• Geomechanics and Engineering
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• 제3권1호
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• pp.29-43
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• 2011

In this paper a semi-analytical approach is proposed to study the lateral behavior of a piled footing under horizontal loading. As accurate computation of stresses is usually needed at the interface separating the footing (pile) and the soil, this important location should be appropriately modeled as zero-thickness joint element. The piled footing is embedded in elastic soil with either homogeneous modulus or modulus proportional to depth (Gibson's soil). As the pile is the principal element in the piled footing system, a limited parametric study is carried out in order to investigate the influence of footing dimensions and the interface conditions on the lateral behavior of the pile. Hence, the pile behavior is examined through its main governing parameters, namely, the lateral displacement profiles, the bending moments, the shear forces and the soil reactions. The numerical results are presented for Poisson's ratio of 0.2 to represent a large variety of sands and Poisson's ratio of 0.5 to represent undrained clays.

• 한국지반환경공학회 논문집
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• 제2권4호
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• pp.51-61
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• 2001

본 논문에서는 지반의 상대다짐도(RC)와 매입말뚝의 근입비에 따른 하중-침하 거동을 연구하기 위하여 모형실험과 하중전이 함수를 이용한 해석을 수행하였다. 모형시험에서 말뚝은 근입비(L/D)를 15, 20, 25로 설치하였고, 지반의 상대다짐도를 85%, 95%로 각각 조성하였으며 말뚝주면은 시멘트를 주입하였다. 본 논문은 매입말뚝의 해석을 위하여 Vijayvergia의 하중전이 모델, Castelli 모델, Gwizdala의 탄소성-완전소성 모델, coyle의 제안식 등을 사용하여 실험결과와 비교하였으며, 매입말뚝의 하중-침하 거동을 예측하는데 가장 적합한 하중전이 방법을 제안하였다. 하중전이 함수에 의한 지지력 예측 결과 매입말뚝의 극한 지지력은 Coyle의 제안식이 실측값에 가장 근접한 것으로 나타났으며, 초기 하중-침하 거동은 Castelli에 의한 함수가 가장 유사하게 하중-침하 거동을 평가하는 것으로 나타났다. 매입말뚝의 축하중 해석결과 하중전이법에 의해 평가된 주면마찰력이 실측값보다 과소평가 되는 것으로 나타났다.

• 한국지반공학회논문집
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• 제39권11호
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• pp.33-40
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• 2023

본 연구에서는 산화마그네슘계 내화물(Magnesium oxide-based refractory)을 함유한 팽창성 지반에서의 말뚝기초 거동을 분석하였다. 고정단 말뚝이 설치된 모형토조에 용융마그네시아(Fused magnesia, FM)를 활용하여 지반의 융기를 유도하였으며, FM함유량(FM_c = 30%, 50%, 70%)을 변화하여 시간에 따른 깊이별 융기량과 말뚝의 축력을 분석하였다. FM_c가 증가할수록 더 큰 융기량이 측정되었으며, 시료의 표면으로 갈수록 융기량이 누적되어 깊이에 따라 융기량이 감소하였다. 그러나 깊이별 융기율의 차이와 그에 따른 팽창압의 차이로 인하여 FM_c = 30%와 50%일때 말뚝에 뚜렷한 압축력과 인장력이 발현되었으며, FM_c = 70%일 때에는 말뚝 전체에 인장력만이 발현되었다. 이런한 결과는 산화마그네슘계 내화물이 포함된 혼합토 내의 말뚝거동을 분석하는데 중요한 자료로 활용할 수 있을 것으로 판단된다.

