• Geomechanics and Engineering
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• v.34 no.6
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• pp.665-681
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• 2023

Liquefaction is one of the most devastating geotechnical phenomena that severely damage vital structures and lifelines. Before constructing structures on problematic ground, it is necessary to improve the site and solve the geotechnical problem. Among ground improvement methods dealing with liquefaction, gravel drain (GD) columns and deep soil mixing (DSM) columns are popular. In this study, the results of a series of seismic experiments in a 1g environment on a structure located over liquefiable ground with different thicknesses reinforced with GD and DSM techniques were presented. The dynamic response of the reinforced ground system was investigated based on the parameters of subsidence rate, excess pore water pressure ratio, and maximum acceleration. The time history of the input acceleration was applied harmonically with an acceleration range of 0.2g and at frequencies of 1, 2, and 3 Hz. The results show that the thickness of the liquefiable layer and the frequency of the input motion have a significant impact on the effectiveness of the improvement method and all responses. Among the two techniques used, DSM in thick liquefied layers was much more efficient than GD in controlling the subsidence and rupture of the soil under the foundation. Maximum settlement values, settlement rate, and foundation rotation in the thicker liquefied layer at the 1-Hz input frequency were higher than at other frequencies. At low thicknesses, the dynamic behavior of the GD was closer to that of the DSM.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.1
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• pp.194-202
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• 2017

In this study, we measured and analyzed electrical noise signals present in devices and systems operated in industrial facilities. Based on the analytic findings, we studied the most effective improvement measures for eliminating such noise signals. Leakage current and ground current generate data interferences in communication systems, and therefore we measured leakage current and ground current. We also measured and analyzed electrical noises in power systems to predict noise pathways and interference routes. Furthermore, we proposed the most effective and reliable improvement measures for blocking off various noise signals and safely eliminating them by improving the internal wiring of the facilities and grounding systems. As a final step, we conducted the proposed improvement measures and confirmed that they helped to improve the operations of the device sand systems in service by re-measuring electrical noise signals and comparing them with those measured before the proposed improvement measures were implemented.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.467-472
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• 2010

Individual vacuum pressure method is soft ground improvement technique, in which a vacuum pressure can be directly applied to the vertical drain board to promote consolidation and strengthening the soft ground. This method does not require a surcharge load, different to embankment or pre-loading method. In this study, given the inner displacement of the ground where the individual vacuum pressure is applied, this dissertation aimed to reproduce the state of stress in the ground that is subject to the constraints created by the depth of improvement area. Modified Cam Clay theory which made it possible to take into account the isotropic displacement of the ground was applied to the NAP-IVP used simulation; the conception of equivalent permeability proposed by Hird was also applied so that the 3-dimensional real construction effect of drain materials could be reflected in the analysis.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.10a
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• pp.147-158
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• 2001

In general, two methods have been used to predict settlement of soft ground. One method is Terzaghi's one dimensional consolidation theory which gives time-settlement relationship using the standard consolidation test results. The other is forecasting method of ground settlement to be occured in the future using in-situ monitoring data. The above both methods have some defects in application manner or in itself especially in very deep and soft clayey ground. In view of the lessons and experiences of soft ground improvement projects, several techniques were proposed for more accurate theorectical calculation of consolidation settlement as follows ; ① Subdivision of soft ground, ② Consideration of secondary compression, ③ Using the modified compression index, etc. And also, revised hyperbolic fitting method was suggested to minimize the error of predicted future settlement. In addition, revised De-Beer equation of immediate settlement of loose sandy soil was proposed to overcome the tendency to show too small settlement calculation results by original De-Deer equation. And also, considering the various effects of settlement delay in the improved ground by vertical drains, time-settlement caculation equation(Onoue method) was revised to match the tendency of settlement delay by using the characteristics of discharge capacity decreases of vertical drain with time elapse by the pattern of hyperbolic equation.

