Vibration Characteristics Of Group Piles In Freeze-thaw Foundations Under Vertical Loading

As a traditional form of artificial foundation,piled foundations are suitable for all kinds of complex geological conditions,and since the "One Belt,One Road" initiative,a large number of projects in cold regions have been implemented.Due to various conditions,the research on pile foundations in the frozen soil area is focused on the static load performance and creep analysis of piles,but the pile foundations are subject to constant load of the superstructure in the normal use process,and also subject to dynamic load brought about by the operation of vehicles,etc.The dynamic load effect will affect the mechanical characteristics of pile foundations in the frozen soil,so the research on the dynamic response characteristics of pile foundations in the freezing and thawing ground environment and the influencing factors is a subject of The study of the dynamic response of pile foundations in freeze-thaw ground environment and the influencing factors is therefore an important topic.In this paper,on the basis of the research on the dynamic response of pile foundations at home and abroad,the dynamic model test of group pile in saturated soil and frozen thawed ground is carried out and the calculation model is established by using finite element software.The research has important application value for the study of group pile dynamic problems in permafrost areas,and the specific research contents of this paper are as follows:(1)To address the problem of dynamic response of group piles in saturated soil under vertical load,this thesis carried out indoor model tests on group piles under vertical load,and analysed the dynamic characteristics of group piles-saturated soil-bearing platform under different parameters such as number of piles,length-to-diameter ratio,pile spacing ratio and bearing mass.(2)A dynamic interaction model test system for group pile-frozen-thawed soil-bearing platform was developed,and a model test rig for vertical vibration of high bearing platform monopile and group pile foundation on saturated foundation with freeze-thaw cycle was established to study the vertical vibration characteristics of high bearing platform monopile and group pile foundation in unfrozen soil,frozen soil,thawed soil and then frozen soil and thawed soil after reciprocal cycle.The important effects of different parameters such as freezing depth,freezing temperature,pile spacing ratio,pile diameter ratio and mass of the bearing platform on the amplitude-frequency curve of the group pile bearing are investigated comparatively by controlling for single factor variations.The discussion of the vibration amplitude-frequency curves of single piles and group piles shows that the resonant frequency of vertical vibration of group piles is much higher than that of single piles.In addition,the change of soil quality during the freezing and thawing process has an important influence on the evolution of group pile vibration characteristics.The group pile resonance frequency is low when unfrozen,and gradually increases with the increasing freezing depth during the freezing process,while the group pile resonance frequency gradually decreases when the foundation is thawed,and the group pile resonance frequency after complete thawing will be slightly higher than the unfrozen resonance frequency.(3)The finite element simulation of saturated frozen porous media and saturated unfrozen porous media was realized by using the method customized by the secondary development of finite element software,and the numerical calculation model of vertical vibration of high bearing platform group pile foundation in freeze-thaw double layer foundation was established.The model test results are in good agreement with the finite element calculation results,indicating the reasonableness of the method in this paper.