Shaking Table Test Study On Seismic Response Characteristics And Influencing Factors Of Pile Foundation In Saturated Sand

The smooth construction of Padma bridge railway connecting line project is of great significance.As an important project in the "the Belt and Road",the project has a positive impact on promoting the connectivity of the Pan-Asian region,enhancing China’s influence in the region,and promoting China’s construction to the world.Deep liquefiable sandy layer is widely distributed in the project area,and earthquakes occur frequently in this area.The existing research results show that the bridge pile foundation is seriously damaged during the earthquake,and sand liquefaction is an important influencing factor.At present,there are few studies on the seismic performance of pile foundations in deep saturated sand sites in the Ganges Delta,and the relevant engineering design and construction are lack of theoretical guidance and data support.In order to better serve Padma bridge and similar overseas projects in the later stage,relevant research topics are proposed for the seismic performance of pile foundation in deep saturated sand.The main research contents and results are as follows:1.Taking the pile foundation of a section of Padma bridge railway connecting line project in Bangladesh as the prototype,the shaking table model test is carried out to analyze the influence of seismic wave characteristics on the horizontal movement and bearing characteristics of pile foundation.The results show that with the increase of ground motion intensity,the acceleration amplification coefficient of soil changes from bottom-up increase gradually to "s" shape distribution;The horizontal motion of the structure moves from high frequency to low frequency,and the frequency band becomes wider;The amplification factor of horizontal motion of superstructure is reduced from 4.56 to 2.75,but this effect is not obvious on the bearing platform;The movement of bearing platform and superstructure has a great influence on each other;The pile top and the middle of the pile body(8D away from the soil surface)are the most unfavorable positions for earthquake resistance,which should be strengthened;the typical failure mode of pile foundation in deep saturated sand field is instability and settlement of pile foundation caused by sand vibration liquefaction.2.The finite element simulation calculation of shaking table model test is carried out based on OPENSEES with high calculation efficiency.Through comparison with the data obtained from the test,it shows that the numerical simulation calculation can well restore the seismic response of the site and structure,but the structural resonance will have a certain impact on the simulation results.It is suggested to select Imperial wave as the loading seismic wave for subsequent analysis.3.Based on the results of OPENSEES finite element simulation,tornado diagram method and first-order second moment method are used as the main analysis methods to analyze the seismic response sensitivity of ground motion intensity,material parameters and pile foundation structure.It is found that there is a linear or low nonlinear relationship between ground motion intensity,material parameters and seismic response;The intensity of ground motion is the controlling factor of the seismic response of pile foundation;The influence of density and internal friction angle of liquefiable sand on the seismic response of pile foundation is higher than that of other material parameters;Under the condition of this thesis,the pile diameter controls the horizontal displacement of the structure,and prolonging the pile length is more conducive to the bending resistance of the pile foundation;Raising the height of the pile cap will significantly increase the horizontal displacement of the pile cap and the bending moment of the pile foundation.