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The increasing use of geogrid in various geotechnical projects has made the evaluation of the shear behavior of soil reinforced with geogrid become particularly important. In this article, a series of large-scale direct shear tests have been performed on sand and gravel samples reinforced with geogrid. The purpose of the experiments was to investigate the impact of the geogrid mesh size and the relative density of the samples on the shear strength coefficient of the interface between soil and geogrid. In this study, 5 geogrids with different mesh sizes and one type of geotextile were used. According to the results, the average shear strength coefficient of sand and gravel samples reinforced with geogrid for different normal stresses and different relative densities was obtained between 0.72 and 0.94. As the relative density increases, the interface shear strength coefficient decreases, this means that the denser the sand, the more the shear strength of the sand/geogrid interface decreases. Based on the results, it was found that the contribution of particle interlocking in the shear resistance of the sand/geogrid interface is particularly important, so that the shear resistance coefficient of the interface increases with the increase in the size of the geogrid mesh. [ABSTRACT FROM AUTHOR]

This paper provides insight into the causes of post-peak strength loss for textured geomembrane (GMX) and nonwoven geotextile (NGT) interfaces. The NGT can be part of a geosynthetic drainage composite (GDC) or a stand-alone NGT. The study used ring shear tests where one of the two interface materials was replaced after reaching a residual strength condition and the test was restarted to measure the change in interface strength. The interface strength loss from peak to large displacement (LD) strength primarily comes from three mechanisms: (1) geomembrane wear, (2) breakage and combing of fibers in the NGT, and (3) reduction of the hook and loop effect between GMX asperities and fibers of the NGT. The source of interface strength loss from LD strength to the residual value mainly comes from breakage and continuous combing of NGT fibers parallel to the direction of shear in ring shear tests. Scanning electron microscopy photographs of the GMX and NGT before and after shearing confirm wear and smoothing of GMX asperities and the combing of NGT fibers in the direction of shear. [ABSTRACT FROM AUTHOR]

In this study, we proposed a new method for preventing the uplift of a pipe using geocells, to improve the workability of the pipelines and increase the uplift resistance. As a fundamental study, push-up tests were conducted on the model pipe to verify the effectiveness of the geocell reinforcement. The experimental results showed that geocell reinforcement increased the peak resistance by more than 1.5 times and the resistance at large displacement (at a displacement of 40 mm) by more than 3 times at maximum, compared to the unreinforced method, indicating that geocell reinforcement is an effective countermeasure against pipe uplift. The combination of geocells and geotextiles increased the resistance at large displacement (at a displacement of 40 mm) by 1.41 times more than only geocell, contributing significantly to the increase in uplift resistance. In particular, increasing the number of geocells downward from the top of the pipe (on the side of the pipe), and integrating the left and right geocells with the geotextile, increased considerably the peak resistance and resistance at large displacement (at a displacement of 40 mm). • Novel method to prevent uplift of pipes using geocells proposed. • Geocell reinforcement achieves greater resistance against pipe uplift. • Better resistance achieved when there are more geocells below the top of the pipe. • Uplift resistance increased greatly with a combination of geocell and geotextile. [ABSTRACT FROM AUTHOR]

Introduction/purpose: Geosynthetic materials have been successfully used for soil reinforcement to improve bearing capacity. In this article, geotextiles are used as tension material for the reinforcement of a mixture based on dredged sediment from the Cheurfas dam (Mascara) and quarry sand. Methods: Immediate bearing index tests were carried out in the laboratory to study the mixing behaviour, and the three-point bending flexural test was carried out on prismatic specimens to study the traction capacity of the mixture. Mixture samples are selected and tested without reinforcement. Then, by placing one, two and three layers of geotextile at a certain depth of the sample, the effects of a number of layers and type of geotextile and geogrid on increasing the bearing capacity of the mixture are discussed. Results: The results of these tests show that the bearing capacity of the samples reinforced by geotextile and geogrid is increased compared to that of the unreinforced samples. Based on the results obtained from ProctorIPI, their values do not permit the movement of construction machinery during the construction of pavement layers. The Immediate Bearing Index values are found sufficient for pavement layers. Geotextile introduction increases traction strength and improves stress distribution on soil samples, with the effect being significant for woven geotextile blends. Conclusion: All things considered, the results point to the possibility of using reinforced local soils as an affordable and practical option for building pavements. To guarantee long-term performance and optimise building methods, more research is advised. [ABSTRACT FROM AUTHOR]

Geosynthetic materials (i.e., geogrids, geotextiles and other geocomposites) act as an interlayer system and are widely used in construction applications. In pavement structures, geosynthetic layers provide potential benefits such as reinforcement, reflective cracking mitigation, increased fatigue life, and improved drainage and filtering. However, few studies have addressed the installation and construction practices of geosynthetics in pavements. Furthermore, the study of geosynthetics and their contribution during construction are limited. In this paper, a full-scale field study was conducted and three trial sections were constructed; two types of geosynthetics, a fibreglass geogrid and a geogrid composite, were installed in the asphalt binder course and at the interface between the subgrade and base layer, respectively, to be compared with a control section without geosynthetic reinforcement. Trial sections were instrumented to monitor the pressure applied on the subgrade, the strain in the base lift of the asphalt binder course, the temperature, and the moisture within the pavement structure during construction. In addition, post-construction field testing was performed to measure the stiffness of the pavements after construction. The results indicated that geosynthetic-reinforced pavements can maintain pavement resilience during construction and significantly mitigate the disturbances caused by construction activities. The geogrid embedded in the asphalt layer was demonstrated to reduce the pressure at the subgrade caused by paving equipment by 70% compared with the control section, while simultaneously reducing the longitudinal and transverse strain at the bottom of the asphalt layer by 54% and 99%. Observations from the geogrid composite test section also demonstrate the potential to minimize the impacts of future freeze–thaw at the subgrade due to the improved drainage and indirect insulation effect. [ABSTRACT FROM AUTHOR]

