• Geomechanics and Engineering
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• v.3 no.2
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• pp.117-130
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• 2011

The methods of design available for geocell-supported embankments are very few. Two of the earlier methods are considered in this paper and a third method is proposed and compared with them. In the first method called slip line method, plastic bearing failure of the soil was assumed and the additional resistance due to geocell layer is calculated using a non-symmetric slip line field in the soft foundation soil. In the second method based on slope stability analysis, general-purpose slope stability program was used to design the geocell mattress of required strength for embankment. In the third method proposed in this paper, geocell reinforcement is designed based on the plane strain finite element analysis of embankments. The geocell layer is modelled as an equivalent composite layer with modified strength and stiffness values. The strength and dimensions of geocell layer is estimated for the required bearing capacity or permissible deformations. These three design methods are compared through a design example. It is observed that the design method based on finite element simulations is most comprehensive because it addresses the issue of permissible deformations and also gives complete stress, deformation and strain behaviour of the embankment under given loading conditions.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 1998.10a
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• pp.419-424
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• 1998

The deduction methods for forced displacement depths caused by sea dike construction often assumed the shape of forced displacements and heaving. To investigate the shape of forced displacements and heaving, a model tests was performed. Results of the tests are as follows; 1) The shape of forced displacements can be assumed ellipse. 2) The shape of heaving can not be assumed uniform shape like a circle and Extents of heaving was varied with the loading height and width. 3) The shape of forced displacements caused by step construction, pebble embankments and soil embankments, also investigated.

• Journal of the Korean Geotechnical Society
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• v.23 no.6
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• pp.53-66
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• 2007

A series of model tests were performed to investigate the soil arching effect in embankments supported by piles with geosynthetics. In the model tests, model piles with isolated cap were inserted through the holes in a steel plate, which could be operated up and down. Then geosynthetics was laid on the pile caps below sand fills. The settlement of soft ground was simulated by lowering the plate. As the plate was lowered, the soil arching was mobilized in the embankments. The deformation of both the sand fills and geosynthetics were captured by camera. Also the loads acting on pile cap and the tensile strain of geosynthetics were monitored by data logging system. Model tests showed that the embankment loads transferred on pile cap by soil arching Increased rapidly with settlement of the soft ground. In case of the absence of geosynthetics, the loads acting on pile caps dropped to residual value after peak value, whereas loads on pile caps gradually increased until constant value in case of geosynthetic-reinforced. This illustrated that reinforcing with the geosynthetics has a good effect to restrain the settlement of embankments. Also, the deformation shape of geosynthetics between pile caps was circular. The embankment loads transferred on pile caps can be estimated by considering both soil arching and tensile strain of geosynthetics in embankments supported by piles with geosynthetics.

• Journal of the Korean Geotechnical Society
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• v.22 no.3
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• pp.13-21
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• 2006

Geosynthetic damage has attracted a major attention since the introduction of geotextiles for civil engineering applications. In this study 3 pilot trial embankments were carried out to investigate the behaviours of reinforced embankments over soft cohesive soils and to find the optimum methodology of embankments over soft soils. As the seamed part of polyester mat (PET, tensile strength 15 ton) used in the first full-scale field test was ruptured under progressing rotational slope failure because of unexpectedly rapid construction of embankments, the excessive pore water pressures were measured. On the soil behavior where tension explosion of mat was continued, pore pressure larger than the one caused by embankment height was measured. Especially, at the depth of 5.0 m under the ground pore pressure increased over long term. It was discussed with respect to the height of embankment and heaving behavior of soft soils.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.336-345
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• 2010

GS E&C was awarded the contract for the construction of Hanoi - Hai Phong Expressway Package EX-7 from Station Km 72+000 to Station Km 81+300 in December 2008. This project is the $7^{th}$ contract package of the 105.5 km long expressway near Hai Phong city, which includes a FCM-styled bridge along with high embankments over soft ground. For these high embankments, there is a need to treat the soft soil for improving the overall stability during construction and for reducing the post-construction settlement of the expressway. The Designer of this project had adopted four (4) different types of ground improvement techniques to treat the soft ground, including the prefabricated vertical drains (PVD), sand drains (SD), pack drains (PD, or sometimes called packed sand drains), and sand compaction piles (SCP). The main focus of soft soil treatment should be paid attention to the residual settlement after construction. In current design, however, it appeared that the secondary compression (or creep) of the improved soil layer and the consolidation settlement of the lower untreated compressible soil layer have been neglected in the estimation of the post-construction settlement. These uncalculated residual settlements may not only unsatisfy the design criteria but also raise serious problems during service period of this expressway. In this paper, the subsoil condition and current design were reviewed focusing on the employed soft soil treatment method and expected residual settlement.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.1695-1704
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• 2008

The problems associated with constructing high-speed concrete track embankments over soft compressible soil has lead to the development and/or extensive use of many of the ground improvement techniques used today. Drains, surcharge loading, and geosynthetic reinforcement, have all been used to solve the settlement and embankment stability issues associated with construction on soft soils. However, when time constraints are critical to the success of the project, owners have resorted to another innovative approach. Especially, the design criteria of residual settlement is limited as 30mm for concrete track embankment, it is very difficult to satisfy this standard using the former construction method. Pile net method consist of vertical columns that are designed to transfer the load of the embankment through the soft compressible soil layer to a firm foundation and one or more layers of geosynthetic reinforcement placed between the top of the columns and the bottom of the embankment. This paper will present the guidelines for the design of pile net method to supported embankments. These guidelines were developed based on a review of current design methodologies and a parametric study of design variables using numerical modeling.

