• Interaction and multiscale mechanics
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• v.5 no.4
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• pp.369-383
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• 2012

In this paper, soil-structure interaction analysis has been presented for beams resting on multilayered geosynthetic-reinforced granular fill-soft soil system. The soft soil and geosynthetic reinforcements are idealized as nonlinear springs and elastic membranes, respectively. The governing differential equations are solved by finite difference technique and the results are presented in non-dimensional form. It is observed from the study that use of geosynthetic reinforcement is not very effective for maximum settlement reduction in case of very rigid beam. Similarly the reinforcements are not effective for shear force reduction if the granular fill has very high shear modulus value. However, multilayered reinforced system is very effective for bending moment and differential settlement reduction.

• Journal of the Korean GEO-environmental Society
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• v.1 no.1
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• pp.27-33
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• 2000

Stone columns is ground improvement method which is composed of compacted gravel or crushed stone inserted into the soft ground consisting of loose sand and clay by replacement method. Generally stone columns are constructed in silty clay, above 70% replacement rate for increasing the bearing capacity and shear strength. Low replacement stone columns method is limited below 30% at replacement rate-premising strength increase of clay ground is estimated efficiently. This study, laboratory model tests were conducted to investigate the consolidation drainage promotion and shear strength increase effect in soft ground with replacement rate by stone columns. The settlement reduction effect and settlement reduction coefficients increase with increasing the replacement rate in composite ground. The results of model tests indicate that consolidation promotion effect is proved. The increasing strength of composite ground was verified by vane shear tests.

• Journal of the Korean GEO-environmental Society
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• v.7 no.1
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• pp.5-18
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• 2006

Stone column or granular compaction pile have been used in widely during the several decades as a technique to reinforce soft cohesive soils and increase bearing capacity, accelerate consolidation settlement of the foundation soil. The bearing capacity of the granular compaction pile is governed mainly by the lateral confining pressure mobilized in the native soft soil to restrain bulging collapse of the granular pile. Therefore, the technique becomes unfeasible in soft, compressible clayey soils that do not provide sufficient lateral confinement. This paper presents the main results of numerical study of granular compaction pile which is partly mixed with lean concrete. 3D finite element analyses are performed with composite reinforced foundations by both granular compaction pile and partly mixed granular compaction pile with lean-mixed concrete. Finally, a regression formula for calculating settlement reduction coefficients is proposed in this study by using numerical analysis results and applicability of the proposed method is identified by a series of parametric study about settlement reduction coefficients.

• Geomechanics and Engineering
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• v.15 no.3
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• pp.851-859
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• 2018

There are two primary causes of the ground movement due to tunnelling in urban areas; firstly the lost ground and secondly the groundwater depression during construction. The groundwater depression was usually not considered as a cause of settlement in previous research works. The main purpose of this study is to analyze the combined effect of these two phenomena on the transverse settlement trough. Centrifuge model tests and numerical analysis were primarily selected as the methodology. The characteristics of settlement trough were analyzed by performing centrifuge model tests where acceleration reached up to 80g condition. Two different types of tunnel models of 180 mm diameter were prepared in order to match the prototype of a large tunnel of 14.4 m diameter. A volume loss model was made to simulate the excavation procedure at different volume loss and a drainage tunnel model was made to simulate the reduction in pore pressure distribution. Numerical analysis was performed using FLAC 2D program in order to analyze the effects of various groundwater depression values on the settlement trough. Unconfined fluid flow condition was selected to develop the phreatic surface and groundwater level on the surface. The settlement troughs obtained in the results were investigated according to the combined effect of excavation and groundwater depression. Subsequently, a new curve is suggested to consider elastic settlement in the modified Gaussian curve. The results show that the effects of groundwater depression are considerable as the settlement trough gets deeper and wider compared to the trough obtained only due to excavation. The relationships of maximum settlement and infection point with the reduced pore pressure at tunnel centerline are also suggested.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.4
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• pp.715-722
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• 2016

Most of the domestic railroad tracks are ballast track and repetitive maintenance is required in this track. Therefore, it is necessary to optimize maintenance process for maintenance cost reduction and more effective maintenance. For this, it is important to develop a reasonable settlement progressive model of ballast layer. However, the behavior of ballast is different to that of soils, since ballast is composed of large coarse gravel. Thus, in this study, we carried out numerical analysis by using the discrete element method (PFC 2D) for better understanding of ballast settlement and development of reasonable settlement progressive model. And, we evaluated the settlement of ballast according to particles shape, porosity and loading conditions.

