Contribution of raft to resist lateral loads in a piled raft foundation- Experimental findings

The Combined pile raft foundation (CPRF) is considered to be an efficient type for tall buildings since it accounts for raft contribution to both vertical and lateral loads. Traditionally, in a pile raft foundation, the contribution of raft to resist loads is ignored due to the fact that its analysis requires complicated soil-structure interaction. Hence this simplification may lead to an uneconomical design. While research on vertical resistance of raft in CPRF is considerable, research on its horizontal resistance is yet very limited. To address this issue, in this research the contribution of the components of pile-raft foundation to lateral loads is evaluated experimentally. Ten small scale combined piled raft models were fabricated and instrumented with load cells at pile top to find raft contribution in resisting vertical and lateral load. Load cells were composed of strain gauge rosettes in Wheatstone bridge arrangements. The vertical static load of 5350 N was applied through steel plates and the lateral incremental load of 1500 N was applied using the hydraulic machine. The number of piles was varied from 1 to 25 with s/d ratio of 6.67 and 3.44. The results show that raft in a piled raft system is contributing in resisting 10-60% of the applied lateral load which is highly dependent on the number of piles. The percentage contribution of the raft to the lateral load decreases with the increase in the number of piles. Furthermore, it was also shown that in case of piled raft, the rear piles are resisting more lateral load than the front piles depending on the vertical load level.