This paper addresses unpaved and paved roads improved with geosynthetics, such as geotextiles, geogrids and geocells. The paper examines the mechanisms associated with the use of geosynthetics to improve roads, describes the principles of the design methods used to quantify the benefits of geosynthetics used in unpaved and paved roads, presents case histories to demonstrate the use of geosynthetics to solve challenging road problems, and discusses the relevance of tests and trials to real roads. This paper is supplemented by four presentations in pdf format that contain more than 800 slides. These four presentations are updated versions of the four presentations made during a one-day short course at the 11th International Conference on Geosynthetics held in Seoul, Korea, in September 2018. The paper that follows contains a summary of each of the four presentations, with special emphasis on key issues. [ABSTRACT FROM AUTHOR]

Geotextile is one of the reinforcement materials adopted in many engineering structures. Conventional geotextiles have a limited reinforcement effect due to the insufficient friction strength between geotextiles and soils. This paper proposes a novel type of geotextile with stitched transverse ribs to improve the reinforcement effect. A series of large-scale direct shear tests have been conducted, and the improvement characteristics between conventional geotextiles, geogrids, and the novel geotextiles have been studied. The results show that the novel stitched transverse rib geotextiles can significantly increase the shear strength compared to conventional geotextiles and geogrids. Moreover, due to the restraint and friction effect of ribs on the soils, the reinforcement effect of the novel geotextile is increased with increasing ribs. Insights from this study can provide a new understanding of the novel stitched transverse ribs geotextile's reinforcement mechanism in engineering. [ABSTRACT FROM AUTHOR]

One of the most effective ways to increase the longevity of pavement structures is through the integration of geosynthetic reinforcement. Geosynthetics are synthetic materials such as geotextiles, geogrids, or geocomposites that are added to the interface between the subgrade and the base layer of a pavement structure. To evaluate the effect of various parameters on the structural benefits of geosynthetic reinforcement on the pavement structure of low-volume traffic flexible pavements, a finite element (FE) study was performed using the ABAQUS program. These parameters included the geosynthetic type, geosynthetic tensile stiffness, subgrade stiffness, and base thickness. The FE rutting curves for the 100 cycles were calibrated using the mechanistic–empirical (M-E) transfer functions, which were then used to calculate the long-term rutting curves. The traffic benefit ratio (TBR) was initially calculated based on the calibrated rutting curves for each pavement layer. The calculated TBRs were then used as an input in AASHTOWare to compute the base effective resilient modulus (MR-eff) and the factor of base course reduction (BCR). The results showed that adding one layer of geosynthetics enhanced the rutting performance of pavement structures significantly (up to 8.9 in TBR, 322% in MR-eff, and 64% in BCR). Geogrids showed higher benefits than geotextiles due to the interlocking between base aggregates and geogrid aperture. The values of TBR, MR-eff, and BCR increase with the increasing tensile stiffness of the geosynthetics and the rutting target and with the decreasing subgrade stiffness. The results also demonstrated peak values of TBR, MR-eff, and BCR for a base thickness of 25.4 cm. [ABSTRACT FROM AUTHOR]

The use of geosynthetics has become a common and unavoidable practice in geotechnical engineering, agriculture and environmental engineering. The main disadvantages of earthen construction materials are their insufficient tensile strength and inadequate water permeability or impermeability, depending on the problem to be solved. Such shortcomings are successfully solved by incorporating appropriate geosynthetics (geotextile, geogrid, geocells, geomembrane etc.) into earthen structures. The most used geosynthetic is geotextile, which can provide practically all functions expected from such a product. The aim of this paper was to present and analyse the relative results of multiple tensile tests performed on two nonwoven (NW) geotextiles to provide a realistic insight into the variability of their tensile properties. The obtained results showed a very similar variability of the tensile properties of the tested geotextiles. [ABSTRACT FROM AUTHOR]

Track thermal buckling is one of the primary safety issues of continuously welded rail tracks. It has been shown that transition zones of open deck steel bridges are more prone to track buckling, as the thermal loads from the bridge and lower track lateral resistance in this region can destabilize the track in the lateral plane. The aim of this paper is to assess the possibility of reinforcing the ballast layer with geotextiles to mitigate the track buckling problem in the transition zones. To do so, a number of laboratory experiments are performed using one and two layers of geogrids and various depths of ballast layer. Single tie push tests are performed on the track and force-displacement curves are derived for the sleepers. It is shown that adding the geotextile layer to the ballast layer can increase its lateral resistance by up to 41%. The results are then introduced in the numerical model of a track developed in Abaqus finite element software for track buckling analysis. It is shown that adding the geogrid layer can increase the track buckling temperature by up to 11.33 °C, an increase of almost 21%, compared to that of an unreinforced track. • Laboratory investigation of lateral track resistance with reinforced ballast layer with different number of geotextile layers. • Increased lateral resistance of track with geogrid reinforcement of up to 41%. • Numerical analyses of track buckling in the transition zone of open deck steel bridges with reinforced ballast layer. • An increase of 21% is achieved for buckling temperature of a track reinforced with geogrid layer. [ABSTRACT FROM AUTHOR]

Stabilization of excavations and retaining walls are important issues in the geotechnical field. The use of new and novel methods in excavation sites, and providing safe conditions for the final aim of the project is one of the challenging matters in this regard. Excavation in sandy soils, due to lack of enough cohesion for its stability, faces serious problems. In order to solve this problem, using special techniques to improve stability is a very important subject. Geosynthetics (i.e. geotextile, geogrid, and geocell) are among the new techniques, which could enhance the stability and performance of sandy soils. In this research, 3D finite different analysis was performed to investigate unreinforced and reinforced excavations using geotextile, geogrid, and geocell elements and their comparison. Results indicated that in the case of using geotextile, geogrid and geocell the critical depth of excavation increased up to 3.125, 2.75, and 2.25 times of unreinforced excavation, respectively. [ABSTRACT FROM AUTHOR]

