• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.916-923
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• 2005

In this study, to observe aging effect of undrained shear behavior for Nak-Dong River sand, undrained static and cyclic triaxial tests were performed with changing relative density ($D_r$), consolidation stress ratio($K_c$) and consolidation time. As a result of the test, the modulus of elasticity to all samples estimated within elastic zone by the micro strain of about 0.05% in case of static shear behavior increased with the lapse of consolidation time significantly, so aging effect was shown largely. Also strength of phase transformation point(S_{PT}$) and strength of critical stress ratio point($S_{CSR}$) increased with the lapse of consolidation time. Undrained cyclic shear strength($R_f$) obtained from the failure strain 5% increased in proportion to relative density($D_r$) and initial static shear stress($q_{st}$), $R_f$ of consolidated sample for 1,000 minutes increased about 10.6% compared to that for 10 minutes at the loose sand, and $R_f$ increased about 7.0% at the medium sand. In situ application range of $R_f$ to the magnitude of earthquake for Nak-Dong River sand was proposed by using a increasing rate of $R_f$ as being aging effect shown from this test result.

• 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.

• Geomechanics and Engineering
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• v.11 no.5
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• pp.639-655
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• 2016

The effect of particle breakage and intermediate principal stress ratio on the behaviour of crushable granular assemblies under true triaxial stress conditions is studied using the discrete element method. Numerical results show that the increase of intermediate principal stress ratio $b(b=({\sigma}_2-{\sigma}_3)/({\sigma}_1-{\sigma}_3))$ results in the increase of dilatancy at low confining pressures but the decrease of dilatancy at high confining pressures, which stems from the distinct increasing compaction caused by breakage with b. The influence of b on the evolution of the peak apparent friction angle is also weakened by particle breakage. For low relative breakage, the relationship between the peak apparent friction angle and b is close to the Lade-Duncan failure model, whereas it conforms to the Matsuoka-Nakai failure model for high relative breakage. In addition, the increasing tendency of relative breakage, calculated based on a fractal particle size distribution with the fractal dimension being 2.5, declines with the increasing confining pressure and axial strain, which implies the existence of an ultimate graduation. Finally, the relationship between particle breakage and plastic work is found to conform to a unique hyperbolic correlation regardless of the test conditions.

• Journal of the Korean Geotechnical Society
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• v.15 no.4
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• pp.133-152
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• 1999

The cyclic triaxial test was carried out to research liquefaction characteristics and sample disturbance effects of silty sand soils at the west coast in Korea. First, liquefaction in silty sand was generated when axial strain approached to $\pm10%$ of strain and behavior of pore pressure was similar to the formula suggested by Seed, Martin, and Lysmer(1975). Also, it was found that dilatancy was generated at failure. Secondly, the liquefaction evaluation methods suggested by many researchers were carried out and the results were compared. In these methods the weak depth in liquefaction was similar and the method carried out by cyclic triaxial test on remolded sample showed the least safety factor. Thirdly the stress ratio by cyclic triaxial test was compared with that obtained from SPT N-value as a kind of empirical methods. It was found that the effect of sample disturbance was relatively small when SPT N-value was less than 20, but there were large differences in safety factor and resistance of liquefaction in soil by the effects of disturbance and remolding when SPT N-value was more than 20.

• Journal of Industrial Technology
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• v.22 no.A
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• pp.153-159
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• 2002

This paper is an experimental work of estimating friction angle of very coarse grained soil such as rubble mound by performing laboratory experiments. Two crushed rocks of rubble mound were used for tests. Triaxial compression tests with drained conditions were performed to measure friction angles of soils prepared by mixing the crushed soil having an identical coefficient of uniformity with different maximum grain size distribution. Centrifuge model experiments with those soils were also performed to measure angle of repose and to estimate friction angle of soil from measuring the slope of slip line in the active stress state. Model tests were carried out by changing the G-levels of 1G and 50G. From triaxial compression tests, the measured value of friction angle of soil is in the range of $41{\sim}57^{\circ}$. The measured value of repose angle is in the range of $32{\sim}35^{\circ}$. The values of friction angle are found not so sensitive to the maximum grain size of soil as long as the coefficient of uniformity is identical. Estimated value of friction angle from measuring the slope of slip line in the active stress state is in the range of $30{\sim}46^{\circ}$. Thus, the estimated angle of friction are found to be greater in the order of the measured angle of repose, the estimated value from the slope of active state, and triaxial compression test results. On the other hand, the measured values of friction angle from triaxial tests were compared with empirical equations, based on the relation between friction angle and void ratio. Equations proposed by Helenelund(l966) and Hansen(1967) found to be relatively reliable to estimate friction angles of soil.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.75-83
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• 2002

