• Journal of the Korean Geotechnical Society
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• v.28 no.12
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• pp.53-64
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• 2012

In this study, the modified cyclic triaxial tests with Joomunjin standard sand are performed for dynamic deformation characteristics, such as Young's moduli and damping ratio. The cyclic triaxial test is equipped with Local Displacement Transducer (LDT) on the outside of a cell which has a range from $10^{-4}$ to $10^{-1}$ of shear strains, ${\gamma}$ (%), instead of conventional cyclic triaxial test which has linear variable displacement transducer (LVDT) with low precision. With the small strain control, tests were carried out at various loading rates, void ratios, and effective confining pressures. Based on the test results, such as dynamic deformation characteristics, shear modulus, and damping ratio, it is found that the test can measure more range of medium strains (0.02-0.2%) than results obtained from conventional test (resonant column test). For the medium strain range, dynamic deformation characteristics investigated by the cyclic triaxial test are also different from those predicted by nonlinear model in conventional test.

• Geomechanics and Engineering
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• v.36 no.4
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• pp.317-328
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• 2024

Adopting a rational engineering methodology for building structures on sandy-clay soil layers has become increasingly important since it is crucial when structures erected on them often face seismic and cyclic wave loads. Such loads can cause a reduction in the stiffness, strength, and stability of the structure, particularly under un-drained conditions. Hence, this study aims to investigate how the dynamic properties of sand-clay mixtures are affected by loading frequency and clay content. Cyclic triaxial tests were performed on a total of 36 samples, comprising pure sand with a relative density of 60% and sand with varying percentages of clay. The tests were conducted under confining pressures of 50 and 100 kPa, and the samples' dynamic behavior was analyzed at loading frequencies of 0.1, 1, and 4 Hz. The findings indicate that an increase in confining pressure leads to greater inter-particle interaction and a reduced void ratio, which results in an increase in the soil's shear modulus. An increase in the shear strength and confinement of the samples led to a decrease in energy dissipation and damping ratio. Changes in loading frequency showed that as the frequency increased, the damping ratio decreased, and the strength of the samples increased. Increasing the loading frequency not only reflects changes in frequency but also reduces the relative permeability and enhances the resistance of samples. An analysis of the dynamic properties of sand and sand-clay mixtures indicates that the introduction of clay to a sand sample reduces the shear modulus and permeability properties.

• Journal of the Korean Geotechnical Society
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• v.15 no.6
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• pp.307-317
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• 1999

The purpose of this study is to utilize conventional procedures for evaluation of liquefaction potential and to compare the results obtained by modified detailed method based on Korean earthquake magnitude (M=6.5). Liquefaction potential is assessed by comparing liquefaction strength of soil and cyclic shear stress generated in the soil layers during earthquakes. The cyclic shear stress is computed from the earthquake response analysis, and liquefaction strength of soil is evaluated by using results from cyclic triaxial tests. The cyclic triaxial tests are performed on many different conditions of sample ; relative densities(50%, 60%, and 70%), initial effective confining pressures (70kPa, 100kPa, and 150kPa), and fine contents(10%, 20%, and 30%). From the result of comparing the conventional procedure with the modified detailed method, it is found that the modified detailed method tends to evaluate larger safety factor against liquefaction in the weak sand site$(FS \leq1.5)$. Therefore in this case, it is suggested that liquefaction potential should be evaluated by using the modified detailed method based on cyclic triaxial tests. It is also found that in modified detailed method based on earthquake magnitude 6.5, critical depth where liquefaction can be generated is around 15m from the ground surface.

• Geomechanics and Engineering
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• v.29 no.5
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• pp.497-508
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• 2022

Tailings fluidization (i.e., tailings behave as being fluidized) under cyclic loading is one concern during the construction of tailings dams, especially in the shallow tailings layers. The primary goal of this study is to evaluate the responses of tailings under cyclic loadings and the tailings potential for fluidization. A series of cyclic triaxial undrained and drained tests were performed on medium and dense tailings samples under various cyclic stress ratios (CSR). The results indicated that axial strain and excess pore water pressure accumulated over time due to cyclic loading. However, the accumulations were dependent on CSR values, densities, and drainage conditions. The fluidization potential analysis in this study was then evaluated based on the obtained cyclic axial strain and excess pore water pressure. As a result, tailings samples were stable (unfluidized) under small CSR values, and the critical CSR values, where the tailings fluidized, varied depending on the density of tailings samples. Tailings fluidization is triggered as cyclic stress ratios reach critical values. In this study, the critical CSR values were found to be 0.15 and 0.40 for medium and dense samples, respectively.

