The Role of Granular Cushion in Load Sharing of Unconnected Piled Rafts in Clayey Soils

Karam Khalifa,Mohammed Fattah,Nahla Salim

doi:10.30684/etj.v39i12.2076

Abstract

Over the past few decades, interest has grown about the role of the piled raft structure in soils. A structural fill cushion separates the piles from the raft in the form of an unconnected piled raft base (UCPRF). Given the advantage of this structure, the load is dispersed between the raft and the piles by the cushion. The cushion serves as a load redistributor between the raft and the piles. Load dispersion capability of the system was theoretically estimated using PLAXIS finite element analysis software in this study. The effect of cushion thickness on settlement reductions was investigated as well. Obtained results showed that the pile head has the greatest axial stress in the piled raft system., however decreased along the length of the pile according to finite element analysis. The unconnected head's maximum axial load is transferred down to a point a certain distance below the pile head (approximately two meters in the studied model). Above the top two meters, the axial stress in the pile begins to decrease, following the same pattern as the connected system. The thickness of the cushion affects the load sharing between the cushion and the piles. As the cushion thickness increases, the axial stress at the pile head decreases

Highlights

Structural rafts are used for supporting structures and construction in general
The settlements of connected and unconnected piled raft systems are shown in Figure) 3(
When compared to the traditional pile group model, the maximum settlement of the linked piled raft has decreased by 37%, while the maximum settlement of the unconnected piled raft has decreased by 45 percent

Summary

Introduction

If the shallow conditions of the subsoil (unsafe loading or unstable settlements) are unfavorable, the piles are used to redistribute the entire load to more suitable soil layers. Settlements, both total and individual, are usually deciding factors in the selection of piled raft foundations. The total load transferred from the building to the soil surface and connected piles are distributed by the raft according to their relative stiffness. The piles were assumed to support the overall load in the design of piled foundations. The contribution of the raft is taken into account in piled raft foundation systems to verify the ultimate bearing capacity and usability of the overall system. In a piled raft system, they found that pile stiffness, raft rigidity, and pile length to width ratio all had an impact on load sharing around piles

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