• Proceedings of the Korean Geotechical Society Conference
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• 1992.10a
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• pp.145-148
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• 1992

This paper reports the application of field tests to weak ground. In this study, field and laboratory tests were performed in the west seashore of KOREA(Ildo, Sore, Kunsan, Youngam). Applied tests are standard penetration test, cone penetration test, dilatometer test, field vane test, unconsolidated undrained test, oedometer test and other fundametal material properties tests. The results of in-situ test are used to estimate soil types and undrained shear strengths of five clay local deposits. SPT results showed low reliability and FVT war also demonstrated the best field test to weak clayey deposits.

• Journal of the Korean Geotechnical Society
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• v.23 no.4
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• pp.113-123
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• 2007

In order to ensure the stability of reinforced structures backfilled with low permeability soil, it is very important to determine the change in undrained pullout capacity compared to drained pullout capacity prior to design. In this research, a series of numerical analyses on laboratory pullout tests have been performed on different materials (clean sand, 5, 10, and 15% silty sand), different overburden pressures (30, 100 and 200 kPa), and different drainage conditions (drained and undrained) in order to compare drained pullout capacity with undrained pullout capacity. The results of numerical analysis also have been compared with the results of the laboratory pullout tests. The analysis results show that both drained and undrained pullout capacity are influenced by silt contents and increase with increase of friction angle of the soil and overburden pressure. In undrained condition, the effective stresses acting on the reinforcement decrease as excessive pore pressures are generated, resulting in decrease in pullout capacity; 57% for 30 kPa, and 70% for 100 and 200 kPa. These results show a good agreement with the results of the laboratory pullout tests performed under the same condition.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.1039-1046
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• 2005

After clay particles have been sediment isotropically, the clay deposits have been consolidated under $K_0$-stress system. Therefore, in order to predict the behavior in-situ of normally consolidated clays, the laboratory test should be enforced under $K_0$-stress system and should obtain the characteristics of normally consolidated clays. And relationship of stress-strain on clay is effected on not only method of consolidation but also characteristic of visco-plastic behavior. Saturated clay is effected more this trend. So, rate of strain is considered to understand exact stress-strain relationship. In this study, the series of undrained triaxial compression tests were preformed on remolded specimens which was made by slurry of clay, consolidated under $K_0$-stress systems. And the undrained triaxial compression test were preformed to examine behavior of stress-strain relationship due to rate of shear strain relationship due to rate of shear strain.

• Geomechanics and Engineering
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• v.30 no.3
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• pp.219-231
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• 2022

Geotechnical materials such as silt, fine sand, or coarse granular soils may be unstable under undrained shearing or during rainfall infiltration starting an unsaturated state. Some researches are available describing the instability of coarse granular soils in drained or undrained conditions. However, there is a need to investigate the instability mechanism of unsaturated silty soil considering the effect of degree of compaction and net confining stress under partially and fully drained conditions. The specimens in the current study are compacted at 65%, 75%, & 85% degree of compaction, confined at pressures of 60, 80 & 120 kPa, and tested in partially and fully drained conditions. The tests have been performed in two steps. In Step-I, the specimens were sheared in constant water content conditions (a type of partially drained test) to the maximum shear stress. In Step-II, shearing was carried in constant suction conditions (a type of fully undrained test) by keeping shear stress constant. At the start of Step-II, PWP was increased in steps to decrease matric suction (which was then kept constant) and start water infiltration. The test results showed that soil instability is affected much by variation in the degree of compaction and confining stresses. It is also observed that loose and medium dense soils are vulnerable to pre-failure instability i.e., instability occurs before reaching the failure state, whereas, instability in dense soils instigates together with the failure i.e., failure line (FL) and instability line (IL) are found to be unique.

• 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.16 no.1
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• pp.75-81
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• 2000

The anisotropy of soils has an important effect on stress-strain behavior. In this study, an attempt has been made to implement artificial neural network model for modeling the stress-strain relationship and predicting the undrained shear strength of normally consolidated clay with varying consolidation pressure ratios. The multi-layer neural network model, adopted in this study, utilizes the error back-propagation loaming algorithm. The artificial neural networks use the results of undrained triaxial test with various consolidation pressure ratios and different effective vertical consolidation pressure fur learning and testing data. After learning from a set of actual laboratory testing data, the neural network model predictions of the undrained shear strength of the normally consolidated clay are found to agree well with actual measurements. The predicted values by the artificial neural network model have a determination coefficient$(r^2)$ above 0.973 compared with the measured data. Therefore, this results show a positive potential for the applications of well-trained neural network model in predicting the undrained shear strength of cohesive soils.

• Geotechnical Engineering
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• v.2 no.3
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• pp.37-50
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• 1986

The uncertainties encountered in the stability analysis for the foundation of offshore structures on clay are formulated in probabilistic terms and used to evaluate the reliability of the foundation design. The major sources of uncertainty are: soil properties, f.ave loads, and methods of analysis. The major part of the uncertainty in safety factor is contributed by the uncertainty in the undrained shear strength. All sources of uncertainties that affect the shear strength of clay are modeled and systematically analyzed. The in situ undrained shear strengths are evaluated by laboratory tests and cone penetration tests. The undrained shear strengths from the laboratory test and CPT, respectively at Statfjord B site in the North Sea, are used as an example in risk analysis. Using the CPT alone, the failure probability on sliding of gravity platform at Statfjord B is much larger than the failure probability using the laboratory undrained shear strengths. The major uncertainty of using the CPT as the estimate of th2 undrained shear strength of clay results from the correlation between the cone resistance and the undrained shear strength.

• Geotechnical Engineering
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• v.10 no.3
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• pp.41-54
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• 1994

This study aims at investigating the mechanism and operation of cubical triaxial test developed by Lade in order to obtain analysis on the clayey foundation deformation. A comparison on deviator stress, pore water pressure and stress path is made between test results of clay using the cubical consolidated undrained test as well as plane strain test.

• Proceedings of the Korean Geotechical Society Conference
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• 1996.10a
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• pp.285-294
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• 1996

• Geotechnical Engineering
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• v.12 no.6
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• pp.153-162
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• 1996

The undrained creep tests with isotropically and anisotropically overconsolidated clays were performed to investigate the effects of anisotropic consolidation on the undrained creep rupture behavior. Results of tests showed that the undrained creep rupture behaviors were iuluenced significantly by stress history including overconsolidation ratio and consolidation pressure ratio$(\sigma_{3c}/\sigma_{le})$. That is. the creep strength of clay increases with the increase of both overconsolidation ratio and consolidation pressure ratio. It, therefore, is dangerous to decide the possibility of creep rupture of clay by the isotropically consolidated creep rupture test in the case of the coefficient of earth pressure lower than 1.0. And the creep strength of clay could be obtained by the equation of the upper yield strength suggested by Finn and Shead(1973) irrespective of both overconsolidation ratio and consolidation pressure ratio.