• Journal of Navigation and Port Research
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• v.33 no.2
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• pp.119-125
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• 2009

The effect of plastic board drains (PBDs)on ground improvement was checked out considering three crucial factors: ground settlement, undrained shear strength, and residual water head. First, the settlement analysis including initial settlement induced by reclamation of sand mat was conducted by back calculation analysis with measured data. Its result showed toot the PBDs used for this site worked well on improving soft ground. Secondly, the undrained shear strength was investigated by laboratory and in-situ tests including unconsolidated-undrained triaxial compression (UU) tests, unconfined compression tests, in-situ vane tests, and cone penetration tests. From the test results, they showed that the undrained shear strength of the improved ground by PBDs was significantly increased as well as the strength increasing ratio especially $10{\sim}15m$ below the ground surface on site. Thirdly, the residual water head measurement from the in situ dissipation test was found the same as the static water head, which indicated primary consolidation was completed and the effect of soil improvement with PBDs can be confirmed.

• Proceedings of the KIEE Conference
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• 2006.04a
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• pp.291-293
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• 2006

• Journal of the Korean GEO-environmental Society
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• v.16 no.7
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• pp.35-42
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• 2015

Grouting method has been widely used for the ground improvement and stabilization: mostly to block or control the ground water in the early years and to improve the ground, repair the structure in recent years, ever increasing its use. Despite many advantages so far, the existing grouting method also has some shortcomings including uncertain permeation of grouting with gravity type if the voids between the soil particles are narrow, and problems due to the relaxation of the neighboring ground when injected using injection pressure. As an alternative, a vibration injection method with constant amplitude and frequency has been developed in recent years, with the vibration grouting being reported to have a permeability increasing effect of grout material compared with the positive pressure injection type. Accordingly, the purpose of this study is to investigate the improvement effect of the vibration grouting that applies short-period vibration energy by varying vibration cycle, vibration time and ground conditions to evaluate the strength enhancing effect of grouting materials, expansion effect of grouting body, ground improvement effect of the grouting and the penetration characteristics of the rock joint. The findings of this study show the improved compressive strength of grout, expansion of grouting body and increased penetration rate, according to the vibration compared with non-vibration under the loose soil condition.

• Environmental and Resource Economics Review
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• v.31 no.4
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• pp.619-644
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• 2022

The purpose of this study is to estimate the economic benefit of improving ground water quality in Jeju Island, where groundwater pollution has recently become a social issue and various water quality improvement projects are being promoted. By applying the contingent valuation method, an online survey was conducted on Jeju Island residents to analyze the response data of 542 respondents and estimate the mean willingness to pay using 16 models. The estimation of the double-bounded dichotomous choice model confirmed that each household was willing to pay 28,008 won per year, with the willingness to pay estimated at a minimum of 17,762 won and a maximum of 37,416 won based on different models. The total annual benefit for Jeju Island's ground water quality improvement was estimated to be about 8.66 billion won , and socioeconomic factors influencing willingness-to-pay were investigated. This study is expected to serve as a foundation for the development of environmental improvement policies by assisting in the understanding of Jeju Island's unique water resource environment.

• Journal of the Korean Geotechnical Society
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• v.29 no.11
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• pp.29-47
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• 2013

This study undertook research on the sections of 90 harbor structures which applied a pile-type soil improvement using the soil-cement pile and then, determined the minimum replacement rate for each section, showing sufficient stability in all relevant studies including numerical analysis. The reliability of the numerical analysis was verified by a centrifuge model test. As a result of the study, it was revealed that when the foundation soil is too soft ($s_u$ = under 15 kPa), it is unsuitable to apply a pile-type ground improvement to a soil improvement regardless of types of super structures. And a pile-type soil improvement was found to be suitable for a harbor structure with the relative stiffness ratio (n) of less than 50~75 at a maximum and the 2~3 MPa strength of the soil-cement pile. Furthermore the governing factor for the minimum replacement rate for the pile-type soil improvement was turned out to be the allowable horizontal displacement. Therefore, the primary review to see the applicability of the pile-type soil improvement requires the evaluation of horizontal displacements.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.123-131
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• 2009

The study decided the improvement depth of soft ground of deep mixing method through 2 and 3 dimension finite element method and following results were acquired. 1. 2 dimension analysis shows settlement 10% more estimated than 3 dimension analysis. 2. When the rate of replacement is under 5%, the settlement sharply increased. 3. The most economical design for the levee was decided 3.0m for width direction, 6.0m for length direction and 8.0m for improvement depth. 4. When the soft ground is developed through deep mixing method, the decision of improvement should be decided through 3 dimension analysis than 2 dimension analysis.