• Geotechnical Engineering
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• v.10 no.1
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• pp.7-18
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• 1994

A new model for describing the behavior of clay under monotonic and cyclic loading is proposed. This model uses the hyperbolic representation for the stress -strain relationship in overconsolidated state and it describes undrained effective stress path on the basis of the critical state theory. The developed constitutive model by using an energy dissipation equation can describe the behavior of clay in heavily overconsolidated state as u.ell as lightly overconsolidated state under monotonic loading. In order to extend the model for the behavior of clay under cyclic loading, a shift function of undrained stress spacing ratio is introduced in the constitutive model developed for monotonlc loading. A single additional parameter is required to represent the cyclic effect and it can be reasonably deter mined from the test results. The measured behavior in undrained cyclic triaxial tests has been easily and precisely predicted by the newly developed constitutive model.

• Geotechnical Engineering
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• v.6 no.3
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• pp.41-52
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• 1990

To investigate the liquefaction potential of sands, a series of untrained cyclic triaxial compression tests is carried out on the samples of Ottawa, Joomoonjin, Hn river and Hongseung sands. The constitutive equations of sands are derived to explain the mechanical behavior of sands under cyclic stresses, and are applicable to liquefaction analysis. The following results are obtainded in this study. 1. Sands with the lower confining pressure or relative density are to be easily liquefied, and when the amplitude of cyclic stress are large, liquefaction takes places over only a few cycles. 2. Stress ratio, porewater pressure ratio and cyclic shear strains are to be good criteria to evaluate liquefaction potential of sands. 3. Hongseung sands which contains some silty clay shows higher dynamic properties than other sands. 4. The dynamic behaviors of undisturbed Hongseung sand are about same as those of dense sands. It is noted that undisturbed Hongseung sand shows higher liquefaction potential than the samples made by pluviation under same relative density, 5. The constitutive equations of soils under cyclic loads are developed based on the theory of elasto-plasticity, logarithmic stress-strain rela'tionship, non-associated flow rule and the concept of the boundary surface. The derived equations is applicable to predict the behavior of sands under cyclic loads and liquefaction potential with a higher accuracy. 6. Based on results of the study it may be concluded that cracks of the foundations and dislocation of the structures at Hongseung earthquakes(Oct. 7, 1978, Richter scald 5.2) are not brought by the liquefaction process.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.2
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• pp.171-177
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• 2011

Tensile tests were conducted at low temperatures for the steel materials which are used for outer shell of the vessels making transit through the polar regions. The selected steel materials were GL-DH32, GL-DH36 and GL-EH36. In comparison with the results at room temperature, the yield stress increases approximately by 10 to 13 percent at $-30^{\circ}C$ and by 13 to 19 percent at $-50^{\circ}C$ while the tensile strength increases about by 9 percent at $-30^{\circ}C$ and 11 to 14 percent at $-50^{\circ}C$. To obtain true stress-true strain, i.e. correct plastic hardening characteristics, Bridgman's(1952) necking correction formula was introduced taking triaxial state of stresses after onset of diffuse necking into consideration. Photographs of fractured surfaces were taken by using Scanning Electron Microscope immedately after tensile tests completed and one for GL-EH36 has been presented in this paper.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.1025-1028
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• 2009

Earth and rock fill dam is our typical dam because of their inherent flexibility and adaptability to various fundation conditions. In order to secure structural safety, rockfill materials are used angular particles obtained by blasting parent rock or rounded particles collected from river beds. Concrete-faces rockfill dams(CFRD) and Concrete-faces gravelfill dams(CFGD) have become popular in the last 20 years as s result of their good performance and low cost compared with the rockfill dam. These Dams are also constructed by the materials. A key factor in the design of the dams is the deformations induced during construction and upon reservoir filling. These can be predicted using the stress-strain and strength properties can be adequately define. However the stress-strain properties of rockfill are difficult to determine because the properties are affected by such factors as particle grading, size and shape of particles, stress conditions, and particle crushing. In our study, testing of the behavior of the rockfill materials are essential prerequisites to the realistic analysis and design of the CFGD. This paper deals with laboratory testing of particle crushing among the study.

• Journal of the Korean Geotechnical Society
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• v.19 no.3
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• pp.15-22
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• 2003

The appropriate description of the stress-anisotropy and time-dependent behavior of cohesive soils is very important in representing the real soil behavior. In this study, two constitutive relations have been incorporated based on the generalized viscous theory: one is the plastic constitutive relation adopted to capture the stress-anisotropy with a few model parameters; the other is the rate-dependent constitutive relation adopted to describe the strain rate-dependent behavior, an important time-dependent behavior in cohesive soils. The incorporated and proposed constitutive model has relatively a few model parameters and their values need not to be re-evaluated at different strain rates. The proposed model has been verified and investigated with the anisotropic triaxial test results obtained by using the artificial homogeneous specimens.

