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Reliability Based Design of Pile Raft Foundation | ||
| Engineering and Technology Journal | ||
| Article 1, Volume 28, Issue 12, 2010, Pages 2361-2378 PDF (370.4 K) | ||
| DOI: 10.30684/etj.28.12.7 | ||
| Authors | ||
| Tania M. Al-Ani; Namir K.S. Al-Saoudi | ||
| Abstract | ||
| The Combined Piled Raft Foundation (CPRF) is a modern concept in which the total load coming from the superstructure is partly shared by the raft through contact with soil and the remaining load is shared by piles through skin friction and/or base capacities. A CPRF system is economical compared to the traditional “piled foundation” design where the pile cap is assumed to be sustained by piles only. A “case study” (Basrah elevated water tank project) is studied thoroughly in this work. The 1365 m3 elevated water tank located at 3 nearby sites was originally designed as a piled foundation with 25 bored piles for each site (0.7m diameter and 24m length). Theoretical analysis reveals that the piles have an allowable capacity of 2245 kN. On the other hand static pile tests were preformed on 17 piles out of 75 piles and it appeared that the allowable capacity demonstrated erratic values below the expected pile capacity. A re-analysis of the pile raft is performed establishing the CPRF concepts. The case study was modeled by STAAD Pro computer package to determine the loads on both piles and soil with the corresponding settlement values. The reliability aspects of behavior of both “piled foundation” and CPRF are investigated. In this approach the influence of autocorrelation for the stiffness modulus (of both piles and soil) and raft thickness are considered. The safety of both systems is obtained in terms of traditional factor of safety (FS) and reliability index (b). The results showed that the “piled foundation” system is “unsafe” for 3 criteria for both FS and b. On the other hand, the CPRF is “safe” for the 4 criteria for FS concept while it is “unsafe” for 3 criteria for b. | ||
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