• 한국지반공학회지:지반
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• 제12권2호
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• pp.9-18
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• 1996

실험실에서 재 성형한 정규압밀점토에 대하여 실시된 일련의 삼축압축시험 거동결과를 등방단일경화구성모델에 의한 예측치와 비교검토한다. 이 모델사용에 필요한 열한개의 계수는 등방압밀공시체에 대한 비배수삼축압축시험 결과로부터 간단히 결정된다. 이렇게 결정된 계수를 활용한 이 모델로 이방압밀공시체를 대상으로 한 비배수삼축압축시험시의 응력-변형률 및 간극 수압의 거동이 예측된다. 또한 등방압밀공시체 및 이방압밀공시체를 대상으로 실시한 배수삼축 압축시의 응력-변형률 및 체적변형률 거동예측에도 이 모델을 적용하였다. 예측치와 시험치의 비교결과 비배수삼축압축시험의 경우는 등방압밀공시체와 이방압밀공시체 모두에 좋은 일치를 보이고 있다. 그러나 배수삼축압축시험의 경우는 초기 체적변형률의 예측치가 시험치보다 약간 작게 나타나다가 파괴점에 근접함에 따라서는 예측치가 시험치보다 커지는 경향을 보이고 있다. 그러나 전반적인 응력 -변형률거동은 좋은 일치를 보이고 있음을 알 수 있다. 따라서, 본 연구결과 이 모델은 정규압밀점토의 거동예측에 적용성이 충분히 있다고 생각된다.

• Geomechanics and Engineering
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• 제17권5호
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• pp.497-505
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• 2019

Biocementation based on the microbially induced calcite precipitation (MICP) process is a novel soil improvement method. Biocement can improve significantly the properties of soils by binding soil particles to increase the shear strength or filling in the pores to reduce the permeability of soil. In this paper, results of triaxial consolidated undrained (CU) tests and constant shear drained (CSD) tests on biocemented Ottawa sand are presented. In the CU tests, the biocemented sand had more dilative behaviour by showing a higher stress-strain curves and faster pore pressure reducing trends as compared with their untreated counterparts. In the CSD tests, the stress ratio q/p' at which biocemented sand became unstable was higher than that for untreated sands, implying that the biocementation will improve the stability of sand to water infiltration or liquefaction.

• Geomechanics and Engineering
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• 제33권1호
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• pp.41-51
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• 2023

Cementitious materials such as Ordinary Portland Cement (OPC), fly ash, lime, and bitumen have been employed for soil improvement over the years. However, due to the environmental concerns associated with the use of OPC, substituting OPC with calcium sulfoaluminate (CSA) cement offers good potential for ground improvement because it is more eco-friendly. Although earlier research has investigated the stabilizing effects of CSA cement-treated sand, no attempt has been made to examine soil behavior under high confining pressure. As a result, this study aimed to investigate the shear strength and mechanical behavior of CSA cement-treated sand using a consolidated drained (CD) triaxial test with high confining pressure. The microstructure of the examined sand samples was investigated using scanning electron microscopy. This study used sand with CSA cement contents of 3%, 5%, and 7% and confining pressures of 0.5, 1.0, and 1.5 MPa. It revealed that the confining pressures and CSA cement content significantly affected the stress-strain and volumetric change behavior of CSA cement-treated sand at high confining pressures.

• Geomechanics and Engineering
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• 제23권4호
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• pp.301-311
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• 2020

In this study, shear strength behavior of fine-grained soils was investigated under unsaturated conditions. The samples in the unsaturated state were subjected to a net normal stress (σ-u_a) of 40 kPa and different matric suctions (u_a-u_w) of 50, 100 and 150 kPa. The matric suction values applied in the triaxial tests were selected according to the bubbling pressures determined from the SWC curves. The study was carried out on prepared re-constituted cylindrical samples by uniaxial consolidation of soil slurries. First, consolidated drained (CD) triaxial compression tests were performed on the saturated samples and the cohesion and angle of internal friction were determined. After that, drained triaxial compression tests under matric suctions were performed on the unsaturated samples. In order to obtain unsaturated test results, cohesion and internal friction angle values of saturated samples were used. The nonlinear surface representing the shear strength surface was approximated consisting of two planes (double planar surface). The reason for the nonlinear behavior of some soils is that the amount of sand content contained in it is relatively high and the bubbling pressure/permanent water content value is relatively low.

• Geomechanics and Engineering
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• 제1권1호
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• pp.35-52
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• 2009

A significantly thick zone of steep slopes is commonly encountered above groundwater table and the soils within this zone are unsaturated with negative pore-water pressures (i.e., matric suction). Matric suction contributes significantly to the shear strength of soil and to the factor of safety of unsaturated slopes. However, infiltration during rainfall increases the pore-water pressure in soil resulting in a decrease in the matric suction and the shear strength of the soil. As a result, rainfall infiltration may eventually trigger a slope failure. Therefore, understanding of shear strength characteristics of saturated and unsaturated soils under shearing-infiltration (SI) conditions have direct implications in assessment of slope stability under rainfall conditions. This paper presents results from a series of consolidated drained (CD) and shearing-infiltration (SI) tests. Results show that the failure envelope obtained from the shearing-infiltration tests is independent of the infiltration rate. Failure envelopes obtained from CD and SI tests appear to be similar. For practical purposes the shear strength parameters from the CD tests can be used in stability analyses of slopes under rainfall conditions. The SI tests might be performed to obtain more conservative shear strength parameters and to study the pore-water pressure changes during infiltration.