• Proceedings of the KSR Conference
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• 2009.05a
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• pp.1519-1524
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• 2009

Construction of high-speed concrete track embankments over soft ground needs many of the ground improvement techniques. Drains, surcharge loading, and geosynthetic reinforcement, have all been used to solve the settlement and embankment stability issues associated with construction on soft soils. However, when time constraints are critical to the success of the project, another measures should be considered. Especially, since the design criteria of residual settlement is limited as 30mm for concrete track embankment, it is very difficult to satisfy this allowable settlement by using the former construction method. Pile net method consist of vertical columns that are designed to transfer the load of the embankment through the soft compressible soil layer to a firm foundation and one or more layers of geosynthetic reinforcement placed between the top of the columns and the bottom of the embankment. In this paper, three cases with different embankment height and number of geosynthetic reinforcement, were studied through FEM analysis for efficient use of pile net method.

• Structural Engineering and Mechanics
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• v.56 no.4
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• pp.507-534
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• 2015

The present work investigates the behavior of the embankment models resting on soft soil reinforced with ordinary and stone columns encased with geogrid. Model tests were performed with different spacing distances between stone columns and two lengths to diameter ratios (L/d) of the stone columns, in addition to different embankment heights. A total number of 42 model tests were carried out on a soil with undrianed shear strength $${\sim_\sim}10kPa$$. The models consist of stone columns embankment at s/d equal to 2.5, 3 and 4 with L/d ratio equal 5 and 8. Three embankment heights; 200 mm, 250 mm and 300 mm were tested for both tests of ordinary (OSC) and geogrid encased stone columns (ESC). Three earth pressure cells were used to measure directly the vertical effective stress on column at the top of the middle stone column under the center line of embankment and on the edge stone column for all models while the third cell was placed at the base of embankment between two columns to measure the vertical effective stress in soft soil directly. The performance of stone columns embankments relies upon the ability of the granular embankment material to arch over the 'gaps' between the stone columns spacing. The results showed that the ratio of the embankment height to the clear spacing between columns (h/s-d) is a key parameter. It is found that (h/s-d)<1.2 and 1.4 for OSC and ESC, respectively; (h is the embankment height, s is the spacing between columns and d is the diameter of stone columns), no effect of arching is pronounced, the settlement at the surface of the embankment is very large, and the stress acting on the subsoil is virtually unmodified from the nominal overburden stress. When $(h/s-d){\geq}2.2$ for OSC and ESC respectively, full arching will occur and minimum stress on subsoil between stone columns will act, so the range of critical embankment height will be 1.2 (h/sd) to 2.2 (h/s-d) for both OSC and ESC models.

• Journal of the Korean Geotechnical Society
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• v.28 no.9
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• pp.5-15
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• 2012

Field monitoring data for embankments in thirteen road construction sites at coastal area of the Korean Peninsula were analyzed to investigate the characteristics of lateral flow in soft grounds, to which vertical drain methods were applied. First of all, the effect of the embankment scale on the lateral flow was investigated. Thicker soft soils and lager relative embankment scale produced more horizontal displacements in soft grounds. Especially, if thick soft grounds were placed, the relative embankment scale, which was given by the ratio of thickness of soft ground to the bottom width of embankments, became larger and in turn large horizontal displacement was produced. And also higher filling velocity of embankments induced more horizontal displacements in soft grounds. The other major factors affecting the lateral flow in soft ground were the thickness and undrained shear strength of soft grounds, the soil modulus and the stability number. Maximum horizontal displacement was induced by less undrained shear strength and soil modulus of soft grounds. Also more stability numbers produced more maximum horizontal displacements. When the shear deformation does not develop, the stability number was less than 3.0 and the safety factor of bearing was more than 1.7. However, if the stability number was more than 5.14 and the safety factor of bearing was less than 1.0, the unstable shear failure developed in soft ground. 50mm can be recommended as a criterion of the allowable maximum horizontal displacement to prevent the shear deformation in soft ground, while 100mm can be recommended as a criterion of the allowable maximum horizontal displacement to prevent the shear failure in soft ground.

• Journal of the Korean Geotechnical Society
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• v.30 no.6
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• pp.5-21
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• 2014

It has been pointed out that the collapses of unsaturated road embankments caused by earthquake are attributed to high water content caused by the seepage of the underground water and/or the rainfall infiltration. Hence, it is important to study influences of water content on the dynamic stability and deformation mode of unsaturated road embankments for development of a proper design scheme including an effective reinforcement to prevent severe damage. This study demonstrates dynamic centrifugal model tests with different water contents to investigate the effect of water content on deformation and failure behaviors of unsaturated road embankments. Based on the measurement of displacement, the pore water pressure and the acceleration during dynamic loading, dynamic behavior of the unsaturated road embankments with about optimum water content and the higher water content than the optimum one have been examined. In addition, an image analysis has revealed the displacement field and the distributions of strains in the road embankment, by which deformation mode of the road embankment with higher water content has been clarified. It has been confirmed that in the case of higher water content the settlement of the crown is large mainly owing to the volume compression underneath the crown, while the small confining pressure at the toe and near the slope surface induces large shear deformation with volume expansion.