Due to rapid growth in infrastructure sector, the construction of high-rise buildings is becoming very popular among all the countries. Engineers face significant issues with high rise buildings, particularly in terms of structural and foundation aspects. Many old design approaches can't be used with certainty since they involve extrapolation far beyond the domains of existing experience, hence structural and geotechnical engineers are being compelled to use more advanced analysis and design methodologies. The current study is an attempt to predict the bearing capacity and settlement behavior of Piled-Raft footing when embedded into cohesionless deposit. The numerical analysis has been carried out to examine the effect of numerous key parameters of pile and Raft such as pile length (10, 15, 20 m), pile diameter (0.3, 0.4, 0.5 m), pile number (16, 20, 24), pile spacing (2D, 3D, 4D) (where “D” is diameter of the pile), Raft thickness (0.4, 0.5, 0.6 m), and angle of internal friction of soil (25°, 30°, 35°) on load-settlement behavior of the Piled- Raft foundation using ABAQUS software. A constant spacing between the piles, i.e. 3D was used throughout the analysis. The results of numerical investigation revealed an improvement in bearing capacity and a reduction in settlement value on increasing length, diameter and number of piles and also with increasing angle of internal friction. The current study not only increases the bearing capacity of the foundation but provides a cost-effective foundation technique to engineers.

Numerous techniques have been presented by different researchers to analyze Piled Raft. In order to analyze pile foundation, soil can be modeled as spring, continuous medium, or porous media. Pile can also be modeled as spring or continuous medium. This study includes three main stages: a short description of different types of analysis methods of pile foundation, writing a computer program based on the finite element method (FEM) for analyzing Piled Raft foundation (in this program, foundation is modeled as a flexible plate, soil and pile are modeled by Winkler springs), and comparison of different concepts of pile group design.

A Shallow foundation on cohesionless soil cannot support greater weights; Piled Raft foundations are recommended because they combine the load-bearing qualities of piles and Raft. Combined Piled Raft Foundations (CRPF) are efficient for tall buildings because they account for both vertical and lateral loads. In a pile Raft foundation, the Raft’s load-resistance is disregarded due to soil-structure interaction. Simplification may lead to an uneconomical design. While study on Raft’s vertical resistance is extensive, its horizontal resistance is limited. In the present study, 160 mm x 160 mm pile-Raft model with different pile spacing and pile length was tested. Studies showed that pile length and spacing of pile improve bearing capacity and reduce settlement of Raft. The pile Raft system rests 65 percentage of the lateral load, depending on pile spacing and its length. Pile spacing and pile length lessen the Raft’s lateral load contribution. Furthermore, as increasing in pile spacing reduces Raft overturning by 60 percentage. Upgrade pile Raft system design may make a cheaper and more efficient option for skyscrapers and make this foundation system more economical design.

1. Introduction Several numerical studies have been carried out to analyze the behavior of Piled Raft foundations, but very few experimental studies are reported in literatures (Cooke RW, 1986). The conventional approach for the design of Piled Raft foundations ignores the Raft load sharing and it has been assumed that the piles carry the whole of structural loads (Hemsley JA, 2000). This approach is unduly conservative and lead to an uneconomic design. Only when the piles cap is elevated from the ground level, this design method is valid. In a Piled Raft foundation, pile-soil-Raft interaction is complicated. The available laboratory studies are mainly focused on steel piles. The present study aimed to evaluate the behavior of Piled Raft foundations in sand, using experimental physical models...

In the case of problematic soils and tall buildings where the design requirements cannot be satisfied merely by a Raft foundation, it is of common practice to improve the Raft performance by adding a number of piles so that the ultimate load capacity and settlement behavior can be enhanced. In this study, the effect of spatial variability of soil parameters on the bearing capacity of Piled Raft foundation is investigated based on the random field theory using the finite difference software of FLAC3D. The coefficient of variation (COV) of the soil’ s undrained shear strength, the ratio of standard deviation to the mean, was considered as a random variable. Moreover, the effect of variation of this parameter on the bearing capacity of Piled Raft foundation in undrained clayey soils was studied taking the Monte Carlo simulation approach and the normal statistical distribution. According to the results, taking into account the soil heterogeneity generally results in more contribution of the Raft in bearing capacity than that of the homogenous soils obtained by experimental relationships, which implies the significance of carrying out stochastic analyses where the soil properties are intensively variant.

1. Introduction: In conventional design of pile foundations, all loads are taken by the piles, i. e. the contact pressure between the Raft and the soil is neglected. In the last decades, geotechnical engineers have started to take this pressure into account in design of pile foundation. Such a foundation, where the Raft and the piles interact to transfer the loads to the ground, is in this dissertation called Piled Raft foundation or Piled Raft...