• Proceedings of the KSR Conference
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• 2004.10a
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• pp.1065-1070
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• 2004

Recenlty, there are many cases that structures are constructed on soft ground in domestic. Generally in those cases, appropriate geotechnical techniques for the ground are needed. In this study, an example for ground improvement of OO railroad station construction site is introduced and analyzed. The ground conditions of this site which is soft ground are that N value is under 6, average depth and ground water table is 24.4m, GL-1.7. So, as a countermeasure technique for bearing reinforcement, Compaction Grouting System (CGS) method was applied on construction site. To estimate the application of CGS method, piezo cone penetration test and static pile loading test were carried out during the construction. Results of analysis show that CGS method for improving the bearing capacity of soft ground is applicable for the ground well.

• Journal of the Korean GEO-environmental Society
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• v.13 no.11
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• pp.93-101
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• 2012

SCP is a construction method that maximizes the effects of ground improvement by creating sand piles, which are formed by the compaction within soft ground. SCP is mainly used for consolidation and drain effects in clayey soils, and as a liquefaction countermeasure through effects such as compaction in loose sandy soils. In the design of SCP, if the sand piles with high stiffness are not taken into account, it can become a design that overly considered safety, and increased construction costs are highly likely to cause economic disadvantages. The changes in stress conditions and compaction mechanisms in the subsurface have been identified to a certain extent by study findings to date. However, the studies that considered SCP and in-situ ground as composite ground are fairly limited, and therefore, those studies have not achieved enough results to fully explain the relevant topics. In this study, the ground improved by SCP was regarded as the composite ground that consists of SCP and in-situ ground. Moreover, employing a CID test, this study examined the changes in the stress conditions of in-situ ground according to the installation of SCP through the relations between $K_0$ and SCP replacement ratio. At the same, whether the SCP installation procedure can be recreated in a laboratory was examined using a cyclic triaxial test. According to the test results, the changes in the stress conditions of the original ground occurred most largely in an initial stage of SCP installation, and after a certain time point, the vibration for SCP installation did not have a great influence on the changes in the stress conditions of the ground. Moreover, in order to recreate the behaviors of in-suit ground according to SCP in a laboratory, cyclic loading, which corresponds to casing vibration, was concluded to be essentially required.

• Journal of the Korean GEO-environmental Society
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• v.13 no.9
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• pp.5-16
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• 2012

In the case of using the soil materials created by cutting in-situ ground directly without adjusting particle size, it is recommendable to seek the compaction property or material constant required for filling design or density control through indoor test, and many studies on this subject have been carried out during that time. The researches conducted during that time, however, were focused on the mixed materials with different diameters that exist in a natural condition. There has been no study conducted using coal fly ash that is by-product of the thermal power plant that is actively considered as the building materials. Therefore, this study was aimed at implementing compaction test and examining the basic engineering property in order to explore the influence of crushing the particles through compacting the admixture of crushed stone and coal fly ash produced from thermal power plant on its engineering property, and then the impact of the admixture volume of each material on compaction property and material property by conducting the One-Dimensional Compression Test. As result of compaction test, the optimum moisture ratio of coal fly ash was shown to be approx. 23%. As result of compaction test in accordance with the mixed ratio of coal fly ash and crushed stone under the same compaction energy and moisture ratio, dry unit weight tended to drop when the mixed ratio of coal fly ash exceeded 30%, while it reached approx. $1.81gf/cm^3$ when the mixed ratio was 30%. As result of One-Dimensional Compression Test in accordance with the mixed ratio of crushed stone and coal fly ash, the change in void ratio by particle crushing was at the highest level in the case of coal fly ash 100%, while the lowest level in the case of crushed stone 100%. In the case of mixed materials of crushed stone and coal fly ash, compression index was at the lowest level in case of coal fly ash 30%, and therefore this ratio of mixed material was judged to be the most stable from an engineering aspect.

