Experimental and Numerical Investigation of Load Sharing Ratio for Piled Raft Foundation in Granular Soils

If the rigidity and the bearing capacity of the soil under a superstructure are not efficient to bear loads of structures, a common remedy is to increase the depth of the footing to transmit loads to soil layers having high bearing capacity (well graded dense gravel, gravelly sand, hard clay, rock, etc.) by using the pile group. Piled raft foundation (PRF) has come a significant footing system of late years due to that it combines load-carrying capacities of piles and raft. Therefore, extensive empirical, numeric and analytical studies have been carried out for reliable design of these footing system. Nonetheless, the load sharing ratio (LSR) between the driven piles and the raft received no attention from researchers. It is aimed to examine the LSR between the driven pile group and the raft in this study. Therefore, a testing apparatus was set up, and loading tests were carried out including the raft and the piled raft cases. Thus, the LSR of the piles and the raft were measured by means of the tests, and the effect of the pile length and relative density on this ratio was also investigated. The model of the test setup was determined numerically for same loading conditions and the material properties by using ABAQUS software. From the test and finite element analysis results, it has been found that rafts share foundation loads at such levels that should not be ignored. Vertical settlements of raft foundations at certain loads are found to be greater than the settlements of piled raft foundations at the same loads. Relative density was observed to be effective in the range of 1-2% on the LSR of the piles in PRFs. In addition to this, the length of the pile was found to be more effective on this ratio in the range of 11-14%.