• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.09a
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• pp.98-106
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• 2001

The deformation characteristics of cohesionless soils in Korea were investigated using resonant column tests. Total 60 samples, which were sampled from sedimentary and residual soils and reconstituted using controlled particle-size distributions, were prepared. The confining pressure applied in the tests ranges from 20 kPa to 500 kPa. The test results ware categorized into 3 groups including clean sands, silt and silty sand, and residual soils. Based on test results, the small-strain shear modulus(G$_{max}$) and damping ratio(D$_{min}$) were determined and the effects of confinement on G$_{max}$ and D$_{max}$ were characterized. The empirical correlations predicting G$_{max}$ were suggested for 3 group soils. Nonlinear deformational characteristics of clean sands are significantly affected by confining pressure and the ranges and mean curves for G and D are suggested considering the range of confining Pressure. The silt and silty sand and residual soils were weakly affected by confining pressure, so the representative ranges and curves, independent of confining pressure, were proposed.d.posed.d.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.5 no.5
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• pp.11-21
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• 2002

A series of model tests is performed to evaluate the relationship between soil and a buried pipe in soil undergoing lateral movement. As the result of the model tests, a wedge zone and plastic flow zones could be observed in front of the pipe. And also an arc failure of cylindrical cavity could be observed at both upper and lower zones. Failure shapes in both cohesionless and cohesive soils are nearly same, which was investigated failure angle of $45^{\circ}+{\phi}/2$. In the cohesionless soil, the higher relative density produces the larger arc of cylindrical cavity. On the basis of failure mode observed from model tests, the lateral earth pressure acting on a buried pipe in soil undergoing lateral movement could be applying the cylindrical cavity extension mode. The deformation behavior of soils was typically appeared in three divisions, which are elastic zones, plastic zones and pressure behavior zones.

• Journal of the Korean Geotechnical Society
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• v.17 no.5
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• pp.115-128
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• 2001

본 논문에서는 반복하중이나 지진하중을 받는 지반-구조물 시스템의 설계에 필수적인 변수인 전단탄성계수와 감쇠비에 대한 연구를 국내에 존재하는 비점성토 지반에 대하여 수행하였다. 국내 퇴적토지반 및 풍화토지반에서 채취된 자연시료와 입도분포를 조정하여 제작한 시료를 포함하여 총 60개의 시료에 대하여 20kPa에서 500kPa의 구속응력 범위에서 공진주 시험을 수행하고, 이를 조립질 사질토, 실트 및 실트질 모래, 풍화토의 3개의 그룹으로 나누어 결과를 정리하였다. 저변형률 영역의 변형특성인 최대전단탄성계수와 최소감쇠비에 대하여 구속응력의 영향을 확인하였다. 최대전단탄성계수를 예측하는 경험식을 3개의 그룹별로 제안하였다. 최소감쇠비는 구속응력에 따른 분포영역을 제시하였다. 세립분이 적은 조립질 사질토의 경우, 비선형 변형특성이 구속응력의 영향을 뚜렷이 받고 있어 이를 주요한 변수로 고려하여 대표곡선과 분포영역을 제안하였다. 구속응력의 영향을 적게 받는 실트 및 실트질 모래와 풍화토는 구속응력에 관계없이 대표곡선과 분포영역을 제안하였다. 제안된 각 시료의 대표곡선과 기존의 Vucetic-Dobry와 Seed-Idriss가 제안한 곡선과 비교하였다. 본 논문의 연구결과는 국내지반의 비점성토 지반에 대한 지진해석이나 동하중을 받는 시스템의 해석시 유용하게 사용될 것으로 판단된다.

• Journal of the Korean Geotechnical Society
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• v.20 no.7
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• pp.25-32
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• 2004

This paper examines the results of full-scale field tests on micropiles and side resistance is evaluated with respect to axial displacements and soil properties. Both cohesive and cohesionless soils are included in this evaluation. For all practical purposes, the developed load-displacement relationship and the geotechnical soil properties for each micropile and soil type can be used to represent the available data well through normalized average values and empirical correlations. There is a significant difference in load-carrying capacity between micropiles and drilled shafts that results primarily from the micropile pressure-grouting installation effects on the state of stress in the ground. The results show that micropiles can have a significant increase of capacity over larger-diameter drilled shafts at shallower depths with D/B < 100 or so. In cohesive soils, the typical increase is on the order of 1.5 with values as high as 2.5. For cohesionless soils, the typical increases are in the range of 1.5 to 2.5 with values as high as 6.

