The Significance of Raft Flexibility in Pile Group and Piled Raft Design

An important aspect of the design of pile groups and piled rafts is the checking of axial loads, lateral loads and bending moments in each of the piles to ensure that they are structurally sound, but most commercially available pile analysis programs assume that the raft or pile cap is rigid. This paper explores the importance of taking the flexibility of the pile cap into account in making assessments of the load and moment distributions. The case of a hypothetical soil profile is considered first and then the case of a super tall building in Korea is considered. The differences between the computed axial loads for a rigid raft and for the actual raft thickness are presented, and it is shown that consideration of the actual thickness of the raft is essential to avoid having to design for unrealistically large loads in the outer piles within the group.