• Applied Microscopy
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• v.36 no.4
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• pp.251-258
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• 2006

Crystal-bearing cells are rarely encountered in the softwoods and their regular occurrence, e.g., in species of Abies, Picea, Ginkgo, and Pinus, is of considerable diagnostic significance. Thus, this study discusses the distribution and types of crystals in North American Abies species to provide additional information for wood anatomy and identification through light and scanning electron microscopies. Prismatic crystals, elongate crystal s, and styloids are identified, in descending order of frequency, in Abies concolor, A. grandis. and A. magnifica, A. nobilis (=A. procera), A. lasiocarpa, and A. amabilis but not in A. balsamea and A. fraseri. Differently from the other species, A. lasiocarpa shows the tendency of more elongate crystals and styloids than prismatic crystals. A. concolor contains crystal sands, prismatic crystals, elongate crystals, and styloids both in the axial and ray parenchyma cells, whereas the other species show prismatic crystals, elongate crystals, and styloids only in the ray parenchyma cells. Ray parenchyma cells containing crystal sand and axial parenchyma cells having crystal sand, prismatic crystals, elongate crystals, and styloids are probably reported here for the first time in A. concolor. In conclusion, the presence or absence of crystals appears to be the most powerful diagnostic character for separating A. concolor, A. grandis, and A. magnifica from A. nobilis (=A. procera), A. lasiocarpa, A. amabilits, A. balsamea, and A. fraseri.

• Journal of the Korean Geotechnical Society
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• v.31 no.3
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• pp.51-62
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• 2015

Shear behavior obtained by direct shear tests is dependent on shear box and boundary condition. The objective of this study is to analyze problems of conventional direct shear test (type-A) and provide the reliable results by developing type-C direct shear apparatus. Experimental tests are carried out for Ulleung sand by using type-A and -C direct shear devices. The soil specimens, which are prepared at the relative density of 60%, and are applied to vertical confining stresses of 50, 100, 200, 300, and 400 kPa, are sheared at a constant shear strain rate of 0.5 mm/min. By comparing the results obtained by type-A and -C direct shear apparatus under constant normal load (CNL) condition, the performance of new one is verified. In addition, two constrained conditions including constant normal load (CNL) and constant pressure (CP) are applied to type-C one. Experimental results show that type-A direct shear apparatus has some problems such as rotating of loading plate and upper shear box, and the frictional forces between soil and inner wall of upper shear box. Thus, the shear strengths obtained by type-A device are overestimated or underestimated depending on shear box and boundary condition. On the other hand, type-C device produces clear and consistent test results regardless of constrained conditions. This study represents that type-C direct shear apparatus not only can solve the problems of type-A direct shear apparatus but provide the reliable results.

• Journal of the Korean Geotechnical Society
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• v.28 no.8
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• pp.43-53
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• 2012

In the conventional design of a piled raft, the axial resistance offered by the raft itself is typically neglected and only that of the group pile is accounted in estimating the total axial resistance of the piled raft. As a consequence, piled rafts are usually designed conservatively by neglecting the raft resistance. In this study, a series of centrifuge model tests have been performed to compare the axial behavior of a group pile with that of a piled raft (both having 16 component piles with an array of $4{\times}4$) in sands with different relative densities and in clays with different preconsolidated pressures. The test results revealed that, with respect to the allowable settlement of 25 millimeters for bridge foundations, the piled raft resistances were greater than those of the group pile by 13% for dense sand, by 22% for loose sand, by 30% for stiff clay, and by 22% for soft clay. Furthermore, the ratio of piled raft resistance to group pile resistance increased as the settlement increased.

• Journal of the Korean Geosynthetics Society
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• v.11 no.2
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• pp.1-9
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• 2012

In order to review the utility of Lade's single hardening constitutive model, a series of isotropic compression-expansion tests and consolidated drained triaxial tests including as CTC, TC, RTC, and OSP were performed by Baekma river sand with various of stress path. Parameters required in model were determined using these tests. The accuracy of analysis was reviewed by back analysis of test results used to determine the 11 parameters of soil property through the test of each stress path. Also. for verifying the accuracy of prediction for the stress-strain behavior using failure criterion related 9 parameters with correlational equation and constant and yield criterion related parameters h, ${\alpha}$ and ${\eta}_1$, when stress path is different with each other, it has been obtained in the review result of stress path dependent characteristics of the constitutional model through the analyzing results of CTC, TC, RTC, OSP, and fine silica sand tests.

• Geotechnical Engineering
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• v.13 no.4
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• pp.37-54
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• 1997

This paper is to investigate the bearing capacity and the failure mechanism of slope subjected to strip surcharges adjassent to embankment slope of sandy soil. Parametric model tests under plain strain condition were performed by changing width of footing, relative density of slope materials, and position of footing from the crest of slopes. For model tests, Jumunjin standard sand was used as the slope material and its relative density was 45% and 70%, respectively. The angle of slope was formed with 1 : 1.5 and 1 2. Rigid model footings, made of aluminuu were used with their widths of 4, 7, 10 and 12cm. For the position of model footing, position ratios, distance of model footing from the crest of slope divided by footing width, were 0, 0.5, 1, 2, 3, 4, 5. Failure mechanism was observed by using ink colored sands and markers inserted in model slopes. Ultimate bearing capacity obtained from tests was analyzed and compared with limit equilibrium method, limit analysis method and empirical equation. Characteristics of load-settlement curves and failure mechanism were also analyzed and compared with the existing theories. Thus, their effects on ultimate bearing capacity of model footing adjacent to slope were assessed.

