Performance of Piled Raft Foundations for Addis Ababa Soils

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Addis Ababa University


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 v 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.