• Geomechanics and Engineering
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• v.29 no.4
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• pp.435-449
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• 2022

In this paper, unreinforced and geogrid-reinforced soil foundations were modeled by discrete element method and this performed under surface strip footing loads. The effects of horizontal position of geogrid, vertical position, thickness, number, confining pressure have been investigated on the footing settlement and propagation of tensile force along the geogrids. Also, interaction between rectangular tunnel and strip footing with and without presence of geogrid layer has been analyzed. Experimental results of the literature were used to validation of relationships between the numerically achieved footing pressure-settlement for foundations of reinforced and unreinforced soil. Models and micro input parameters which used in the numerical modelling of reinforced and unreinforced soil tunnel were similar to parameters which were used in soil foundations. Model dimension was 1000 mm* 600 mm. Normal and shear stiffness of soils were 5*10⁵ and 2.5 *10⁵ N/m, respectively. Normal and shear stiffness of geogrid were 1*10⁹ and 1*10⁹ N/m, respectively. Loading rate was 0.001 mm/sec. Micro input parameters used in numerical simulation gain by try and error. In addition of the quantitative tensile force propagation along the geogrids, the footing settlements were visualized. Due to collaboration of three layers of geogrid reinforcements the bearing capacity of the reinforced soil tunnel was greatly improved. In such practical reinforced soil formations, the qualitative displacement propagations of soil particles in the soil tunnel and the quantitative vertical displacement propagations along the soil layers/geogrids represented the geogrid reinforcing impacts too.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.383-393
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• 2006

This paper investigates strength characteristics and stress-strain behaviors of geogrid mixing reinforced lightweight soil. The lightweight soil was reinforced with geogrid in order to increase its compressive strength. Test specimens were fabricated by various mixing conditions including cement content, initial water content, air content and geogrid layer and then unconfined compression tests were carried out. From the experimental results, it was found that unconfined compressive strength as well as stress-strain behavior of lightweight soil were strongly influenced by mixing conditions. The more cement content that is added to the mixture, the greater its unconfined compressive strength. However, the more initial water content or the more air foam content, the less its unconfined compressive strength. It was observed that the strength of geogrid reinforced lightweight soil was increased due to reinforcing effect by the geogrid for most cases except cement content less than 20%. In reinforced lightweight soil, secant modulus $(E_{50})$ was increased as the strength increased due to the inclusion of geogrid.

• Journal of the Korean Geotechnical Society
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• v.22 no.7
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• pp.37-44
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• 2006

This paper investigates strength characteristics and stress-strain behaviors of geogrid mixing reinforced lightweight soil. The lightweight soil was reinforced with geogrid in order to increase its compressive strength. Test specimens were fabricated by various mixing conditions including cement content, initial water content, air content and geogrid layer and then unconfined compression tests were carried out. From the experimental results, it was found that unconfined compressive strength as well as stress-strain behavior of lightweight soil was strongly influenced by mixing conditions. The more cement content that is added to the mixture, the greater its unconfined compressive strength. However, the more initial water content or the more air foam content, the less its unconfined compressive strength. It was observed that the compressive strength of reinforced lightweight soil increased reinforcing effect by the geogrid for most cases. Stress-strain relation of geogrid mixing reinforced lightweight soil showed a ductile behavior rather than a brittle behavior. In reinforced lightweight soil, secant modulus ($E_{50}$) also increased as its compressive strength increased due to the inclusion of geogrid.

• Journal of the Korean Society for Railway
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• v.5 no.2
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• pp.93-103
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• 2002

Reinforced earth structure has been regarded as general structure in order to achieve efficient land utilization as well as securing safety in railway service lines in other countries, but there are no construction actual results in Korea. In this study, the soil-geogrid interaction mechanism was investigated experimentally and numerical analysis was performed to predict Pull-out behaviour of geogrid embedded in reinforced earth body. This experimental data and analysis result can not contribute to understand the soil-geogrid interaction mechanism at soil-geogrid interface but also be used in design practice of the railway reinforced earth structures.

