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Keywords: piled raft, finite elements, elasto-plastic analysis, central piles, differential settlement, bending moment.

Summary

The philosophy of using piled rafts with a central pile group to directly control differential settlement, was investigated by many researchers, for example Padfield and Sharrock [1]. In most of the available studied cases the soil profile was uniform stiff clay and little attention was given to the effect of the central pile group on the resulting bending moments. In the present paper a detailed parametric study is performed on a hypothetical square building, founded on a piled raft with a central pile group. Seven different soil profiles are investigated via three dimensional elasto-plastic finite element analyses. The investigated soil types included combinations of dense sand, medium sand, stiff over consolidated clay, medium clay and soft to medium clay. The effect of central pile support on the raft deformed shape and bending moments are studied. Comparisons with the cases of corresponding un-piled raft and piled rafts with uniformly distributed pile group are made.

The results of the parametric study prove the efficiency of this philosophy regarding the control of differential settlement. This efficiency greatly depends on the stratification of the supporting soil. Good results were obtained in the case of uniform soil profiles rather than in the case of two layered soil profile, in which the strength of the soil layer beneath the pile tip is greater than that of the top layer. For point bearing piles, at high load levels the absolute value of differential settlement may exceed that of corresponding uniformly distributed pile group. In this case an increasing number of uniformly distributed piles tends to be more reliable for control of differential settlement. The central pile arrangement, resulted in a considerable reduction in maximum raft bending moments, however the distribution of bending moment in the raft in this case differs from the case of uniformly distributed piles and the peak values of bending moment are not located at column positions as usual in the case of uniformly distributed pile group.

References

1: C.J. Padfield, M.J. Sharrock, "Settlement of structures on clay soils", CIRIA special publication, No. 27, 1983.

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Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	Civil-Comp Proceedings ISSN 1759-3433 CCP: 89 PROCEEDINGS OF THE SIXTH INTERNATIONAL CONFERENCE ON ENGINEERING COMPUTATIONAL TECHNOLOGY Edited by: M. Papadrakakis and B.H.V. Topping Paper 181 Three-Dimensional Numerical Investigation of the Efficiency of Piled Rafts with a Central Pile Group A.A. Hemada¹ and A.Y. Akl² ¹Department of Soil Mechanics, Housing and Building National Research Centre, Giza, Cairo, Egypt ²Department of Structural Engineering, Cairo University, Giza, Egypt doi:10.4203/ccp.89.181 purchase the full-text of this paper Full Bibliographic Reference for this paper A.A. Hemada, A.Y. Akl, "Three-Dimensional Numerical Investigation of the Efficiency of Piled Rafts with a Central Pile Group", in M. Papadrakakis, B.H.V. Topping, (Editors), "Proceedings of the Sixth International Conference on Engineering Computational Technology", Civil-Comp Press, Stirlingshire, UK, Paper 181, 2008. doi:10.4203/ccp.89.181 Keywords: piled raft, finite elements, elasto-plastic analysis, central piles, differential settlement, bending moment. Summary The philosophy of using piled rafts with a central pile group to directly control differential settlement, was investigated by many researchers, for example Padfield and Sharrock [1]. In most of the available studied cases the soil profile was uniform stiff clay and little attention was given to the effect of the central pile group on the resulting bending moments. In the present paper a detailed parametric study is performed on a hypothetical square building, founded on a piled raft with a central pile group. Seven different soil profiles are investigated via three dimensional elasto-plastic finite element analyses. The investigated soil types included combinations of dense sand, medium sand, stiff over consolidated clay, medium clay and soft to medium clay. The effect of central pile support on the raft deformed shape and bending moments are studied. Comparisons with the cases of corresponding un-piled raft and piled rafts with uniformly distributed pile group are made. The results of the parametric study prove the efficiency of this philosophy regarding the control of differential settlement. This efficiency greatly depends on the stratification of the supporting soil. Good results were obtained in the case of uniform soil profiles rather than in the case of two layered soil profile, in which the strength of the soil layer beneath the pile tip is greater than that of the top layer. For point bearing piles, at high load levels the absolute value of differential settlement may exceed that of corresponding uniformly distributed pile group. In this case an increasing number of uniformly distributed piles tends to be more reliable for control of differential settlement. The central pile arrangement, resulted in a considerable reduction in maximum raft bending moments, however the distribution of bending moment in the raft in this case differs from the case of uniformly distributed piles and the peak values of bending moment are not located at column positions as usual in the case of uniformly distributed pile group. References 1 C.J. Padfield, M.J. Sharrock, "Settlement of structures on clay soils", CIRIA special publication, No. 27, 1983. purchase the full-text of this paper (price £20) go to the previous paper go to the next paper return to the table of contents return to the book description purchase this book (price £95 +P&P)
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