Properties of rigid-pile composite foundation based on FDM-PFM coupling method

In order to reveal the mechanical nature of granular cushion and deeply investigate the effect of granular cushion on the performance of rigid-pile composite foundation, a finite differential-particle flow (FDM-PFM) coupling method is proposed, and a coupling model for the static loading test of a single rigid-pile composite foundation is set up. Then, the calculation results are compared with the in-situ test results of a composite foundation of a high-rise building, with good accordance being found, which means that the proposed coupling method is effective, and that the macro and micro parameters are properly selected. Finally, further simulations are performed to analyze the effects of different cushion materials on the properties of rigid-pile composite foundation. The results show that (1) with the increase of cushion stiffness, the settlement decreases, the pile-to-soil stress ratio increases, and the penetration of the pile top into the cushion decreases; (2) the range of negative skin friction area of the pile is determined as follows: 0.30 L of medium and coarse sand, 0.25 L of crushed stone, and 0.20 L of graded sand and stone; and (3) with the increase of cushion stiffness, the negative skin friction decreases, while the axial force of the pile increases.