• Journal of the Korean Geotechnical Society
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• v.28 no.3
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• pp.15-23
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• 2012

An internal friction angle, which is one of strength parameters of granular soils, can be obtained from direct shear tests or triaxial tests. The result of traixial tests can be influenced by various experimental conditions such as confining pressure, shearing rate, specimen diameter and height, and end constraint. In this study, undrained and drained shearing behaviors of Nakdong River sand were investigated for loose (Dr = 40%) and dense (Dr = 80%) specimens with 5, 7, and 10 cm in diameter. Friction angles such as undrained total stress friction angle, undrained effective stress friction angle, and drained friction angle obtained from Mohr's stress circle slightly increased and then decreased as a diameter of a specimen increased from 5, 7 to 10 cm, regardless of relative densities. The difference between friction angles caused by different specimen size was at maximum 4.5 degrees for undrained total stress friction angle of dense specimen. In most cases, there was little difference between friction angles of large and small specimens, which was less than 2 degrees. The difference between an effective friction angle from undrained tests and a drained friction angle from drained tests was at maximum 7 degrees for loose samples but negligible for dense samples.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.15 no.1
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• pp.141-154
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• 2012

This study was launched to verify the effective composition of plant species and its management program most suited for the dredged soiled area near Nakdong River Site 14. The improvement methods of planting base and the composition of plants such as silver grass, reed, and some colonies in aesthetic effect were studied. To search the management methods to decrease the confining pressure risen from the burried seeds which would consequently harm the previously seeded plants, experimental construction process was measured on the site. The purpose of this experiment was to figure out which part of the improvement on the plant base has the most significant effect for the revegetation of infertile, dredged soil, to verify the easily seeded, developing plants among seeded plants, and finally, to find the restoration model using plants near the dredged soil around riverside. 8 seeded plants and 23 invaded species were appeared which among the emerged plants, development of Aster yomena MAKINO, Lotus corniculatus var. japonica Regel, Trifolium repens L, and Dianthus longicalyx Miq were proved to be brought up well. Difference risen from the seed composition were not noticeable until 150day since the germination was proceeded mainly by Aster yomena MAKINO. The experimental plot with dredging sand+organic fertilizer method of construction and dredging sand+soil conditioner method showed most development while the effect of the plot with only the soil base of dredging sand stayed low. Another important method for the management of infertile, dredged soil base would be the removal of disturbing species which the experiment showed the tied relationship between the removal of disturbing species and development of seeding plants. Although this study was carried out focused on the Nakdong River Project, the study suggests the general management program that the removal of disturbing species such as Humulus japonicus Sieboid & Zucc. and Pueraria lobata (Willd.) Ohwi in times around rainy season(60days after seedling) would be effective for the easy growth of revegetation plants.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.105-117
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• 2002

In the design of foundations for the super-structures such as transmission towers and oil-platforms, the foundations must be considered as a medium to resist cyclic tensile forces. In this study, the uplift capacity of the drilled shaft used as the medium resisting to this pattern of forces is investigated by performing cyclic uplift test of a small model-drilled shaft constructed in compacted granite soil in a steel chamber. In this test, the behavioral difference between a pile loaded on the top of the pile and a pile loaded at the bottom of the pile was investigated intensively. The load transfer curves obtained from the test were investigated by changing the confining pressure in the chamber. The load tests also included creep test and cyclic test. It is found from the tests that uplift capacity of the shaft loaded at the bottom is greater than that of the shaft loaded on the top of the pile. It is found also from the creep test that the pile loaded at the bottom was more stable than the shaft loaded on the top. If a pile loaded at the bottom is pre-tensioned, the pile will be most effective to the creep displacement. It is found also from the cyclic tests that apparent secant modulus obtained in a cycle of the load increases with the number of cycles.

• Journal of the Korean Geotechnical Society
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• v.22 no.7
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• pp.73-83
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• 2006

The behaviour characteristics of Granular Compaction Pile (GCP) are mainly governed by the lateral confining pressure mobilized in the soft soil matrix to restrain the bulging failure of the granular compaction pile. The GCP method is most effective in soft soil with undrained shear strength ranging $15{\sim}50kPa$. However, the efficiency of this method reduces the more compressible soil conditions, which does not provide sufficient lateral confinement. In the present study, the GCP method reinforced with uniformly graded permeable concrete is suggested for the extension of application to the soft ground. Also, large triaxial compression tests are conducted on composite-reinforced soil samples for verification of availability of the suggested method and the settlement estimation method of the reinforced GCP is proposed. Furthermore, for the verification of the proposed method, predicted settlements by the proposed method are compared with results of 3-dimensional numerical analyses. In addition, parametric studies are performed together with detailed analyses of relevant design parameters.

• Journal of the Korean Geotechnical Society
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• v.21 no.4
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• pp.65-70
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• 2005

Many case histories of re-liquefaction phenomena seem to support the idea that sand deposits, if they once have been liquefied, could be reliquefied again by a subsequent earthquake even though the earthquake is smaller than the previous one. The magnitude of the strains induced in the initial liquefaction has a significant influence on the resistance of the sample to re-liquefaction. The deposits undergoing liquefaction experience large shear strain during liquefaction. And this previous strain changes the microstructure into highly anisotropic structure such as columnlike structure and connected voids. This type of anisotropy is so unstable that it can reduce re-liquefaction resistance. It is blown that the extent of anisotropic structural change depends on the gradation characteristics of ground. The purpose of this study is to estimate the correlation between the gradation characteristics of the sand and the ratio of re-liquefaction resistance to liquefaction resistance. In this study, 1-g shaking table tests were carried out on five different kinds of sands. During the tests the values of excess pore pressure at various depths and surface settlements were measured. Re-liquefaction resistances were not affected by the initial void ratio and the effective confining pressures, and the deposits of all test sands which had once been liquefied were reliquefied in the cyclic loading number below 1 to 1.5. The ratio of re-liquefaction resistance to liquefaction resistance linearly decreased as $D_{10}/C_u$ increased, and was constant as about 0.2 above the value of $D_{10}/C_u$, 0.15 mm.