Study On Cyclic Settlement Of Pile-Supported Embankment Friction Pile In Silt Soil And Its Application In High-Speed Railway Design

As an important part of the national transportation industry,high-speed railway contributes a lot to the development of national economy.During the operation of high-speed railway,the moving load will strengthen the dynamic stress response of roadbed.In this case,pile-supported embankment pile will accumulate settlement under cyclic load.Because of the high standard of settlement control in high-speed railway engineering,it is important to calculate and control the settlement of high-speed railway foundation reasonably.The main work is as follows:(1)This paper introduces the load transfer mode of pile embankment,and then analyzes the pile-soil interaction under cyclic loading.The basic principle of load transfer method and the established load transfer model of pile shaft and pile tip is listed.Then the deformation and failure mechanism of pile foundation and the weakening model of pile-soil interface under cyclic load are discussed,which lays a foundation for the calculation of the cumulative settlement of pile under vertical cyclic load.After that,the cyclic vibration effect of pile foundation is briefly introduced.(2)The cyclic settlement data of the cyclic loading test of large-scale model pile is analysed.The cumulative settlement of pile will increase with the increase of the number of cycles.A higher Pcyc/Pu leads to faster accumulation in the pile settlement,and a higher Pm/Pu intensifies this process.The pile under cyclic loading can be divided into stable type,serviceable type and unstable type.After that,according to the bearing capacity and deformation characteristics of pile under cyclic loading,a chart with three zones determined by the combination of Pcyc/Pu and Pm/Pu is developed to describe the settlement development of the piles:stable zone,serviceable zone and unstable zone.In order to meet the long-term settlement control standard of high railway foundation,the settlement should be located in the stable zone.For the serviceable type,an analytical model considering soil modulus weakening under cyclic loading was developed and validated with the test results to assess the cumulative settlement of the pile under combined static and cyclic loads.Then,a set of calculation method for the user interface is designed by MATLAB GUI.On this basis,the calculation model is extended to clay and sand soil foundation,and its universality is verified through the selection of parameters in the model.(3)Based on the analysis and calculation of cyclic settlement,the key problems of pile-supported embankment design under cyclic loading are summarized.Therefore,a set of design methods of pile-supported embankment under cyclic loading is summarized.A case study is presented by unitizing the proposed method to design piles to support the embankment of high-speed railways.When the settlement of pile is located in the stable zone and close to the serviceable zone,the bearing capacity of foundation can be maximized and the construction cost can be saved while the stability is guaranteed.Otherwise,the original design needs to be optimized.