• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.1115-1122
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• 2011

Reinforced-Roadbed materials are usually composed of crushed stones. Repeated load application can induce deformation in the reinforced-roadbed layer so that it causes irregularity of track. Thus it is important to develop a prediction model of elastic modulus based on stress-strain relation under repeatitive load in order to investigate behavior of reinforced roadbed. The prediction model of elastic modulus of the material can be obtained from repeated triaxial test. However, a proper size of the sample for the test must be used. In this study, a large repeatitive triaxial test apparatus with the sample size of diameter of 30 cm and height of 60cm was adapted for performing test of the crushed stone reinforced-roadbed considering large particle size to get resilient modulus Mr. The obtained resilient modulus was compared to shear modulus obtained from mid size resonant column test. The sample size effect is somewhat large enough so that it is required to design a scale factor based on similarity law in order to use smaller samples for getting elastic modulus of the crushed stone reinforced-roadbed material. A scale factor could be obtained from this study.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2006년도 춘계 학술발표회 논문집
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• pp.1224-1227
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• 2006

It has been recognized unsaturated soil behaviour playing an important role in geomechanics. Up to now, only a few experimental data are available for the technical difficulties related to both volume changes and suction measurements. In this study, the volume changes of unsaturated compacted silty soil were monitored with proximeter (i.e. non-contactable transducer) during various triaxial compression tests, which gave a realistic estimation in the volume changes of unsaturated soil sample. The measurement of volume changes were performed with 0.5% of the maximum error under the axial strain ratio of less than 10%. The experimental results have revealed that the mechanical behaviour of unsaturated soil can be significantly affected by the matric suction. During the shearing processes, the level of maximum deviator stress under the initial suction pressure of 50kPa was higher than that under the initial suction pressure of 10kPa. On the other hand, the volume changes became smaller under the increase in the initial suction pressure.

• 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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• 제17권5호
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• pp.445-452
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• 2019

Gel-type biopolymers have recently been introduced as environmentally friendly soil binders and have shown substantial strengthening effects in laboratory experimental programs. Although the strengthening effects of biopolymer-treated sands have been verified in previous direct shear tests and uniaxial compression tests, there has been no attempt to examine shear behavior under different confining stress conditions. This study therefore aimed to investigate the strengthening effects of biopolymer-treated sand using laboratory triaxial testing with a focus on confining pressures. Three representative confining pressure conditions (${\sigma}_3=50kPa$, 100 kPa, and 200 kPa) were tested with varying biopolymer contents ($m_{bp}/m_s$) of 0.5%, 1.0%, and 2.0%, respectively. Based on previous studies, it was assumed that biopolymer-treated sand is susceptible to hydraulic conditions, and therefore, the experiments were conducted in both a hydrated xanthan gum condition and a dehydrated xanthan gum condition. The results indicated that the shear resistance was substantially enhanced and there was a demonstrable increase in cohesion as well as the friction angle when the biopolymer film matrix was comprehensively developed. Accordingly, it can be concluded that the feasibility of the biopolymer treatment will remain valid under the confining pressure conditions used in this study because the resisting force of the biopolymer-treated soil was higher than that in the untreated condition, regardless of the confining pressure.

• 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.

• 한국지반환경공학회 논문집
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• 제3권3호
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• pp.53-63
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• 2002

최근까지 우리나라의 암성토의 침하량을 산정하기 위해 가정된 탄성계수를 이용한 선형탄성해석 외에 다른 방법들이 시도되지 않고 있다. 특히 해상투기된 사석으로 구성된 방파제 구조물의 침하량을 정확히 산정하는 것은 거의 불가능하였다. 이 연구에서는 북제주의 채석장에서 채취한 3조의 다공질의 북제주의 화산암시료에 대해 대형삼축압축시험을 수행하였고 비선형모델을 이용하여 삼축압축시험을 수치해석으로 모사하였다. 실험과 해석에 의한 응력-변형률 거동이 비교되어 사석에 대한 하이퍼볼릭 구성모델의 적용성을 조사하였다. 비교 결과 두 응력-변형률 거동이 잘 일치하므로 하이퍼볼릭 모델은 느슨한 암성토체의 침하량을 산정하는데 적절한 것으로 판단되어진다.

