• Geotechnical Engineering
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• v.8 no.2
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• pp.45-58
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• 1992

An elasto-plastic constitutive model for geological materials, which satisfies the flezibility and stability at the same time, can be used in a number of geotechnical problems. Using the spacing ratio of critical state, a flexible model is proposed based on the stability of modified Camflay model. The spacing ratio of critical state can be simply evaluated, and practically used in describing the undrained shearing behavior of clay. The proposed model has precisely predicted the stress paths and stress -strain relationships, compared with the modified Camflay model, with respect to undrained triaxial test results. Besides, the effects of strain rate, creep, and relaxation can also be considered. Using the quasi-state boundary surface, the constitutive relations are well predicted. Therefore, it is found that the assumption of associative flow rule is well posed for undrained behavior of normally consolidated clay.

• Journal of the Korean GEO-environmental Society
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• v.12 no.8
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• pp.13-24
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• 2011

In the part of geotechnical engineering, soils are classified as either the coarse grained soil or the fine-grained soil following the fine content($F_c$=50%) according to the granularity, and appropriate design codes are used respectively to represent their mechanical behaviour. However, sand-clay mixtures, which are typically referred to as intermediate soils, cannot be easily categorized as either sand or clay. In this study, several monotonic undrained shear tests were carried out on Silica sand fine mixtures with various proportions, and a wide range of soil structures, ranging from one with sand dominating the soil structure to one with fines controlling the behaviour, were prepared using compaction method or pre-consoldation methods in prescribed energy. The shear strength of mixtures below the threshold fines content is observed that as the fines content increases, maximum deviator stress ratio decrease for dense samples while an increase is noted for loose samples. Then, by using the concept of fines content and granular void ratio, the monotonic shear strength of the mixtures was estimated. It was found that the shear behavior of mixtures is greatly dependent on the skeleton structure of sand particles.

• Computers and Concrete
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• v.31 no.5
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• pp.395-403
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• 2023

The paper investigates the effect of two parameters - sand content (SC) and grain migration during shearing - on the mechanical properties of gravel-sand mixtures. Consolidated undrained (CU) triaxial tests were carried out on eight series of mixtures containing gravel (1<d<16 mm) and sand (0.1<d<1 mm). The prepared mixtures have sand contents of 0, 10, 15, 20, 40, 54, 94 and 100%, and a relative density of 60%. The transition sand content (TSC) is experimentally defined and marks the transition from gravel-driven to sand-driven behavior. For SC<TSC, the dry density of the mixture increases with SC. This induces an increase in undrained peak strength and dilative trend. The slope and position of the critical state line (CSL) are also deeply dependent on SC. At SC=TSC, the mixtures exhibit the largest dry density and yield the highest undrained peak strength and the largest dilative trend. During shearing, large internal migration of grains was observed at the TSC, causing heterogeneity in the sample. Analysis of the CSL deduced from the final points of the triaxial tests shows that, at the TSC, failure appears to correspond to the behavior of the coarsest fraction of the soil. This fraction is located in the upper part of the sample, where the sand particles had been eliminated by suffusion. On the other hand, in the more stable materials, the CSL is consistent with the bulk grain size distribution of the soil.

• Journal of the Korean Geotechnical Society
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• v.20 no.8
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• pp.49-58
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• 2004

The cone pressuremeter test (CPM) is a new in-situ test which combines a standard cone penetration test with a pressuremeter. The cone pressuremeter tests in clay are presented and analyzed. An analytical solution of CPM incorporated non-linear soil behavior with no volume change is presented, and curve fitting technique is proposed to make use of both the loading and unloading portions of the pressuremeter test. The proposed method is accomplished by putting greater emphasis on the unloading portion. Twenty CPM tests are analyzed using the proposed method, and the derived undrained shear strength of soil is compared with other tests such as field vane tests and laboratory tests. The interpreted soil parameters had resonable values when compared to other in-situ and laboratory test results. The cone pressuremeter has provided reliable measures of undrained shear strength using curve fitting method.