• Journal of the Korean Geotechnical Society
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• v.36 no.9
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• pp.21-32
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• 2020

In this study, series of cyclic triaxial tests and shear velocity measurement were conducted using Pohang sand, which was taken from liquefaction observed area, to verify the liquefaction characteristics of Pohang. The cyclic resistance ratio(CRR) was derived based on the test results. A specimen was reconstituted into 40% and 80% relative density conditions and then a series of cyclic triaxial tests and shear-wave velocity measurement were conducted. As a result, the effect of particle distribution and relative density to liquefaction resistance was verified. The liquefaction resistance of Pohang sand was evaluated by comparing with other liquefaction resistance of sands from previous research. In addition, the liquefaction resistance curve from field observation data was used to verify the reliability of results from this study by measured shear-wave velocity.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.1126-1133
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• 2005

The effects of mean particle size and uniformity coefficient of dredged soils to the liquefaction resistance strength and dynamic characteristics are experimentally studied in this paper. Representative 4 mean particle sizes and 3 uniformity coefficients were selected and 12 representative particle size distribution curves which have different mean particle sizes and uniformity coefficients, were artificially manufactured using the real dredged river soil. Cyclic triaxial tests and torsional shear tests were carried out to analyze the effect of mean particle size and uniformity coefficient to the liquefaction resistance strength and dynamic characteristics of soils.

• Geomechanics and Engineering
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• v.3 no.2
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• pp.83-108
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• 2011

The effect of non-plastic fines (silt) on liquefaction and pore pressure generation characteristics of saturated sands was studied through undrained stress controlled cyclic triaxial tests using cylindrical specimens of size 50 mm diameter and height 100 mm at different cyclic stress ratios and at a frequency of 0.1 Hz. The tests were carried out in the laboratory adopting various measures of sample density through various approaches namely gross void ratio approach, relative density approach, sand skeleton void ratio approach, and interfine void ratio approach. The limiting silt content and the relative density of a specimen were found to influence the undrained cyclic response of sand-silt mixtures to a great extent. Undrained cyclic response was observed to be independent of silt content at very high relative densities. However, the presence of fines significantly influenced this response of loose to medium dense specimens. Combined analyses of cyclic resistance have been done using the entire data collected from all the approaches.

• Geomechanics and Engineering
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• v.33 no.3
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• pp.243-259
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• 2023

Turkey is one of the most important earthquake regions in Europe. This region has been exposed to many earthquakes of different magnitudes from past to present. It is of great importance to determine the dynamic properties of the soils for structures to be built in earthquake zones. In order to minimize the damages that may occur, the behavior of the soils under repeated loads should be known and taken into consideration in the design. In this study, 4 different point borings were taken near active fault lines in the North Anatolian fault zone (NAFZ). In order to determine the dynamic parameters of soils, both dynamic triaxial (TRX) and resonant column (RC) tests were carried out on undisturbed samples at every 5 m. As a result of the experiments, V_s and G_max values were obtained from the field and differences were determined. The dynamic behavior of the soil was examined at varying depths with the comparison of reference models in the literature and compatible results were obtained. Finally, the behavior at the transition region is highlighted. As a result, three shear modulus and dumping ratio models have been proposed for clay soils to be used in different soil conditions.

• Geomechanics and Engineering
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• v.7 no.3
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• pp.297-316
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• 2014

This paper presents a detailed study focused on investigating the effects of silt content on the static and dynamic properties of sand-silt mixtures. Specimens with a low-plastic silt content of 0, 15, 30 and 50% by weight were tested in static triaxial, cyclic triaxial, and resonant columns in addition to consolidation tests to determine such parameters as compression index, internal friction angle, cohesion, cyclic stress ratio, maximum shear modulus, normalized shear modulus and damping ratio. The test procedures were performed on specimens of three cases: constant void ratio index, e = 0.582; same peak deviator stress of 290 kPa; and constant relative density, $D_r$ = 30%. The test results obtained for both the constant-void-ratio-index and constant-relative-density specimens showed that as silt content increased, the internal friction angle, cyclic stress ratio and maximum shear modulus decreased, but cohesion increased. In testing of the same deviator stress specimens, both cohesion and internal friction angle were insignificantly altered with the increase in silt content. In addition, as silt content increased, the maximum shear modulus increased. The cyclic stress ratio first decreased as silt content increased to reach the threshold silt content and increased thereafter with further increases in silt content. Furthermore, the damping ratio was investigated based on different silt contents in three types of specimens.

• Geomechanics and Engineering
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• v.10 no.3
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• pp.325-334
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• 2016

Rock salt is a near-perfect material for gas storage repositories due to its excellent ductility and low permeability. Gas storage in rock salt layers during gas injection and gas production causes the stress redistribution surrounding the cavity. The triaxial cyclic loading and unloading tests for rock salt were performed in this paper. The elastic-plastic deformation behaviour of rock salt under cyclic loading was observed. Rock salt experienced strain hardening during the initial loading, and the irreversible deformation was large under low stress station, meanwhile the residual stress became larger along with the increase of deviatoric stress. Confining pressure had a significant effect on the unloading modulus for the variation of mechanical parameters. Based on the theory of elastic-plastic damage mechanics, the evolution of damage during cyclic loading and unloading under various confining pressure was described.