Buried pipes may transport substances that can be harmful to people and the environment. These structures may be subjected to damages caused by soil movements and external interference, such as surcharges and excavations. Different applications of geosynthetics have demonstrated that they can be used to protect buried pipes and to minimize the consequences of pipe burst. This paper discusses results of large scale laboratory tests on a flexible pipe buried in unreinforced and geosynthetic reinforced soils subjected to surface surcharges. The pipes were buried in a cohesionless soil and different types of reinforcements were tested, with a wide range of tensile stiffness values. The results obtained show that the arrangement of the reinforcement enveloping the pipe reduced significantly pipe displacements and deflections. The efficiency of the reinforcement depended on its type and physical and mechanical properties. The open geogrid tested showed less reinforcement efficiency due to the passage of soil particles through its aperture during the tests. A theoretical solution available for pipes in unreinforced soils was extended to the reinforced situation with good agreement between predictions and measurements and showed that the presence of the reinforcement is equivalent to the pipe being buried in a significantly stiffer unreinforced soil. • The study investigates an innovative application of geosynthetics for the protection of buried pipes. • The effects of different reinforcement arrangements on the deformations of the pipe and stresses in the soil are analysed. • A solution for the estimate of pipe deflections in unreinforced soil is extended to the reinforced soil case. • The results of the investigation are relevant to engineering applications of buried pipes in industrial and urban areas. [ABSTRACT FROM AUTHOR]

This paper presents the suitability of geogrids made from areca leaf sheaths, as soil reinforcement. The performance of areca geogrids was evaluated through the model footing tests and the same has been compared with the performance of synthetic polymer geogrids as well as coir geotextiles. The effect of embedment depth of areca geogrid within the sand bed on its bearing capacity was presented along with the behavior of multilayered areca geogrid-reinforced sand beds. The performance comparison of areca geogrid-reinforced sand beds with coir geogrid and polymer geogrid-reinforced sand beds showed that the areca grids provided improved performance. [ABSTRACT FROM AUTHOR]

This paper presents experimental and numerical investigations of dense sand slopes supporting an embedded strip footing, considering both unreinforced and geotextile-reinforced cases. The effect of footing location, defined in terms of embedment depth D and edge distance e, on the bearing capacity of the footing was investigated. The results show that the bearing capacity of the footing increased with an increase in D and e. The inclusion of one layer of geotextile reinforcement in the dense sand slope further increased the bearing capacity. This benefit was expressed in terms of BCRu, which is defined as the ratio of the ultimate bearing capacity for the reinforced case to the ultimate bearing capacity for the unreinforced case. The maximum value of BCRu(≈ 2·5 − 3) was observed for D/B = 0 and e/B = 0 where B is the width of the footing, while the minimum value of BCRu(≈ 1·5) was obtained for D/B = 1 and e/B = 3. [ABSTRACT FROM AUTHOR]

This paper presents both experimental and numerical study on a slope made up of c-ϕ soil. The effect of different reinforcements such as geotextile and geogrid are also studied in both cases. Small shaking table tests are conducted on the model slope to evaluate the different parameters like acceleration amplifications and horizontal deformation at different levels of the slope. In addition to the variation of the c-ϕ nature of the soil, the variation of water content is also done for the model soil slope. The effect of variation of frequency level, base shaking and a number of reinforcement layers are also studied. Using PLAXIS, numerical models are developed for both unreinforced and reinforced soil slope made up of c-ϕ soil. Comparison of the results as obtained from the experimental study is done with those of the numerical models. Results presented either in tabular form or graphically and from the results acceptability of the models is also discussed. [ABSTRACT FROM AUTHOR]

Mechanical and hydraulic properties of recycled concrete aggregate (RCA) were evaluated for use as backfill in mechanically stabilized earth (MSE) walls. Large-scale drained triaxial tests, direct shear tests and pullout tests were performed to obtain mechanical properties of RCA interacting with various geosynthetics. Long-term filtration (LTF) tests were performed to evaluate hydraulic conductivity of RCA-geotextile systems. Results showed that the RCA had an internal friction angle of 49°, which was within the typical range. The RCA-uniaxial geogrid had the highest interface friction angle of 36° – and the interface friction angles of RCA-biaxial geogrid, RCA-nonwoven geotextile, and RCA-woven geotextile were 32°, 26° and 22°, respectively. Reinforced RCA showed comparable pullout capacity to reinforced sand. No slippage was observed between the RCA and geotextiles or geogrids, and the failures occurred mainly due to rupture of the geotextiles and geogrids during the pullout test. Results of the LTF tests showed that, over a filtration period of 2500 h, the ratio of mean hydraulic conductivity of RCA only to that of RCA-nonwoven geotextile and RCA-woven geotextile systems remained between 0.91 and 3.2, suggesting that the clogging of the geotextiles with RCA was minimal. [ABSTRACT FROM AUTHOR]

This study was conducted to evaluate the performance of geosynthetic reinforced asphalt pavements through full-scale and laboratory testing. The study also investigated the field cracking performance of geosynthetic test sections under accelerated loading and validated with the laboratory cracking performance results. Three sections were constructed including: control, geogrid and geosynthetic reinforced AC. After applying the accelerated loading, cores and slabs were extracted from the wheel path (W) and outside of the wheel path (OW) to evaluate the impact of accelerated loading on cracking performance of AC. The laboratory cracking performance and shear bond strength were assessed using Indirect Tension Asphalt Cracking Test (IDEAL-CT), Interlayer Shear bond Strength (ISS), Bending beam Fatigue (BBF), and Texas overlay tests. Additionally, strain response on top of pre-existing notch was also analyzed from the accelerated test sections to monitor field cracking potential of reinforced AC and to validate it with laboratory cracking performance. According to the BFF, OT and ISS results, the W AC showed degraded performance compared to OW AC, however, IDEAL-CT test results mentioned that W AC showed better cracking performance compared to OW AC. Overall, geosynthetic reinforced AC showed better laboratory cracking performance and lower shear bond strength. At full-scale section, higher tensile strains were registered indicating that geosynthetic reinforcement can undergo potentially larger displacement without failing in the pre-existing crack area. Both laboratory and field test results compliment the findings of each other. • Laboratory performance of field collected geosynthetic reinforced asphalt concrete (AC) was evaluated. • Field cracking performance of geosynthetic reinforced AC was investigated under accelerated loading. • Better performance for outside of wheel path collected AC compared to within wheel path collected samples. • Geosynthetic interlayers degraded the shear bond strength of asphalt concrete. • Geosynthetic reinforcement can undergo larger displacement without failing in the pre-existing crack area. [ABSTRACT FROM AUTHOR]

