Experimental Study On Bearing Performance Of Caisson-Cushion-Pile Deepwater Composite Foundation Under Vertical Loads

Caisson-cushion-pile composite foundation is an emerging foundation set up in the cross-sea bridge construction, successfully applied in Greece Rio-Antirion bridge. Association the Science and technology program of Ministry of Communication Research on large bridge foundation type and design methods suitable for water depths greater than 50m deep water foundation, with the engineering background of Qiongzhou strait Bridge, based on the indoor model test and Flac3D as an auxiliary, the vertical bearing capacity of composite foundation was studied. The main work and conclusions are as follows:1. The indoor model test for the foundation has been carried out aiming at studying the soil pressure distribution, the stress mechanism of piles, the displacement model of the foundation, the dynamic change of pile-soil load sharing ratio or ratio of pile-soil stress in the loading process.2. Under the vertical loads, the soil pressure distribution along the longitudinal or the transverse presents approximately convex function curve:bigger in the middle, smaller on the edge, which remains in the whole loading process.3. The foundation has negative side friction appearring at the top of piles, which results in the effect that the maximum axial force is no longer at the top of the pile and the specific location is influenced by cushion thickness. In fact, the thicker the cushion, the lower this location.4. The settlement curve declines gradually, then the ultimate bearing capacity determined by the settlement limits. Cushion thickness is positively correlated with the settlement, in contrast, the ultimate bearing capacity is negative.5. Using the theory of rigid pile composite foundation calculate the settlement of the indoor model test, and the results are in good agreement with the experimental data. In addition, verifying the feasibility of the Qiongzhou Strait Bridge design using the same theory, and the result shows that it has been met the safety and suitability requirements.6. Flac3D is used to simulate the indoor load test, focusing on the effects of cushion thichness on the foundation settlement and carrying capacity.