• Geomechanics and Engineering
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• v.25 no.3
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• pp.195-205
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• 2021

Time effect on the deformation and strength characteristics of geogrid reinforced sand retaining wall has become an important issue in geotechnical and transportation engineering. Three physical model tests on geogrid reinforced sand retaining walls performed under various loading conditions were simulated to study their rate-dependent behaviors, using the presented nonlinear finite element method (FEM) analysis procedure. This FEM was based on the dynamic relaxation method and return mapping scheme, in which the combined effects of the rate-dependent behaviors of both the backfill soil and the geosynthetic reinforcement have been included. The rate-dependent behaviors of sands and geogrids should be attributed to the viscous property of materials, which can be described by the unified three-component elasto-viscoplastic constitutive model. By comparing the FEM simulations and the test results, it can be found that the present FEM was able to be successfully extended to the boundary value problems of geosynthetic reinforced soil retaining walls. The deformation and strength characteristics of the geogrid reinforced sand retaining walls can be well reproduced. Loading rate effect, the trends of jump in footing pressure upon the step-changes in the loading rate, occurred not only on sands and geogrids but also on geogrid reinforced sands retaining walls. The lateral earth pressure distributions against the back of retaining wall, the local tensile force in the geogrid arranged in the retaining wall and the local stresses beneath the footing under various loading conditions can also be predicted well in the FEM simulations.

• Journal of the Korean Geotechnical Society
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• v.21 no.10
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• pp.5-16
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• 2005

Geosynthetic-reinforced and pile-supported embankments have been increasingly used and researched around the world. The inclusion of one or multiple geosynthetic reinforcements over the pile is intended to enhance the efficiency of load transfer from soft ground to piles, to reduce total and differential settlement and increase global or local stability. In this paper, the reinforcement effectiveness and arching effect of the geogrid-reinforced and pile-supported embankments have been studied in terms of field model tests and numerical analysis with varying the space between piles and reinforcement. 2-dimensional numerical analysis has been conducted using the FLAC (Fast Lagrangian Analysis of Continua) program. And load transfer mechanisms between soil-piles-geogrid were investigated. The mechanisms of load transfer can be considered as a combination of embankment soil arching, tension geogrid, and stress concentration due to the stiffness difference between pile and soft ground. Based on the field model test and numerical analysis results, it was found that the geosynthetic reinforcement slightly interferes with soil arching, and helps reduce differential settlement of the soft ground. Also. at the D/b=3 (D: spacing of pile cap, b: diameter of pile), the total settlement is reduced by about $40\%$ compared to that without reinforcement. For $D/b{\ge}6$, the effectiveness of geogrid reinforcement in reducing settlement is negligible.

• Journal of the Korean Geosynthetics Society
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• v.20 no.2
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• pp.13-22
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• 2021

Pile or column supported embankments have been increasingly employed to construct highway or railway embankments over soft soils. Piles or columns of stiffer material installed in the soft ground can provide the necessary support by transferring the embankment load to a firm stratum using a soil arching. However, there has been reported to occur a relatively large differential settlement between the piles and the untreated soils. Geosynthetic reinforced pile or column supported embankment (GRPS) is often used to minimize the differential settlement. Two dimensional finite element anlyses have been performed on both the column supported embankments and the geogrid reinforced column supported embankments by using a PLAXIS 2D to evaluate the soil arching effect. Based on the results obtained from finite element analyses, the stress reduction ratio decreases as the area replacement ratio increases in the column supported embankments. For the geogrid reinforced column supported embankments, the geogrid reinforcemnt can reduce differential settlements effectively. In additon, the use of stiffer geogrid is appeared to be more effective in reducing the differential settlements.

• Geomechanics and Engineering
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• v.24 no.6
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• pp.589-597
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• 2021

The present study evaluates geocell reinforced slope behavior. A three dimensional analysis is carried out to simulate soil and geocell elastoplastic behavior using the finite difference software FLAC3D. In order to investigate the geocell reinforcement effect, the geocell aperture size, thickness, geocell placement condition and soil compaction had been considered as variable parameters. Moreover, a comparison is evaluated between geocell reinforcing system and conventional planar reinforcement. The obtained results showed that the pocket size, thickness and soil compaction have considerable influence on the geocell reinforcement slope performance. Moreover, it was found that the critical sliding surface was bounded by the first geocell reinforcement and the slope stability increases, by increasing the vertical space between geocell layers. In addition, the comparison between geocell and geogrid reinforcement indicates the efficiency of using cellular honeycomb geosynthetic reinforcement.

