the hydraulic conductivity measured during construction, whereas hydraulic conductivity of the other seven samples was practically unchanged. Based on these observations, the following reduction factors are suggested for installation damage and near-term service conditions (<6 yr) for the geosynthetics used at this site: GCD permittivity or transmissivity - 4.0, GCD ply adhesion - 2.0, geomembrane tensile strength - 1.5, and GCD-geomembrane interface friction - 1.0. No recommendation is made regarding a factor for the hydraulic conductivity of GCLs. © 2010 Elsevier Ltd.
Volume 30, Issue , February 2012, Pages 16-23
B. Indraratna | C. Rujikiatkamjorn | A. S. Balasubramaniam | G. McIntosh
Application of vacuum assisted preloading is an imperative method when a considerable load is required to meet the desired rate of settlement and an increase in the undrained shear strength upon consolidation. Moreover, where lateral displacements at the edge of a coastal embankment need to be controlled, application of vacuum pressure with a cut off offers the optimum solution. To facilitate vacuum propagation, vertical drains are usually employed in conjunction. The installation of vertical drains using a steel mandrel creates significant remoulding of the subsoil surrounding the drains thereby, reducing soil permeability and adversely affecting the soil consolidation process. In this paper, the simulation of vacuum assisted consolidation using the spectral method and finite element analysis is carried out. Subsequently, the 2D and 3D numerical multi-drain analyses are conducted to predict the excess pore pressures, lateral and vertical displacements. The performance of two selected case histories at the sites of Suvarnabhumi Airport, Thailand and Tianjin Port, China are discussed and analysed. The numerical predictions are then compared with the available field data. Finally, a procedure for the design of vertical drains is presented with a worked-out example. © 2011.
Volume 29, Issue 1, February 2011, Pages 74-82
J. Saowapakpiboon | D. T. Bergado | P. Voottipruex | L. G. Lam | K. Nakakuma
This paper presents the study of PVD improved reconstituted specimen with and without vacuum preloading on large-scale consolidometer in the laboratory tests. Subsequently, the results of the laboratory tests were analyzed and simulated by 2D (axisymmetric) finite element method (FEM) to back-analyze and confirm the related design parameters which were used further in subsequent numerical experiments. The laboratory test results indicated that the increased hydraulic conductivity in the smear zone of PVD with vacuum preloading (Vacuum-PVD) resulted in the increase in the coefficient of horizontal consolidation (Ch) by 16% as well as the decrease in the ratio between the horizontal hydraulic conductivity of the undisturbed zone (Kh) to the horizontal hydraulic conductivity in the smear zone (Ks) or (Kh/Ks) of about 10%. The Vacuum-PVD and PVD only have the same settlement magnitudes with similar equivalent loads. © 2010.
Volume 32, Issue , June 2012, Pages 69-81
S. J M Van Eekelen | S. J M Van Eekelen | A. Bezuijen | H. J. Lodder | H. J. Lodder | A. F. Van Tol | A. F. Van Tol
A series of twelve 3D laboratory model tests was performed on piled embankments. In this first part of a two-part study, the measured load distribution, deformation, and strains are presented and analysed. In the second part, the measurements are compared with calculations using EBGEO (2010), and suggestions are given for improvements to this calculation model.In the test series, the vertical load parts on the piles, on the geosynthetic reinforcement (GR), and on the subsoil could be measured separately. This makes it possible to compare the test results with the separate parts of the analytical models. For the test conditions (static load, laboratory scale), smooth relationships were obtained between the net load on the fill (top load on fill minus subsoil support) and several measured parameters, such as load distribution and deformation. Consolidation of the subsoil resulted in an increasing load transferred through the GR, and also an increase of arching. The measured response to consolidation depends on the fill's friction angle. A higher friction angle gives more arching during consolidation.Loading on the geosynthetic reinforcement is concentrated on the strips lying above and between adjacent piles (the " GR strips" ). The line load on a GR strip has the distribution of an inverse triangle, although the load may be even more concentrated around the pile caps than this indicates. This follows from the measured shape of the deformed GR.A geogrid gives negligible differences in comparison with a geotextile. No difference is found between the use of a single biaxial grid layer and two uniaxial grid layers positioned directly on top of each other. Only limited differences were found between a situation with one grid layer, and one where two grid layers were used with a layer of granular material in between. © 2011 Elsevier Ltd.
Volume 29, Issue 3, June 2011, Pages 222-232
Liping Wang | Ga Zhang | Jian Min Zhang
The behavior of geotextile-reinforced embankments during an earthquake was investigated using centrifuge model tests, considering a variety of factors such as gradient of slope, water content of soil, geotextile spacing, and input shaking wave. The geotextile-reinforcement mechanism was revealed on the basis of the observations with comparison of the unreinforced embankment. The geotextile significantly decreases the deformation of the embankment and restricts sliding failure that occurs in the unreinforced embankment during an earthquake. The displacement exhibits an evidently irreversible accumulation with a fluctuation during the earthquake which is significantly dependent on the magnitude of input shaking. The peak strain of the geotextile exhibits a nearly triangular distribution in the vertical direction. The embankment can be divided into two zones, a restricting zone and restricted zone, where the soil and geotextile, respectively, play an active restriction role in the soil-geotextile interaction. The soil restricts the geotextile in the restricting zone, and this restriction is transferred to the restricted zone through the geotextile. The strain magnitude of the geotextile and the horizontal displacement of the geotextile-reinforced embankment decrease with increasing geotextile layers, with decreasing water content of the soil, with decreasing gradient of the slope, and with decreasing amplitude of the earthquake wave. © 2010 Elsevier Ltd.
Volume 32, Issue , June 2012, Pages 95-103
Xiaoming Yang | Xiaoming Yang | Jie Han | Sanat K. Pokharel | Sanat K. Pokharel | Chandra Manandhar | Chandra Manandhar | Robert L. Parsons | Dov Leshchinsky | Izhar Halahmi
Accelerated pavement testing (APT) is an effective method in evaluating pavement performances by applying controlled wheel loading under environmental conditions. This note presents the findings from an accelerated pavement test on unpaved road sections involving geocell reinforcement of sand bases. A total of four unpaved road sections were constructed. Sections 1 and 4 were unreinforced sections first with sand bases and then replaced with aggregate bases after failure. Sections 2 and 3 were sand sections reinforced with novel polymeric alloy (NPA) geocell under an aggregate cover layer. Rut depths developed in each section were measured after a certain number of wheel passes. Horizontal strains at different locations in the NPA geocell were monitored by strain gages. Test results demonstrated that the NPA geocell had a significant effect in improving the stability of unpaved roads and reducing the permanent deformation. Under the particular test condition, the NPA geocell-reinforced sand layer behaved equivalently to the A-1-a aggregate of the same thickness. The deformations of the geocell-reinforced road sections were analyzed. The test also revealed the importance of keeping the geocell structure intact to ensure the adequate performance of NPA geocell-reinforced bases. Strain gage measurements showed that the NPA geocell beneath the wheel path experienced tensile stresses whereas the geocell outside the wheel path experienced compressive stresses. © 2011 Elsevier Ltd.