FEM modelling of a large piled raft for settlement control in weak rock

Use of piles for transferring structural load to suitable load bearing strata and settlement control in alluvial/diluvial deposits is widespread. This paper investigates the application of a group of 1072 piles for controlling settlement of an important and sensitive structure founded on weak rock. 2D axi-symmetrical and 3D finite element models are employed to model the 9.0 m thick and 76 m diameter circular raft, underlying soil/rock and a mix of annular and orthogonal pile layout. Effectiveness of pile foundation in reducing settlement is assessed by comparing the results with the case of raft foundation alone. Results of 2D axi-symmetrical and 3D FEM models are also compared and it is concluded that the numerically efficient 2D axi-symmetrical FEM model is capable of simulating the behaviour of this complicated 3D problem with reasonable accuracy.