• Geomechanics and Engineering
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• v.5 no.1
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• pp.17-36
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• 2013

Settlement of the piled raft can be estimated even after years of completing the construction of any structure over the foundation. This study is devoted to carry out numerical analysis by the finite element method of the consolidation settlement of piled rafts over clayey soils and detecting the dissipation of excess pore water pressure and its effect on bearing capacity of piled raft foundations. The ABAQUS computer program is used as a finite element tool and the soil is represented by the modified Drucker-Prager/cap model. Five different configurations of pile groups are simulated in the finite element analysis. It was found that the settlement beneath the piled raft foundation resulted from the dissipation of excess pore water pressure considerably affects the final settlement of the foundation, and enough attention should be paid to settlement variation with time. The settlement behavior of unpiled raft shows bowl shaped settlement profile with maximum at the center. The degree of curvature of the raft under vertical load increases with the decrease of the raft thickness. For the same vertical load, the differential settlement of raft of ($10{\times}10m$) size decreases by more than 90% when the raft thickness increased from 0.75 m to 1.5 m. The average load carried by piles depends on the number of piles in the group. The groups of ($2{\times}1$, $3{\times}1$, $2{\times}2$, $3{\times}2$, and $3{\times}3$) piles were found to carry about 24%, 32%, 42%, 58%, and 79% of the total vertical load. The distribution of load between piles becomes more uniform with the increase of raft thickness.

• Journal of the Korean Geotechnical Society
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• v.16 no.3
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• pp.47-55
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• 2000

본 연구에서는, 유전자 알고리즘을 이용한 piled raft 기초의 최적설계 기법을 제시하였다. 최적설계에 사용한 목적함수는 구조물의 사용한계에 해당하는 부등침하량과 piled raft 기초의 시고비용 차원에서의 말뚝과 raft의 총 중량으로 하였다. 유전자 알고리즘은 다읜의 적자생존의 법칙을 따르는 자연진화 법칙을 바탕으로 한 최적화 기법이다. 본 연구에서는 piled raft 기초의 해석방법으로 Clancy(1993)가 제시한 "hybrid" 해석방법을 사용하였으며, 유전자 알고리즘기법은 Goldberg(1989)가 제시한 단순 유전자 알고리즘(SGA)을 적용하였다. 또한 유전자 알고리즘을 이용한 최적설계기법의 유효성을 평가하기 위해 설계예제 및 매개변수변화연구를 통해 piled raft 기초시스템의 중요 설계인자들에 대한 분석을 수행하였다. 매개변수변화연구로부터 말뚝의 길이와 raft의 두께가 증가할수록 piled raft 기초시스템의 전체 중량은 일정한 값에 점차적으로 수렴하였으며, 지반의 강정, raft의 두께 말뚝의 길이 및 강성이 증가할수록 말뚝의 최적위치는 raft의 중앙에 집중되는 경향으로 나타났다.경향으로 나타났다.

• Geomechanics and Engineering
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• v.35 no.6
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• pp.617-626
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• 2023

In this study, three-dimensional numerical parametric study was conducted to explore deformation mechanisms of grouped piled-raft-foundation due to lateral load in clays. Effects of load intensity, loading angle, soil stiffness, pile diameter, pile spacing and pile length on foundation deformations were explored. It is found that the smallest and largest movements of pile foundation are induced when the loading angles are 0° and 30°~60°, respectively. By increasing loading angle from 0° to 30°~60°, the resultant horizontal movements and settlements increase by up to 20.0% and 57.1%, respectively. Since connection beams can substantially increase integrity of four piled raft foundation, resultant horizontal movements, settlements and bending moments induced in the piled raft foundation decrease by up to 54.0%, 8.8% and 46.3%, respectively. By increasing soil stiffness five times, resultant horizontal movements and settlements of pile foundation decrease by up to 61.7% and 13.0%, respectively. It is indicated that effects of connection beam and soil stiffness on settlements of pile foundation are relatively small. When pile diameter is less than 1.4 m, deformations of piled raft foundation decrease substantially as a reduction in the pile diameter. Two dimensional groups are proposed to develop calculation charts of horizontal movements and settlements of pile foundation. The proposed calculation charts can directly estimate movements of piled raft foundation under arbitrary loading, ground and pile conditions.

