• Title/Summary/Keyword: piled raft foundation

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Analysis of the piled raft for three load patterns: A parametric study

  • Chore, H.S.;Siddiqui, M.J.
    • Coupled systems mechanics
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    • v.2 no.3
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    • pp.289-302
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    • 2013
  • The piled raft is a geotechnical construction, consisting of the three elements-piles, raft and the soil, that is applied for the foundation of a tall buildings in an increasing number. The piled rafts nowadays are preferred as the foundation to reduce the overall and differential settlements; and also, provides an economical foundation option for circumstances where the performance of the raft alone does not satisfy the design requirements. The finite element analysis of the piled raft foundation is presented in this paper. The numerical procedure is programmed into finite element based software SAFE in order to conduct the parametric study wherein soil modulus and raft thickness is varied for constant pile diameter. The problems of piled raft for three different load patterns as considered in the available literature (Sawant et al. 2012) are analyzed here using SAFE. The results obtained for load pattern-I using SAFE are compared with those obtained by Sawant et al. (2012). The fair agreement is observed in the results which demonstrate the accuracy of the procedure employed in the present investigation. Further, substantial reduction in maximum deflections and moments are found in piled raft as compared to that in raft. The reduction in deflections is observed with increase in raft thickness and soil modulus. The decrease in maximum moments with increase in soil modulus is seen in raft whereas increase in maximum moments is seen in piled raft. The raft thickness and soil modulus affects the response of the type of the foundation considered in the present investigation.

A Case Study of the Piled Raft Foundation (Piled Raft 기초 적용사례 분석)

  • 김홍택;강인규;최효범;박시삼
    • Proceedings of the Korean Geotechical Society Conference
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    • 2002.03a
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    • pp.597-604
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    • 2002
  • The piled raft foundation Is an innovative design concept to reduce both the maximum settlement and differential settlements caused by concentrated building loads and load eccentricities, and also to reduce the bending moments of the raft. The main concern given in the design of piled raft foundations is proper judgments both of relative proportions of loads carried by the raft and piles, and of the effect of the pile support on the maximum and differential settlements In the present study, the piled raft foundation used in the foundation system of Richensia Building at Youido, Seoul is introduced and is carried out analyzing the results of field tests such as plate load tests, large plate load test, pile load test, and piled raft load test.

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Laboratory Test of Piled-Raft Foundation Improved by Gravel Mat (Gravel Mat로 보강된 말뚝지지 전면기초의 실내모형실험)

  • Seo, Young-Kyo;Lee, Jeong-Hoon
    • Journal of Ocean Engineering and Technology
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    • v.25 no.2
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    • pp.47-54
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    • 2011
  • A piled raft foundation is one of the systems used to reduce the settlement of structures. However, the general design method for a piled raft foundation system assumes that the piles only support external loads, which exclude the bearing capacity of the raft itself. In this study, an experimental model test was performed to evaluate the raft capacity for the external load on the sand. Additionally, a part of the sandy ground under the raft was replaced with a gravel mat to reinforce the piled raft foundation system and increase the bearing capacity. Then, parametric studies of the reinforced ground were performed to determine the displacement and load-sharing ratio of the piled raft foundation system.

A Parametric Study to Estimate the Behavior of a Piled Raft Foundation Influenced by Ground Conditions (지반조건이 Piled Raft 기초의 거동에 미치는 영향 평가를 위한 매개변수 연구)

  • You, Kwang-Ho;Jung, Yeun-Hak
    • Journal of the Korean Geotechnical Society
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    • v.32 no.8
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    • pp.35-46
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    • 2016
  • In this study, a sensitivity analysis was carried out by using numerical analysis under the consideration that it is difficult to analyze the behavior of real piled raft foundations on different ground conditions through a real scale test. The program used for numerical analysis is FLAC 3D based on the finite difference method. Piles were modelled by using pile element that is one of the structure elements of FLAC 3D and the ground and raft were modelled by using continuum element. With a fixed pile arrangement of $3{\times}3$, the diameter, length, space of piles, and ground conditions were selected as sensitivity parameters and their mutual correlation were investigated. As a result, the bigger and longer pile diameter, length and pile space are, the bigger the bearing capacity of the piled raft becomes. When pile space exceeded a specific value, however, the piled raft foundation behaved like a shallow foundation supported by only a raft. Also it can be confirmed that the better ground conditions are, the more total bearing capacity of the piled raft foundation increases.

Evaluation of Bearing Capacity of Piled Raft Foundation on OC Clay using Centrifuge and Numerical Modeling (원심모형 실험과 수치해석을 이용한 과압밀 지반에서의 piled raft 기초의 지지력 평가)

  • Park, Jin-Oh;Choo, Yun-Wook;Kim, Dong-Soo
    • Proceedings of the Korean Geotechical Society Conference
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    • 2009.03a
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    • pp.376-387
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    • 2009
  • Piled raft foundation is a geotechnical composite construction to support the superstructure by pile-soil-raft interaction. General conventional design for piled raft doesn't consider the contribution of a raft. This is very conservative and requires more piles to satisfy the factor of safety. It is important to evaluate the load sharing features of piled raft. In this research, this characteristics of piled raft evaluated using both centrifuge and numerical modelings. The ultimate bearing capacity of piled raft foundation was also evaluated and predicted through comparisons of ultimate bearing capacity of single pile (SP), unpiled raft (UR), freestanding pile group (FPG) and piled raft (PR). $\xi_{pr}$ and $\eta$ were determined by centrifuge model tests to simply evaluate the ultimate bearing capacity of piled raft and bearing capacity of piled raft was predicted using the calibrated numerical model based on the centrifuge tests and laboratory tests data.