• Journal of the Korean Geosynthetics Society
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• v.17 no.1
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• pp.127-137
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• 2018

Gravel Compaction Pile (hereinafter referred to as GCP) is a ground improvement technique by packing crushed stones on fragile clay ground, pressing it, and forming stakes on the foundation. Although many researchers have analyzed stress behavior of GCP composite ground on domestic GCP technique using laboratory experiment and field experiment, analyses of stress behavior according to the difference of stiffness of mat foundation loaded on the upper foundation of GCP composite ground have not been done actively. Therefore, this study aimed to identify the stress concentration ratio in accordance with the difference of basis stiffness by interpreting figures. To perform this, replacement ratio was changed and modelled using ABAQUS, software for finite element analysis and analyzed the stress concentration ratio, amounts of settlement, and maximum amounts of horizontal displacement of composite ground in accordance with the difference of stiffness. An analysis showed that the stress concentration ratio of rigid foundation was highly assessed than unloading of flexible foundation in case of unloading, while amounts of settlement under flexible unloading condition were slightly higher than under rigid condition. This indicates that the characteristic of stress behavior on the different stiffness of upper foundation needs to be clarified. In addition, the maximum horizontal displacement was generated in a constant level regardless of the difference of stiffness.

• The Journal of Engineering Geology
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• v.26 no.4
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• pp.485-495
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• 2016

To reinforce and improve the soft ground under a breakwater while using materials efficiently, the replacement ratio and leaving periods of surcharge load are optimized probabilistically. The results of Bayesian updating of the random variables using prior information decrease uncertainty by up to 39.8%, and using prior information with more samples results in a sharp decrease in uncertainty. Replacement ratios of 15%-40% are analyzed using First Order Reliability Method and Monte Carlo simulation to optimize the replacement ratio. The results show that replacement ratios of 20% and 25% are acceptable at the column jet grouting area and the granular compaction pile area, respectively. Life cycle costs are also compared to optimize the replacement ratios within allowable ranges. The results show that a range of 20%-30% is the most economical during the total life cycle. This means that initial construction cost, maintenance cost and failure loss cost are minimized during total life cycle. Probabilistic analysis for leaving periods of shows that three months acceptable. Design optimization with respect to life cycle cost is important to minimize maintenance costs and retain the performance of the structures for the required period. Therefore, more case studies that consider the maintenance costs of soil structures are necessary to establish relevant design codes.

• Journal of the Korean GEO-environmental Society
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• v.20 no.2
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• pp.19-28
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• 2019

Grounds of the western coast of the Korean Peninsular are mostly composed of soft and cohesive soils, and it is necessary to carry out soil improvement before construction. The CGS (Compaction Grouting System) method has been commonly applied for the purpose of not only improving soft ground but also serving as the pile foundation of a bridge. In this paper, the CGS method was applied to the Incheon International Airport facility site, which consists of reclaimed landfill and soft clay soil, so as to evaluate the applicability of this soil improvement method to soft clay ground formations. Futhermore, results of construction were intensively studied along with a series of field experiments and theoretical consideration. The cone penetration tests were performed to assess the ground improvement effect of the CGS method. Consequently, the application of CGS method led to an increase in soil strength enough to be used as the pile foundation to support the bridge at the site. In addition, the size of the upper grout-bulb was estimated by adopting the cavity expansion theory and compared with that of actual grout bulb exhumed in the field. Therefore, it is proved that the cavity expansion theory can be utilized to predict and evaluate the improvement of soft ground.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.3
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• pp.155-164
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• 2019

