• 대한토목학회논문집
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• 제13권2호
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• pp.237-242
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• 1993

기초 지반이 몇개의 토층으로 구성된 경우 그 지지력은 각 토층의 강성도와 두께 및 위치 등에 의해 영향을 받는다. 따라서 기초 설계시에 기초의 지지력을 정확히 구하고 파괴면을 예측하기 위해서는 토층의 상태를 지지력 계산에 고려해야 한다. 본 연구에서는 기초 지반이 사질지반이고 중간에 상대적으로 조밀한 지층을 포함하는 경우에 조밀한 층의 두께나 위치가 기초의 지지력 및 파괴모양에 미치는 영향을 극한 해석의 상한한계(upper bound)쪽에서 완전해에 가까운 해를 구하는 K.E.M(Kinematical Element Method)을 이용하여 검토 하였으며, 기초 폭(B)의 3/5 B보다 깊지 않은곳에 조밀한 층이 위치하는 경우에는 기초의 지지력 과 파괴모양이 조밀한 층의 영향을 받는 것으로 나타났다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2006년도 춘계 학술발표회 논문집
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• pp.1032-1037
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• 2006

This thesis studied effects of the excavation around railroads on the deformation of the lateral ground and neighboring railroads. The conclusions of the study are as follows. 1. When the depth of excavationis 10m, the influential area should be 35m for soft clay, 20m for normal clay, 15m for hard clay, 15m for loose sand, 12m for slightly dense sand, and 8m for dense sand. 2. When the influential area is 10m, the allowable excavation depth should be 2.5m for soft clay, 4.8m for normal clay, 7.5m for hard clay, 7.2m for loose sand, 8.8m for slightly dense sand, and 10m for dense sand. 3. When the influential area is 20m, the allowable excavation depth should be 4.5m for soft clay, and up to 10m for the other five kinds of soil. 4. When the influential area is 30m, the allowable excavation depth should be 7.5m for soft clay, and up to 10m for the other five kinds of soil. 5. When the influential area is 35m, the allowable excavation depth should be up to 10m for all kinds of soil.

• The Korean Journal of Ceramics
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• 제6권1호
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• pp.1-5
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• 2000

Particle packing properties are important to develop high technology products in the field of cement and concrete. Two types of particle packing models for aggregates with sand and cement were introduced: the loose and the dense aggregate packing. Aggregate packing models with randomly generated sand and cement particles in the interstices of aggregates fit the Furnas model very well. Different aggregate models show different packing properties with the experimental results. Main reason for the difference with the experimental results is due to sand rearrangement in the loose aggregate packing model and to aggregate relaxation in the dense aggregate packing model. In the experimental situation, aggregates seem to be more disordered and have a relaxed packing structure in the dense packing, and sands seem to have a more rearranged packing structure in the loose packing model.

• Geomechanics and Engineering
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• 제15권1호
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• pp.695-710
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• 2018

Formation of a soil plug in an open-ended pile is a very important factor in determining the pile behavior both during driving and during static loading. The degree of soil plugging can be represented by the incremental filling ratio (IFR) which is defined as the change in the plug length to the change of the pile embedment length. The experimental tests carried out in this research contain 138 tests that are divided as follows: 36 tests for single pile, 36 tests for pile group ($2{\times}1$), 36 tests for pile group ($2{\times}2$) and 30 pile group ($2{\times}3$). All tubular piles were tested using the poorly graded sand from the city of Karbala in Iraq. The sand was prepared at three different densities using a raining technique. Different parameters are considered such as method of installation, relative density, removal of soil plug with respect to length of plug and pile length to diameter ratio. The soil plug is removed using a new device which is manufactured to remove the soil column inside open pipe piles group installed using driving and pressing device. The principle of soil plug removal depends on suction of sand inside the pile. It was concluded that the incremental filling ratio (IFR) is changed with the changing of soil state and method of installation. For driven pipe pile group, the average IFR for piles in loose is 18% and 19.5% for L/D=12 and 15, respectively, while the average of IFR for driven piles in dense sand is 30% and 20% for L/D=12 and L/D=15 respectively. For pressed method of pile installation, the average IFR for group is zero for loose and medium sand and about 5% for dense sand. The group capacity increases with the increase of IFR. For driven pile with length of 450 mm, the average IFR % is about 30.3% in dense sand, 14% in medium and 18.3% for loose sand while when the length of pile is 300 mm, the percentage equals to 20%, 17% and 19.5%, respectively.

