| Jointless bridge not only have advanced comfortable driving performance,but also have a lower expenditures on maintenance.With those advantages,it has been widely used in foreign countries for nearly half a century.China has joined the rank of researching on this type of jointless bridge in recent years.There are two mainly types of jointless bridge basically,including the semi-integral abutment jointless bridge(IAJB)and the integral abutment jointless bridge(SIAJB).Within them,,the integral and seismic performance of IAJB is inferior to that of SIAJB.Nevertheless,SIAJB possesses longer span and better performance on absorbing the deformation of main beam.Researchers found that micro pile in a row,supported under sleeper beam,can effectively improve the seismic performance of SIAJB.However,as a special pile shaft,the research history of micro pile on dynamic response is very short at home and abroad,and deficiency research can't reflect the influence of pile and soil-related parameters on micro pile-soil interaction.Therefore,in order to explore the earthquake resistant mechanism of SIAJB that sleeper beam is supported by micro pile,it's essential to master the size and the influence form soil-pile-related parameters and the mechanical method on micropile-soil dynamic interaction.To make a deep investigation on seismic performance of micro pile foundation,some shaking table tests on dynamic response of micropile foundation with different shapes and materials were carried out.The dynamic response features of micro-pile soil system as basic frequency,first order damping ratio,amplification factor of peak acceleration,strain time history reaction,shaft moment,deformation and soil resistance were investigated.And then extensive analysis on different shaft material,size,and type of soil surrounding pile also were done by using ABAQUS software.The specific works done in this paper are as followings:(1)By taking this type of micro-pile as the researching background,a series of shaking table tests on micro pile with different shaft shapes were designed and conducted.Through changing the amplitude of excitation,sinusoidal wave and type of seismic waves,as well as the shaft shape,the influence of above parameters on response of micro pile-soil dynamic interaction system with sand condition were studied to consider the basic frequency and damping ratio of system and acceleration peak amplification factor,etc.The results show that different shapes of cross section have little influence on the dynamic response of micro pile foundation,of which mainly depends on the effective width of pile.(2)Based on the shaking table test,a kind of dynamic p-y curve applicable for medium density sand was derived.The response of simplified FEM of micro piles of dynamic p-y curve was used and compared with the static p-y curve.The applicability of the static p-y curve under dynamic interaction of micro pile-soil was analyzed.The results show that traditional static p-y curve can't be applied to micro pile,but the dynamic one obtained from experiment is suitable.(3)On the basis of the experimental results,a parametric analysis was carried out by using ABAQUS.And the influence of above parameters on the dynamic response of the micro pile were studied.Its results show that pile shaft material has a significant influence on the dynamic response of micro pile,such as the peak moment and its embedded depth,the deformation and the reaction of the pile shaft,and those influence is mainly caused by the elastic modulus.The results also show that large pile diameter can lead to a significant bending moment at the bottom of micro pile.The bigger the pile diameter is,the weaker the dynamic deformation is.The smaller the diameter of the pile is,the faster the growth trend of the soil reaction in the upper soil.The main factors that affect the dynamic response of the micro pile foundation under the condition of sandy soil is the compressive modulus,while under the cohesive soil is the cohesive force. |
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