Abstract:
Due to structural requirements or failure of the already constructed pile foundations to carry the intended superstructure loads, it is necessary to use piled-raft foundations. In addition to the above, even if the raft sustains bearing capacity but fails in the settlement, then piled-raft is introduced to reduce the total and differential settlement. Since this foundation system is not commonly used in the construction industry in Sri Lanka, there is uncertainty among design engineers regarding the load-sharing mechanism of piled-raft foundations. This paper investigated the load transfer mechanism of the Piled-Raft through a literature review. There are 3 types of piled-raft design philosophies: namely, the conventional approach, the creep pile approach, and the differential settlement control approach. Further, based on the above design philosophies, 3 different design methods were compared in this study. Under the first design method, the piled-raft foundation is divided into several units, and the overall settlement is estimated by considering the interaction factor between piled-raft units. However, this method does not define load sharing between pile and raft. The second design method used a piled-raft interaction factor of 0.8 to define the load-sharing ratio among the piles and the raft. The third design method is only applicable to strip rafts and there are several limitations to this method. Based on the analysis, the second method reported that there was a 6.9% error between actual piled-raft interaction values and assumed values for the selected hypothetical examples. However, by comparing the above design methods, it can be concluded that the second design method which uses the piled-raft interaction factor of 0.8 gives a more reliable analysis.
