Dynamic Response Of High-piled Foundation In Layered Soil Under Cyclic Loading

As a common form of deep foundation,high-piled foundations are widely used in complex and difficult projects such as wharf in Marine environment,sea-crossing bridges,and viaducts of high-speed railway lines.The slenderness ratio of the pile body of the high-piled foundation is much larger than that of the rigid short pile,and it is easier to lose stability or produce large deformation under the action of dynamic load,which will lead to the destruction of the pile foundation and the superstructure of the pile foundation.Scour can reduce the strength and rigidity of the pile-soil system and become one of the major causes for the failure of the structure of the high-pile foundation.Due to geological deposition and other reasons,the soil layer has natural layered characteristics,and the physical properties of each layer of foundation soil are often different.Therefore,the stratification of the soil fields has a significant influence on the internal force and deformation of the laterally loaded piles.In engineering practice,pile foundation influenced by soil-structure interaction may have complex dynamic response under the lateral excitation of the pile top,so the lateral bearing capacity of pile foundation must meet the requirements of use.In recent years,many scholars at home and abroad have studied the mechanical properties of pile foundations under vertical loads,but there are relatively few studies on the lateral dynamic response of pile foundations under the action of reciprocating lateral loading.Therefore,it is significant to study the dynamic characteristics of laterally-loaded piles on the basis of considering the characteristics of pile foundation and site and the pile-soil interaction.In order to accurately reveal the effect of scouring on the dynamic response of the high-piled foundation in layered soil,a dynamic model of the laterally loaded high pile in layered soil is established employing Hamilton’s principle based on the modified Vlasov foundation model.Then,the finite difference method is used to obtain the numerical matrix containing the control equations of the high piles to achieve accurate modeling of the soil-structure interaction（SSI）system affected by scour,so as to solve the natural frequencies of the high piles affected by scour;Green’s function method obtains the analytical solution of the forced vibration of the pile foundation.Finally,the finite element software is used to carry out numerical comparison analysis of pile foundation under different working conditions,and the following conclusions are obtained:（1）The dynamic model of the partially-embedded laterally-loaded single pile in layered soil based on the modified Vlasov foundation model can accurately predict the impact of scouring on its dynamic characteristics.（2）As the scour degree intensifies,the first-order natural frequencies of the high pile in layered soil decrease significantly.The subgrade reaction coefficient of each layer of soil in the modified Vlasov foundation model decreases,and the shear coefficient increases.When the length of the non-embedded section of the pile satisfies l₁≥L/2（L is the pile length）,the response amplitudes of the pile top of the partially-embedded high-piled foundation in the layered soil are greater than 0.01m,that is,the single pile has presented lateral instability under dynamic load.（3）As the elastic modulus of the first layer of soil increases,the response amplitudes of the pile top decrease significantly,while the displacement amplitudes at the inverted point of the pile body increase,and the first-order natural frequencies of the pile increase.If the elastic modulus of the soil increases by about 0.5 times,1 time,and 2 times,the first-order natural frequencies of the high-piled foundation increase by about 10%,20%,and 30%,respectively.（4）The first-order frequency of the pile foundation decreases with the increase of the slenderness ratio of the pile,and the variation law of the higher-order frequencies is complex.At the same time,the displacement of the pile top has also increased significantly.In this paper,the effects of the layered soil on the dynamic response of the high pile are studied by numerical calculation and parameter analysis.In the study of the dynamic behavior of the high-pile foundation,we fully consider the site characteristics and the pile-soil interaction,which is of great significance for revealing the dynamic characteristics of the pile foundation.The research results will provide theoretical guidance for the dynamic design of laterally loaded high piles,and enrich the dynamic research content of high-piled foundations in layered soil.It has important theoretical significance and application value.