• Journal of the Korean Geosynthetics Society
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• v.19 no.1
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• pp.93-101
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• 2020

In order to predict the nonlinear behaviour of the soil, the elasto-plastic hyperbolic model was selected, which was considered to be relatively simple and highly predictable. The soil parameter determination and the behavior analysis program were developed by formalizing the functions related to the constitutive model. Each soil parameter was determined from the results of the drained triaxial compression tests of Baekma river sand with the change of relative density. The stress-strain behavior was predicted using the soil parameters determined under each condition. As a result, the deviator stress for the axial strain is verified to have a good match between the measured value and predicted value at each relative density. In the relationship between the volumetric stain and the axial strain, when the relative density is loose, the measured value and predicted value tend to match, and when relative density is dense, the predicted value of the volumetric strain appears somewhat smaller than the measured value due to the limitation of the constitutive model.

• Journal of the Korean Geotechnical Society
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• v.21 no.7
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• pp.55-62
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• 2005

The use of the bearing capacity equation is subjected to several uncertainties. In this study, estimation of the bearing capacity of footings based on the cone resistance q$_{c}$ is investigated. Non-linear finite element analyses based on a state-dependent stress-strain model were performed to obtain the load-settlement responses of axially loaded circular footings. Various soil and footing conditions, including different relative densities, depths of embedment, and footing diameters were considered in the analyses. Based on the finite element results, load-settlement curves were obtained and used to determine the unit limit bearing capacity in terms of the cone resistance q$_{c}$ for footings subjected to surcharge. Values of the unit bearing capacity for different embedment depths were in a narrow range, while considerable variation was observed with relative density D$_{R}$. It was observed that the unit limit bearing capacity normalized with respect to q$_{c}$ decreases as D$_{R}$ increases for a given surcharge.

• Journal of the Korean Geotechnical Society
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• v.29 no.11
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• pp.119-127
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• 2013

Recently, several researches on the development of new economical foundation types have been performed to support floating structures as many offshore structures have been constructed. This study focused on the evaluation of bearing capacity of group suction piles, which are connected by a concrete pile cap. The offshore floating structures are mainly subjected to horizontal loading, so the horizontal bearing capacities of the group suction piles were analyzed by performing 3-dimensional finite element analyses. The group suction piles are expected to behave as a rigid pile due to its shallow embedded depth. Therefore, the detailed soil modeling was necessary to simulate the bearing behavior of soils under low confining pressure. The modulus and the strength of soils were modelled to increase with effective confining pressure in soils. For the parametric study, the center-to-center spacing between piles was varied and two soil types of clay and sands were applied. The analyses results showed that the yielding load of the group pile increased with the increase of the pile spacing and the yielding load of the group piles with 5D spacing was about 3 times larger than that of the single pile with free rotation.

• Journal of the Korean Geotechnical Society
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• v.29 no.11
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• pp.61-72
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• 2013

The consolidation tests are conducted to investigate the soil particle crushing stress for understanding the secondary compression characteristics of carbonate sandy sabkha soil caused by particle crushing under a high confining stress. The rate of secondary crushing compression ($C_{{\alpha}{\epsilon}}{^*}$) is introduced instead of the rate of secondary compression to define the characteristic of the particle crushing compression settlement ($S_s{^*}$). Void ratio ($e_p{^*}$) and settlement ($H_p{^*}$) in particle crushing are used as a reference point of secondary behavior, and the ratio of primary compression index ($C_c$) to secondary crushing compression ($C_{{\alpha}{\epsilon}}{^*}$), $C_{{\alpha}{\epsilon}}{^*}/C_c$ value was changed from 0.0105 to 0.0187. When comparing with quartz sands, secondary compression settlement of sabkha is very large due to particle crushing which is not usually observed in quartz sand. It is observed that as the depth of sabkha layer becomes deep, the $S_s{^*}$ and $C_{{\alpha}{\epsilon}}{^*}$ increase under the same stress level.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.1
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• pp.93-103
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• 2017

Many countries are interested in the development of the Antarctic area because of the abundant resources and living things of high research value. Korea completed the second Antarctic research station in 2014 and spurring the development of the Antarctic area by constructing runway for the airplanes and a third Antarctic research station. However, frozen soils, unlike typical soils, are sensitive to creep behavior due to the influence of ice and unfrozen water. The creep tests for evaluating creep behaviors on the frozen soils require expensive laboratory equipments and large amount of time. Thus, various empirical models had been developed to describe the unconfined compressive creep behavior of frozen soils. In this study, new analytical creep model on frozen sands was proposed by modifying Ting's Tertiary creep model with a new parameter considering fine contents. Thus, the unconfined compressive creep tests were conducted with the frozen specimens of dense Jumoonjin sand with fine contents of 0, 5, 10 and 15% under various loads at -$5^{\circ}C$, -$10^{\circ}C$ and -$15^{\circ}C$. Consequently, the modified Tertiary creep model with a new parameter for fine contents are not enough for the description of the acutal creep behavior of the frozen sand and new framework should be developed.