Test Study On The Capacity Of Large Pile Under Bridge

On the basis of a lot of in-situ tests, indoor tests, numerical analysis and comparing analysis, a test method has been presented to ascertain the limit bearing capacity of a large-scale pile. A medium-sized shear test for the side of pile and a triaxial test for the tip of pile have been adopted respectively to accurately determine the friction resistance on the side and the bearing capacity on the tip of a pile. The stress distribution of large-scale drilled piles under bridge has been analyzed with numerical method and the result indicates that the joint element can be adopted to simulate accurately the interaction between soil and pile. The result from the method has been compared with results from the in-situ test, and its accuracy has been proved. (1) The requested bearing capacity of a large-scale pile foundation for highway bridge is so large that it is difficult to determine accurately its limit bearing capacity with tests or experimentations. The current methods of pile test such as static load test, dynamic test, dynamic-static compound method and Osterberg self-balance method, etc. are improbable to obtain an accurate result for the large-scale pile foundation under bridges. So a simulated test method is put forward to determine the bearing capacity of pile foundation according to the characteristic of pile foundation with a large bearing capacity for highway bridge. (2)The simulated test method for determining the limit bearing capacity of the large-scale piles is based on Mohr-Coulomb criterion. Modeling tests have been adopted to confirm the limit friction resistance and limit tip resistance and then confirm the limit bearing capacity of the piles combining with finite element method. In the modeling test, limit friction resistance is determined with medium-sized shear strength index of each stratum. Considering the factors such as stratum, piling craft and actual stress, the shear coefficient between soil and concrete can be confirmed. Limit tip resistance is obtained according to the compressive strength of the stratum around the tip of piles under the actual stress, which can be obtained with triaxial test, and then limit bearing capacity of the tip is determined. The influence of slurry and the comparability such as shape and size of the model and so on has been considered carefully during the process of design and production of the model. (3) The characteristic of stress distribution of drilling piles under the bridge has been analyzed with elastic-plastic finite element method. Considering the property of stratums around the pile, the process of stress and displacement in the pile and the soil surrounding the pile during the load are analyzed. The distribution of the stress and displacement in the pile and soil under the static load is obtained, which is important to analyze the transfer mechanism of stress between the pile and soil. It also indicates that the interaction between soil and pile can be simulated accurately with joint element when the finite element method is adopted. (4) The distribution of stress, shear strength and friction resistance between the pile and soil under the large bridges over the Song Hua River in Zhaoyuan and Long Hua have been provided with the simulated test method. Through comparing with the results from the in-situ tests, it has been proved that the limit bearing capacity of the pile obtained with the simulated test method is accurate and this method has a wide application prospects because it is fast, economic and unlimited by the field and so on.