• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.1132-1143
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• 2008

A single Column/Shaft which extended the pile to the column of the bridge with same diameter has better safety and economical profit, but it usually has larger lateral displacement due to lateral loads such as wind, earthquake, wave, etc. A series of horizontal pile load testing were performed to study the lateral behavior of single column/shaft with varying different free lengths and embedded pile lengths. Eight instrumented test piles were cast-in-placed by bonding strain gauges at certain locations on both faces of the pile to measure bending moment, from two-way loadings. Linear variable differential transformers(LVDTs) were installed to measure the lateral pile displacement. Based on this, it is found that the test single column/shaft with different free lengths shows different failure modes. If the test pile has a longer free length, the failure occurs at the near the ground surface, but the shorter one's failure occurs at the below the ground surface.

• 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.

• Geomechanics and Engineering
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• 제5권6호
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• pp.519-540
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• 2013

This paper presents an optimal design method for determining pile lengths of piled raft foundations. The foundation settlement is evaluated by taking into account the raft-pile-soil interaction. The analysis of settlement is simplified by using Steinbrenner's equation. Then the total pile length is minimized under the settlement constraint. An extended sequential linear programming technique combined with an adaptive step-length algorithm of pile lengths is used to solve the optimal design problem. The accuracy of the simplified settlement analysis method and the validity of the obtained optimal solution are investigated through the comparison with the actual measurement result in existing piled raft foundations.

• Geomechanics and Engineering
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• 제5권3호
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• pp.223-240
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• 2013

In the present study an attempt was made to predict the complex nonlinear parameters of the soil-pile system subjected to the vertical vibration of rotating machines. A three dimensional (3D) finite element (FE) model was developed to predict the nonlinear dynamic response of full-scale pile foundation in a layered soil medium using ABAQUS/CAE. The frequency amplitude responses for different eccentric moments obtained from the FE analysis were compared with the vertical vibration test results of the full-scale single pile. It was found that the predicted resonant frequency and amplitude of pile obtained from 3D FE analysis were within a reasonable range of the vertical vibration test results. The variation of the soil-pile separation lengths were determined using FE analysis for different eccentric moments. The Novak's continuum approach was also used to predict the nonlinear behaviour of soil-pile system. The continuum approach was found to be useful for the prediction of the nonlinear frequency-amplitude response of full-scale pile after introducing the proper boundary zone parameters and soil-pile separation lengths.

• 한국지반공학회논문집
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• 제35권8호
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• pp.17-30
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• 2019

실제 시공된 말뚝들의 재하시험 자료 및 매입 PHC말뚝의 설계 자료로부터 전체지지력에 대한 주면마찰력의 분담율인 SRF를 분석하였다. 현장에서 시험 시공된 말뚝의 SRF는 말뚝의 종류, 상대근입길이, 지반의 종류, 재하시험의 종류에 상관없이 42~99%이었다. 매입 PHC말뚝에 대한 설계 자료에서 구한 SRF는 말뚝의 직경, 상대근입길이에 상관없이 풍화암에 소켓된 경우 20~53%의 범위에 분포하였다. 사용말뚝으로 실제 시공된 매입 PHC말뚝에서 재항타 동재하시험 자료로부터 구한 SRF는 말뚝의 직경, 상대근입길이, 지반의 종류에 상관없이 4~83%의 범위에 분산되어 분포하였다. 사용말뚝에서 SRF가 낮은 수준으로 나타나는 이유는 매입 PHC말뚝의 주면고정액의 충전이 제대로 이루어지지 않은 채 시공된 현황으로 볼 수 있었으며 따라서 주면고정액의 시공관리에서 시급하게 개선해야 할 현황이었다. 풍화암에 소켓된 매입 PHC말뚝의 설계에서 사용하고 있는 극한지지력 산정공식으로 계산한 주면마찰력의 SRF는 실제 현장 시공 말뚝의 SRF보다 평균적으로 2.2배 정도로 낮은 수준으로 평가되었다. 이는 설계에서 사용하고 있는 산정공식에 의한 극한주면마찰력이 매우 낮은 수준으로 계산되기 때문이다. 따라서 SRF를 만족시킬 수 있는 새로운 주면마찰력 산정공식의 제안 필요성이 있는 것으로 판단된다.

• 한국산학기술학회논문지
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• 제22권6호
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• pp.267-274
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• 2021