• 한국지반공학회지:지반
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• 제14권6호
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• pp.153-166
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• 1998

본 논문은 균질 및 비균질 낙동강 사질토 지반에서 수평 및 경사하중을 받은 강관 말뚝의 수평거동에 대한 모형실험 결과들을 고찰하였다. 비균질 지반은 상부와 하부층의 2개층으로 이루졌다. 본 연구의 목적은 말뚝의 수평거동에 대한 경사하중$(Q_\beta)$, 말뚝 근입길이에 대한 하부지반의 높이비 (H/S), 그리고 상.하부지반의 지반반력계수비$(E_{h1}E_{h2})$의 영향에 관하여 실험적인 연구를 수행하고 이러한 영향들을 정량화 할 수 있는 실험결과를 얻었다. 모형실험 결과들에 의하면, 비균질 지반에서 수평거동은 다른 인자들보다 $E_{h1}E_{h2}$에 더 의존하는 것으로 나타났다. 균질지반에 대한 비균질 지반의 수평변위비$(y_{H/L}/y_{H/L=0}$)와 말뚝 근입길이에 대한 하부지반의 높이비(H/L)의 관계는 지수 함수식으로 회귀분석 되었다. 경사하중을 받는 경우의 휨 모멘트-깊이 관계는 수평하중을 받는 말뚝의 경우와 상이하게 나타났으며, 상대밀도 90%에서는 최대 휨모멘트 발생깊이는 수평하중을 받는 경우보다 약 70% 깊어졌다.

• Advances in concrete construction
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• 제10권1호
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• pp.49-59
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• 2020

Precast concrete elements in accelerated bridge construction (ABC) extends from superstructure to substructure, precast pile foundation has proven a benefit for regions with fragile ecological environment and adverse geological condition. There is still a lack of knowledge of the seismic behavior and performance of the precast pile foundation. In this study, a 1/8 scaled model of precast pile foundation with elevated cap is fabricated for quasi-static test. The failure mechanism and responses of the precast pile-soil interaction system are analyzed. It is shown that damage occurs primarily in precast pile-soil interaction system and the bridge pier keeps elastic state because of its relatively large cross-section designed for railways. The vulnerable part of the precast pile with elevated cap is located at the embedded section, but no plastic hinge forms along the pile depth under cyclic loading. Hysteretic curves show no significant strength degradation but obvious stiffness degradation throughout the loading process. The energy dissipation capacity of the precast pile-soil interaction system is discussed by using index of the equivalent viscous damping ratio. It can be found that the energy dissipation capacity decreases with the increase of loading displacement due to the unyielding pile reinforcements and potential pile uplift. It is expected to promote the use of precast pile foundation in accelerated bridge construction (ABC) of railways designed in seismic regions.

• Geomechanics and Engineering
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• 제31권5호
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• pp.477-488
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• 2022

Pile composite foundation (PCF) has been commonly applied in practice. Existing research has focused primarily on semi-infinite media having equal pile lengths with little attention given to the effects of inclined bedrock and dissimilar pile lengths. This investigation considers the effects of inclined bedrock on vertical loaded PCF with dissimilar pile lengths. The pile-soil system is decomposed into fictitious piles and extended soil. The Fredholm integral equation about the axial force along fictitious piles is then established based on the compatibility of axial strain between fictitious piles and extended soil. Then, an iterative procedure is induced to calculate the PCF characteristics with a rigid cap. The results agree well with two field load tests of a single pile and numerical simulation case. The settlement and load transfer behaviors of dissimilar 3-pile PCFs and the effects of inclined bedrock are analyzed, which shows that the embedded depth of the inclined bedrock significantly affects the pile-soil load sharing ratios, non-dimensional vertical stiffness N₀/wdE_s, and differential settlement for different length-diameter ratios of the pile l/d and pile-soil stiffness ratio k conditions. The differential settlement and pile-soil load sharing ratios are also influenced by the inclined angle of the bedrock for different k and l/d. The developed model helps better understand the PCF characteristics over inclined bedrock under vertical loading.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.1125-1131
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• 2008

In this study, Calibration Chamber Tests for cast-in-place piles in sand were performed for measuring behavior properties of piles. These tests were examined effects of various parameters of soil conditions including the relative density($D_R$), the coefficient of earth pressure, and investigated differences between cylindrical pile and taper-shaped pile with the same volumes. The important effect factors of foundation behavior were investigated by considering embedded depth of piles and shapes of piles, and inspected details of lateral behavior of piles. These results were verified reliabilities of each methods for comparing the results estimated with tests and the results by proposed estimating solutions in the past.

