• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.520-529
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• 2006

그 동안 몇 차례 오스터버그 셀$(O-cell^{\circledR})$을 이용한 양방향 말뚝 재하시험기법이 국내에 성공적으로 소개/적용된 바 있다. 이 방법은 상대적으로 새롭고 독특한 방법으로서 시험비용과 기존 재래적인 시험방법이 적용상 제한을 받는 경우나 대규모 시험에서 발생할 수 있는 문제점들을 극복할 수 있다. 국내에서는 설계목적을 위한 시험말뚝 뿐 아니라 설계하중이 큰 실제말뚝에 대한 시험이 증가하는 추세에 있다. 이 논문에서 소개하는 양방향 재하시험 방법을 적용하면 기존의 소규모 재하시험 방법에서 발생될 수 있는 주면 마찰력과 선단지지력의 분리측정이나 각각의 지지력에 대한 극한상태를 확인하지 못하는 한계를 극복할 수 있고 시험하중이 270MN을 초과하는 경우까지 적용할 수 있는 장점을 갖고 있다. 본 논문에서는 오스터버그 셀을 이용한 정적 재하시험 방법에 대하여 말뚝종류별로 상세히 기술하였으며 이 시험방법의 장점과 국내현장에 적용되었던 사례를 소개하였다.

• Journal of the Korean Geotechnical Society
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• v.15 no.2
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• pp.165-180
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• 1999

Static load tests were performed for open-ended piles, closed-ended piles, piles with grouted toe, and base-grouted piles by using calibration chamber. Then vertical bearing capacities determined from load tests were compared with each other. The stability of base-grouted pile during a simulated seaquake was investigated by changing the penetration depth. Also, static load tests and seaquake tests for 2-piles and 4-piles group were performed. The bearing capacity of the pile grouted inside the toe was 11.2~30.8% less than that of open-ended pile because of reduction of base resistance due to disturbance of base soil under pile toe. The bearing capacity of a base-grouted pile was 23.8~33.9% more than that of an open-ended pile and was similar to that of a closed-ended pile. The bearing capacity of base-grouted group pile was increased ; the bearing capacity of base-grouted 2-piles group increased 14.6~31.8% compared to that of open-ended 2-piles group, and that of base-grouted 4-piles group increased 15.3~22.4% compared to that of open-ended 4-piles group. During the simulated seaquake in deep sea, stability of base-grouted pile was found to be dependent on the pile penetration depth. During seaquake motion, single long base-grouted pile longer than 20m was stable and short base-grouted pile shorter than 12m failed. But relatively long base-grouted pile longer than 12m kept mobility state. Bearing capacity of base-grouted group pile with penetration depth less than 7m was degraded a little bit ; so, base-grouted group pile could maintain mobility condition.

• Journal of the Korean Geotechnical Society
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• v.20 no.7
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• pp.107-117
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• 2004

A series of model tests were conducted to investigate how the number of reinforcement layers, stiffnesses, types of reinforcement material and buried depth of a flexible pipe can affect bearing capacity-settlement curve at a loose sand foundation. In the test results, whereas the type of failure in unreinforced sand was local shear, the type of failure, for model tests with more than 2 reinforcement layers in loose sand, was general shear: The number of the optimum reinforcement layers was found to be two: Stiffness and type of reinforcement were more important than the maximum tensile strength of reinforcement in improving bearing capacity. When the depth of buried pipe from the sand surface was less than the width of the footing, test results showed that both bearing capacity and ultimate bearing capacity of buried pipe in unreinforced sand significantly decreased, and the type of failure in the reinforced sand changed from general shear to local shear.

• Journal of the Korean GEO-environmental Society
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• v.2 no.2
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• pp.13-22
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• 2001

In this study, centrifuge model tests were fulfilled to investigate the characteristics of bearing capacity of paper ash as a filling material. The model tests were done varying the footing width and gravity level. The settlement and vertical soil pressure by loading were measured. The results from the tests were compared with the one from FLAC program using finite difference method and bearing capacity theory. After all, it was shown that the characteristics of load-settlement represented the local shear failure, which the settlement ratio s/B showed inflection point around 25~30%. As g-level and footing width were increasing, the load strength was increasing. The ultimate bearing capacity from the tests was very closed the results from Terzaghi's theory. As the distance from footing center was increasing, the vertical soil pressure was decreasing. If E/B is higher than 7, the stress by loading was almost increasing. The vertical displacement from loading was the largest one around under the footing and was almost occurred when the depth>4cm and E/B is higher than 5.0.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6C
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• pp.267-275
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• 2009

The steel pipe of steel-concrete composite piles increases the pile strength and induces the ductile failure by constraining the deformation of the inner concrete. In this research, the load-movement relations and the reinforcement effect by the outer steel pipe in the steel-concrete composite pile were analyzed by performing three-dimensional numerical analyses, which can simulate the yielding behavior of the pile material and the elasto-plastic behavior of soils. The parameters analyzed in the study include three pile materials of steel, concrete and composite, pile diameter and loading direction. As the results, the axial capacity of the composite pile was 1.9 times larger than that of the steel pipe pile and similar with that of the concrete pile. At the allowable movement criteria, the horizontal capacity of the composite pile was 1.46 times larger than that of the steel pile and 1.25 times larger than that of the concrete pile. In addition, the horizontal movement at the pile head of the composite pile was about 78% of that of the steel pile and about 53% of that of the concrete pile, which showed that the movement reduction effect of the composite pile was significant and enables the economical design of drilled shafts.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.2
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• pp.357-367
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• 2017

