Performance of Piled Raft Foundations for Addis Ababa Soils
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Date
2004-03
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Addis Ababa University
Abstract
This thesis presents the investigation of the performance of the concept of piled raft
foundation compared to the conventional pile and raft foundation for Addis Ababa soils.
The investigation has been carried out using soil profiles in Addis Ababa where highrise
buildings are going to be constructed and have been already constructed. To
support the results of the investigation, soil profile from Wabe Shebele River bridge site
has been also considered.
In this work, first, different design philosophies and method of analysis have been
discussed. From already available methods of analysis, the hybrid method of analysis
has been chosen for its computational efficiency. The program is validated by anaysing
examples available in literature and has already been analyzed using 3D finite element
code (FLAC 3D).
Then, two case studies have been made to explore the performance of the piled raft for
Addis Ababa soils. The first case is the Awash bank head quarter building, which is
going to be constructed near national theater. The second case considered is the soil
profile on which the former marine transport authority building is constructed. For both
cases, comparison has been made among raft, pile, and piled raft foundation based on
settlement and bending moment.
Another case study, conducted to supplement the out come of the foregoing two cases, is
the abutment foundation of Wabe Shebele River Bridge. This case specifically
conducted aiming at reducing the total settlement of the foundation that is above the
permissible limit for masonry abutment. For the this case, the results have shown that
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two fifth of the number of piles required for conventional piles can be reduced using
piled raft design concept. When raft alone is used, the settlement exceeds the
permissible value.
Generally, it has been observed that piled raft concept is very advantageous in
minimizing the total and differential settlements as compared to the conventional raft
foundation. It also reduces number of piles required as compared to the conventional
pile foundation. For the cases investigated in this work, the reduction in number of
piles ranges from 25% to 45% of that required for conventional pile foundation, though
the variation in raft bending moment and other issues are no considered in detail.
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Keywords
Soils