This work presents a study on tensile properties of geosynthetic materials. There were investigated six samples of geofabrics and geogrids with different structures including woven geotextile fabrics, nonwoven geotextile fabrics, warp-knitted geogrids and extruded geogrid. The study determined tensile properties of geosynthetics including tensile strength, strain at the maximum load and tensile load at a specified strain. The authors carried out creep and relaxation tests. It was found that the structure type significantly affects viscoelastic properties of geosynthetics materials. The article presents some results of numerous tests, which may be used to pre-select geosynthetics materials.

Abstract An in situ controlled millisecond delay blasting (MDB) experiment was conducted to study the liquefaction behaviour of a sandy field and the liquefaction-induced deformation and damage to a shallowly buried reinforced concrete structure and an embankment. The pore pressure within the foundation soil, the acceleration and strain responses of the concrete structure and the deformation of the embankment were monitored during a series of blasts. Liquefaction and even sand boils were successfully produced by the explosive loading. Considerable (uneven) settlement and tilt were observed in the concrete structure, and unrecoverable strains were detected by several strain gauges. Uneven settlement also caused some visible cracks near the crest of the embankment, which, based on comparative studies, can be largely alleviated by using geogrids and geotextiles within the foundation soils. The field experiment reported in this study demonstrates that the aforementioned MDB technique and the developed scheme are effective in creating a liquefied site, which can be used to study the post-liquefaction behaviour of nearby structures. Highlights • Millisecond delay blasting is effective in creating a liquefied site. • Evident displacement and uneven settlement of the structures occur. • Uneven settlement causes visible cracks near the crest of the embankment. • Geogrids and geotextiles within the foundation soils largely alleviate the settlement. [ABSTRACT FROM AUTHOR]

Abstract Use of geotextile-encased sand columns (GESC) to improve weak soils is an emerging technology that has great promise for field applications. This paper contains the results of a numerical study with the goal of quantifying the benefits of geotextile encasement under different conditions. A three-dimensional finite difference method implemented in FLAC3D 5.01 was used to evaluate the performance of a vertically loaded individual GESC installed in loose sand. The numerical model was first verified using the results of experimental tests performed on 150-mm diameter GESC installed in loose sand. The influence of various parameters was investigated in this study, including GESC diameter and length, soil thickness, geotextile encasement length, geotextile stiffness, and friction angle and dilation angle of the infill material. The results of the numerical model showed that vertically loaded GESC of smaller diameter experienced less settlement and lateral expansion than those of larger diameter. The geotextile material with higher stiffness had a substantial influence on the performance of GESC. The maximum effective geotextile encasement length depended on the load on the column head or the compressibility of the column. [ABSTRACT FROM AUTHOR]

Abstract In 2013, the authors wrote a paper which was published in the Journal of Geotextiles and Geomembranes on the failure of 171-mechanically stabilized earth (MSE) walls reinforced with geotextiles or geogrids, Koerner and Koerner (2013). The paper generated many reprint requests via both the publisher and the authors, and it won the best paper of the year award. Furthermore, it generated considerable awareness of the situation and generated additional case histories while providing details of such failures. Presently, we have 320 failures which are reported in this paper. The database includes 99 cases of excessive deformation and 221 cases of collapse of at least part of the respective walls. The main statistical findings (including the original 171 failures) are as follows: 1. 313 (98%) were private (as opposed to public) financed walls. 2. 253 (79%) were located in North America; the vast majority being in the U.S. 3. 240 (75%) were masonry block faced. 4. 226 (71%) were 4–12 m high. 5. 301 (94%) were geogrid reinforced; the other 6% were geotextile reinforced. 6. 246 (77%) failed in less than four years after their construction (12 of which actually failed during construction). 7. 232 (73%) used silt and/or clay backfill soils in the reinforced zone. 8. 245 (76%) had poor-to-moderate compaction. 9. 317 (99%) were caused by improper design or construction (incidentally, none were caused by geosynthetic manufacturing material failures). 10. 201 (63%) were caused by internal or external water (the remaining 37% were caused by soil related issues). While the number of reported walls in this paper is almost double the number reported in 2013, the change in percentages of the above items is relatively small with the notable exceptions of walls failing in longer time intervals (by 9%) and even greater use of fine grained backfill soils (by 12%). As with the original paper, updated opinions and recommendations in several of the above listed areas are presented. Also, several new types of failures are reported, such as guard fence instability and soil erosion at the toe of the wall. However, the overall critical issues continue to occur and no lessening of failures is apparent with this new set of data. The critical issues are the following; • fine grained silt and clay soils continue to be used for the reinforced zone backfill. • poor placement and compaction of these same fine grained backfill soils is regularly reported. • drainage systems and utilities continue to be located within the reinforced soil zone. • there is little attempt at water control either behind, beneath or above the reinforced soil zone, and. • design details appear to be inadequate or not followed by the installation contractor. While the issues reported in 2013 did indeed prompt the initiation of an inspector's certification program (Geosynthetic Certification Institute - Inspector Certification Program) it has not been very successful and has attracted only 24-participants to date. Hopefully this updated paper will energize the parties involved and the MSE reinforced wall community at large to take appropriate action in correcting the situation described herein. [ABSTRACT FROM AUTHOR]

