• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.1
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• pp.406-411
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• 2012

The undrained strength of soils is open determined from the results of the piezocone penetration. The reliability of the value of the undrained strength lies on the cone factor value, whose evaluation needs a lot of experimental data and investigation for each site. In this study, the cone factors were evaluated for the northeastern part of Shiwha area in Gyunggi province using the experimental data of the field vane, unconfined compression, and UU triaxial compression tests. The values of the conventional cone factors $N_{kt}$, $N_{ke}$, $N_{{\Delta}u}$, and the new factor $N_e$ were determined to be 12, 11, 3, and 13, respectively. It was observed that there is a remarkable relationship between $N_{{\Delta}u}$ and the pore pressure ratio Bq.

• Journal of the Korean Geotechnical Society
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• v.23 no.5
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• pp.89-100
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• 2007

In this study, various field and laboratory tests were performed to investigate the characteristics of shear strength and bearing behavior to be considered in the estimation of stability and trafficability in early stage of stabilization process in marine clay dredged deposit. Site characterization was carried out to grasp the basic properties of the deposit. Field vane test, unconfined compression test and direct shear test were conducted to evaluate the shear strength distribution for varied depths, and the characteristics of shear strength and stress-strain behavior of the crust layer. Plate load tests were also performed to estimate the bearing capacity and to assess load-settlement behavior and failure pattern of the deposit. The bearing capacity was also estimated using previously proposed methods for double-layered clay deposit. The estimated bearing capacity was compared with the results of the plate load tests and then, the applicability of the estimation method was discussed.

• Journal of the Korean GEO-environmental Society
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• v.11 no.7
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• pp.33-43
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• 2010

The physical characteristics of the marine clay in the Korean Peninsula, specifically Pusan areas of the south coast of Korea, were previously studied and reliable data from harbor construction projects were used for the relationship analysis of geotechnical strength parameters. The sample of marine clay classified to ML, MH, CL, CH and ML-CL from USCS were included for the analysis while the samples classified to SC were excluded in order to raise the degree of data analysis. Geotechnical strength properties, such as undrained shear strength, sensitivity ratio, and effective friction angle were analyzed and evaluated using the data obtained from unconfined compression test, triaxial compression test and field vane test. Abnormal values were extracted through statistical analysis. Moreover, the reliability of the results was improved by performing the evaluation of disturbance. Linear regression analysis was used for the relationship analysis, between undrained shear strength and depth. The relationship equation between undrained shear strength and depth was derived from the analysis of unconfined and triaxial compression test data of samples obtained at same location. Consequently, The relationship between depth and undrained shear strength is $S_u=0.015148D+0.04624$ and the undrained shear strength derived from the triaxial compression test was estimated to be about 1.26 of derived from the unconfined compression test.

• Journal of the Korean Geotechnical Society
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• v.30 no.2
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• pp.65-76
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• 2014

For soil improvement, sand mats or sand compaction piles are often constructed on soft marine clays. In such cases, some amounts of sand and clay are inevitably mixed. Sand or gravel often exists in the weathered soils near the slope surface. This research investigates the effect of mixing sand content on consistency limits and shear strength of clays. Firstly, sand was mixed with kaolinite or bentonite at 0, 9, 17, 23, 29, 33, 50% and then liquid and plastic limits were measured. Both plastic and liquid limits decreased as a sand content increased. The water content of clay-sand mixtures with different sand content increased by 10% or 20% step by step and then their undrained shear strength was measured using a portable vane shear device called Torvane. For all cases, undrained shear strength of clay-sand mixtures decreased rapidly until reaching a certain value. Their state changed from undrained to drained state gradually as the sand content increased, which caused their undrained shear strength to decrease. On the other hand, a series of direct shear tests were also conducted on such clay-sand mixtures to investigate the effect of sand content on cohesion and angle of internal friction. It was found from clay-sand mixtures that their cohesion decreased but angle of internal friction increased as the sand content increased.

• Journal of Power System Engineering
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• v.21 no.5
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• pp.20-28
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• 2017

The steady-state, incompressible and three-dimensional numerical analysis was performed to investigate the flow fields around the seabed tiller used for soil improvement in coastal fisheries and the pulling force and buoyancy generated by tiller operation. The turbulence model used in this study is a realizable $k-{\varepsilon}$. As a results, at a stationary current or a current speed of 1.2 knots, where rotor rotates in a clockwise direction, a typical vortex pair appears near the tip of the rotor except for the edge, and the strength of the vortex pair increases with the number of revolutions of the rotor. The pulling force of the tiller rotating in the counterclockwise direction increases with the number of revolutions. Also, when the current flows at 1.2 knots and the rotor rotates clockwise, the pulling force of the tiller acts on the upstream side irrespective of the number of rotations of the rotor, so that no force is applied. The buoyancy of the tiller acts on the seawater surface if the flow direction inside the rotor is the same as the direction of rotation of the rotor, regardless of the current velocity, otherwise it acts on the seabed.

