• Geomechanics and Engineering
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• 제16권2호
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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.

• Geomechanics and Engineering
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• 제35권6호
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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.

• 한국지반공학회논문집
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• 제32권8호
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• pp.35-46
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• 2016

본 연구에서는 지반조건에 따른 실제 piled raft 기초의 거동을 실규모 시험을 통해 분석하기가 어려운 점을 감안하여 수치해석을 이용한 민감도분석을 수행하고자 하였다. 수치해석에 사용한 프로그램은 유한차분법 기반의 FLAC 3D이다. 말뚝의 수치해석 모델링은 FLAC의 구조요소 중 하나인 말뚝요소를 사용하여 모델링하였고, 지반과 래프트는 연속체 요소를 이용하여 모사하였다. 말뚝의 배열은 $3{\times}3$으로 고정하고 말뚝직경, 말뚝길이, 말뚝간격 그리고 지반조건을 민감도 매개변수로 선정하고 상관관계를 규명하였다. 그 결과, 말뚝직경이 크고 말뚝의 길이가 길수록, 그리고 말뚝의 간격이 넓을수록 piled raft 기초의 전체 지지력은 증가하는 것으로 나타났다. 그러나 지반조건에 따라 말뚝간격이 일정 간격 이상이 될 경우, piled raft 기초의 거동이 래프트만으로 지지되는 얕은기초와 유사한 거동을 보였다. 또한 지반조건이 좋아질수록, piled raft 기초의 전체 지지력은 증가함을 확인할 수 있었다.

• Coupled systems mechanics
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• 제5권1호
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• pp.41-58
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• 2016

The study deals with physical modeling of a typical building frame resting on pile raft foundation and embedded in cohesive soil mass using finite element based software ETABS. Both- the elements of superstructure and substructure (i.e., foundation) including soil is assumed to remain in elastic state at all the time. The raft is modelled as a thin plate and the pile and soils are treated as interactive springs. Both- the resistance of the piles as well as that of raft base - are incorporated into the model. Interactions between raft-soil-pile are computed. The proposed method makes it possible to solve the problems of uniformly and large non-uniformly arranged piled rafts in a time saving way using finite element based software ETABS. The effect of the various parameters of the pile raft foundation such as thickness of raft and pile diameter is evaluated on the response of superstructure. The response included the displacement at the top of the frame and bending moment in columns. The soil-structure interaction effect is found to increase displacement and increase the absolute maximum positive and negative moments. The effect of the soil- structure interaction is observed to be significant for the type of foundation and soil considered in the present study.

• Geomechanics and Engineering
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• 제29권2호
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• pp.183-192
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• 2022

Piled raft foundations are widely used and effective in supporting high-rise buildings around the world. In this study, a piled raft system was numerically simulated using PLAXIS 3D. The settlement comparison results between the actual building measurements and the three-dimensional (3D) numerical analysis, were in good agreement, indicating the usefulness of this approach for the evaluation of the feasibility of using a piled raft foundation in Ho Chi Minh City subsoil. The effects were investigated of the number of piles based on pile spacing, pile length, raft embedment on the settlement, load sharing, bending moments, and the shear force of the piled raft foundation in Ho Chi Minh City subsoil. The results indicated that with an increased number of piles, increased pile length, and embedding raft depth, the total and differential settlement decreased. The optimal design consisted of pile numbers of 60-70, corresponding to pile spacings is 5.5-6 times the pile diameter (D_p), in conjunction with a pile length-to-pile diameter ratio of 30. Furthermore, load sharing by the raft, by locating it in the second layer of stiff clay, could achieve 66% of the building load. The proposed model of piled raft foundations could reduce the total foundation cost by 49.61% compared to the conventional design. This research can assist practicing engineers in selecting pile and raft parameters in the design of piled raft foundations to produce an economical design for high-rise buildings in Ho Chi Minh City, Viet Nam, and around the world.

• Geomechanics and Engineering
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• 제20권5호
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• pp.433-445
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• 2020

A new code, called PRaFULL (Piled Raft Foundation Under Lateral Load), was developed for the analysis of laterally loaded Combined Pile Raft Foundation (CPRF). The proposed code considers the contribution offered by the raft-soil contact and the interactions between all the CPRF system components. The nonlinear behaviour of the reinforced concrete pile and the soil are accounted. As shallower soil layers are of great relevance in the lateral response of a pile foundation, PRaFULL includes the possibility to consider layered soil profiles with appropriate properties. The shadowing effect on the ultimate soil pressure is accounted, when dealing with pile groups, as proposed by the Strain Wedge Model. PRaFULL BEM code obviously requires less computational resources compared to FEM (Finite Element Method) or FDM (Finite Difference Method) codes. The proposed code was validated in the linear elastic range by comparisons with the code APRAF (Analysis of Piled Raft Foundations). The reliability of the procedure to predict piled raft performance was then verified in nonlinear range by comparisons with both centrifuge tests and computer code PRAB.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2002년도 기초기술학술발표회
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• pp.77-89
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• 2002

To analyze a bearing capacity for pile groups, a number of model tests have been done and theoretical methods studied. In the case of design of group pile bearing capacity is calculated with only pile capacity. But uncertainty of bearing capacity and behavior of foundation cap(raft) leads to conservative design ignoring bearing effects of foundation cap. In the case of considering bearing capacity of foundation cap, the simple sum of bearing capacity of foundation cap and pile groups cannot be the bearing capacity of total foundation system. Since cap-pile-soil interaction affects the behavior of pile groups. Thus, understanding cap-pile-soil interaction is very important in optimal design. In this paper, the piled raft behavior is studied through model tests of 2$\times$2, 2$\times$3, 3$\times$3 pile group. Changes of behavior of pile group foundation by touching effects of foundation cap with soil are studied. Also changes of spacing between piles. Foundation cap is made of rigid steel plate and piles are made steel pipes. From this model tests, the changes of behavior changes of pile groups by touching effects of foundation cap with soil are studied.

• 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.

• 한국지반공학회논문집
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• 제24권10호
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• pp.17-24
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• 2008

본 연구에서는 전면지지 말뚝기초의 비선형적 거동을 보다 간편하게 모사할 수 있는 2차원 유한요소기법을 개발하였다. Raft는 Mindline 이론에 근거한 평판유한요소로 모델링 하였으며, 하중 재하에 따른 말뚝의 비선형적 거동을 모사할 수 있는 말뚝거동 모델을 제안하였다. 전면지지 말뚝기초의 비선형적 침하거동에 대한 개발된 수치기법의 적용성을 검증하기 위하여 실내실험 계측자료와 유한요소 해석결과와 비교하였으며, 비선형적 침하거동을 잘 모사할 수 있음을 확인하였다.

• Geomechanics and Engineering
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• 제21권4호
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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.