• 한국지반공학회논문집
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• 제23권8호
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• pp.69-76
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• 2007

테이퍼말뚝의 연직거동은 지반의 응력상태와 내부마찰각, 말뚝의 벽면마찰각, 말뚝의 테이퍼 각도에 영향을 받는다. 본 논문에서는 테이퍼 각도가 말뚝의 연직거동에 미치는 영향을 조사하기 위해서 가압토조를 이용한 모형말뚝시험을 실시하였다. 시험결과에 따르면 말뚝의 테이퍼 각도가 커질수록 주면마찰력은 커지고 선단지지력은 감소하였으나, 단위 선단지지력의 경우 보통 상대밀도의 지반에서는 말뚝의 테이퍼 각도에 비례해서 증가하였으나 조밀한 지반에서는 테이퍼 각도에 따라 감소하였다. 그리고 말뚝의 전체지지력에 대한 주면마찰력의 비율은 테이퍼 각도가 커짐에 따라 그리고 지반의 상대밀도가 작아짐에 따라 증가하는 경향을 보였다. 또한 말뚝의 단위 체적당 전체지지력은 지반이 느슨할 때는 테이퍼 각도에 따라 증가했지만 조밀한 지반에서는 테이퍼 각도에 따라 감소하였다. 따라서 테이퍼말뚝은 조밀한 지반보다는 느슨한 지반에서 더 경제성이 있는 것으로 나타났다.

• Geomechanics and Engineering
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• 제31권1호
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• pp.53-69
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• 2022

In densely built areas, the development of underground transportation systems often involves twin excavations, which are sometimes unavoidably constructed adjacent to existing piled foundations. Because soil stiffness degrades with induced stress release and shear strain during excavation, it is vital to investigate the piled raft responses to subsequent excavation after the first tunnel in a twin-excavation system. The effects of deep excavations on existing piled foundations have been extensively investigated, but the influence of twin excavations on a piled raft is seldom reported in the literature. In this study, three-dimensional numerical analyses were carried out to investigate the influence of sand density on an existing piled raft (with a working load on top of the raft) due to twin excavations. A wide range of relative density (D_r) from loosest (30%), loose to medium (50% and 70%), and densest (90%) were selected to investigate the effects on settlement and load transfer mechanism of the piled raft during twin excavations. An advanced hypoplastic sand model (which can capture small-strain stiffness and stress-state dependent dilatancy of sand) was adopted. The model parameters are calibrated against centrifuge test results in sand reported in the literature. From the computed results, it is found that twin excavations in loose sand (D_r=30%) caused the most significant settlement. This is because of the higher stiffness of denser sand (D_r=90%) than that of loose sand. In contrast, a much larger tilting (maximum magnitude=0.18%) was computed in dense sand than in loose sand after the completion of the first excavation. As far as the load transfer mechanism along the piles is concerned, an upward load transfer to mobilize shaft resistance is observed in loose sand. On the contrary, a downward load transfer is observed in dense sand.

• Geomechanics and Engineering
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• 제10권4호
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• pp.455-470
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• 2016

In ballasted railway tracks, ballast fouling due to finer material intrusion has been identified as a challenging issue in track maintenance works. In this research, deformation characteristics of crushed stone-sand mixtures, simulating fresh and fouled ballasts were studied from laboratory and a 3-D discrete element method (DEM) triaxial compression tests. The DEM simulation was performed using a recently developed DEM approach, named, Yet Another Dynamic Engine (YADE). First, void ratio characteristics of crushed stone-sand mixtures were studied. Then, triaxial compression tests were conducted on specimens with 80 and 50% of relative densities simulating dense and loose states respectively. Initial DEM simulations were conducted using sphere particles. As stress-strain behaviour of crushed stone-sand mixtures evaluated by sphere particles were different from laboratory specimens, in next DEM simulations, the particles were modeled by a clump particle. The clump shape was selected using shape indexes of the actual particles evaluated by an image analysis. It was observed that the packing behaviour of laboratory crushed stone-sand mixtures were matched well with the DEM simulation with clump particles. The results also showed that the strength properties of crushed stone deteriorate when they are mixed by 30% or more of sand, specially under dense state. The results also showed that clump particles give closer stress-strain behaviour to laboratory specimens than sphere particles.