• Geomechanics and Engineering
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• v.13 no.4
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• pp.641-651
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• 2017

Ground improvement with use of geosynthetic products is globally accepted now. The present paper discusses the improvement in bearing capacity of square footing placed at surface of cohesionless soil reinforced with geocell. Mohr-Coulomb failure criterion has been used in the observations. To study effects of geocell with respect to planar geogrid, model tests were conducted on planar reinforcement also. A comparative study of unreinforced soil and soil reinforced with plane geogrid and geocell has also been made. Numerical analysis results obtained by PLaxis have been compared with those obtained from model tests and were found to be in good agreement. A parametric study revealed the role of length of reinforcement, spacing between layers, placement of reinforcement from top surface etc. on bearing capacity. A design example given in paper illustrates the savings in cost of construction of footing on reinforced sand. The study shows that there is improvement in bearing capacity with respect to unreinforced soil which is of the order of 86%. Similarly settlement reduction is 13.07% for single layer of geocell which for double layers of geocell is 693% and 86.48% respectively. The cost reduction in case of reinforced soil is 35% as compared to unreinforced soil.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.1315-1323
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• 2010

This paper deals with a case study on a unique slope failure in a liner system of a municipal solid waste containment facility during construction because the sliding interface is not the geomembrane/compacted low permeability soil liner (LPSL) but a soil/soil interface within the LPSL. From the case study, it is concluded that compaction of the LPSL should ensure that each lift is kneaded into the lower lift so a weak interface is not created in the LPSL, and the LPSL moisture content should be controlled so it does not exceed the specified value, .e.g., 3% - 4% wet of optimum, because it can lead to a weak interface in the LPSL. In addition, drainage materials should be placed over the geomembrane from the slope toe to the top to reduce the shear stresses applied to the weakest interface, and equipment should not move laterally across the slope if it is unsupported but along the slope while placing the cover soil from bottom to top.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.115-125
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• 2003

This paper presents the results of design case study on soil-reinforced segmental retaining walls in tiered configuration. Six different field walls were examined to investigate the appropriateness of their designs within the context of the current design guidelines based on limit equilibrium. Slope stability analysis against the compound failure mode, which is frequently ignored during design, was additionally performed based on the method recommended by FHWA design guidelines. The results indicate that the as-built designs of some of the walls examined do not meet the minimum factors of safety for the external and Internal stabilities, and for the compound failure mode. The implications of the findings from this study are discussed.

• Journal of the Korean Geotechnical Society
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• v.21 no.8
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• pp.95-105
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• 2005

Generally, a modified version of limit equilibrium method can be used to evaluate a slope stability of the geosynthetic reinforced soil slopes. In most cases, resisting effects of geosynthetic reinforcement are dealt with considering an increased shear strength on the potential slip surface. However, it is not clear that the methods satisfy all three equilibrium equations. As we know, the pattern of normal stress distribution along the slip surface is the key factor in calculating the safety factor of slopes. In this study, the new slope stability analysis method in which not only reinforcing effects of geosynthetics can be considered but also all three equilibrium equations can be satisfied was proposed with assuming the normal stress distribution along the slip surface as quadratic curve with horizontal $\chi-coordinate$. A number of illustrative examples, including published slope stability analysis examples for the reinforced and unreinforced soil slopes, loading test of large scale reinforced earth wall and centrifuge model tests on the geotextile reinforced soil slopes, were analyzed. As a result, it is shown that the newly suggested method yields a relatively accurate factor of safety for the reinforced and unreinforced soil slopes.

• Geomechanics and Engineering
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• v.12 no.4
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• pp.579-593
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• 2017

Geosynthetic reinforced soil retaining walls can be employed as railway embankments to carry large static and dynamic train loads, but very few studies can be found in the literature that investigate their dynamic behavior under simulated wheel loading. A large-scale dynamic test on a reinforced soil railway embankment was therefore carried out. The model embankment was 1.65 meter high and designed to have a soilbag facing. It was reinforced with HDPE geogrid layers at a vertical spacing of 0.3 m and a length of 2 m. The dynamic test consisted of 1.2 million cycles of harmonic dynamic loading with three different load levels and four different exciting frequencies. Before the dynamic loading test, a static test was also carried out to understand the general behavior of the embankment behavior. The study indicated the importance of loading frequency on the dynamic response of reinforced soil railway embankment. It also showed that toe resistance played a significant role in the dynamic behavior of the embankment. Some limitations of the test were also discussed.

• Journal of the Korean Geosynthetics Society
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• v.10 no.2
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• pp.55-66
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• 2011

This paper presents the results of an investigation on the failure mechanism of geosynthetic reinforced soil walls in back-to-back configuration using 1-g reduced-scale model tests as well as discrete element method-based numerical investigation. In the 1-g reduced scale model tests, 1/10 scale back-to-back walls were constructed so that the wall can be brought to failure by its own weight and the effect of reinforcement length on the failure mechanism was investigated. In addition, a validated discrete element method-based numerical model was used to further investigate the failure mechanism of back-to-back walls with different boundary conditions. The results were then compared with the failure mechanisms defined in the FHWA design guideline.