On the Comparison Between the Approximate And Precise Methods of Piled Raft

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Mechanics, Materials Science & Engineering, May 2016

ISSN 2412-5954

On the Comparison Between the Approximate And Precise Methods of Piled Raft Foundation Analysis Abbasali Taghavi Ghalesari 1

Department of Civil Engineering, Babol Noshirvani University of Technology, Babol, Iran DOI 10.13140/RG.2.1.5128.7446

Keywords: piled raft foundation, soil-structure interaction, 3D FE method, approximate method.

ABSTRACT. Use of raft foundation to support heavy and tall building may provide the overall safety factor against design loads but the average and differential settlement could exceed the allowable value. On the other hand, utilizing . This foundation is a composite geotechnical system of three bearing components: raft, pile group and soil. The applied load on the raft is transferred to the underlying soil by the contribution of raft and piles. Therefore, considering the interaction effect between the components is essential. It causes some complexities in predicting the behavior of piled rafts. Thus, on this basis, so many different methods were developed. In this study, a comparison between these different methods including approximate and precise methods are presented. Based on the results, a three-dimensional finite element analysis gives perfectly satisfactory results in the prediction of bearing and settlement behavior of piled rafts.

Introduction. In recent years, piled raft foundations have been widely used in practice to support heavy and high-rise buildings due to weight and rigidity of the superstructure. When a raft foundation provides the required bearing capacity but the settlement values exceed the allowable limits, an addition of fewer piles in comparison with pile groups could improve the settlement behaviour of the foundation. The expression of piled raft foundations is in no manner new and has been explained by several authors, including Zeevaert [1], Davis and Poulos [2], Hooper [3], Sommer et al. [4] and Franke [5], among many others. The mechanism of load transmission in piled raft foundation is so complicated. Thus, different methods from simplified methods to more rigorous methods were developed. In addition to laboratory tests and field studies such as centrifuge test, shaking table test and full-scale modelling, several empirical, analytical and numerical methods have been presented to predict the behaviour of piled rafts under static vertical to dynamic loads. A comparison between the results of different methods of piled raft analysis through some examples is considered in this study. The results of these methods were compared with the results of three-dimensional finite element method as a precise solution. The 3D FE method is capable for considering the interaction effect of the piled raft components. Analysis methods. Approximation methods. Hongladaromp et al. [6] presented an approach that considered the soil as an elastic continuum, the raft as a thin plate and the piles as springs. In this method, the interaction effects between the piles were ignored. Poulos [7] presented a program, GARP, based on finite difference method with the consideration of pile-raft interaction. The piles were allowed to reach their ultimate bearing capacities and a local bearing failure was allowed for the raft. A similar method was solution was used to calculate the soil displacements. For a single pile, load-settlement curve was assumed hyperbolic to consider the non-linearity of piles. Kitiyodom and Matsumoto [9] presented a method where the piles were modelled by elastic beam elements and the interaction between the MMSE Journal. Open Access www.mmse.xyz

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