Abstract This paper investigates the cyclic loading responses of a strip footing supported by a geosynthetic reinforced fill embankment. A series of large-scale model footing tests were conducted first to investigate the accumulation of permanent footing displacement and residual vertical soil stress over large number of load cycles. The embankment fill was a heavily compacted silty sand and the reinforcement was a flexible geogrid, so that the model test configurations were representative of actual field conditions. Both permanent displacement and residual stress accumulated asymptotically with load cycles and majority of the build-up occurred over the first few hundred cycles. The potential effect of load interruptions was part of the study. Depending on how cyclic load interruption was implemented, it may or may not induce a trailing effect on subsequent cyclic loading responses. To have more in-depth understanding, these footing tests were also investigated numerically based on a soil model that can capture the unload-reload stress-strain loop over large number of load cycles. Reasonably good agreement between experimental observations and numerical predictions was also achieved. [ABSTRACT FROM AUTHOR]

Abstract Plate anchors are frequently used to provide resistance against uplift forces. This paper describes the reinforcing effects of a geocell-reinforced soil layer on uplift behavior of anchor plates. The uplift tests were conducted in a test pit at near full-scale on anchor plates with widths between 150 and 300 mm with embedment depths of 1.5–3 times the anchor width for both unreinforced and geocell-reinforced backfill. A single geocell layer with pocket size 110 mm × 110 mm and height 100 mm, fabricated from non-perforated and nonwoven geotextile, was used. The results show that the peak and residual uplift capacities of anchor models were highest when the geocell layer over the anchor was used, but with increasing anchor size and embedment depth, the benefit of the geocell reinforcement deceases. Peak loads between 130% and 155% of unreinforced conditions were observed when geocell reinforcement was present. Residual loading increased from 75% to 225% that of the unreinforced scenario. The reinforced anchor system could undergo larger upward displacements before peak loading occurred. These improvements may be attributed to the geocell reinforcement distributing stress to a wider area than the unreinforced case during uplift. The breakout factor increases with embedment depth and decreased with increasing anchor width for both unreinforced and reinforced conditions, the latter yielding larger breakout factors. Calibrated numerical modelling demonstrated favorable agreement with experimental observations, providing insight into detailed behavior of the system. For example, surface heave decreased by over 80% when geocell was present because of a much more efficient stress distribution imparted by the presence of the geocell layer. [ABSTRACT FROM AUTHOR]

Geogrids have been found to improve the performance of unbound aggregate layers in transportation applications by providing confinement and arresting movement through interlock between individual aggregate particles and their apertures. Geogrid reinforcement offers an effective remedial measure when railway structures are susceptible to track geometry defects resulting from excessive movement and particle reorientation within the ballast layer. This paper presents an ongoing research study at the University of Illinois aimed at quantifying the effects of geogrid reinforcement on the shear strength and permanent deformation behaviour of geogrid-stabilised railroad ballast. Geogrids with triangular, rectangular and square apertures were tested in the laboratory experiments. Cylindrical ballast specimens were prepared and tested with geogrids placed at different heights within the specimen using a large-scale triaxial apparatus. An imaging-based discrete-element-method approach was developed to model triaxial test results and investigate geogrid-reinforcement mechanisms. With the capability to create actual ballast aggregate particles as three-dimensional polyhedron elements having the same particle-size distributions and imaging quantified average shapes and angularities, the modelling was able to capture the ballast behaviour with and without geogrid reinforcement reasonably accurately. [ABSTRACT FROM AUTHOR]

This report presents a new large-scale test apparatus (LSTA) developed to assess the efficiency of a geosynthetic reinforcement for the limitation of deformations of a geosynthetic lining system (GLS) over a 0.5 m wide cavity. Two experiments were conducted. The first one involved a geosynthetic clay liner, a nonwoven needle-punched geotextile and a high-density polyethylene geomembrane. For the second experiment, a 50 kN/m polyvinyl alcohol geogrid was imbedded within the sand layer below the geosynthetic clay liner to provide reinforcement above the cavity. An overburden pressure varying from 10 to 100 kPa was applied to the top of the GLS. Strain gauges were used to measure the strain within the geogrid and the geomembrane. The results proved that the 50 kN/m geogrid reinforcement beneath the geomembrane reduced the maximum strain within the geomembrane, compared to the case where the geomembrane was unreinforced, by 25% on average. The results showed that the overall strain within the geomembrane was 31% to 42% less than that of the geogrid above the cavity. Finally, the results showed that the spatial distribution of the strain within the geomembrane and that of the geogrid differed because of a conical shape of the collapsed zone. [ABSTRACT FROM AUTHOR]

The increased use of geosynthetics in road constructions has resulted in a need to better understanding of geosynthetics properties for the use in design and quality control. For this purpose, the regulations for use of geosynthetics for road embankments and subgrades were created in Lithuania. It was found that other European countries such as Germany and United Kingdom use not only harmonised European standards, but also has their own regulations for geosynthetics. This study indicates the relationship between regulations in Lithuania and other countries. Calculation conception and regulations for controlling characteristics were introduced first time in Lithuanian road construction market. The use of those regulations will increase the quality of construction and life time of road pavement structures.

