• Journal of the Korea Concrete Institute
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• v.18 no.5 s.95
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• pp.695-702
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• 2006

The stress distribution and the critical stresses in concrete pavements were analyzed using formulations in the transformed field domains when dual-wheel single-, tandem-, and tridem-axle loads were applied. First the accuracy of the transformed field domain analysis results was verified by comparing with the finite element analysis results. Then, the stress distribution along the longitudinal and transverse directions was investigated, and the effects of slab thickness, concrete elastic modulus, and foundation stiffness on the stress distribution were studied. The effect of the tire contact pressure related to the tire print area was also studied, and the location of the critical stress occurrence in concrete pavements was finally investigated. From this study, it was found that the critical concrete stress due to multi-axle loads became larger as the concrete elastic modulus increased, the slab thickness increased, and the foundation stiffness decreased. The number of axles did not tend to affect the critical stress ratio except for a small foundation stiffness value with which the critical stress ratio became significantly larger as the number of axles increased. The critical stress location in the transverse direction tended to move into the interior as the tire contact pressure increased, the concrete elastic modulus increased, the slab thickness increased, and the foundation stiffness decreased. The critical stress location in the longitudinal direction was under the axle for single- and tandem-axle loads, but for tridem-axle loads, it tended to move under the middle axle from the outer axles as the concrete elastic modulus and/or slab thickness increased and the foundation stiffness decreased.

• Journal of the Korean Geotechnical Society
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• v.27 no.1
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• pp.41-52
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• 2011

The hypothesis on effective stress of unsaturated soil is validated by $K_0$ consolidation results of triaxial tests for the compacted residual soil. The stress characteristic curve (SSCC) can describe unsaturated soil behavior on water contents, which was defined from shear strength or from soil water characteristic curves. In this study, it was found that the stress path of $K_0$ consolidation can also define the SSCC. The effective stress was defined by SSCC. $K_0$ paths for various matric suctions could be described as a unique line by effective stress. The measured values of $K_0$ were interpreted by effective stress as a constant with respect to matric suction. Since the SSCC from $K_0$ consolidation agrees with that from the shear strength, the SSCC from soil water retention curve could describe effective stress behavior consistently on both $K_0$ consolidation path and stress at failure. The effective stress based on SSCC can describe the entire unsaturated behavior from consolidation to failure.

• Journal of the Korean Geotechnical Society
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• v.16 no.3
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• pp.77-88
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• 2000

연약지반상에 하중 경감을 목적으로 발포성 폴리스티렌(Expanded Polystyrene)을 사용하는 사례가 최근 꾸준히 증가하고 있다. 공법의 요점은 연약지반상에 축조되는 상부구조물에 의한 응력증가를 감소시켜서 결국에는 침하를 방지하기 위한 것이다. 이것을 지오폼(geofoam)이라고 하는데, 지오폼은 교대나 옹벽의 뒷채움재로 사용할 경우 횡토압을 감소시키기 때문에 옹벽이나 교대의 뒷채움재료로 사용하기도 한다. 이와 같이 그 사용이 꾸준히 증가하고 있지만 뒷채움이나 연악지반상에 사용할 때 지오폼의 거동을 예측하는 적절한 수치모델이 아직은 개발되자 않았다. 본 연구에서는 지오폼의 응력-변형 특성을 연구하고 그 탄소성 예측모델을 제시하였다. 이를 위하여 삼축압축시험을 실시하였으며 구속응력과 지오폼의 밀도를 다양하게 변화시켜 그 응력-변형특성을 조사하고 회귀분석을 통하여 비선형 구성모델을 제시하였다. 그 결과 지오폼은 탄성 선형모델보다 탄소성모델 특성에 더 가까운 것을 알 수 있었으며 체적변화율과 축방향 변형률에는 특별한 상관 관계가 있음을 알 수 있었다.