• Journal of the Korean Geosynthetics Society
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• v.18 no.1
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• pp.1-9
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• 2019

This study investigated settlement and scouring characteristics of artificial reef reinforced with various reinforcement types to reduce settlement and scouring. Three reinforcement types were prepared: geogrid, geogrid-bamboo mat (GBM) and seaweed-pile mat (SPM). Various laboratory tests such as bearing capacity test, large size settlement test, two-dimensional flow scour test were performed according to different soil types (sand, silt, clay). Laboratory test results indicated that bearing capacity of seabed with a reinforced artificial reef increased and its settlement and scour depth reduced for all reinforcement types. Especially, reinforcement effect tends to be greater in clay soft ground rather than sand and silt grounds.

• 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.

• Journal of the Korean Geotechnical Society
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• v.29 no.3
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• pp.15-27
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• 2013

A vacuum pressure method has been developed to solve many problems in the conventional surcharge method such as embankments, and its application has increased in the country. Recently, to control target settlements in the field, there have been many studies on the comparison of settlements between vacuum pressure method and surcharge load method in the same conditions. In this study, the settlement characteristics of soil subjected to vacuum pressure and surcharge pressure are discussed. The results indicate that if vacuum pressure is applied to the improvement of soft ground, there will be inward lateral displacement and the vacuum pressure will induce generally less settlement than a surcharge load of the same magnitude. The range of settlement reduction ratio is 0.54~0.67 based on Hooke's law, 0.91 based on field cases, 0.81 based on laboratory oedometer tests, 0.75 based on the theory of elasticity and coefficient of volumetric compressibility and 0.77~0.93 in its recent applications to the thick soft ground.

• Journal of the Korean Geotechnical Society
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• v.39 no.11
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• pp.23-31
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• 2023

The escalating settlements observed in concrete slab tracks pose a significant challenge in Korea, raising concerns about their adverse impact on the safe operation of high-speed railways and the substantial costs involved in restoration. A primary contributor to these settlements is identified as the utilization of rock materials sourced from tunnel construction, incorporated into the lower subgrade without the requisite soil mixing to achieve an appropriate particle size distribution. This study employs numerical analysis to evaluate the efficacy of partial reinforcement in reducing settlements in rock-filled lower subgrades. Column-shaped reinforcement areas strategically positioned at regular intervals in the lower subgrade induce soil arching in the upper subgrade, leading to a concentration of soil loads on the reinforced areas and consequent settlement reduction. The analysis employs finite element methods to investigate the influence of the size, stiffness, and spacing of the reinforced areas on settlement reduction in the lower subgrade. The numerical results guide the formulation of an optimal design approach, proposing a method to determine the minimum spacing required for reinforcements to effectively limit settlements within acceptable bounds. This research contributes valuable insights into addressing the challenges associated with settlement in concrete slab tracks, offering a basis for informed decision-making in railway infrastructure management.

• Journal of the Korean Geosynthetics Society
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• v.6 no.4
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• pp.7-13
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• 2007

When the structure such as roadway, railway are constructed on abandoned coal mine area, the countermeasure to prevent settlements is necessary. In this study, numerical analyses are performed to evaluate the effect of the various countermeasures. As a results, the method which is filling the coal mine is more effective than that of reinforcing the ground above the coal mine. The ground settlement decreases hyperbolically with increasing the filling ratio of the coal mine. Also, the relationship between the filling ratio and the settlement reduction ratio is discussed precisely.