This paper is to investigate the mechanical characteristics of light-weighted soils (LWS) consisting of expanded polystyrene(EPS), dredged clays and cement by using both uniaxial and triaxial compression tests. The mechanical characteristics of the compressive strength of LWS are analysed with varying initial water contents of dredged clays, EPS ratio, cement ratio, and curing stress. In the triaxial compression state, it is found that the compressive strength of LWS containing EPS is independent on the effective confined stress. As the EPS ratio decreases($A_E$<2%) and cement ratio increases($A_c$>2%), the behavior characteristics of triaxial compressive strength-strain relationship is similar to that of cemented soil which decreases rapidly in compressive strength after ultimate compressive strength. For the applications of LWS to ground improvements which require the compressive strength of up to 200kPa, the optimized EPS ratio and initial water content of dredged clay are estimated to be 3~4% and 165~175%, respectively. Also, the ultimate compressive strength under both triaxial test and uniaxial compression states are almost constant for a cement ratio of up to 2% and then critical cement ratio of this LWS shall be 2%.

• Tunnel and Underground Space
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• v.32 no.3
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• pp.219-230
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• 2022

The Geo-Reservoir Experimental Analogue Technology (GREAT) cell was designed to recreate the thermal-hydro-mechanical conditions of deep subsurface in the laboratory. This apparatus can generate a polyaxial stress field using lateral loading elements, which rotate around the longitudinal axis of a sample and is capable of performing a fluid flow test for samples containing fractures. In the present study, numerical simulations were carried out for triaxial compression tests using the GREAT cell and the mechanical behavior of samples under different conditions of lateral loading was investigated. We simulated an actual case, in which triaxial compression tests were conducted for a polymer sample without fractures, and compared the results between the numerical analysis and experiment. The surface strain (circumferential strain) of the sample was analyzed for equal and non-equal horizontal confining pressures. The results of the comparison showed a good consistency. Additionally, for synthetic cases with a fracture, we investigated the effect of the friction and type of fracture surface on the deformation behavior.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.10 no.1
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• pp.82-90
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• 2007

In order to analyse the strength problems for an unsaturated soil, it is required to examine closely the characteristics of the parameters of shear strength which was changed with the metric suction and void ratio. To this ends, a triaxial compression test was conducted on the three samples-granular soil, cohesive soil and silty soil. The specimen was made by pressing the static pressure on the mold filled soil and was controled the void ratio with the different compaction ratio. And the test was performed by using the modified apparatus of the triaxial compression tester. The range of matric suction was 0-90 kPa.The measured results for the deviator stress and parameters of shear strength were analysed with the void ratio and the compaction ratio, and they were examined closely the characteristics of the strength for an unsaturated soil.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.1
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• pp.195-202
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• 1994

In this research, a lot of triaxial test results (CID) are analyzed to study the curvature characteristics of failure envelope of sand and parametric relationship between shear strength and state parameter by Been and Jefferies. In the conventional triaxial tests, correction for the change of sectional area of a sample and for membrane influence is essential especially in order to determine critical state (or steady state) condition more correctly. Based on the test results, a model to express the shear strength of fine sand as a function of density and stress level is presented and curvature characteristics of shear failure envelope and parametric relationship between state parameter and shear strength parameters are evaluated.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.03a
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• pp.67-74
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• 2002

An experimental assessment on the dynamic behavior of saturated sand which can consider the irregular characteristics of earthquakes was proposed. The equivalent uniform stress concept presented by Seed and Idriss has been applied to evaluate the liquefaction resistance strength to simplify earthquake loading. However, it was known that the liquefaction resistance strength of soil based on the equivalent uniform stress concept can't exactly mirror the dynamic characteristics of the irregular earthquake motion. In this study, estimation of the criterion of the liquefaction resistance strength was determined by applying real earthquake loading to the cyclic triaxial test. From the test results, relationships between excess pore water pressure and the earthquake characteristics such as magnitude or duration were determined. Magnitude scaling factors to determine the soil liquefaction resistance strength in seismic design were also proposed.