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

This thesis is based on the project of appropriate structural and design method of super large bridge foundation in deep water with depth greater than 50 m. The foundation type of caisson-cushion-pile deepwater composite foundation is studied, taking QiongZhou strait bridge as the engineering background. In combination with model test, theoretical analysis and calculation of the case, the bearing performance of the new type of foundation form is investigated.At present, the caisson-bedding - pile is only used for industrial and civil buildings, not applied to the domestic bridge deep water foundation engineering. The test and numerical simulation research mainly focuses on the vertical bearing capacity and settlement calculation. The study of the long-span Bridges under heavy level of horizontal load is rare, The common horizontal bearing theory analysis and calculation method of piles is only applied to the active piles with caps. It’s not applied to the pile composite foundation any more. The new theory and method of calculation need to be put forward.The Model tests of composite foundation of pile-cushion-caisson were conducted, in the test, firstly, a caisson made by steel plate was used, and grand soil、gravel cushion, steel pipe piles were replaced respectively by medium sand、breccia and steel pipes. Press cell, strain gauges and displacement meter were selected as observing tools. Then jacks provided vertical and lateral force, observation instruments recorded the vertical and lateral capacity of composite foundation. After that, the affection of thickness of cushion、pile distance and vertical press on the foundation were studied. At last, the failure forms of the foundation and their prevention methods were put forward.The theory calculation methods of single pile were summarized, deduced based on Cerruti solution as well as the generation load method such as pile lateral passive load calculation method,based on p-y curve method of the main response of piles and soil under the function of passive loading method, using numerical calculation method, the pile body internal force contrast model test results, verify the validity of the numerical calculation method; Based on the level of pile composite foundation bearing capacity of pile soil stress ratio calculation method; In addition, put forward the caisson simplified model-pad-pile composite foundation and the corresponding calculation method, realize the horizontal bearing capacity of the new basic theoretical calculation, using the calculation method for the calculation of a set of model test, the theoretical calculation results are in good agreement with those obtained with the test results, the calculation method can be applied to engineering practice.By using the above new methods to analyze conceptual design schemes of QiongZhou strait bridge, the results showed that the value of lateral capacity of foundation were larger than standard one, which proves that the above composite foundation system and design parameters can well satisfied practice requires.