In this study, the soil-structure interaction(SSI) effect on the seismic response of LNG storage tanks was investigated according to the type of foundation. For this purpose, a typical of LNG storage tank with a diameter of 71m, which is constructed on a 30m thick clay layer over bedrock was selected, and nonlinearity of the soil was taken into account by the equivalent linearization method. Four different types of foundations including shallow foundation, piled raft foundation, and pile foundations(surface and floating types) were considered. In addition, the effect of soil compaction in group piles on seismic response of the tank was investigated. The KIESSI-3D, which is a SSI analysis package in the frequency domain, was used for the SSI analysis. Stresses in the outer tank, and base shear and overturning moment in the inner tank were calculated. From the comparisons, the following conclusions could be made: (1) Conventional fixed base seismic responses of outer tank and inner tank can be much larger than those of considering the SSI effect; (2) The influence of SSI on the dynamic response of the inner tank and the outer tank depends on the foundation types; and (3) Change in the seismic response of the structure by soil compaction in the piled raft foundation is about 10% and its effect is not negligible in the seismic design of the structure.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.1228-1236
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• 2006

In soft ground, There are many case that Bridge Abutment is constructed after soil improvement in order to reduce the Negative Friction and prevent from Lateral Soil movements of Bridge Abutment. That section of Horizontal Subgrade Reaction $Modulus(K_h)$ derivation has much important mean due to Horizontal Stability of Abutment. It is come from behavior of Pile and Soil within depth of $1/\beta$. After Soil Improvement, however, If Bridge Abutment was construction, It's not impossible to carry out Field Investigation After Ground of Improved at design stage. Therefore, It's not able to derivate Horizontal Subgrade Reaction $Modulus(K_h)$. Therefore, in this case of study compare with Field Construction Test Data in order to derivation of Horizontal Subgrade Reaction $Modulus(K_h)$ and Reliability in terms of ground of Bridge Abutment by Sand Compaction Pile(SCP) during design of The 2nd Bridge Connection Road of Incheon International Airport. In this paper determine, Soil Property(The rate of strength increase, $c_u$ so on) and Horizontal Subgrade Reaction $Modulus(K_h)$ after soil improvement at design stage.

• Journal of the Korean Geotechnical Society
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• v.27 no.3
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• pp.55-61
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• 2011

Generally, the Box-Culvert in levee is destroyed by various reasons. Especially when Box-Culvert is installed over the pile foundation in soft ground, the failure occurrs for 1) the weakness of compaction in Box-Culvert side by the differential settlement between outer ground and inner soil prism, 2) hydraulic fracturing and disturbance of Box-Culvert side soil by the repeated acting of seepage pressure at flood time. Also the side of Box-Culvert is difficult to compact and the shear resistance is reduced by more than 1/3 for the reduction of friction caused by the difference of material property. In this study, a series of model tests are conducted for the analysis of the development mechanism of outer ground and inner soil prism by the differential settlement using the pile foundation in soft ground, and cavity suppressed technique is suggested by the analysis of base plate enlargement effect.

• Journal of the Earthquake Engineering Society of Korea
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• v.24 no.5
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• pp.211-217
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• 2020

Earthquake preparedness has become more important with recent increase in the number of earthquakes in Korea, but many existing structures are not prepared for earthquakes. There are various types of liquefaction prevention method that can be applied, such as compaction, replacement, dewatering, and inhibition of shear strain. However, most of the liquefaction prevention methods are applied before construction, and it is important to find optimal methods that can be applied to existing structures and that have few effects on the environment, such as noise, vibration, and changes in underground water level. The purpose of this study is to estimate the correlation between the displacement of a structure and variations of pore water pressure on the ground in accordance with the depth of the sheet file when liquidation occurs. To achieve this, a shaking table test was performed for Joo-Mun-Jin standard sand and an earth pressure, accelerometer, pore water pressure transducer, and LVDT were installed in both the non-liquefiable layer and the liquefiable layer to measure the subsidence and excess pore water pressure in accordance with the time of each embedded depth. Then the results were analyzed. A comparison of the pore water pressure in accordance with Hsp/Hsl was shown to prevent lateral water flow at 1, 0.85 and confirmed that the pore water pressure increased. In addition, the relationship between Hsp/Hsl and subsidence was expressed as a trend line to calculate the expected settlement rate formula for the embedded depth ratio.