• Journal of the Korean GEO-environmental Society
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• v.1 no.1
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• pp.51-56
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• 2000

Granular piled raft systems have been effectively used in soft ground foundation not only to reduce settlements but also to improve bearing capacity. In the present study, the finite element method of analysis on a basis of the plate theory is proposed to predict non-uniform settlements at the interface between the raft and foundation soils. To verify the validity of the proposed method of analysis and the predicted settlements of granular piled raft systems, comparisons are made with the results presented in the previous research(Kim et al., 1999). Finally, behavior characteristics with various patterns of the granular piled raft systems and effects of the settlement reduction are analyzed in connection with the design parameters.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.03a
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• pp.29-49
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• 2000

• Geomechanics and Engineering
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• v.5 no.6
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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.

• Journal of the Korean Geotechnical Society
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• v.24 no.10
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• pp.17-24
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• 2008

In this study, two-dimensional finite element method has been developed to simply consider the nonlinear load-settlement behavior of piled raft foundation subjected to vertical loads. The raft is modeled as the plate finite element based on Mindline's theory and the pile is modeled as the proposed simple pile model that is easy to consider the complex nonlinear load-settlement behavior between pile and soil. The developed numerical method has been compared with the settlement data of lab-scaled experiment and numerical solutions to verify that the developed numerical method shows satisfactory prediction for the nonlinear load-settlement of piled raft foundation.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.379-386
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• 2001

Piled raft foundations are usually used to reduce total and differential settlements of superstructures. In the piled raft foundations, the raft is often on its own able to provide adequate bearing capacity and only few widely spaced piles are added to the foundation to keep settlements be1ow a certain limit. In this paper, experimental studies on the load sharing ratio between piles and raft are carried out. Also, for evaluating the application of optimum design technique using a genetic algorithm, optimal locations of files are compared with the results of laboratory model tests. from tile results of laboratory model tests, there are found that the load sharing ratio between files and raft is depended on the number of piles and stiffness of raft, and the optimal locations of piles became concentrated on the middle of rafts. From these results of laboratory model tests, the optimum technique using a genetic algorithm is acknowledged to the application in the piled raft.

• Journal of the Korean Geotechnical Society
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• v.22 no.4
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• pp.95-104
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• 2006

For the interests in the economical and safe design of foundation system, the concern on the piled raft or disconnected piled raft foundation system is increasing now. In this study, the behavior and the effects of the disconnected piled raft foundation not studied actively in this country were examined using the triaxial compression tests in place of laboratory model tests. The triaxial test samples were prepared with Jumunjin standard sand and the carbon rods, which simulate the ground soil and piles respectively. After the sample in which carbon rods were arranged was laid inside the triaxial chamber, the confining pressure was applied and then loading test was conducted. To analyze the reinforcing effects of the disconnected piled raft foundation, a few number of tests were carried out by changing the number, the diameter and the length of the model piles. As a result of this study, in the disconnected piled raft foundation system, even though the number of pile is few and the diameter of pile is small, the settlement of the foundation system decreased greatly.

• Geomechanics and Engineering
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• v.16 no.2
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• pp.187-194
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• 2018

Application the pile group foundation to reduce overall settlement of the foundation and also avoid a very fruitful settlement of foundations, inconsistent was carried out. In such a case, in event that the Foundation, not as a mere pile group, which as a system consisting of a broad foundation with pile Group, economic design criteria will be provided in spite of high safety. A new approach in the design of the Foundation can be introduced as the piles are just a tool to improve the parameters of soil hardness; that it can work with detachable piles from raft. Centralized arrangement of piles as the most optimal layout of piles in reducing inconsistent settlement, which is the lowest value of resulting layout in this differential settlement. Using the combination of piles connected and disconnected to form the raft, bending moment created in the raft is reduced. It also concentrated arrangements have greatest effect in reducing amount of moment applied to the raft.