Numerical investigation of optimized piled raft foundation for high-rise building in Germany

O A Abdel-Azim,K Abdel-Rahman,Y M El-Mossallamy

doi:10.1007/s41062-019-0258-4

O A Abdel-Azim, K Abdel-Rahman + Show 1 more

Open Access

https://doi.org/10.1007/s41062-019-0258-4

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Abstract

Piled rafts have been used as a foundation system for high-rise buildings worldwide in different soil conditions, e.g., in soft to stiff clay as well as in medium-to-dense sand. Piled raft is currently used not only to control the foundation settlement but also to minimize the required raft thickness to reach the most optimized foundation design. The purpose of this study is to investigate the behavior of piled raft as a foundation system for Frankfurt over-consolidated clay based on the well-monitored Messeturm building in Germany. The numerical tool used in analysis is Plaxis 3D finite element software with hardening soil material model. The piled raft foundation behavior will be evaluated based on the total settlement, differential settlement and the pile skin friction. Based on this study, it was found that the chosen foundation system “plied raft foundation” for Messeturm was an optimized solution for the proposed building.

Highlights

When constructing a low-rise building on a bearing layer of soil, shallow foundations can be used, but if the building is a high-rise building and contains a number of basements, raft foundation is normally chosen to support the entire structure
Due to Frankfurt clay nature as mentioned before, the clay was overloaded by heavy loads with average stress ranging between 500.0 and 2500.0 kPa, so the Over Consolidation Ratio (OCR) ranged over specific values and it was difficult to find out the exact value of OCR without performing a consolidation test
Several values of OCR will be investigated using values above and below 1.50. Another technique for defining the over-consolidation pressure is adopted in the hardening soil model which is the pre-overburden pressure (POP) technique instead

Summary

Introduction

When constructing a low-rise building on a bearing layer of soil, shallow foundations can be used, but if the building is a high-rise building and contains a number of basements, raft foundation is normally chosen to support the entire structure. Oh et al [15] used finite element (Plaxis) and finite difference (FLAC) methods to study the behavior of piled raft in sandy and clayey soil They found that the maximum settlement depends mainly on the number of piles and the pile spacing. Mil [22] used Plaxis 3D finite element program to investigate the behavior of piled raft in stiff clay He found that by increasing the pile spacing-to-diameter ratio more than 6 will increase the settlement significantly as discussed in [23]. The verification of the presented numerical model will be compared via two cases; the first case is a simple single pile developed by Katzenbach [24, 25] as a conceptual verification, while the other case is Messeturm building, made by Sommer [26] and El-Mossallamy [6] Both cases were founded on over-consolidated Frankfurt clay, so it is important firstly to state the main properties of Frankfurt subsoil formation. For Frankfurt clay, El Mossallamy [6] reported that the difference between the short-term and long-term conditions is minor, and for a single pile, the effect is about 6.0% to 15.0%, while for piled raft case, the effect of consolidation may reach 30%

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Findings

Conclusions