• Geomechanics and Engineering
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• v.14 no.4
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• pp.345-354
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• 2018

Currently, layered geogrid method (LGM) is the commonly practiced technique for reinforcement of slopes. In this paper the geogrid-box method (GBM) is introduced as a new approach for reinforcement of rock-soil slopes. To achieve the objectives of this study, a laboratory setup was designed and the slopes without reinforcements and reinforced with LGM and GBM were tested under the loading of a circular footing. The effect of vertical spacing between geogrid layers and box thickness on normalized bearing capacity and failure mechanism of slopes was investigated. A series of 3D finite element analysis were also performed using ABAQUS software to supplement the results of the model tests. The results indicated that the load-settlement behavior and the ultimate bearing capacity of footing can be significantly improved by the inclusion of reinforcing geogrid in the soil. It was found that for the slopes reinforced with GBM, the displacement contours are widely distributed in the rock-soil mass underneath the footing in greater width and depth than that in the reinforced slope with LGM, which in turn results in higher bearing capacity. It was also established that by reducing the thickness of geogrid-boxes, the distribution and depth of displacement contours increases and a longer failure surface is developed, which suggests the enhanced bearing capacity of the slope. Based on the studied designs, the ultimate bearing capacity of the GBM-reinforced slope was found to be 11.16% higher than that of the slope reinforced with LGM. The results also indicated that, reinforcement of rock-soil slopes using GBM causes an improvement in the ultimate bearing capacity as high as 24.8 times more than that of the unreinforced slope.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.958-967
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• 2004

This paper deal with cause and analysis about case of collapsed reinforced-soil retaining wall. The analysis of the cause was carried through experimentation, slop stability analysis and literature study. The experimentation treated the large direct shear test, the hydraulic conductivity test and the other basic test through backfill extracted from collapsed reinforced-soil retaining wall. The ultimate tensile strength was established by rib tensile strength test of geogrid. The analysis of internal and external stability of reinforced-soil retaining wall was performed on the basis of parameters. The result of analysis, reinforced-soil retaining wall and the slope at the dry season are stable. However, the factors that fine-grained soil at hydrometer test exceed the standard of the design, rainfall duration is too long at the time of collapse and monthly pricipitation is heavy are cause of the collapse.

• Proceedings of the KSR Conference
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• 2001.10a
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• pp.534-539
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• 2001

This paper presents the critical speed analysis of geogrid-reinforced rail roadbeds on soft soil. A rail roadbed on soft ground must be designed to avoid intolerable stress in the underlying soil and to give sufficient support for the rail system. At high speeds, the deformation of rail systems will gain dynamic amplification, and reach excessive values as a certain speed, here termed critical speed is approached. The elastic Winkler foundation model was used to predict the critical speed of geogrid-reinforced rail roadbeds on soft soil and the model properties were determined by the in-situ cyclic plate load test. Based on the parametric study of elastic beam on Winkler foundation model, the critical speed increase with the increase of the flexural risidity of subgrade EI and the stiffness coefficient of Winkler foundation k. From the in-situ cyclic load tests and analysis of elastic beam on Winkler foundation model, the critical speed increase with increase in number of reinforced layer and non-dimensional value for depth of first geogrid layers and the thickness of reinforced rail roadbed u/d.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.10a
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• pp.285-292
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• 1999

The cyclic plate load test were peformed to determine the behavior of reinforced soft ground with multiple layers of geogrid. Five series of test were conducted with varying the soil profile conditions which including the ground level, type of soil, and the thickness of each soil layer. The plate load test equipment was slightly modified to apply the cyclic load. Based on the cyclic plate load test results, the bearing capacity ratio(BCR), subbase modules, shear modules, the elastic rebound ratio, and reinforcing parameters are presented.

• Proceedings of the KSR Conference
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• 1999.11a
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• pp.415-422
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• 1999

The general concept of reinforced roadbed in the high-speed railway is to cope with the soft ground for the bearing capacity and settlement of foundation soil. The cyclic plate load tests were performed to determine the behavior of reinforced ground with multiple layers of geogrid underlying by soft soil. Five series of test were conducted with varying the soil profile conditions including the ground level, type of soil, and the thickness of each soil layer. Based on these plate load tests, laboratory model tests under cyclic loading were conducted to know the effect of geogrid reinforcement in particular for the high-speed rail roadbed. The permanent settlement and the behavior of earth pressure in reinforced roadbed subjected to a combination of static and dynamic loading are presented.

• 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.