Abstract

The application of piled raft foundations for supporting high rise buildings has significantly increased over the last few years. The economic benefits of piled raft foundations in comparison with alternative approaches have encouraged this popularity, but this comes with additional complexity for load sharing calculations in a multi-parameter problem. These parameters are, but not limited to: soil density, pile length, pile spacing, raft geometry, and pile installation technique. The complexity of piled raft foundation design demands further research in a range of different engineering aspects.
In this study, the load sharing mechanism of a piled raft foundation in sandy soil was investigated through small scale tests and three dimensional numerical analyses. The effects of density in homogeneous and layered soil, sand particle size distribution, pile installation method, and raft width were studied through experimental analyses. Experimental tests were performed on a shallow footing, single pile and single piled raft unit in clean Silica sand. The results of small scale tests reveal that soil density changes the load sharing mechanism of a displacement piled raft—the pile share increases in denser soil. However, this result does not hold in non-displacement piled rafts where load sharing is independent of soil density. Furthermore, it is observed that particle size distribution has inconsiderable effects on piled raft behavior.
One of the experimental tests on non-displacement piled rafts was employed to calibrate the 3D numerical model, which was further expanded into 2x2 and 3x3 piled raft foundations. The load sharing outputs of the aforementioned models were compared for a given settlement ratio. This comparison reveals that the number of piles has an inconsiderable impact on the load sharing of non-displacement piled raft given that the piles are identical in size and a minimum spacing among them is respected. The numerical analysis confirms that the conducted experimental tests on non-displacement piled rafts are applicable to predict the load sharing in practical cases. Therefore, an empirical model was developed to achieve this goal under various settlement ratio and pile spacing. The proposed empirical models were validated against the available centrifuge and field test results in the literature.
A widely accepted analytical model in the literature was modified based on the previously conducted experimental results. The proposed model calculates the load sharing as a function of settlement and pile spacing ratio in homogeneous and layers soils.