Geocell is an effective type of geosynthetics for improving the performance of reinforced soil foundations due to provision of lateral confinement for the infill soil. In this research, in order to study the bearing pressure-settlement response of geocell-reinforced sand, a reduced-scale physical model is developed and geocells with various geometrical dimensions (height, pocket size, and width) produced from woven geotextile are used to reinforce sand bed. Strip footing model is then loaded monotonically to ultimate failure level, and the influence of geocell geometrical properties on the improvement in bearing capacity and settlement of footing is described. The results show that by increasing height and decreasing pocket size of geocell, the beneficial effect of geocell reinforcement increases substantially. For the highest geocell used in the tests at settlement level of 6%, improvement in bearing capacity and percentage reduction in footing settlement are obtained as 2.1 and 48%, respectively. The optimum width of geocell is determined five times the foundation width beyond which the improvement effect is negligible. It is also concluded that substituting a single layer of geocell reinforcement with 2 half-height and 4 quarter-height geocell layers results in 10% and 22% decrease in the ultimate bearing capacity, respectively. [ABSTRACT FROM AUTHOR]

In this study, a full-scale high-speed railway embankment model was established for assessment of the tensile force of the geogrid embedded in the sand cushion. Water bags were distributed around pile caps to create a model of the subsoil. The settlement of the subsoil was determined by the vertical deformation of the water bags. The tensile force of the geogrid, induced by the spreading force of the embankment, and caused by the vertical loads applied to the geogrid, were separately measured by two types of optical fiber sensing approaches, i.e., the pulse-prepump–Brillouin optical time domain analysis (PPP–BOTDA) and fiber Bragg grating (FBG) sensors. After the completion of the construction of the embankment, the measured tensile force of the geogrid, caused by the spreading force, is about 12% of that calculated by using the BS8006 standard. During the process of subsoil consolidation, the soil arching in the embankment fully develops as the subsoil settlement increases. At the ultimate limit state, the largest tensile force of the geogrid caused by the vertical loads occurs at the edge of the pile cap, which is about 34% of that calculated by using BS8006. As a design method, BS8006 calculates the tensile force of the geogrid at the ultimate limit state, and the experimental results reveal that the computational procedure specified in BS8006 is safe for determination of the tensile force of the geogrid. [ABSTRACT FROM AUTHOR]

In geotechnical and transportation engineering, especially road constructions in cuts and deep excavation problems are solved by using different supporting excavation methods. Soil reinforcements are chosen due to easy and economic application. In this study, behavior of supported slopes with geotextiles and geogrids were analyzed by performing experiments on slope models in the laboratory. In the experiments, a static loading was applied to find failure surface and deformations for each case. Additionally, slopes were designed by using Plaxis program. At the end of the study, experimental and analytic models were compared and also behavior of models were presented. [ABSTRACT FROM AUTHOR]

The pullout test is one of the methods commonly used to study pullout behavior of reinforcements. In the current research, large pullout tests (i.e. 100 × 60 × 60 cm) have been conducted to investigate the possibility of pullout resistance enhancement of clays reinforced with HDPE geogrid embedded in thin layers of sand. Pullout tests on clay–geogrid, sand–geogrid and clay–sand–geogrid samples have been conducted at normal pressures of 25, 50 and 100 kPa. Numerical modeling using finite element method has also been used to assess the adequacy of the box and geogrid sizes to minimize boundary and scale effects. Experimental results show that provision of thin sand layers around the reinforcement substantially enhances pullout resistance of clay soil under monotonic loading conditions and the effectiveness increases with increase in normal pressures. The improvement is more pronounced at higher normal pressures and an optimum sand layer thickness of 8 cm has been determined for maximum enhancement. Results of numerical analysis showed the adequacy of the box and geogrid length adopted as well as a relatively good agreement with experimental results. [ABSTRACT FROM AUTHOR]

Geotextiles have been demonstrated to be effective in reducing erosion and subsequent slope degradation processes. However, most studies devoted to assessing the effectiveness of those elements have considered small or intermediate slope gradients (normally ≤30°), whereas real engineering works often lead to steeper slopes needing protection. In addition, although a large amount of laboratory studies exist on this topic, there are few articles reporting field experiments which consider large plots, real precipitation and prolonged study periods. This paper is the first of two in which the performance of erosion control geotextiles on steep slopes (45° and 60°) has been assessed. In this paper, the influence of geotextiles on runoff and soil loss reduction was evaluated. The second paper focuses on the effects of geotextiles on the establishment and growth of vegetation on the slope. The research was carried out on an experimental embankment built in Pamplona (Spain) following standard construction procedures in order to resemble real engineering slopes. Two biological geotextiles (jute net and coir blanket) and a synthetic polyester geogrid, installed in two positions (surface-laid and buried), were evaluated and compared with a vegetated hydroseeded control plot. After each significant rain event, runoff and soil loss amounts produced on each plot were recorded. The results showed that coir and jute geotextiles produced 2–3 times larger runoff volumes than the control plots on both the 45° and 60° slopes, whereas the synthetic geogrid did not give significantly different runoff rates from the control (at p<0.05). Geotextiles were more effective in reducing soil loss at 45° than at 60°. The most effective treatment was the surface-laid geogrid, with a median Soil Loss Reduction Effectiveness (SLRE) of 76% and 53% for the 45° and the 60° slopes, respectively. At 45° the coir blanket showed lower soil losses than the control (median SLRE of 61%), but at 60° its protection action was more irregular (median SLRE of only 8%). The jute net and the buried geogrid produced lower erosion rates (median soil loss of 3.2gm−2 and 2.1gm−2, respectively) than the control (median soil loss of 3.6gm−2) at 45°, but at 60° the erosion rates observed were similar to those of the control. In short, the surface-laid geogrid produced the lowest soil loss rates. However, when buried, the geogrid did not effectively control erosion, at least not that of the upper soil layer. Thus, its surface installation seems to be a better option. In cases where burial is preferred for aesthetic reasons (i.e. hiding the geogrid), a higher soil loss must be assumed. [ABSTRACT FROM AUTHOR]

Many of the pavement structures fail well before their design life owing to the poor quality of construction materials, inadequate compaction, inadequate preparation of the subgrade, overloading, etc. Two options are available to improve the longevity of the pavement. The first option is by increasing the thickness of different pavement layers and the other option is by increasing the rigidity of the layers within the system so as to reduce the stresses transferred to the lower layers. Of these two methods it has been widely observed that increasing the strength and rigidity of the pavement layers is a more efficient method to lower the stresses on the pavement layers thereby increasing the life of the pavement. In the present research work, the improvement in the strength and stiffness of the subbase layer in a flexible pavement system through the use of geosynthetic layers was investigated by conducting field plate load tests and a series of laboratory plate load tests. The improvement in the strength of the pavement is reflected by the increase in modulus of the section reinforced with geosynthetic layers. This paper will describe the field and laboratory tests, interpretation of the data from these tests, and the application of this data for design of flexible pavements and their economic analyses. [ABSTRACT FROM AUTHOR]

