• Journal of the Korean Geotechnical Society
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• v.31 no.9
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• pp.17-27
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• 2015

We perform a series of experimental tests to evaluate whether the shear strength of clean sands can be reliably predicted from shear wave velocity. Isotropic drained triaxial tests on clean sands reconstituted at different relative densities are performed to measure the shear strength and bender elements are used to measure the shear wave velocity. Laboratory tests reveal that a correlation between shear wave velocity, void ratio, and confining pressure can be made. The correlation can be used to determine the void ratio from measured shear wave velocity, from which the shear strength is predicted. We also show that a unique relationship exists between maximum shear modulus and effective axial stress at failure. The accuracy of the equation can be enhanced by including the normalized confining pressure in the equation. Comparisons between measured and predicted effective friction angle demonstrate that the proposed equation can accurately predict the internal friction angle of granular soils, accounting for the effect of the relative density, from shear wave velocity.

• Journal of the Korean Geotechnical Society
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• v.30 no.2
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• pp.33-42
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• 2014

The shear strength and deformation characteristics of granular soils at low confining stresses differ from those with high confining stresses. Thus, the clear understanding of geotechnical problems related to the low confining stress state such as the stability of shallow foundations, embankments, slope failure, debris flow characteristics and liquefaction as well as the various laboratory model tests is needed. In this study, drained triaxial compression tests with the cell pressures from 5 kPa to 300 kPa were performed on dry Jumunjin sand. The results show that the internal friction angle and deformation modulus are dependent on the confining stress. Also, the correlations between them on the dense and loose sand were established.

• Geotechnical Engineering
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• v.7 no.4
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• pp.25-34
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• 1991

In this study, relationships between CBR values tested by Korean Standards (KS CBR) and the elastic moduli from CU compression tests are developed for the subgrade soils. Triaxial compression and KS CBR tests are carried out on five types of samples from 15 points in Korean ezpressways. Triaxial compression tests are performed under 3 types of coifining pressures to generalize the CBR -elastic modulus relationship as functions of confining pressured and mean principal stresses. From the regression analyses of experimental results, equations for relationships between the KS CBR and elastic moduli of roadbed Boils are proposed. An equation for the relation- ship between the KS CBR and the maximum dry density of roadbed soil is also proposed.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.335-342
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• 2003

In order to analyze the deformational behavior accurately, the in-situ testing technique which provides the reliable deformational characteristics at whole strain ranges, needs to be developed. The pressuremeter is a unique method for assessing directly the in-situ shear modulus of soils with strain amplitude. This paper introduces a new alternative, the cavity strain measuring system in pressuremeter designed for whole strain ranges of $10^{-5}$%∼20%. Not only in the synthetic calibration chamber but also in the field, the pressuremeter tests were performed to determine the compliance of the new developed pressuremeter system. The variation in shear modulus with strain amplitude above $5\times 10^{-2}$% was reliably determined by the developed pressuremeter. It is concluded that the major cause of error in small cavity strain measuring is not from the cavity strain measuring system but from the friction between measuring arm and membrane during unloading-reloading loops.

• Earthquakes and Structures
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• v.11 no.1
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• pp.83-107
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• 2016

In this study, the response and behavior of machine foundations resting on dry and saturated sand was investigated experimentally. A physical model was manufactured to simulate steady state harmonic load applied on a footing resting on sandy soil at different operating frequencies. Total of (84) physical models were performed. The parameters that were taken into consideration include loading frequency, size of footing and different soil conditions. The footing parameters are related to the size of the rectangular footing and depth of embedment. Two sizes of rectangular steel model footing were used. The footings were tested by changing all parameters at the surface and at 50 mm depth below model surface. Meanwhile, the investigated parameters of the soil condition include dry and saturated sand for two relative densities; 30 % and 80 %. The dynamic loading was applied at different operating frequencies. The response of the footing was elaborated by measuring the amplitude of displacement using the vibration meter. The response of the soil to dynamic loading includes measuring the stresses inside soil media by using piezoelectric sensors. It was concluded that the final settlement (St) of the foundation increases with increasing the amplitude of dynamic force, operating frequency and degree of saturation. Meanwhile, it decreases with increasing the relative density of sand, modulus of elasticity and embedding inside soils. The maximum displacement amplitude exhibits its maximum value at the resonance frequency, which is found to be about 33.34 to 41.67 Hz. In general, embedment of footing in sandy soils leads to a beneficial reduction in dynamic response (displacement and excess pore water pressure) for all soil types in different percentages accompanied by an increase in soil strength.

