Effect of Piles Arrangement on the Performance of Piled- Raft Foundations

Summary
Piled-raft foundation is a complex system that divide the overall load between the piles and raft upon pile-soil-raft interaction. Piles mainly act as a settlement reducer. Piled-raft foundations with different piles arrangement and soil type, i.e. medium clay and dense sand, were modeled in 3-D finite element software, PLAXIS 3-D Foundation. Influence of piles on differential settlement depends on the piles arrangement and soil properties. The numerical results showed that in two adjacent and symmetrical foundations on sand under uniform surcharge, when corner piles were removed and longer piles were placed close to the symmetry axes of the foundations, the foundation settlement and rotation decreased considerably (at least 50%). For piled-raft foundation on soft with placement of longer piles in the center raft and shorter piles out of center, the optimal piles arrangement was achieved, while in dense sand piles concentration in the central region of raft was optimal arrangement. These later results obtained from rafts on clay and sand with different surcharge that has been analyzed to attain equal 154mm settlement.
 
Introduction
One of the effective ways to improve the footing bearing capacity is using pile foundations. The piled-raft foundation is a new design concept as one of the effective methods of foundation to reduce settlements of structures.  In piled raft foundation role of raft foundation is to provide adequate bearing capacity and role of pile foundation is mainly to act as settlement reducers. In this paper 3-D finite element analysis of piled raft foundations on dense sand and medium clay was studied. The purpose of the present study is to investigate the role of piles arrangement in reducing settlement of the piled raft foundation.
 
Methodology and Approaches
Numerical method used for analysis of piled raft foundation, due to complex soil-structure interaction. A 3-D finite element software, PLAXIS 3-D Foundation utilized to analyze three dimensional models of piled raft foundation. The model results validated among settlements of Messe–Torhaus structure in Germany which was modeled in ABAQUS. Different pile arrangement plan in dense sand and medium clay was molded. Soil behavior was modeled by Mohr-Coulomb elastoplastic model.
 
Results and Conclusions
Piles arrangement has a significant influence on the performance of piled raft foundation. Numerical results show that appropriate arrangement of piles which has maximum reduction in settlement strongly depends on soil type. Additionally, increasing the piles length has more influence on the performance of piled raft foundation, rather than pile diameter growth, when the volume of concrete in piles bodies has been constant.