The increased use of geosynthetics in road constructions has resulted in a need to better understanding of geosynthetics properties for the use in design and quality control. For this purpose, the regulations for use of geosynthetics for road embankments and subgrades were created in Lithuania. It was found that other European countries such as Germany and United Kingdom use not only harmonised European standards, but also has their own regulations for geosynthetics. This study indicates the relationship between regulations in Lithuania and other countries. Calculation conception and regulations for controlling characteristics were introduced first time in Lithuanian road construction market. The use of those regulations will increase the quality of construction and life time of road pavement structures. [ABSTRACT FROM AUTHOR]

Abstract: A series of experiments have been carried out to develop an understanding of the performance improvement of soft clay foundation beds using stone column-geocell sand mattress as reinforcement. It is found that with the provision of stone columns, of adequate length and spacing, about three fold increases in bearing capacity can be achieved. While with geocell-sand mattress it is about seven times that of the unreinforced clay. But if combined together, the stone column-geocell mattress composite reinforcement, can improve the bearing capacity of soft clay bed as high as by ten fold. The optimum length and spacing of stone columns giving maximum performance improvement are, respectively, 5 times and 2.5 times of their diameter. The critical height of geocell mattress can be taken equal to the diameter of the footing, beyond which, further increase in bearing capacity of the composite foundation bed is marginal. [Copyright &y& Elsevier]

Abstract: This paper presents numerical analysis on the behavior of geocell-reinforced retaining structures with various layouts. The constitutive model adopted for materials consisted of a nonlinear elastic stress–strain relationship with Mohr–Coulomb yield criterion. The strength parameters of the materials were obtained from relevant tests. For verification of the numerical model, three model-scale gravity-type walls with different facing angles were analyzed, and the finite difference program FLAC was utilized in the analysis. The results of the verification show good agreement in predicting the potential slip surface as well as estimating the critical load causing the wall to fail. The verified numerical model was then employed to study various layouts of retaining structures, which were constructed with the same amount of geocells, to compare the failure mode as well as the deformation of the structure. It has been found, irrespective of gravity type or facing type, the structure that extends the length of geocells in some layers to serve as reinforcement performs well in reducing the deformation of the structure and decreasing the potential slip zone. Moreover, with lengthening geocell layers as reinforcements, extended facing-type structures of various facing angles were analyzed. The results show that a wall with a facing angle less than 80° will significantly reduce the lateral displacement of the wall face. Further, the lateral earth pressures against the back of wall facing are somewhat higher than the horizontal stress in Rankine's active state, while those along the back of the reinforced zone are in at-rest state. [Copyright &y& Elsevier]

Abstract: The aim of this work is to study the effect of a localized impact on a wall made of soil reinforced with geocells. First, two structures were tested with an impacting remote-controlled car. Such experiments, carried out on 1/10th-scale model structures for practical reasons, are designed to mimic the mechanical response of an alveolar geocell reinforcement system. Two types of constitutive materials were considered for the geocells with very different mechanical properties. The test structures were dismantled after the tests to analyse the influence of the impact on the cell layers, especially within their bulk. Examining the video of the tests captured with two high-speed cameras also helped understanding the phenomena that occurred during impact. These experiments were completed by numerical simulations whose objective was to understand more clearly the causes of the phenomena observed either within the dismantled structures or in the videos. [Copyright &y& Elsevier]

Abstract: Ballast being an unbounded granular medium spreads laterally when subjected to high-frequency cyclic loading. To reduce lateral movement of ballast and to optimize track performance, rail tracks can be reinforced with geogrid. In this study, a novel large-scale process simulation test (PST) apparatus that can capture the lateral strain variation upon loading is described. Laboratory tests were conducted to explore the deformation and degradation response of both unreinforced and reinforced ballast under high-frequency cyclic loading. Fresh Latite basalt having an average particle size (D 50) of 35 mm, and geogrids with different aperture sizes were tested. The laboratory experimental results reveal that the ballast deformation (both lateral and vertical) and the breakage during cyclic loading are influenced by the geogrid type and its placement location. Moreover, the lateral strain profiles along the ballast depth have been measured and the geogrid influence zone (GIZ), defined as the distance to which the effect of geogrid in arresting the lateral displacement of ballast exists, has been determined. The GIZ is found to vary from 160 mm (4.60D 50) to 225 mm (6.45D 50) depending on the location of the geogrid. In addition, the optimum geogrid position in the track has been identified to be 65 mm above the subballast. The test results also exemplify the ability of geogrid to arrest lateral displacement of ballast, reduce settlement and minimize particle degradation under high-frequency cyclic loading. [Copyright &y& Elsevier]

Geotextiles and geogrids have been in use for several decades in variety of geo-structure applications including foundation of embankments, retaining walls, pavements. Geocells is one such variant in geosynthetic reinforcement of recent years, which provides a three dimensional confinement to the infihl material. Although extensive research has been carried on geocell reinforced sand, clay and layered soil subgrades, limited research has been reported on the aggregates/ballast reinforced with geocells. This paper presents the behavior of a railway sleeper subjected to monotonic loading on geocell reinforced aggregates, of size ranging from 20 to 75 mm, overlying soft clay subgrades. Series of tests were conducted in a steel test tank of dimensions 700 mm × 300 mm × 700 mm. In addition to the laboratory model tests, numerical simulations were performed using a finite difference code to predict the behavior of geocell reinforced ballast. The results from numerical simulations were compared with the experimental data. The numerical and experimental results manifested the importance that the geocell reinforcement has a significant effect on the ballast behaviour. The results depicted that the stiffness of underlying soft clay subgrade has a significant influence on the behavior of the geocell-aggregate composite material in redistributing the loading system. [ABSTRACT FROM AUTHOR]