Bending and axial forces simultaneously occur at the cross-section of a shotcrete lining reinforced with steel supports due to the tunnel geometry. The shotcrete has changing flexural stiffness depending on the axial forces and, as a result, severely nonlinear behavior. The mechanical properties of a shotcrete-steel composite also depend on the type of steel support. This study presents a fiber section element model considering the effect of axial force to evaluate the nonlinear behavior of a shotcrete-steel composite. Additionally, the model was used to analyze the effects of different types of steel supports on the load capacity. Furthermore, a modified hyperbolic model for ground reaction, including strain-softening, is proposed to account for the ground-lining interaction. The model was validated by comparing the numerical results with results from previous load test performed on arched shotcrete specimens. The changes in mechanical responses of the lining were also investigated. Results show a lining with doubly reinforcement rebar has similar load capacity as a lining with H-shaped supports. The use of more materials for the steel support enhances the residual resistance. For all types of steel reinforcement, the contribution of steel supports during peak load decreases as the ground becomes stiffer.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 2001.11a
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• pp.46-52
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• 2001

본 연구에서는 롤러로 지지된 슬래브 구조물인 연결통로 구조물에 대한 구조해석을 수행하여, 고정하중(사하중)과 활하중 작용시 대상구조물에 발생되는 최대 변위 및 최대 단면력을 해석하였으며, 극한강도설계법에 의하여 극한강도 및 설계강도를 비교·검토함으로써 대상 연결통로 구조물의 안전성을 평가하였다. 구조해석시 대상구조물을 3차원 뼈대 요소 및 shell 요소로 형상화하여 모델링하였으며, 현재 가장 널리 사용되고 있는 범용 구조해석 프로그램인 SAP 2000 Nonlinear에 의해 구조해석을 수행하였다.(중략)

• Journal of the Korean GEO-environmental Society
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• v.2 no.4
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• pp.51-61
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• 2001

A series of model tests and analyses by load transfer function were performed to study load-settlement behaviour with relative compaction ratio of soil and embeded depth of pile. In the model tests, embeded depth ratio(L/D) of pile were installed 15, 20, 25 and relative compaction of soil(RC) is 85%, 95% and then cement were injected at around perimeter of pile. For analysis of embedded pile, the paper were compared results of model tests with analysis results by Vijayvergiya model and Castelli model, Gwizdala model of elastic plasticity-perfect plastic model and then the fitness load transfer mechanism was proposed to predict load-settlement behaviour of embeded pile. The analysis results of predicted bearing capacity by load transfer function, ultimate bearing capacity of embeded pile were approached to measured value and behaviour of initial load-settlement curve were estimated that load transfer function by Castelli were similar to measured value. The result of axial load analysis of bored pile shows that skin friction estimated by load transfer mechanism is investigated more a little than that of measured values.

• Geotechnical Engineering
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• v.8 no.3
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• pp.5-12
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• 1992

This paper performs a study on the influences of shape and installation method on the ultimate uplift capacity of model piles in sand. Several model piles of different shape, such as straight sided, single-underreamed, multi-underreamed and anchor plate are used. The effects of installation method are studied with buried, driven and vibrotriven piles. Based on model test results, it has been found that when the foundation is subjected to atrial up- lift and compressive load as well, a single-underreamed pile is most effective. When the loading is axial uplipt only, it is likely that anchor plate would be most efficient. Installation method and tip configuration of pile have significant influnce on uplift resistance.

• Journal of the Korean Geotechnical Society
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• v.23 no.12
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• pp.61-73
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• 2007

As a part of Load and Resistance Factor Design(LRFD) code development in Korea, in this paper an intensive reliability analysis was performed to evaluate reliability levels of the two static bearing capacity methods for driven steel pipe piles adopted in Korean Standards for Structure Foundations by the representative reliability methods of First Order Reliability Method(FORM) and Monte Carlo Simulation(MCS). The resistance bias factors for the two static design methods were evaluated by comparing the representative measured bearing capacities with the design values. In determination of the representative bearing capacities of driven steel pipe piles, the 58 data sets of static load tests and soil property tests were collected and analyzed. The static bearing capacity formula and the Meyerhof method using N values were applied to the calculation of the expected design bearing capacity of the piles. The two representative reliability methods(FORM, MCS) based computer programs were developed to facilitate the reliability analysis in this study. Mean Value First Order Second Moment(MVFOSM) approach that provides a simple closed-form solution and two advanced methods of FORM and MCS were used to conduct the intensive reliability analysis using the resistance bias factor statistics obtained, and the results were then compared. In addition, a parametric study was conducted to identify the sensibility and the influence of the random variables on the reliability analysis under consideration.