• Proceedings of the Korean Geotechical Society Conference
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• 1999.10a
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• pp.193-200
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• 1999

Since Broms and Bennermark(1967) suggested the face stability criterion based on laboratory extrusion tests and field observations, the face stability of a tunnel driven in cohesive material has been studied by several authors. And recently, more general solution for the tunnel front is given by Leca and Panet(1988). They adopted a limit state design concept to evaluate the face stability of a shallow tunnel driven into cohesionless material and showed that the calculated upper bound solution represented the actual behavior reasonably well. In this study, two factors are simultaneously considered for assessing tunnel face stability: One is the effective stress acting on the tunnel front calculated by upper bound solution; and the other is the seepage force calculated by numerical analysis under the condition of steady state ground water flow. The model tests were performed to evaluate the seepage force acting on the tunnel front and these results were compared with results of numerical analysis. Consequently, the methodology to evaluate the stability of a tunnel face including limit analysis and seepage analysis is suggested under the condition of steady state ground water flow.

• Computers and Concrete
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• v.9 no.1
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• pp.1-19
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• 2012

The size-effect study of various fracture parameters obtained from two parameter fracture model, effective crack model, double-K fracture model and double-G fracture model is presented in the paper. Fictitious crack model (FCM) for three-point bend test geometry for cracked concrete beam of laboratory size range 100-400 mm is developed and the different fracture parameters from size effect model, effective crack model, double-K fracture model and double-G fracture model are evaluated using the input data obtained from FCM. In addition, the fracture parameters of two parameter fracture model are obtained using the mathematical coefficients available in literature. From the study it is concluded that the fracture parameters obtained from various nonlinear fracture models including the double-K and double-G fracture models are influenced by the specimen size. These fracture parameters maintain some definite interrelationship depending upon the specimen size and relative size of initial notch length.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.361-368
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• 2000

In other to examine the compressibility characteristics of cohesive soils in the mouth of the Nakdong river, the oedometer tests were peformed on undisturbed and reconstituted samples obtained by continuous boring typically at 3 different sites. It is meaningful to compare the consolidation behavior of natural clays with a reference state because the natural clays are depending on the stress history, sedimentary environment and geological history. In this study, the insitu state of the Pusan clays was investigated using the concepts of ISL(Nagaraj, 2000) and ICL and SCL(Burland, 1990). And for the purpose of confirming the existence of the underconsolidated clays, a standpipe type piezometer test and a dissipation test by piezocone were performed at their sites. Consequently, the Pusan clays were evaluated as normally consolidated clays.

• Journal of the Korean Geotechnical Society
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• v.18 no.6
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• pp.17-24
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• 2002

The objective of the present research is to evaluate the wave propagation velocity and attenuation characteristics of kaolin clay specimens using ultrasonic testing. Test specimens with known initial micro-fabric were prepared using a two-stage slurry consolidation technique. For a known state of stress conditions, initial void ratio, and micro-fabric, a series of experiments were conducted to evaluate the longitudinal wave propagation velocity and associated damping behavior. The effects of major variables involved in ultrasonic testing of cohesive soil were considered in this study. Ultrasonic velocity was not correlated to the microfabric structure under the given consolidated pressure whereas ultrasonic attenuation was affected by the microstructural properties of the specimen.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.05a
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• pp.135-140
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• 2003

This paper is handling about comparative study on dynamic responses of tracked vehicle on soft soil. Two models of tracked vehicle are used in this paper: a single-body model and a multi-body model. Two different methods for dynamic analysis of tracked vehicle are compared: single-body dynamic analysis and multi-body dynamic analysis. Traveling performances of two tracked vehicles are compared.

• Structural Engineering and Mechanics
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• v.76 no.6
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• pp.725-736
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• 2020

In this work the mixed mode I/III fracture of sandstone has been studied experimentally and numerically. The experimental work used three-point bending specimens containing pre-existing cracks, machined at various inclination angles so as to achieve varying proportions of mode I to mode III loading. Dimensionless stress intensity factors were calculated using the extended finite element method (XFEM) for and compared with existing results from literature calculated using conventional finite element method. A total of 28 samples were used to conduct the fracture test with 4 specimens for each of 7 different inclination angles. The fracture load and the geometry of the fracture surface were obtained for different mode mixities. Prediction of the fracture loads and the geometry of the fracture surface were made using XFEM coupled with a cohesive zone model (CZM) and showed a good comparison with the experimental results.