• Composites Research
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• v.27 no.4
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• pp.123-129
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• 2014

Ceramic matrix composites (CMCs) consist of such reinforcements as carbides, nitrides, borides and oxides, which have high melting points, low density, high modulus and high strength, for the purpose of increasing toughness. These materials are used for heat shielding systems for aerospace vehicles, high-temperature gas turbine combustion chambers, turbine blades, stator vane parts, etc. Oxide CMCs are used for the components of burner and flame holder and the high-temperature gas duct. CMCs are also applied to brake disks, which are subjected to severe thermal shock, and slide bearing parts under heavy loads. The research and development of the CMC are progressed for the strategic purpose in defense and energy industry; for instance, for aerospace applications in the U.S., and for hyper-speed aircraft, gas turbines, and atomic fissions in U.S., Japan, and Europe.

• Journal of the Korean Geosynthetics Society
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• v.16 no.1
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• pp.73-83
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• 2017

Laboratory and in-situ tests were conducted to evaluate the cone factors for the layers with low plasticity containing a lot of silty and sand soils from the west coast (Incheon, Hwaseong and Gunsan areas) and its applicability was evaluated based on these results. The cone factors were evaluated from 19 to 23 based on unconfined compression strengths (qu), from 13 to 13.8 based on simple CU strengths and from 11.6 to 13.1 based on field vane strengths, respectively. The unconfined compression strengths of undisturbed silty soil samples with low plasticity were considerably underestimated due to the change of in-situ residual effective stress during sampling. Half of unconfined compression strength (qu/2) based cone factors of silty soils with low plasticity fluctuated and were approximately 1.8 times higher than simple CU based values of these soils. When evaluating cone factors of these soils, it should be judged overall on the physical properties such as the grain size distribution and soil plasticity and on the fluctuation of the corrected cone resistance and the sleeve friction due to the distribution of sandseam in the ground including pore pressure parameter.

• Journal of the Korean Geosynthetics Society
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• v.16 no.3
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• pp.41-49
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• 2017

In this study, a series of laboratory and in-situ tests such as FVTs and CPTUs were carried out to evaluate undrained shear strength related to quasi overconsolidated characteristics in the near-surface clay at Busan new port. Using unconfined compression and field vane test results, correlation between undrained shear strength and effective overburden pressure, that is, equation of $10+0.262{\sigma}^{\prime}v_0$ (kPa) was obtained. From oedometer tests, OCR is around 1.9 at depths lower than 7 m and OCR below this depth is very close to unit. As stated by Hanzawa et al. (1983), a natural clay deposit in the near-surface, even in normally consolidated state, is more and less apparently overconsolidated due to aging effects such as chemical bonding. Based on this concept, it can be inferred that intercept of equation is mobilized due to chemical bonding irrespective of effective overburden pressure and strength incremental ratio in normally consolidated state is 0.262. From CPTU results, same trend was confirmed. The further study should be necessary to judge whether upper clay is under overconsolidated state due to chemical bonding or not based on the depositional environment.

• Journal of the Korean Geotechnical Society
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• v.17 no.6
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• pp.15-24
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• 2001

In order to evaluate undrained shear strength of clayey soils using Piezocone Penetration Test (CPTu), piezoncone factor is utilized. Commonly, piezoncone factors determined by empirical basis were preferred, which were established by correlation between measurements of piezocone test and undrained strengths obtained from other shearing tests. However, previous studies on the empirical piezocone factors were site-specific and there have been no systematic investigations on the effect of both engineering characteristics of clayey soils and soil non-homogeneity on the piezocone factor. Accordingly, the direct application of the previous results to Korean clayey soils without verification may be inappropriate. In this study, empirical piezocone factors are evaluated by comparing 46 CPTu results of 10 test sites with undrained shear strength obtained from Field Vane Test (FVT) and laboratory triaxial tests. Their reliabilities are investigated by the comparison with the previous piezocone factors and the deviation of data distribution from the mean values. And the effects of referencing test methods and typical engineering characteristics of clayey soils such as overconsolidation ratio (OCR) and plastic Index (I$_{p}$) are examined. Because piezocone factors obtained for various soil conditions are widely distributed, it is not appropriate to use the mean value as a representative. Instead, it is recommended to apply the piezocone factors with OCR, which is found to be a major factor in deriving piezocone factor. The necessitated piezocone factors are presented.d.

• Geotechnical Engineering
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• v.8 no.3
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• pp.23-36
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• 1992

The flat dilatometer(DMT) has been practically used as an in-situ test equipment. It is a simple, rapid and cost-effective tool to characterize the in-situ stress-strain-strength properties of various types of ground materials. However, the results of flat DMT should be validated with considerable data with respect to the known reference values for a specific site. In this study, the applicability of existing relationships which were established for other local deposits is verified by performing the tests in several clay deposits. To compare with the DMT results, field vane tests and cone penetration tests were also carried out in the same field as reference tests, and unconsolidated undrained tests, oedometer tests, and other fundamental material properties tests were conducted on the thin-walled tube samples in the laboratory. The results of the flat DMT combined with empirical correlations are used to estimate soil types, unit weights, coefficients of lateral earth pressure at rest, overconsolidation ratios, constrained moduli and undrained shear strengths of three clay local deposits. It was found that various geotechnical properties estimated from the flat DMT generally well agree with those from the reference tests.