• 한국지반공학회논문집
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• 제17권6호
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• pp.149-162
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• 2001

삼랑진에 위치한 삼랑진양수발전 상.하부댐의 댐마루에 시공 후 종방향 균열이 발생하였다. 이 댐들은 전력을 생산하기 위한 양수발전댐으로 상부댐과 하부댐으로 구성되어 있으며, 매일 10m이상의 수위변화를 받아왔다. 본 논문은 이들 댐중 상부댐에 발생한 종방향 균열의 원인을 찾는데 있다. 균열의 주요 원인은 수위변동으로 인한 것으로 판단되었으며, 이를 검토하기 위해 hyperbolic model을 이용한 수치해석을 수행하였다. 수치해석을 위한 입력자료를 얻기 위해 심벽재료와 사석재료에 대해 일련의 삼축압축시험을 수행하였다. 또한 수위변동으로 인한 주기적인 응력변화를 검토하기 위한 입력자료를 얻기 위해 진동삼축압축시험을 수행하였다. 수치해석결과 반복하중이 작용했을 경우 댐마루에서 깊이 4m까지 구속압력이 음이 되는 것으로 나타났으며, 이로 인해 종방향균열이 발생한 것으로 판단되었다. 이 종방향균열의 깊이는 댐 마루에서 수행한 시험굴에서 확인하였으며, 현장 조사결과와 잘 부합하였다.

• 터널과지하공간
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• 제22권1호
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• pp.12-21
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• 2012

암석의 파괴조건식으로 널리 이용되고 있는 Mohr-Coulomb식과 Hoek-Brown식은 중간주응력을 고려하지 못한다. 그러나 암석의 진삼축압축시험 결과에 의하면 암석의 강도는 중간주응력의 크기에 상당한 영향을 받는 것으로 알려지고 있다. 따라서 암반구조물의 정밀한 안정성 평가를 위해서는 중간주응력의 영향을 고려할 수 있는 파괴조건식이 필요하다. 이 연구에서는 Jiang & Pietruszczak(1988)이 제안한 팔면체면 단면 형상함수를 이용하여 Hoek-Brown 파괴조건식에 근사하는 새로운 3차원 비선형 암석파괴조건식을 제안하였다. 대응되는 선형파괴조건식의 강도예측 결과와 비교검토를 통해 제안한 파괴조건식의 강도예측 성능을 평가하였다. 제안한 파괴조건식을 문헌에 보고된 6개 암종의 진삼축압축시험 결과에 적합시킨 결과 매우 우수한 적합성을 얻었다. 특히, 구속압이 낮은 영역의 진삼축압축강도를 포함한 자료에 대해서는 선형 파괴조건식에 비해 뛰어난 적합성을 보였다.

• 한국해양공학회지
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• 제28권2호
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• pp.133-139
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• 2014

Offshore wind turbines have been constructed extensively throughout the world. These turbines are subjected to approximately $10^8$ horizontal load cycles produced from wind, waves, and current during their lifetimes. Therefore, the accumulated displacement of the foundation under horizontal cyclic loading has significant effects on the foundation design of a wind turbine. Akili(2006) and Achmus et al.(2009) performed cyclic triaxial tests on dry sands and proposed an empirical model for predicting the accumulated plastic strain of sands under long-term cyclic loading. In this study, cyclic triaxial tests were performed to analyze the cyclic loading behaviors of dry sands. A total of 27 test cases were performed by varying three parameters: the relative density of the sands, cyclic load level, and confining stress. The test results showed that the accumulated plastic strain increased with an increase in the cyclic load level and a decrease in the relative density of the sand. The confining stress had less effect on the plastic strain. In addition, the plastic strain at the 1st loading cycle was about 57% of the accumulated strain at 1,000 cycles. Finally, the input parameters of the empirical models of Akili(2006) and Achmus et al.(2009) were evaluated by using the relative density of the sand and the cyclic load level.

• 한국지반신소재학회논문집
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• 제14권1호
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• pp.11-21
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• 2015

본 연구는 대상형 하중이 작용하는 기초지반의 고유이방성에 대한 거동특성을 파악하기 위하여 시화지구 해성점토를 이용하여 일반삼축압축시험과 수평방향의 변형만을 허용하고 중간주응력(${\sigma}_2$) 방향의 변형률(${\varepsilon}_2$)을 0으로 하는 평면변형률 압축 및 신장시험을 실시하였다. 또한 일련의 시험결과에 의해 해석에 필요한 토질매개변수를 결정하였다. 그리고 대상하중이 작용하는 기초지반에 대하여 탄 소성 구성모델 중 자연퇴적점토의 거동특성을 가장 적절하게 설명할 수 있는 Cam-clay 모델을 적용하여 일반삼축압축시험 및 평면변형률시험 조건일 경우에 대하여 수치해석을 실시하였다. 해석결과 연직변위는 평면변형률 압축시험이 일반삼축압축시험에 비하여 18~25% 정도 변위가 크게 발생하였으며, 수평변위도 13~19% 정도 변위가 크게 발생하는 것으로 나타났다.