• Journal of Ocean Engineering and Technology
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• v.28 no.2
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• pp.152-159
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• 2014

KRISO(Korea Research Institute of Ships & Ocean Engineering) designed and manufactured a pilot mining robot called "MineRo" in 2012. MineRo is composed of four track modules. In general, much time and money are needed for deep-sea tests. Therefore, a numerical analysis to predict the dynamic behaviors has to be performed before a deep-sea test. In the numerical analysis, the information about the mining robot and soil properties are the most important factors to analyze the driving performance and dynamic response of MineRo. A terra-mechanics model of extremely cohesive soft soil is implemented in the form of the relationships between the normal pressure and sinkage, and between the shear stress and shear displacement. It is possible to acquire information about MineRo from the CAD model in the design phase. The Wong model is applied to the terra-mechanics model. This model is necessary to acquire many soil coefficients for a numerical analysis. However, in soil testing, the amount of soil property data obtained is limited. Moreover, it is difficult to analyze all of the cases for the many soil coefficients. In this paper, the dynamic behaviors of MineRo are analyzed according to the driving velocity, steering ratio, and variable extremely cohesive soft soil properties using a table of orthogonal arrays. The dynamic responses of MineRo are the turning radius, sinkage, and slip ratio. The relationships between the dynamic responses and variable soil properties are derived for MineRo.

• 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.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.706-713
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• 2004

This paper introduced an alternative method called USCP (Unpenetrated Sand Compaction Pile). In USCP, the toe of the sand pile does not reach to the lower supporting layer. Hence it is possible to reduce the amount of sand required. However, the degree of improvement could not be the same as SCP. Effective soil improvement, nevertheless, might be possible by combining both methods. In this paper, an improved method that cross over both SCP and USCP was discussed. And in order to verify applicability to a clay layer, consolidation behaviors with different conditions were analyzed and compared using FEM(Finite Element Method) based on the elasto-viscosity theory. From the results, it is concluded for the characteristic of settlement of USCP that the lower degree of replacement and the smaller ratio of penetration($H_d/H$), the larger is the settlement of the lower part of the clay layer comparing to the layer with no improvement. It is also concluded that the ratios of allotment of stress (m) calculated from the final settlements with 30% of degree of replacement are $1.8{\sim}3.3$ for $H_d/H=lOO%,\;1.8{\sim}4.0\;for\;H_d/H=75%,\;and\;1.8{\sim}3.8\;for\;H_d/H=50%$. Besides, the ratio of allotment of stress decreased as the degree of replacement decreased.

• Geotechnical Engineering
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• v.11 no.1
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• pp.41-50
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• 1995

In situ clay soils with Ko condition have anisotropic characteristics, varying the response according to the principal stress direction upon loading. But because of their practicality and simplicity, consolidated isotropic undrained compression tests are commonly used in practice to determine the behavior of cohesive soils. In this study to investigate the anisotropic characteristics and the effects of consolidation stress states on the response of normally consolidated clay soils during shearing, triaxial compression and extension tests after consolidating the undisturbed clay soil samples, which are obtained as a block sample to normalized consolidation states under isotropic or Ko state, were carried out. As a result of tests, the anisotropy of the undrained strength was confirmed. Comparing the soil responses between isotropic and Ko consolidation, the undrained strength by isotropic consolidation is overestimated because of its higher mean consolidation pressure. And isotropic consolidation reduces the anisotropy of soil response and influences on the stress-strain behavior and pore pressure response because the animotropic soil structure is partially collapsed during isotropic consolidation process. Also, OCR in overconsolidated soils is decreased by isotropic consolidatiorL Friction angle in eztension is higher than that in compression, but regression analysis shows that friction angle with cohesion in extension is almost the same as that without cohesion in compresslon.