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Finite Difference Modeling of a Piled Raft Foundation with Axisymmetry Condition and Interface Element (축대칭 조건 및 경계면 요소를 이용한 Piled Raft 기초의 유한차분 모델링 연구)

  • You, Kwang Ho;Kim, Hyung Ryul;Bae, Sang Han
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.35 no.4
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    • pp.853-861
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    • 2015
  • In this study, FDM modelling with axisymmetry condition and interface element was verified whether it is reasonable to estimate compositive behavior of a piled raft foundation. To this end, the modelling validity of piled raft foundations was estimated by comparing and analyzing numerical analysis results and laboratory model test results. Also, load bearing ratio of a raft is analyzed by performing sensitivity analysis of foundation parameters with the actual field conditions. As a result of this study, correlation between bearing capacity and vertical displacement of numerical results turned out to be similar with that of a laboratory model test. In addition, ultimate bearing capacity of piled rafts and load bearing ratio of the raft is calculated to be similar in both cases. The load bearing ratio of the raft was also estimated to be in the range of 33% to 52% from the sensitivity analysis. The results were confirmed to be similar to the previous studies. Therefore, it can be inferred that piled rafts can be effectively modelled applying axisymmetry condition and interface element.

A Study on The Settlement Behavior of Foundations for Light-weight Structures on Clay Deposits (연약지반에서 경량구조물 기초의 침하거동에 관한 연구)

  • Lee, Kwang-Yeol;Chung, Chin-Gyo;Yun, Sung-Tae
    • Proceedings of the Korean Geotechical Society Conference
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    • 2007.09a
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    • pp.692-700
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    • 2007
  • There are several types of foundations for light-weight structures, such as low story buildings, on soft clay deposits. Those foundations, such as piled raft, compensated foundation, mat foundation, floating foundation are commonly used rather then end-bearing piles to get more benefits on the construction and cost savings. In this study, settlement behaviors are computed and compared for several types of foundations on soft clay deposits. Also, theoretical expressions of parameters for piled raft system were provided with co-relations for design purposes. The predictions of settlements of piled rafts foundation are proposed based on the pile dimensions and design loads. From this study, the piled raft foundations is more benefits for reducing the settlement of clay deposits, and it is found that the piled raft system is applicable and effective on thick clay deposits, and that differential settlements of the foundation should be managed by designing the configuration of pile lengths.

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Three Dimensional Numerical Analysis of Piled Raft on Soft Clay (연약지반에 시공된 Piled Raft 기초의 3차원 거동 분석)

  • Lee, Jin-Hyung;Jeong, Sang-Seom
    • Journal of the Korean Geotechnical Society
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    • v.23 no.5
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    • pp.63-75
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    • 2007
  • Piled raft is known to be an unfavorable foundation type in soft clay because foundation is associated with both excessive settlement and bearing capacity failure problems. Despite these reasons, in recent decades, an increasing number of structures have been constructed over soft clay area, piled raft concepts arouse interest as the foundation of structures on soft clay area becomes popular. This study described 3 dimensional behavior of piled raft on soft clay based on a numerical study using 3D finite element method. A series of numerical analyses were performed for a various pile lengths and the pile configurations on the raft were subjected to vertical uniform or point loading. Based on the results of the parametric study, comparisons were made among the effect of loading type, various pile length and configurations, and the load-settlement behavior and load sharing characteristics of piled raft were also evaluated. From the results, the characteristic of piled raft on soft clay was examined.

Behavior of a combined piled raft foundation in a multi-layered soil subjected to vertical loading

  • Bandyopadhyay, Srijit;Sengupta, Aniruddha;Parulekar, Y.M.
    • Geomechanics and Engineering
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    • v.21 no.4
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    • pp.379-390
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    • 2020
  • The behavior of a piled raft system in multi-layered soil subjected to vertical loading has been studied numerically using 3D finite element analysis. Initially, the 3D finite element model has been validated by analytically simulating the field experiments conducted on vertically loaded instrumented piled raft. Subsequently, a comprehensive parametric study has been conducted to assess the performance of a combined piled raft system in terms of optimum pile spacing and settlement of raft and piles, in multi-layered soil stratum subjected to vertical loading. It has been found that a combined pile raft system can significantly reduce the total settlement as well as the differential settlement of the raft in comparison to the raft alone. Two different arrangements below the piled raft with the same pile numbers show a significant amount of increase of load transfer of piled raft system, which is in line with the load transfer mechanism of a piled raft. A methodology for the factor of safety assessment of a combined pile raft foundation has been presented to improve the performance of piled raft based on its serviceability requirements. The findings of this study could be used as guidelines for achieving economical design for combined piled raft systems.

Numerical Analysis of Piled-Raft Foundations Considering the Effects of Sand Cushion (샌드쿠션을 고려한 말뚝지지 전면기초의 수치해석)

  • Kim, Nam-Ick;Seo, Young-Kyo
    • Journal of Ocean Engineering and Technology
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    • v.21 no.5
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    • pp.25-32
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    • 2007
  • The piled-raft foundation, a new design concept, is one of the most effective kinds of foundation for reducing settlement of structures. An alternative piled-raft system with disconnection cap and a sand cushion between the pile and raft was also investigated to compare the influence of ultimate bearing capacity and settlement. Load-settlement relation curves were used to evaluate the ultimate bearing capacity. In the numerical analyses, a plane strain elasto-plastic finite element model (Mohr-Coulomb model) was used to present the response of the piled-raft foundation.