Fiber reinforcement represents a promising alternative in projects involving localized repair of slopes and reinforcement of thin soil veneers, where planar reinforcement (e.g., with geotextiles and geogrids) is difficult to implement. Current design methodologies allow quantification of the shear strength of fiber-soil composites in terms of the parameters that independently characterize the soil matrix and fibers. The shear strength of fiber-reinforced soil is considered to have two components, including the shear strength of the soil matrix and the tension mobilized within the fibers. Triaxial compression tests and fiber pullout tests were conducted to evaluate how the fiber tension is mobilized for varying shear strain levels. The results of this evaluation provide insights into whether the shear strength of fiber-reinforced soil is governed by the peak or residual shear strength of unreinforced soil. A revision to existing design methodology is proposed in which the individual contribution of fibers and soil matrix is quantified based on the strain level. The appropriateness of using the peak or residual shear strength of the unreinforced soil for predicting the equivalent shear strength of fiber-soil composites is discussed based on strain compatibility considerations. [ABSTRACT FROM AUTHOR]

A series of axi-symmetry models using finite element analyses were performed to investigate the behavior of circular footings over reinforced sand under static and dynamic loading. Geogrid was modeled as an elastic element and the soil was modeled using hardening soil model which use an elasto-plastic hyperbolic stress-strain relation. Several parameters including number of geogrid layers, depth to the first geogrid layer, spacing between layers and load amplitude of dynamic loading are selected in this paper to investigate the influence of these parameters on the performance of reinforced systems under both static and dynamic loads. The numerical studies demonstrated that the presence of geogrid in sand makes the relationship between contact pressure and settlement of reinforced system nearly linear until reaching the failure stage. The rate of footing settlement decreases as the number of loading cycles increases and the optimum values of the depth of first geogrid layer and spacing between layers is found 20% of the footing diameter. Some significant observations on the performance of footing-geogrid systems with change of the values of parametric study are presented in this paper. [ABSTRACT FROM AUTHOR]

This article examines the possibilities of protecting the empty interior slopes dumps with remaining gap filled with water. [ABSTRACT FROM AUTHOR]

The issues regarding waste landfills are still actual in Romania, but also worldwide, due to the increasing volumes of waste and their impact on the environment. In landfill design geosynthetic materials are used, some of them being required by law. Their use and especially the design of the projects in which they are implemented is often poor. The paper presents some of the actual issues on geosynthetic materials used in landfills, illustrated by some case studies. [ABSTRACT FROM AUTHOR]

Abstract: Cellular structures are widely used in civil engineering. Their design is based on the understanding of the mechanical behavior of geocells. This paper investigates the response of a single geocell to a uniaxial compression test. The geocells were cubic, either 500mm or 300mm on a side. The fill materials were sand and scrapped tire and sand mixtures in different mass ratios. The envelope of the geocell was made up of a hexagonal wire netting cage and a containment geotextile. The response of the geocell is discussed based on the axial load and displacement measurements as well as the change in geocell volume. The axial load was found to be globally governed by the interaction between the fill material and the envelope, which depends on the shape of the wire mesh and the volumetric behavior of the fill material. [Copyright &y& Elsevier]

Methods for analysis of stability and deformation under static and dynamic loading are exported. Stone columns are installed using a process similar to vibro-compaction, except that a gravel backfill is used, and they are typically installed in slightly cohesive soils or silt rather than clean cohesion less soils. In the dry soils, a cylindrical cavity is formed by the vibrator that is filled from the bottom up with gravel/crushed rock. The purpose of this research paper is to provide a review on ground improvement for using reinforced stone columns in geotechnical engineering projects. There is special focus on how to performance and evaluate ground improvement using reinforced stone column for special purposes. The previous results indicated the reinforced stone columns significantly increase the bearing capacity and tension of the soil. Based on previous results, critical values were discussed and recommended. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this study is to evaluate the durability of anti-reflective cracking systems that have a geosynthetic, geotextile or SAMI layer in the interlayer zone. For this purpose, a dynamic test has been designed that simulates the passing of traffic loads on the road surface. Stresses are applied to a two-layer test piece, which represents the pavement structure, with an anti-crack reflection system between the lower part, which is to be reinforced, and the upper part, which is the new pavement. In the lower layer, a longitudinal groove has been made that simulates an initial crack. All interlayer systems delay crack reflection. The test procedure is sensitive to the kind of interlayer system and helps to determine the optimal dosage of tack coat. Moreover, it has been verified that geogrids show higher resistance to repeated loading cycles, and geogrids with a higher stiffness modulus show better behaviour. [Copyright &y& Elsevier]

This article examines the possibilities of protecting the empty interior slopes dumps with remaining gap filled with water. [ABSTRACT FROM AUTHOR]

The measurement of geosynthetic strain is important to the development of numerical models that can predict the behavior of geosynthetic-reinforced flexible pavements. This paper outlines the key issues regarding foil strain gage selection, installation, and calibration on geosynthetics for dynamic strain measurement in roadway applications. The flexible nature of geosynthetics and the interaction of these materials with the adjacent layers of the pavement structure in a dynamic loading application limit the ability to use all types of strain gages and adhesives. While this paper does not cover every type of geosynthetic, it provides sufficient procedural details and illustrations of foil strain gage installations on a variety of geosynthetics (woven geotextiles and geogrids, nonwoven geotextiles and punch/drawn geogrids) and then outlines several alternative methods (wire extensometers, inductance coils and fiber optics) of dynamic strain measurement. While foil strain gages and closely spaced wire extensometers provide a localized value of displacement on a geosynthetic, wire extensometers and inductance coils provide a measure of global displacement (which includes slack in the geosynthetic) and redundancy in total strain measurements. Fiber optics is an emerging and very promising method of accurately measuring strain in geosynthetics, and at least one delivery system has been developed. [ABSTRACT FROM AUTHOR]