• 대한토목학회논문집
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• 제36권3호
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• pp.463-470
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• 2016

베인 전단시험은 흙의 교란을 최소화하면서 점성토의 비배수전단강도를 측정하는 간단한 시험이다. 하지만, 본 논문에서는 베인 전단시험기를 이용하여 모래의 배수전단강도를 측정하기 위한 연구를 수행하였다. 건조한 낙동강모래를 원통형 셀에 느슨하거나 조밀한 상태로 재성형한 다음 상부에서 공기압 실린더로 상재하중(overburden pressure)을 25, 50, 75 또는 100kPa 가한 다음 베인(직경 5cm, 높이 10cm)을 회전시켜 회전 모멘트인 최대 토크를 구하였다. 베인 회전 모멘트와 모래 입자의 마찰 저항 모멘트가 평형을 이룬다는 조건을 이용하여 모래의 마찰각을 구하였다. 점토의 경우에는 베인 전단 시 원통형의 회전체 상하면과 주면에 균일한 비배수전단강도인 점착력이 작용한다고 가정하지만, 사질토를 사용한 본 연구에서는 베인 날 주면에서 형성되는 파괴면을 원기둥, 팔각기둥 또는 사각기둥 형태로 가정하여 각각에 대한 마찰각을 계산하였다. 한편, 본 연구에서 제안한 방법을 검증하기 위해 동일한 모래로 직접전단시험을 실시하여 마찰각을 구하였다. 베인 전단시험으로부터 구한 마찰각은 가정한 파괴면의 형태에 따라 느슨한 모래의 경우 24-42도, 조밀한 모래는 33-53도 사이이며, 직접전단시험 결과는 이 범위 내에 속하였다.

• Geomechanics and Engineering
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• 제37권2호
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• pp.123-133
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• 2024

This study investigates the effects of loading frequency (f) and specimen size on the liquefaction resistance of clean sand. A series of cyclic direct simple shear tests were conducted on Jumunjin sand with varying consolidated relative densities (40% and 80%), f values (0.05, 0.10, and 0.20 Hz), and diameter to height (D/H) ratios (3.63, 3.18, 2.82, and 2.54). The results demonstrated the significant influence of f and D/H ratio on the number of cycles to liquefaction (N_cyc-liq) and the cyclic resistance ratio (CRR₁₅). It was observed that increasing f linearly increased N_cyc-liq. Increasing the specimen height also led to higher N_cyc-liq values irrespective of the f or relative density. Moreover, a positive correlation between CRR₁₅ and f indicated that higher f yielded higher CRR₁₅. This relationship was more pronounced in dense sand than in loose sand. Specimen height also significantly affected CRR₁₅, with increasing the specimen height resulting in higher CRR₁₅ values. Furthermore, the effect of f on CRR₁₅ was less significant compared to the influence of specimen height. The effect of f on the normalized cyclic resistance ratio (NCRR) was relatively negligible for loose sand but more substantial for dense sand depending on the D/H ratio. Data analysis revealed that the NCRR generally decreases as the D/H ratio increases. An interpolation formula was provided to calculate the NCRR based on the D/H ratio regardless of the f and relative density.

• 대한토목학회논문집
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• 제38권1호
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• pp.63-71
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• 2018

본 연구에서는 베인에 작용하는 수평응력과 토크를 측정한 다음 이를 이용하여 모래의 마찰각을 구하는 연구를 수행하였다. 건조한 낙동강모래를 원통형 셀에 느슨하거나 조밀한 상태로 성형한 다음 상부에서 공기압 실린더로 상재하중(overburden pressure)을 25, 50, 75 또는 100kPa 가하여 베인(직경 5cm, 높이 10cm) 회전 시 주변에 작용하는 수평응력과 토크를 실시간으로 측정하였다. 베인 회전에 따른 최대 토크값은 느슨한 모래는 3.5~9.5Nm, 조밀한 모래는 7.4-17.6Nm 사이로 상재하중이 증가할수록 최대 토크값도 증가하였다. 조밀한 정도에 관계없이 $14-20^{\circ}$ 회전 시 최대 토크값에 도달하였으며, 베인날과 토압계의 초기 위치에 따른 최대값의 차이는 나지 않았다. 상재하중에 따라 베인에 작용하는 초기 수평응력비($K_0$)는 평균 0.33-0.35 사이이며, 베인 회전에 따라 수평응력이 전반적으로 증가하다가 모래 입자가 교란되면서 다시 감소하는 경향을 보였다. 실시간으로 측정된 수평응력과 토크를 이용하여 계산된 마찰각은 상재하중이 증가함에 따라 감소하는 경향을 보였으며, 느슨한 모래는 직접전단시험 결과와 유사한 마찰각을 보였다. 하지만, 조밀한 모래의 마찰각은 다소 과대평가하는 경향을 보였다.