• Geomechanics and Engineering
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• v.9 no.6
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• pp.729-742
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• 2015

The aim of the present work was the study of instability in a loose sand from Les Dunes beach in Ain Beninan, Algeria, where the Boumerdes earthquake occurred in 2003. This earthquake caused significant structural damages and claimed the lives of many people. Damages caused to infrastructures were strongly related to phenomena of liquefaction. The study was based on the results of two drained and six undrained triaxial tests over a local sand collected in a region where liquefaction occurred. All the tests hereby analyzed followed compression stress-paths in monotonic conditions and the specimens were isotropically consolidated, since the objective was to study the instability due to static loading as part of a more general project, which also included cyclic studies. The instability was modeled with the second-order work increment criterion. The definition of the instability line for Les Dunes sand and its relation with yield surfaces allowed the identification of the region of potential instability and helped in the evaluation of the susceptibility of soils to liquefy under undrained conditions and its modeling. The dilatancy rate was studied in the points where instability began. Some mixed tests were also simulated, starting with drained conditions and then changing to undrained conditions at different time steps.

• The Journal of Engineering Geology
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• v.24 no.1
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• pp.23-38
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• 2014

The composition of carbonate sands from a sabkha at Ruwais in the UAE differs from that of silica sand, and these sands are crushed easily under low compression pressures. Accordingly, particle crushing of carbonate sand occurs under high pressure, which results in additional settlement and reduces the shear strength. In this study, consolidation and triaxial tests were conducted to analyze the characteristics of carbonate sands following particle crushing. The unusual shear strength graphs of the carbonate sands result from the degree of particle pre-crushing. For the range at p' > p in the p (p')-q diagram, negative (-) excess porewater pressures occur if the axial pressure causes particle crushing that induces exposure of the inner voids. In addition, the q value decreased after particle crushing. In conclusion, the unusual characteristics of the carbonate sands were induced by particle crushing. The triaxial tests revealed that the degree of particle pre-crushing influenced the excess porewater pressure.

• Journal of the Korean Geotechnical Society
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• v.30 no.2
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• pp.33-42
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• 2014

The shear strength and deformation characteristics of granular soils at low confining stresses differ from those with high confining stresses. Thus, the clear understanding of geotechnical problems related to the low confining stress state such as the stability of shallow foundations, embankments, slope failure, debris flow characteristics and liquefaction as well as the various laboratory model tests is needed. In this study, drained triaxial compression tests with the cell pressures from 5 kPa to 300 kPa were performed on dry Jumunjin sand. The results show that the internal friction angle and deformation modulus are dependent on the confining stress. Also, the correlations between them on the dense and loose sand were established.

• Journal of the Korean Geotechnical Society
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• v.31 no.11
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• pp.33-40
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• 2015

Volcanic rocks in Jeju Island indicate the differences in geological and mechanical characteristics from region to region, and have vesicular structure caused by various environmental factors. In this study, triaxial compressive strength tests were conducted for intact rocks sampled in northeastern onshore and offshore, southeastern offshore and northwestern offshore of Jeju Island. The estimated cohesion and internal friction angle from the results of triaxial compression tests were compared and analyzed with absorption, a parameter representing the vesicular properties of basalts in Jeju Island. As a result, it was found that the relationship between cohesion and absorption could be classified clearly, considering two different linear relationships in bulk specific gravity and absorption. As the absorption increases, the cohesion decreases exponentially. In addition, the internal friction angle decreases almost linearly with increasing in the absorption, regardless of the relationships in bulk specific gravity and absorption.

• Journal of the Korean Geotechnical Society
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• v.15 no.1
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• pp.161-173
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• 1999

Settlement analysis based on oedometer test results with or without Skempton-Bjerrum's modification method ( widely used for practical purposes when estimating consolidation settlements of soft clay deposits) has shortcomings that it cannot simulate real stress states and deformation behaviors of soils in case that in-situ loading and deformation conditions are not 1-dimensional. In this study, the stress path method, reflecting various probable stress paths, was employed to normally - consolidated kaolinite samples by using automated triaxial testing device which can control stress paths automatically. From this experimental study, elastic, consolidation, secondary compression and pore pressure development - dissipation behaviors under various stress paths were analyzed and deformation characteristics of soft clays, which can be the basis of rational estimation of settlements, were studied. Also by comparing results of stress path tests with those of 1-dimensional consolidation tests, limitations and problems of conventional methods were clarified.

• Journal of the Korean Geotechnical Society
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• v.31 no.3
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• pp.27-38
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• 2015

Triaxial tests on sand-silt mixture specimens under low and high confining pressures were performed to understand their shear behaviors. The fines content in the mixture is lower than the threshold value. A series of tests under different conditions including fines contents (0%, 9.8%, 14.7%, 19.6%), density of specimen (controlled by different compaction energies of $E_c=22kJ/m^3$, $E_c=504kJ/m^3$), confining pressure (100 kPa, 1 MPa, 3 MPa, 5 MPa) were performed to investigate influences of these factors. Based on the test results, the threshold fines content, where the dominant structure of mixture changes from sand-matrix to fines-matrix, decreases with the increase of confining pressure. Under very high confining pressures, as a result of sand particle crushing, the behavior of the dense specimen is similar to that of the loose specimen which shows hardening, compression behavior, and shear strength increases with increase of fines content. In conclusion, silt is granular material like sand, and its influence on shear behavior of sand-silt mixture is very different from that of plastic fines on sand-fines mixture.