• Journal of the Korean Geotechnical Society
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• v.17 no.5
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• pp.173-180
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• 2001

이방압밀이 실트질모래의 정적재하에 의한 유동파괴거동에 미치는 영향을 연구하기 위하여 비배수삼축압축시험을 수행하였다. 이를 위하여 상대밀도가 약 17%인 공시체를 습윤다짐방법에 의해서 성형하고 4가지의 압밀응력비, 1.0, 0.7, 0.55, $K_{o}$ 로서 압밀시켰다. 시험결과로서 정상상태선은 p-q 공간상에서 압밀응력비에 관계없이 유일한 직선이며 collapse line의 기울기는 압밀응력비가 증가함에 따라 선형적으로 감소한다는 사실을 보여준다. 또한, 유동파괴거동을 보이는 느슨하게 다져진 실트질모래의 잔류강도($S_{us}$ )와 첨두강도($S^{p}$ )와의 관계는 압밀응력비의 크기에 관계없이 $S_{p}$ /$p_{c}$ = $A_{L}$ +$B_{L}$ ($S_{us}$ /$p_{c}$ )로 표현되는 일반식으로 나타낼 수 있으며 계수 $A_{L}$ 및 $B_{L}$은 압밀응력비의 크기에 따라 선형적으로 변하는 경향을 나타낸다.

• Journal of the Korean GEO-environmental Society
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• v.13 no.11
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• pp.93-101
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• 2012

SCP is a construction method that maximizes the effects of ground improvement by creating sand piles, which are formed by the compaction within soft ground. SCP is mainly used for consolidation and drain effects in clayey soils, and as a liquefaction countermeasure through effects such as compaction in loose sandy soils. In the design of SCP, if the sand piles with high stiffness are not taken into account, it can become a design that overly considered safety, and increased construction costs are highly likely to cause economic disadvantages. The changes in stress conditions and compaction mechanisms in the subsurface have been identified to a certain extent by study findings to date. However, the studies that considered SCP and in-situ ground as composite ground are fairly limited, and therefore, those studies have not achieved enough results to fully explain the relevant topics. In this study, the ground improved by SCP was regarded as the composite ground that consists of SCP and in-situ ground. Moreover, employing a CID test, this study examined the changes in the stress conditions of in-situ ground according to the installation of SCP through the relations between $K_0$ and SCP replacement ratio. At the same, whether the SCP installation procedure can be recreated in a laboratory was examined using a cyclic triaxial test. According to the test results, the changes in the stress conditions of the original ground occurred most largely in an initial stage of SCP installation, and after a certain time point, the vibration for SCP installation did not have a great influence on the changes in the stress conditions of the ground. Moreover, in order to recreate the behaviors of in-suit ground according to SCP in a laboratory, cyclic loading, which corresponds to casing vibration, was concluded to be essentially required.

• Korean Journal of Agricultural Science
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• v.10 no.2
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• pp.277-291
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• 1983

In order to investigate the shear characteristics of earth structure after construction. Four sample soils with different gradation were selected and compacted under the optimum moisture content and the maximum dry density. And the direct shear test and the triaxial compression test were performed with those sample soils under various pre-compression loads. The results were summarized as follows; 1. With the increase of the percent passing of No. 200 sieve, the cohesion of soil increased regularly and the internal friction angle of soil decreased with slow ratio. 2. The pre-compression increased the shear strength of compacted cohesive soil. The increase of cohesion was very apparent but the internal friction angle didn't show such regular tendency. 3. With the increase of pre-compression load, the slope of stress-strain curve showed steep at the early stage of horizontal strain. The vertical strain was small at the compression stage and big at the expansion stage. 4. When the vertical stress of shear test with increase in the horizontal strain was small, stress ratio(shear stress vs. vertical stress) of sample showed the largest value and the slope of stress ratio curve showed also steep. 5. When the sample was had the same condition, the cohesion of soil showed bigger value in the triaxial compression test and the internal friction angle of soil showed bigger value in the direct shear test.

