Abstract: Model tests and numerical simulations were carried out to investigate load transfer characteristics of short stiff piles with big caps. With increasing loads, the lateral shear slip damage occurred on ground soil underlying the pile cap, whereas punching shear was found in the vicinity of the pile tip for soft foundation reinforced by short stiff pile with a large cap. Thus, a novel block displacement method was proposed to analyse the load-displacement relationship of ground soil underlying the pile cap, and the load transfer method was put forward for the lower part of the pile. Based on the displacement compatibility of the upper and lower parts for a single pile, the load-displacement relation (P-s curve) for the short stiff pile with the large cap was obtained by using the iteration method. Meanwhile, the calculated P-s curves were compared with the measured results in model tests, which showed a good agreement between them. Furthermore, the presented calculation model investigated the effects of pile cap-body diameter ratio D/d as well as the ratio between the pile length and pile cap diameter L/D on the bearing capacity of the short stiff pile with large pile cap. The results demonstrated that suggested ranges were D/d>2 and L/D<10 for the application of pile reinforced soft foundation with pile caps.

Key words: composite foundation, block displacement method, pile with cap, P-s curve, load transfer method