• Journal of the Korean Geosynthetics Society
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• v.8 no.1
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• pp.25-32
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• 2009

In reclaimed loose sandy layer with dredged soil, liquefaction by the small scale earthquake coud be occurred easily. A study has been carried out to investigate the Liquefaction characteristic on Saemangeum dredged sandy soil, and compared with other results from the literature investigation. A series of undrained cyclic triaxial compression tests were performed on dredged sandy soil of Seamangeum area. The tests were performed at the three different initial relative densities(namely 30%, 50%, 70%), different cyclic stress ratio and different consolidation stress condition. The results of this study showed that cyclic stresses (${\sigma}_d$) increased linearly with increase of consolidation ratio, but the stress ratios (${\sigma}_d/2{\sigma}^{\prime}{_c}$) were almost same. The stress ratios were increased almost linearly with increase of relative density. Compared with other sandy soil, Saemangeum dredged sandy soil showed relatively weak liquifaction characteristics.

• Journal of the Korean earth science society
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• v.25 no.1
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• pp.22-31
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• 2004

Laboratory experiments were conducted in order to find effects of the intermediate principal stress of ${\sigma}_{2}$ on rock fractures and faults. Polyaxial tests were carried out under the most generalized compressive stress conditions, in which different magnitudes of the least and intermediate principal stresses ${\sigma}_{3}$ and ${\sigma}_{2}$ were maintained constant, and the maximum stress ${\sigma}_{1}$, was increased to failure. Two crystalline rocks (Westerly granite and KTB amphibolite) exhibited similar mechanical behavior, much of which is neglected in conventional triaxial compression tests in which ${\sigma}_{2}$ = ${\sigma}_{3}$. Compressive rock failure took the form of a main shear fracture, or fault, steeply dipping in ${\sigma}_{3}$ direction with its strike aligned with ${\sigma}_{2}$ direction. Rock strength rose significantly with the magnitude of ${\sigma}_{2}$, suggesting that the commonly used Mohr-type failure criteria, which ignore the ${\sigma}_{2}$ effect, predict only the lower limit of rock strength for a given ${\sigma}_{3}$ level. The true triaxial failure criterion for each of the crystalline rocks can be expressed as the octahedral shear stress at failure as a function of the mean normal stress acting on the fault plane. It is found that the onset of dilatancy increases considerably for higher ${\sigma}_{2}$. Thus, ${\sigma}_{2}$ extends the elastic range for a given ${\sigma}_{3}$ and, hence, retards the onset of the failure process. SEM inspection of the micromechanics leading to specimen failure showed a multitude of stress-induced microcracks localized on both sides of the through-going fault. Microcracks gradually align themselves with the ${\sigma}_{1}$-${\sigma}_{2}$ plane as the magnitude of ${\sigma}_{2}$ is raised.

• Journal of the Korean Geotechnical Society
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• v.36 no.12
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• pp.117-124
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• 2020

The present research focuses on a methodology to describe shearing response of clay with respect to temperature. An increase of temperature shifts the normal consolidation line to move down in the plane of void ratio and mean effective stress. The critical state line, however, does not move as much as the normal consolidation line in accordance with temperature increase. As temperature increase, therefore, the difference between the critical state mean effective stress and the pre-consolidation pressure reduces. To reflect this easily, the present study applies a bounding surface consisting of two parts divided by the critical state mean effective stress. This study calibrated a bounding surface for the soft Bangkok clay and performed elemental simulation for undrained triaxial compression tests. The elemental simulation showed that the model can describe the mechanical response upon temperature of clay without complex hardening and evolution rules compared to the experimental data.

• Journal of the Korean Geotechnical Society
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• v.23 no.3
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• pp.41-50
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• 2007

The results from normally consolidated isotropic drained and undrained triaxial compression tests (NCIU and NCID) on sand with high silt content were presented in this paper. The experiments were performed on specimens of Nak-dong River sand with 63% silt content under effective confined pressures, 100 kPa to 400 kPa. From test results, Sandy silt became initially compressive but eventually appeared to provide dilatancy response throughout the entire stress-strain curve The behavior of sandy silt was more difficult to characterize than that of clay and sand due to lower plastic characteristic. Especially, the samples exhibited dilatancy development during shear after failure. The shear behavior and shear strength parameters of sandy silt can be determined as stress-strain behaviors are described by the Mohr-Coulomb failure criterion. The shear behaviors were observed increasing dilatancy volume change tendency with strain-softening tendency after failure. In this paper, the behavior of dilatancy depends on not only sand content but also fine content with low-cohesion during shear in the samples of sandy silt.