• Journal of the Korean Geotechnical Society
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• v.29 no.8
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• pp.15-25
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• 2013

In order to examine the unsaturated shear strength characteristics of compacted weathered gneiss soils, the constant water content compression (CWCC) test was carried out. Specimens were made by static compaction under two densities conditions. The shear behavior in accordance with an initial suction obtained by varying initial degrees of saturation was evaluated. The suction could be directly measured by the use of the ceramic disk and the pore-water pressure transducer. The results of the peak shear strength from the CWCC test were examined using the relationship with Mp line from triaxial test under the saturated state, that is, by means of the suction stress which was calculated using the measured suction. In addition, the applicability of the suctions stress to the unsaturated shear behaviour of compacted weathered gneiss soils was discussed by applying Suction stress-SWCC Method (SSM).

• Geomechanics and Engineering
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• v.17 no.6
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• pp.507-513
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• 2019

Reinforced soil and Expanded Polystyrenes (EPS) mixture (RSEM) is a geomaterial which has many merits, such as light weight, wide strength range, easy for construction, and economic feasibility. It has been widely applied to improve soft ground, solve bridge head jump, fill cavity in pipeline and widen highway. Reutilizing dredged sediment to produce RSEM as earthfill can not only consume a large amount of waste sediment but also significantly reduce the construction cost. Therefore, there is an urgent need understand the basic stress-strain characteristics of reinforced dredged sediment-EPS mixture (RDSEM). A series of cyclic triaxial tests were then carried out on the RDSEM and control clay. The effects of cement content, EPS beads content and confining pressure on the cyclic stress-strain behaviour of RDSEM were analyzed. It is found that the three stages of dynamic stress-strain relationship of ordinary soil, vibration compaction stage, vibration shear stage and vibration failure stage are also applicative for RDSEM. The cyclic stress-strain curves of RDSEM are lower than that of control clay in the vibration compaction stage because of its high moisture content. The slopes of backbone curves of RDSEMs in the vibration shear stage are larger than that of control clay, indicating that the existence of EPS beads provides plastic resistance. With the increase of cement content, the cyclic stress-strain relationship tends to be steeper. Increasing cement content and confining pressure could improve the cyclic strength and cyclic stiffness of RDSEM.

• Geomechanics and Engineering
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• v.24 no.6
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• pp.519-529
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• 2021

In coal mining activities, the abutment stress of the coal has to undergo cyclic loading and unloading, affecting the strength and seepage characteristics of coal; additionally, it can cause dynamic disasters, posing a major challenge for the safety of coal mine production. To improve the understanding of the dynamic disaster mechanism of gas outburst and rock burst coupling, triaxial devices are applied to axial pressure cyclic loading-unloading tests under different axial stress peaks and different pore pressures. The existing empirical formula is use to perform a non-linear regression fitting on the relationship between stress and permeability, and the damage rate of permeability is introduced to analyze the change in permeability. The results show that the permeability curve obtained had "memory", and the peak stress was lower than the conventional loading path. The permeability curve and the volume strain curve show a clear symmetrical relationship, being the former in the form of a negative power function. Owing to the influence of irreversible deformation, the permeability difference and the damage of permeability mainly occur in the initial stage of loading-unloading, and both decrease as the number of cycles of loading-unloading increase. At the end of the first cycle and the second cycle, the permeability decreased in the range of 5.777 - 8.421 % and 4.311-8.713 %, respectively. The permeability decreases with an increase in the axial stress peak, and the damage rate shows the opposite trend. Under the same conditions, the permeability of methane is always lower than that of helium, and it shows a V-shape change trend with increasing methane pressures, and the permeability of the specimen was 3 MPa > 1 MPa > 2 MPa.

• Geotechnical Engineering
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• v.4 no.1
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• pp.17-28
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• 1988

Among several types of element tests to predict soil behalf.iota in a laboratory, the torsion shear apparatus, in which the directions of principal stresses could be rotated during shearing, wra explained. In this study, this torsion shear apparatus was improved so as to be used in tests on clay specimens . And some undrained torsion shear tests u.ere performed on remolded specimens of Ko-consolidated clay to investigate the influence of reorientation of the principal stress directions on the stress-strain behavior The soil behavior by the torsion shear apparatus without torque was compared It.ith that by the conventional triaxial compression tests . The stress path, provided by both vertical loads and torque during torsion shear tests, has much effect on the stress-strain behavior, the pore pressure and the effective principal stress ratio . The rotation angle of the principal stress and the b-value were gradually increased with increasing shear strain, but converged to the values at failure.

• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.27-38
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• 2003

The characteristics and prediction model of the shear strength of unsaturated residual granite soils were studied in this paper. In order to investigate the influence of the net normal stress on the shear strength, unsaturated triaxial tests and SWCC tests were carried out by varying the net normal stress. Experimental data for unsaturated shear strength tests were compared with predicted shear strength envelopes obtained from existing prediction models. It was shown that the soil-water characteristic curve and the shear strength of the unsaturated soil varied with the change of the net normal stress. Therefore, to achieve a truly descriptive shear strength envelope for unsaturated soils, the effect of the normal stress on the contribution of matric suction to the shear strength has to be taken into consideration. In this paper, a modified prediction model f3r the unsaturated shear strength was proposed.