• Geomechanics and Engineering
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• v.15 no.4
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• pp.987-995
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• 2018

In this study, a relationship between small-strain shear modulus ($G_{max}$) and overconsolidation ratio (OCR) based on shear wave velocity ($V_S$) measurement was established to identify the stress history of centrifuge model ground. A centrifuge test was conducted in various centrifugal acceleration levels including loading and unloading sequences to cause various stress histories on centrifuge model ground. The $V_S$ and vertical effective stress were measured at each level of acceleration. Then, a sensitivity analysis was conducted using testing data to ensure the suitability of OCR function for the tested cohesionless soils and found that OCR can be estimated based on $V_S$ measurements irrespective of normally-consolidated or overconsolidated loading conditions. Finally, the developed $G_{max}$-OCR relationship was applied to centrifuge models constructed and tested under various induced stress-history conditions. Through a series of tests, it was concluded that the induced stress history on centrifuge model by compaction, g-level variation, and past overburden load can be analysed quantitatively, and it is convinced that the OCR evaluation technique will contribute to better interpret the centrifuge test results.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.3 no.1
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• pp.62-69
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• 2000

Topography influences shallow landslide initiation through both concentration of subsurface flow and the gradient on slope stability. A model for the topographic influence on shallow landslide initiation developed by Mongomerry et al (1994) is applied to 24 places with similar terrain and subsurface flow. The criterion of landslide prone areas developed by Korea Forestry Administration (1998) is likely to misinterpreted under the condition of heavy rainfall. Soil saturation can be predicted by this model. This relative soil saturation can be used to analyze the stability of each topographic point in the case of cohesionless soils with spatially constant thickness and saturated conductivity. The three different stages of steady state rainfall predicting to cause instability in each topographic points provide a good measure of shallow landsliding possibility.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.673-678
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• 2002

Laboratory calibration chamber tests for cone penetrometers, pressuremeters and dilatometers in cohesionless soil specimens have been conducted by numerous researchers. However, there have been only few applications to compacted or preconsolidated cohesive soils. Therefore, for the first time, Calibration Chamber System was developed in Korea University. This can be attributed to the extremely time consuming and laborious process involved in the preparation of large cohesive soil specimens in addition to other complexities involving instrumentation for pore pressure monitoring and the need for maintaing saturation by back pressure. Chamber System with similar principle as LSU Chamber System was made of more strengthen and complementary form by increasing system diameter(1.2m), carrying out 1st and 2nd consolidation process in one system for smooth and safe work, accurate Data Aquisition.

• Geotechnical Engineering
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• v.13 no.4
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• pp.109-120
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• 1997

In the working stress conditions, the strain level in a soil mass experienced by existing structures and during construction is less than about 0.1-1%. In order to analyse the deformational behavior accurately, the in-situ testing technique which provides the reliable deformational characteristics at small strains, needs to be developed. The purpose of this paper is to measure the small-strain shear modulus of soils by using pressuremeter test(PMT). PMT is a unique method for assessing directly the in-situ shear modulus of soils with strain amplitude. For the accurate small strain measurements without initial disturbance effect, the unloading-reloading cycle was used and the measured modulus was corrected in view of the relevant stress and strain levels around the PMT probe during testing. Not only in the calibration chamber but in the field, PMT tests were performed on the cohesionless soils. The variation in shear modulus with strain amplitude ranging from 10-2% to 0.5% was reliably determined by PMT PMT results were also compared with other in-situ and laboratory test results. Moduli obtained from different testing techniques matched very well if the effect of strain amplitude was considered in the com pall son.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.2
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• pp.485-500
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• 2018

The behavior of cement-based permeation grouting is divided into three different groups depending on the grain size distribution of the soils: (1) zone of cement-based permeation grouting not feasible; (2) zone of cement-based permeation grouting feasible; and (3) zone in which an accelerating agent should be added to limit the penetration depth. In the cement-based permeation grouting feasible zone, the concept of a representative pore radius was proposed. The ratios of the representative pore radius to the mean pore radius were obtained by performing laboratory test and comparing with clogging theory; these values were in the range of 1.07 and 1.35 depending on the grain size distribution of the soils. In addition, a functional relationship between the lumped parameter (${\theta}$), the representative pore radius and the w/c ratio were derived by comparing and matching experimental results with predictions from theory. In the zone in which the accelerating agent should be added, the controlling process of gel time to limit the penetration depth was experimentally verified. The test results matched well with those obtained from theory utilizing the developed grout penetration program on condition that the viscosity increasing tendency of grout suspension with time is properly taken into account.