말뚝의 허용횡방향지지력을 결정하는 방법으로는 지반반력법과 극한횡방향지지력에 근거한 방법이 많이 쓰이고 있는데 설계시 지반반력법에 근거한 방법만을 적용하는 경우가 있다. 본 연구에서는 지반조건과 말뚝머리 구속조건 그리고 말뚝길이에 따른 말뚝의 허용지지력을 이들 두 가지 방법을 적용하여 구하고 상호 비교함으로써 해석에서 고려한 조건들이 말뚝의 허용횡방향지지력 결정법에 미치는 영향을 알아보고자 하였다. 연구결과에 따르면 말뚝머리 구속조건 및 말뚝길이에 상관없이 연약 점성토 지반에 설치된 말뚝의 경우 지반반력법에 의한 허용횡방향지지력이 설계를 지배함을 알 수 있었고 점성토의 비배수강도가 커짐에 따라 극한횡방향지지력을 통한 허용횡방향지지력이 설계를 지배함을 알 수 있다. 사질토 지반에 설치된 말뚝의 경우 느슨한 사질토지반에 설치된 말뚝머리 자유인 짧은말뚝의 경우를 제외하고 모든 경우에 있어 극한횡방향지지력을 통한 허용횡방향지지력이 설계를 지배함을 알 수 있다. 횡방향말뚝의 설게시 허용 횡방향변위량에 근거한 설계만으로 충분하다는 견해도 있지만 본 연구결과에 따르면 극한횡방향지지력에 근거한 허용횡방향지지력의 계산 또한 필요함을 알 수 있었다. 수평지반반력계수는 허용횡방향변위량 이내에서는 말뚝폭에 큰 영향을 받지 않음을 알 수 있었으며 실제 많이 쓰이는 말뚝폭의 범위인 20~90cm 인 경우 말뚝폭의 영향을 무시해도 될 것으로 생각된다.

• Structural Engineering and Mechanics
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• 제59권2호
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• pp.209-226
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• 2016

Integral bridges are typically designed with flexible foundations that include one row of piles. The construction of integral bridges solves difficulties due to the maintenance of expansion joints and bearings during serviceability. It causes integral bridges to become more economic comparing with conventional bridges. Research has been focused not only to enhance the seismic performance of newly designed bridges, but also to develop retrofit strategies for existing ones. The local performance of the pile to abutment connection will have a major effect on the performance of the structure and the embedment length of pile inside the abutment has a key role to provide shear and flexural resistance of pile-abutment connections. In this paper, a simple method was developed to estimate the initial value of embedment length of the pile for retrofitting of specimens. Four specimens of pile-abutment connections were constructed with different embedment lengths of pile inside the abutment to evaluate their performances. The results of the experimentation in conjunction with numerical and analytical studies showed that retrofitting pile-abutment connections with CFRP wraps increased the strength of the connection up to 86%. Also, designed connections with the proposed method had sufficient resistance against lateral load.

• Geomechanics and Engineering
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• 제33권4호
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• pp.341-352
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• 2023

Long-short pile composite foundations bear both vertical and horizontal loads in many engineering applications. This study used indoor model tests to determine the horizontal bearing mechanism of a composite foundation with long and short piles under horizontal loads. A custom experimental device was developed to prevent excessive eccentricity of the vertical loading device caused by the horizontal displacement. ABAQUS software was used to analyze the influence of the load size and cushion thickness on the horizontal bearing mechanism. The results reveal that a large vertical load leads to soil densification and increases the horizontal bearing capacity of the composite foundation. The magnitude of the horizontal displacement of the pile and the horizontal load borne by the pile are related to the piles' positions. Due to different pile lengths, the long piles exhibit long pile effects and experience bending deformation, whereas the short piles rotate around a point (0.2 L from the pile bottom) as the horizontal load increases. Selecting a larger cushion thickness significantly improves the horizontal load sharing capacity of the soil and reduces the horizontal displacement of the pile top.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.944-955
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• 2009

In this thesis the model tests were performed to the pull-out characteristics of a suction pile subjected to a pull-out in sands. For this model tests, three different soil conditions ($D_r$=45, 65, 82%), three pile diameters (D=100, 150, 200mm) and three pile lengths (L=100, 150, 200mm), were changed. And the experimental results were also compared with those by the theoretical methods. The results by the experimental and theoretical analysis are as follows. The ultimate pull-out resistances increased as the relative density of sands, pile diameter, length and the ratio of pile length to diameter increased. The ultimate pull-out resistance by Meyerhof method(1973) overestimated that by the model test, but the results using the soil-pile friction angle suggested by Aas(1966) in the Meyerhof(1973) method were in good agreement with the experimental results.

• Geomechanics and Engineering
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• 제32권4호
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• pp.453-462
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• 2023

Designing pile foundations subjected to the uplift forces such as buildings, oil platforms, and anchors is becoming increasingly concerned. In this paper, the conceptual design of a new type of driven piles called expanding pile is presented and assessed. Some grooves have been created in the shaft of the novel pile, and some moveable arms have been designed at the pile tip. At first, static analyses using the finite element method were performed to evaluate the effectiveness of the innovative pile on the axial bearing capacity. Then its effect on seismic behavior of moment frame is considered. Results show that the expanding arms were provided an ideal anchorage system because of the soil's noticeable locking-up effect increasing uplift bearing capacity. For example at the end of the static tensile loading procedure, displacement decrement up to 55 percent is observed. In addition, comparing the uplift bearing capacity of the usual and new pile with different lengths in sand and clay layers shows noticeable effect and sharp increase up to about two times especially in longer piles. Besides, a sensible reduction in the seismic response and the stresses in the beam-column connection between 23-36 percent are achieved that ensures better seismic behavior of the structures.