• Geomechanics and Engineering
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• 제13권6호
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• pp.1027-1044
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• 2017

Membrane penetration is the most important factor influencing the measurement of volume change for triaxial consolidated-drained shear test for coarse-grained soil. The effective pressure p, average particle size $d_{50}$, thickness $t_m$ and elastic modulus $E_m$ of membrane, contact area between membrane and soil $A_m$ as well as the initial void ratio e are the major factors influencing membrane penetration. According to the membrane deformation model given by Kramer and Sivaneswaran, an analytical solution of the membrane penetration considering the initial void ratio is deduced using the energy conservation law. The basic equations from theory of plates and shells and the elastic mechanics are employed during the derivation. To verify the presented solution, isotropic consolidation tests of a coarse-grained soil are performed by using the method of embedding different diameter of iron rods in the triaxial samples, and volume changes due to membrane penetration are obtained. The predictions from presented solution and previous analytical solutions are compared with the test results. It is found that the prediction from presented analytical solution agrees well with the test results.

• Geomechanics and Engineering
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• 제7권3호
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• pp.279-295
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• 2014

A series of one-dimensional consolidation tests and triaxial creep tests were performed on Nansha clays, which are interactive marine and terrestrial deposits, to investigate their time-dependent behaviour. Based on experimental observations of oedometer tests, normally consolidated soils exhibit larger secondary compression than overconsolidated soils; the secondary consolidation coefficient ($C_{\alpha}$) generally gets the maximum value as load approaches the preconsolidation pressure. The postsurcharge secondary consolidation coefficient ($C_{\alpha}$') is significantly less than $C_{\alpha}$. The observed secondary compression behaviour is consistent with the $C_{\alpha}/C_c$ concept, regardless of surcharging. The $C_{\alpha}/C_c$ ratio is a constant that is applicable to the recompression and compression ranges. Compared with the stage-loading test, the single-loading oedometer test can evaluate the entire process of secondary compression; $C_{\alpha}$ varies significantly with time and is larger than the $C_{\alpha}$ obtained from the stage-loading test. Based on experimental observations of triaxial creep tests, the creep for the drained state differs from the creep for the undrained state. The behaviour can be predicted by a characteristic relationship among axial strain rate, deviator stress level and time.

• 대한토목학회논문집
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• 제7권3호
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• pp.183-193
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• 1987

점토입자(粘土粒子)가 등방적으로 퇴적된 후 $K_0$-압밀(壓密)이력을 받으면 응력유도이방성(應力誘導異方性)을 지니게 되므로 정규압밀점토(正規壓密粘土)의 현위치거동(現位置擧動)을 조사하려면 $K_0$-압밀(壓密)에 의한 영향을 검토할 필요가 있다. 실내에서 반죽성형하여 얻은 점토공시체(粘土供試體)에 대하여 등방압밀 및 $K_0$-압밀을 실시한 후 비배수삼축압축시험 및 배수삼축압축시험을 실시하여 $K_0$-압밀이력의 영향을 검토하였다. $K_0$-압밀이력은 축차응력거동(軸差應力擧動)에 영향을 크게 미치나 유효주응력비거동(有効主應力比擧動)에는 영향이 작다. 특히 비배수시험의 초기변형단계에서는 축차응력거동(軸差應力擧動)에 영향을 크게 미친다. 따라서, $K_0$-압밀시료의 비배수강도거동은 등방압밀비배수시험으로 추정될 수 없다. 그러나, 최대유효주응력비(最大有效主應力比擧動)파괴기준에 의한 파괴포락선은 압밀이력 및 배수조건에 관계없이 유일한 곡선(曲線)이다.

• Geomechanics and Engineering
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• 제35권2호
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• pp.135-147
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• 2023

Sand columns in clayey soil are considered one of the most economical and environmentally-friendly soil-improving techniques. It improves the shear strength parameters, reduces the settlement, and increases the bearing capacity of clayey soils. The aim of this paper is to study the effect of grain shape in sand columns on their performance in improving the mechanical properties of clayey soils. An intensive series of consolidated-drained triaxial tests were performed on clay specimens only and clay specimens with sand columns. The parameters examined during the experimental work were grain shape in sand columns (angular, rounded, sub-rounded) and effective confining pressure (50 kPa, 100 kPa, 200 kPa). The results indicated that there is a significant improvement in the deviatoric stress and stiffness values of specimens with sand columns. Improving deviatoric stress values in the use of angular sand grains was found to be higher than those in the use of sub-rounded and rounded sand grains. A 187%, 159%, and 153% increment in deviatoric stress values were observed for the sand columns with angular, sub-rounded, and rounded grain shapes, respectively. The specimens were observed to be more contractive as the sand column was installed, and as the angularity of grains in the sand column was increased. Sand column installation improves significantly the angle of internal friction, and the effective angle of internal friction increases as the angularity of the sand grains increases.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2002년도 가을 학술발표회 논문집
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• pp.253-258
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• 2002

In this study the confining pressure dependancy of internal friction angle of rock materials are discussed based on the results of a series of large triaxial tests under consolidated-drained condition. The rock materials tested are two kinds of grain-size distribution ;one is well graded, the other poorly graded(a uniform distribution). The obtained results shows that the internal friction angle of rock materials decreases more sharply in low stress level than in high stress level, and the test constants A and b in De Mello's failure criterion on rockfill materials are A =0.683∼l.584, b=0.712∼l.015 for the well graded and A=1.145∼l.523, b=0.788∼0.880 for the poorly graded.