• Journal of the Korean Society for Railway
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• v.20 no.1
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• pp.85-98
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• 2017

In general, under the repetitive dynamic load generated by rail cars running on the track, subgrade soil experiences changes of stress conditions such as deviatoric stress (${\sigma}_d$) and bulk stress (${\theta}$). Due to the repetitive change of deviatoric stress (${\sigma}_d$) with number of loadings, the resilient modulus ($M_R$) can be obtained by using the measured resilient strain (${\varepsilon}_r$) after a sufficient number of loadings. At present, no plausible and unified test method has been proposed to obtain the resilient modulus of railway track subgrade soil. In this study, a possible test method for obtaining the resilient modulus ($M_R$) of railway track subgrade soil is proposed; this test, by utilizing repetitive triaxial compression testing, can consider all the important parameters, such as the confining stress, deviatoric stress, and number of loadings. By adapting and using the proposed test method to obtain $M_R$, $M_R$ values for compacted track subgrade soil can be successfully determined using soil obtained in three field sites of railway track construction with changing water content range from OMC. In addition, shear modulus (G) ~ shear strain (${\gamma}$) relation data were also obtained using a mid-size RC test. A correlation analysis was performed using the obtained G and $M_R$ values while considering the strain levels and modes of strain direction.

• Geotechnical Engineering
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• v.5 no.2
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• pp.45-56
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• 1989

The influence of stress path on the deformation characteristics of clay has been studied through a series of stress-path controlled triaxial tests on artificially sedimented and normally con- solidated Kaolinite. It has been found that there exists a critical stress increment ratio, Kc, in which stress·strain characteristics possesses a linear relationships and beyond Kc, strain hardening. A modified hyperbolic constitutive model for the strain hardening behavior has been formulated based on the Drnevich's hyperbolic function. And, a method of settlement analyses has been Proposed wherein the effect of stress path during consolidation is taken into account.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.1
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• pp.153-166
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• 1991

In an attempt to investigate the effect of intermedate principal stresses which are related to the stress-strain behavior of standard sands, a series of three-Principal stress control tests were conducted for individual stress paths. The results have shown that shear strengths of sands vary with the stress paths. The variations in internal friction angle are accorded with the Habibs stress parameter, b which represents Stress paths, showing on abropt increase at the values between 0.0 and 0.268, a moderate level between 0.268 and 0.682, and a slight decrease between 0.682 and 1.0 However, the friction angles under a triaxial extention state, were found relatively larger than under a triaxial compression state. In general, such veriations were found to have the same tendency without any relevant relation with the density of specimens and confining pressures. Therefore, it is concluded, that the shear strength of sands are positively influeced by the intermediate principal stresses present in the media. And the influnce of intermediate principal stresses on shear strengths of sands found from the present study are well compared with the previous studies by Lade-Duncan and Matsuoka-Nakai revealing a similar tendency within the failure criteria proposed by them.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.4C
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• pp.169-175
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• 2012

Soil water retention characteristics are influenced by factors of the confining stress and hysteresis in the variably saturated soil. In the description of effective stress based on hydraulic characteristics, the contribution of a matric suction to effective stress then varies with depth or is different between the processes of infiltration and evaporation. Unsaturated effective stress can be described based on suction stress characteristic curve, in which a representative soil water retention curve is required to evaluate. Pressure palate extractor tests under various confining stresses were performed and the hysteresis of drying and wetting process was also acquired. In the process of drying or wetting, a unique relationship has been estimated on the effective volumetric water content and the matric suction, which defines suction stress characteristic curve. In the unsaturated shear strength from triaxial tests, the suction stress and the effective stress were evaluated by matric suctions. The failure envelop by effective stress based on soil water retention characteristics was unique and the same as the saturated one. The measured suction stress from triaxial tests was similar to that from the soil water retention curve. Therefore it is verified that a representative soil water retention curve can be defined which is independent of the confining effect under wetting or drying process of the hysteresis.