• Journal of the Korean Geotechnical Society
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• v.22 no.4
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• pp.85-94
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• 2006

Triaxial tests at isotropic confining pressure of 200 kPa were carried out to show the undrained shear behavior of artificially cemented sands, which were cemented by gypsum, and the influences of relative density and DOC (degree of cementation) were investigated from the results. The yield strength, the elastic secant modulus at yield point and the peak frictional angle of cemented sands increased abruptly compared to uncemented sands, and it was checked that cementation exerts more influence on the behavior of sand than the relative density. But after breakage of the cementation bonds, the relative density was more important factor on the behavior of sand than the cementation. Because the compressibility md the excess pore pressure of cemented sands were reduced due to the cementation bonds, the effective stress path of cemented sands was going toward to the total stress path of uncemented sands. The cementation of sand restricted the dialtion of sand at the pre-yield condition, but induced more dilation in the post-yield condition.

• Journal of the Korean Geotechnical Society
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• v.24 no.5
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• pp.79-87
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• 2008

Recently, a new seismic probe, called "MudFork", has been developed and can be utilized for accurate and easy measurements of shear wave velocities of cohesive soils. To expand its use to estimate undrained shear strength and density, a preliminary investigation to correlate these properties with shear wave velocity was attempted. Cone penetration tests and a seismic test, using MudFork, were performed at a silty soil site near Incheon, Korea. Also, undisturbed samples were obtained using thin-wall tube samplers, and the shear wave velocities and undrained shear strengths of the samples were measured in the laboratory. A simple linear relationship between shear strength and shear wave velocity was obtained, and a tentative relationship between density and shear wave velocity was also defined.

• Journal of the Korean Geotechnical Society
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• v.24 no.7
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• pp.17-24
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• 2008

In this study, the triaxial behaviour of an unsaturated soil was analyzed by Bishop stress descriptions. $K_0$ stress paths and those final values were independent of matric suctions after describing by the Bishop stress. The failure criteria could be defined uniquely by the Bishop stress and were also independent of matric suctions. In the low level of matric suctions the failure criteria have a linear relationship and the estimated criterion fits the measured accurately. The variable ${\chi}$ for describing the Bishop stress was a constant theoretically under the low level of matric suctions. The suction stress could be defined at zero deviatoric stress in the failure criteria and increased linearly with respect to matric suctions in both the theory and the experiments.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.4
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• pp.469-476
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• 2023

Soil plasticity models for cyclic and dynamic loads are essential in non-linear numerical analysis of geotechnical structures. While a single yield surface model shows a linear behavior for cyclic loads, J₂-bounding surface plasticity model with zero elastic region can effectively simulate a nonlinearity of the ground response with the same material properties. The radius of the yield surface inside the boundary surface converged to 0 to make the elastic region disappear, and plastic hardening modulus and dilatancy define plastic strain increment. This paper presents the stress-strain incremental equation of the developed model, and derives plastic hardening modulus for the hyperbolic model. The comparative analyses of the triaxial compression test and the shallow foundation under the cyclic load can show stable numerical convergence, consistency with the theoretical solution, and hysteresis behavior. In addition, plastic hardening modulus for the modified hyperbolic function is presented, and a methodology to estimate model variables conforming 1D equivalent linear model is proposed for numerical modeling of the multi-dimensional behavior of the ground.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.2
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• pp.117-127
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• 2010

Gound excavation is frequently executed in unsaturated soil conditions. In this paper, the effect of apparent cohesion in unsaturated soils on the ground behavior during underground excavation is studied. The VPPE (Volumetric Pressure Plate Extractor) test, the unsaturated triaxial test and the trap-door test were carried out to figure out how the behavior of soils varies depending on the variation of apparent cohesion. The test results show that the ground behavior is almost identical if the soil is either fully dry or fully saturated. However, if the soil is partially-saturated with the increase of water content, the ground behaves quite differently. In summary, the apparent cohesion in unsaturated soils plays key roles when excavating underground structures.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.5C
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• pp.255-262
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• 2008

In order to investigate the strength anisotropy of compacted materials, a series of unsaturated and saturated-drained triaxial compression tests was performed. Three different orientation angles of the axial direction of samples with respect to the horizontal plane were investigated: ${\delta}=0$, 45 and 90 degrees. As the results showed, the suction rate on the strength of the unsaturated specimen was not influenced by ${\delta}$. And the effect of the angle ${\delta}$ on the strength was more pronounced on unsaturated specimen as compared to saturated specimen. Moreover, a new procedure was proposed to take into account the effect of the angle ${\delta}$ on the shear strength of unsaturated soils.