• Geomechanics and Engineering
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• 제24권2호
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• pp.143-156
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• 2021

Rail transit lines usually pass through many complicated topographies in mountain areas. The influence of inclined bedrock on the train-induced soil vibration response was investigated. Model tests were conducted to comparatively analyze the vibration attenuation under inclined bedrock and horizontal bedrock conditions. A three-dimension numerical model was built to make parameter analysis. The results show that under the horizontal bedrock condition, the peak velocity in different directions was almost the same, while it obviously changed under the inclined bedrock condition. Further, the peak velocity under inclined bedrock condition had a larger value. The peak velocity first increased and then decreased with depth, and the trend of the curve of vibration attenuation with depth presented as a quadratic parabola. The terrain conditions had a significant influence on the vibration responses, and the inclined soil surface mainly affected the shallow soil. The influence of the dip angle of bedrock on the peak velocity and vibration attenuation was related to the directions of the ground surface. As the soil thickness increased, the peak velocity decreased, and as it reached 173% of the embedded pile length, the influence of the inclined bedrock could be neglected.

• 산업기술연구
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• 제26권B호
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• pp.93-99
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• 2006

Centrifuge model experiments were performed to investigate the confining effects of the sheet piles, installed to the sides of soft clay ground treated with sand compaction piles, on the bearing capacity and concentration ratio of composite ground. For the given g-level in the centrifuge model tests, replacement ratio of SCP and the width of surcharge loads on the surface of ground with SCP, the confining effects of installing the sheet piles on the edges of SCP ground on the bearing capacity, change of stress concentration ratio and failure mechanism were investigated. Kaolin, one of typical clay mineral, and Jumunjin standard sand were used as a soft clay ground and sand compaction pile irrespectively. As results of experiments, lateral confining effect by inserting the model sheet piles fixed to the loading plate was observed. For the strip surcharge loading condition, the yielding stress intensity in the form of the strip surcharge loads tends to increase with increasing the embedded depth of sheet piles. The stress concentration ratio was found not to be influenced consistently with the embedded depth of sheet piles whereas the effect of stress intensity on stress concentration ratio shows the general trend that values of stress concentration ratio are relatively high at the initial stage of loading and tend to decrease and converge to the certain values. For the failure mechanism in the case of reinforced with sheet piles, displacement behavior related to the punching failure, settlement right beneath the loading plate occurred since the soil was confined with sheet piles, was observed.

• 한국지반신소재학회논문집
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• 제20권4호
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• pp.95-103
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• 2021

기존의 말뚝기초는 상부구조물을 지지하거나, 토압을 감소시키는 역할이었다면, 최근에는 상부구조물과 일체화되어 수평저항력을 높이는 사례들이 있다. 따라서, 본 연구는 여러 개의 말뚝으로 보강된 블록 형식의 방파제에 대해 실내모형실험을 수행하였고, 수평저항력을 평가하였다. 실험에서는 말뚝이 근입된 깊이를 변화시켜 말뚝의 수평저항력과 말뚝의 위치별 휨모멘트를 측정하였다. 그 결과 무리말뚝의 근입깊이가 깊어짐에 따라 수평저항력이 커짐을 알 수 있었다. 특히 사석층까지 무리말뚝이 관입된 경우가 블록내에 관입된 경우보다 수평저항력이 1.52배 크게 나타났다. 휨모멘트의 경우 후열말뚝이 전열말뚝보다 크게, 바깥쪽 말뚝이 안쪽 말뚝보다 크게 나타났다. 지반내에서 최대 휨모멘트의 발생 위치는 사석층과 원지반의 경계면에서 나타났다.