• Journal of the Korean GEO-environmental Society
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• v.16 no.6
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• pp.31-38
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• 2015

Recently, the participation on the development of the natural gas pipeline in Russia as well as the recent construction of the second Korean Antarctic research station, the Jangbogo station provide the research interests on the behavior of the permafrost ground. To investigate the effect of fines on the mechanical responses of frozen sands, unconfined compression tests were performed on the frozen sands with 0, 5, 10 and 15% of fine contents at -5, -10 and $-15^{\circ}C$. The poorly graded (SP) Joomunjin sand and kaolinite, silt with low plasticity (ML) were used for the preparation of the frozen soil specimens. The mechanical responses of the tested soils were investigated via unconfined compression tests in the temperature controlled laboratory and analyzed in terms of peak unconfined compressive strength and secant modulus at 50% of the peak strength. As the fine contents increase, the unfrozen water contents increase and thus the strength and stiffness of frozen soils decrease. The increment of the stiffness and strength due to the temperature decrease vary with the fine contents.

• Geotechnical Engineering
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• v.9 no.1
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• pp.21-30
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• 1993

To know the importance of soil paramters which are used to estimate the deformation and porepressure of soil, the sensitivity for soil parameters in elastic analysis is analyzed. Using the consolidation teat results of several cohesive soils, soil parameters are estimated by back analysis method, and from the parameters the deformations and porepressures of the soil are estimated by elastic analysis, In elastic analysis for soil-deformation and porepressure, the sensitivity for the Young's modulus is large, and the esimation of Young's modulus is more important in pro- portion to the size of stress. Using the measured results during initial short period in small stress, the soil parameters can be correctly estimated by back analysis method. To decrease the iteration number in back analysis and to get the better paramters, the initial measurements in more nodes are required and the more accurate initial measurements are required.

• Journal of the Korean Society of Hazard Mitigation
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• v.5 no.2 s.17
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• pp.57-63
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• 2005

In case of general structures, it has been known that the strain amplitude band experienced by the base in a state of service load is less than 1% and most of the base show low, strain amplitude behavior less than 0.01%. In this study examining the influence affected to dynamic behavior in a condition of the low strain amplitude of unsaturated decomposed granite soils, the resonant column test, using some samples in Su-won area, has been performed for each degree of saturation resulted from different void ratios and confined stress. It is found out that the minimum value of the damping ratio occurred in roughly $17{\sim}18%$ according to void ratios regardless of confined pressure in the same manner with the case of the maximum shear elastic modulus; and it is estimated that for the influence of surface tension in the optimum degree of saturation, the damping ratio appears to be least.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.2
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• pp.91-102
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• 1990

The representative tests in this study are performed at a selected site which has the soil layers to analyze the safety and economy of the dynamic analysis for the variable soil conditions. Crosshole test and downhole test of small strain level tests and triaxial test of large strain level test are performed in the soil layers, and in the rock layers, crosshole test and downhole in-situ tests and laboratory sonic test are performed to measure the dynamic shear modulus, damping ratio, and Poisson$\acute{s}$ ratio of the soil and the rock. The correlations between the dynamic soil properties from the tests and the basic soil properties are determined through the regression analysis. The representative design value of the soil is determined by probability analysis of the test results. It is determined from the nonlinear stress-strain model in soils, and the value at small strain level is computed in rocks according to the distribution of the type of soils and the affecting variables. The constitutive value is systematized to be utilized in the analysis of the test results, and computation of the input soil data.

• Journal of the Korean Geotechnical Society
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• v.30 no.11
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• pp.25-37
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• 2014

Clay or sand does not exist alone but various sizes of soil are mixed in the field. In this study, the effect of water content on large deformation of such mixed soils is studied by using soil column tests and a particle method. A soil column with 7 cm in diameter and 13 cm in height, which was made out of kaolinite with sand content of 0, 10, 25, or 50%, was tested for large deformation. Its deformation was monitored with time. While increasing its water content from 40, 60, to 80%, a total of 12 types of soil column tests were carried out. The particle method simulated their deformation with time. A maximum plastic shear modulus, which was a function of undrained shear strength and plasticity index for soils with different water contents, was associated with soil viscosity to simulate large deformation of soil column. When a sand content of soil column was constant, the deformation of soil column increased with increasing water content. When a water content of soil column was constant, large deformation occurred with increasing the sand content. The maximum deformation, which was 22 cm in diameter, was observed in the case of water content of 80% and sand content of 50%. The particle method was able to relatively well simulate such large deformation and stress change of soils.