• The Journal of Engineering Geology
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• v.21 no.2
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• pp.147-156
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• 2011

We conducted laboratory experiments to determine the physical and mechanical properties, and the failure behaviors, of cements for use as grouting material in a $CO_2$-injection borehole. Samples with lour different ratios of water to cement mass (0.4, 1, 2, and 3) were tested. The analyzed properties (porosity, sonic velocity, modulus, and compressive and tensile strengths) varied systematically as a function of the ratio of water to cement (w/c), showing a sharp change between w/c ratios of 0.4 and 1. Triaxial compression tests revealed a clear boundary between brittle and ductile failure depending on the w/c ratio and confining pressure. The present results can be utilized as input parameters for numerical models to understand the initial deformation and failure behavior of grouting cements in a $CO_2$-injection borehole.

• Geotechnical Engineering
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• v.13 no.1
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• pp.35-46
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• 1997

The isotropic single-hardening constitutive model has been applied to predict the behavior of soils during reorientation of principal stresses in the field. The predicted response by the model agrees well with the measured behavior for a series of torsion shear tests performed on hollow cylinder specimens of Ko consoildated clay along various stress -paths. This indicates that the soil behavior during reorientation of principal stresses can be predicted by using the model with application of simple informations given by isotropic compression tests and conventional consolidated-undxained triaxial compression tests. Isotropic elasto-plastic soil behavior has been served during primary loading from both the torsion shear tests and the predictions by the model. However, the directions of maj or principal strain increment given by the model have not coincided with the directions for tests during stress reversal, such as unloading and reloading, within isotropic yield surface for Ko consolidated stress. This indicates that kinematic hardening model instead of isotropic hardening model should be developed to predict the soil behavior during stress reversal. The experimental strain increment vectors in the work-space have been compared with the directions expected for associated and nonassociated flow rules.

• Journal of the Korean GEO-environmental Society
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• v.14 no.10
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• pp.39-47
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• 2013

Recently, there have been various domestic construction activities related to the reclamation of the dredged soils to expand the land use. However, the reclaimed grounds made of the dredged soils cause various problems due to highly compressible and low shear strength nature. Particularly, this nature induces huge problems in case of the harbor facilities and road construction on the reclaimed sites. Furthermore, in the reclamation activities, the marine dredged soils are often used instead of the well sorted sand, which induces problems of compressibilities. Therefore, in this study, the mechanical characteristics of artificial soil mixture of kaolinite representing the marine dredged soils and the pond ash. A large consolidometer is designed and manufactured to produce the artificial soil mixture. To represent various mixing ratio between the fly ash and bottom ash in the pond ash, six samples with the same stress history are made with different mixing ratio among kaolinite, bottom ash and fly ash. Isotropically consolidated and undrained compression tests are performed to investigate the shear characteristics of soil mixtures. Based on the experimental results, as the components of mixed ash increase, the friction angle increase and the cohesion values decrease. Also, the porepressure parameters at failure, Af increase with the mixing components of the pond ash. The portion of bottom ash has more impact on the shear behavior than that of fly ash.

• Journal of the Korean Geotechnical Society
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• v.28 no.7
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• pp.31-40
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• 2012

In most design codes, soils are classified as either sandy or clayey soils, and appropriate design equations for each soil type are used to estimate their soil behaviour. However, sand-fine mixtures, which are typically referred to as intermediate soils, are somewhere at the middle of sandy or clayey soils, and therefore a unified interpretation of soil behaviour is necessary. In this paper, a series of cyclic shear tests were carried out for three different combinations of sand-fine mixtures with various fines content. Silica-sand mixture and fines (Iwakuni natural clay, Tottori silt, kaolinite) were mixed together with various mass ratios, while paying attention to the changes of void ratios expressed in terms of sand structure. The cyclic shear strengths of the mixtures below the threshold fines content were examined with the increasing fines contents. As a result, as the fines contents increased, their cyclic deviator stress ratios decreased for dense samples while it increased for loose samples. Additionally, cyclic deviator stress ratio of the mixtures was estimated using the concept of equivalent granular void ratio.