Testing Study Of The Unsaturated Sandy Soil Dynamic Characteristic And Pile-soil-framed Structure Seismic Performance Research

In recent years, the occurrence of large earthquakes has brought detrimental impact on people’s life. With the development of the society, the damage caused by earthquake disaster will be more serious due to the high concentration of social wealth and population. According to the situation after the earthquake, in order to mitigate and reduce the earthquake damage, more and more researchers and engineers engaged in the research of earthquake disaster have realized that it is necessary to design the superstructure and foundation as a whole. This thesis is mainly focused on the research of dynamic characteristics of soil under the seismic action, soil-structure interaction(soil-structure interaction, referred to as SSI) problem, and through a series of indoor dynamic cyclic shear tests the dynamic characteristic of soil was studied. Based on the available literature, the site effects of four types of sites were analyzed. On this basis, the finite element model was established for the rigid foundation, shallow foundation and the interaction of pile-soil-superstructure. By inputting four different kinds of ground motion in the lower left corner of the model, the dynamic response characteristics of the structure were obtained. Through a series of theoretical analysis and experimental study, this thesis has a deep understanding of the mechanical properties of soil mass and SSI problem. This thesis is divided into four chapters and the main contents of each chapter are as follows:(1)Current research and development about soil-structure dynamic interaction at home and abroad have been summari zed. The advantages and disadvantages of existing research results are reviewed, and the research ideas and methods of the problem are put forward.(2)Cyclic shear tests were carried out to study the influence of different moisture content and shear strain on the dynamic characteristics of unsaturated sandy soil. The influence rules were analyzed and summarized. Dynamic characteristic parameters of unsaturated sandy soil in the experimental site were obtained to lay the foundation for the subsequent finite element modeling analysis.(3)The site effects of four different types of sites were analyzed respectively, through inputing seismic waves at bedrock, the curve of peak acceleration along with the depth of soil layer and the characteristic of the three dimension curve for response spectrum with depth were analyzed. Meanwhile, the stress and strain curves of the finite element for unsaturated soil and saturated soil were analyzed.(4)According to the numerical simulation and experimental results of existing literature, the finite element model was established for the rigid foundation, shallow foundation and the interaction of pile-soil-superstructure by using Opensees finite element analysis software. Based on the comparative analysis, the seismic behavior of the pile-soil-superstructure interaction system was studied from the changes of the maximum horizontal displacement, layer displacement angle, the maximum bending moment and displacement along the pile body.