Study On Dynamical Characteristics Of The Railway Bridge Pile Foundation Under Static-dynamic Load

With the rapid development of economy and the improvement of people's life, the requirement for road and railway transportation is getting higher. As to railway transportation, building high speed railway has been put on the agenda. Most of the foundations of bridges on the newly-built railways are pile foundations, so more and more attention has been given to the dynamic characteristics of the pile foundation subjected to the high speed train load. However, railway dynamic load is remarkably different from dynamic load of the general machinery foundation and the earthquake load. there have been few studies on this topic at present, let alone the report about the field test of full size pile foundation under the traffic loads. Therefore, there is very important theoretical value and practical significance in engineering to make a study of dynamic characteristics of the pile foundation subjected to the train load at a high speed. On the basis of dynamic test of existent railroad pier pile foundation and the static-dynamic load test of Beijing-Shanghai high speed railway pile foundation, combined research method of theoretical analysis, field test and numerical simulation having been applied, the following results and conclusions are obtained:1. A mathematical model about the pile-soil combined effect of finite length pile under exciting force in layered soil is established, in which the effect of soil on the tip and lateral surface has been considered. And by means of integral transformation, a semi-analytical solution of the velocity response of pile top in time domain is obtained. Corresponding MATLAB6.5 program has been written to analyze the influences of soil and pile material parameters on velocity response in frequency domain and time domain when the pile is subjected to semi-sine exciting force and steady state load respectively.2. By making a study of the technique of field static-dynamic load test on pile foundation under big tonnage load, a set of new equipments and technique for the earth-pressure cell for precast piles and filling piles and the Re-bar stress meter for precast piles are brought forward. Extensive research has been carried on technique of field static-dynamicload test on pile foundation under big tonnage load, through which combined test equipments for pile foundation under big tonnage static-dynamic load on pile top have been produced, this solve a key problem in the static-dynamic load test of pile.3. The equivalent linear model is created to simulate soil material's nonlinear characteristic, in which the influence of pile material damping and the state nonlinearity on the soil-pile interface on dynamic response has been considered. By means of developing ANSYS, a general finite element analytic software, a three-dimension model considering the pile-soil combined effect is established. The dynamic characteristics of foundation piles under dynamic cyclic loading have been studied and the influence of soil material's parameters and dynamic load parameters on dynamic characteristics has been analyzed.4. According to the calculation principle of the first natural frequency of the cantilever bar, a dynamic model of bridge pier has been set up. Based on the practical situation of multiple piles foundation, the bridge pier, bearing platform and pile group is analyzed as a group. A multiple piles foundation's three-dimension matrix analytic program is written with the aforementioned model. Finally, the program is used to analyze the dynamic characteristics of pile foundation of bridge pier on Beijing-Shanghai high-speed railway Kunshan test section.5. The main dynamic characteristics of bridge pier pile foundation top, including the range of vibration amplitude, frequency value and the relation with train speed, are studied according to the dynamic test of bridge pier's pile foundation top on existent railways. Controls parameters of static-dynamic test of single pile were given under simulant high speed train load.6. The static-dynamic loading test of single pile was carried out under the simulant high speed train load on soft soil test section of Beijing-Shanghai high speed railway, and the test data of single pile under the high speed traffic loads (simulant high speed train load) were obtained for the first time. Based on the above test data and results, a lot of research has been made on lateral surface friction resistance and axial force of piles under static-dynamic load, the accumulated displacementon the top of the piles under cyclic loading, dynamic displacement's amplitude and the relations between the above items and the number of vibration, etc. The pile's dynamic characteristics and the mechanism of load transmission were analyzed extensively.7. The characteristics and the mechanism of load transmission of prestress concrete pipe pile under static load have been studied according to the test data. A three-dimension analytic model about pile-soil effect under static load has been established. Then the factors affecting load transmission mechanism of precast pipe pile have been analyzed when the soil nonlinearity and the state nonlinearity on the soil-pile interfaces have been considered.