• Journal of the Korean Geotechnical Society
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• v.21 no.8
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• pp.13-26
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• 2005

It was known that the aging effect of sands is insignificant in comparison with clays, and hence the study on this effect had seldom been performed prior to the early 1980s. However, field tests for this effect have been actively carried out since it was investigated that penetration resistance of reformed sands increased with the lapse of time. Recently, the aging effect of sands has also been examined in laboratory testings. In this study, undrained static triaxial tests were performed to evaluate the effect on the Nak-dong River sands, with different .elative densities $(D_r)$, consolidation stress ratios $(K_c)$, and consolidation times. As a result of the tests, it was proved that the undrained cyclic shear strength $(R_f)$ increased with the aged time on the sands. The in situ range of Rf on the sands, which is applicable to the magnitude of earthquake in the Nak-dong River area, was proposed by using the test results.

• Journal of the Korean Geotechnical Society
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• v.24 no.8
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• pp.149-160
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• 2008

Offshore pile foundations are prone to lateral soil pressures resulting from embankment construction for the reclamation on deepwater soft clay. Since the 1990s, offshore reclamation has actively progressed in Korea, connecting with the development of Songdo newtown, Incheon newport, and Busan newport representatively. Special attention has been given to lateral soil-structure interaction problems related to passively-loaded offshore pile foundations. Based on a plane strain large deformation finite element (LDFE) approach, this paper presents the results of investigation into undrained (short-term) and drained (long-term) behavior of passively-loaded offshore pile foundations. This study examines the effects of major factors, such as soil profile, pile head boundary condition, magnitude of embankment load, and average degree of consolidation. The results allowed quantification of differences in the magnitude of lateral soil pressure acting on the piles between undrained and drained phases.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.7 no.3
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• pp.409-413
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• 2006

The accumulated deformation due to the undrained creep causes the general stability problem for the overall soil mass. In this study, the time-dependent constitutive equation, into which a damage law, modified cam clay model, and Perzyna's generalized viscous theory were incorporated, was derived microscopically. The model prediction agreed well with the experimental result including the case of the undrained creep rupture.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2001.10a
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• pp.351-354
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• 2001

Undrained cyclic triaxial compression tests were performed on Saemangeum dredged sand to evaluate factors affecting liquefaction strength and liquefaction behaviour characteristics. The results of these tests show that cyclic liquefaction can occur not only very loose sand(Relative density is 30%) but also dense sand(Relative density is 70%). To evaluate effect of the over consolidation ratio on the liquefaction strength, a series of undrained cyclic triaxial compression test was peformed, and the result of this test showed that the liquefaction of this test showed that the liquefaction strength of Saemangeum dredged sand approximately increased to square root of over consolidation ratio in the range of O.C.R value of 1.0 to 4.0. In the anisotropically consolidated sample tests, the liquefaction strength is increased by increasing the effective consolidation ratio.

• Journal of The Korean Society of Agricultural Engineers
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• v.54 no.1
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• pp.19-26
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• 2012

Soils exhibit creep behavior in which deformation and movement proceed under a state of constant stress or load. In this study, A series of triaxial tests were performed under constant principal stress in order to interpret the undrained creep characteristics of silty sands. Although samples are non-plastic silty sands, the results of tests show that the creep deformation increasing over time. Based on the results of test, Singh-Mitchell model parameters and Generalized model coefficients were calculated. Generalized model showed slightly larger deformation in the primary creep range but secondary creep deformation was almost identical. Although Singh-Mitchell model showed relatively large errors compared to Generalized model because it uses the average of test results, but Singh-Mitchell model can be easily represented by three creep parameters.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.311-317
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• 2008

This study was carried out to improve our understanding about the influence of silt content on the stress-strain of sand under cyclic loading. Soil specimens were prepared by wet-tamping method as same void ratio and specimen's silt contents on total weights was changed from 0% to 20%. Also, effects of the silt contents on the stress-strain response were studied at different anisotropic consolidation ratio, Kc=1.0, 1.5, 2.0 condition. As a result, cyclic shear strength decreased as silt contents increased in same stress ratios. In same silt contents, cyclic shear strength increased as Kc increased in lower silt contents, but in higher silt contents, it had reverse results.