Performance of piled raft foundations subjected to static horizontal loads

A series of static loading tests were conducted vertically and horizontally on piled raft models and their components (single piles and rafts alone) on sand by using a geotechnical centrifuge. Much focus was placed on the load-displacement relationship and the load sharing between the piles and the raft in the piled raft system. Effects of the rigidity at pile head connection on the piled raft behavior were also examined. This paper provides basic information on the performance of piled raft foundations subjected to horizontal loads. Principal findings from the present study are: 1) The stiffness and the resistance of the single pile in piled raft foundations are different from those observed in the isolated single piles of the same size, due to the difference in the confining stress condition around the piles; 2) Piles play important roles in increasing horizontal ultimate resistance of piled raft foundations; 3) The initial horizontal stiffness of a piled raft is not always higher than that of a raft (alone) as the piles reduce the contact pressure between raft and soil, and hence the stiffness of the upper soils; 4) Higher horizontal load is transferred to the piles in the piled raft with rigid pile head connection, which leads to higher initial horizontal stiffness compared with that in the piled raft with hinged pile head connection; 5) The proportion of vertical load carried by the piles in a piled raft remains largely unchanged during horizontal loading, while the proportion of horizontal load carried by the piles increases as the horizontal displacement increases.