| In recent years,as the scale of power cooling towers continues to increase,traditional flexible pile foundation treatment solutions,such as gravel piles,are no longer able to meet the engineering needs of large and super large cooling towers.More and more projects are using rigid pile composite foundation treatment schemes.The stability of the rigid pile composite foundation under seismic action is the key to ensuring the safe operation of the cooling tower,but there is currently no clear standard to regulate and guide its anti-liquefaction measures.Therefore,it is necessary to explore the mechanical properties of the rigid pile composite foundation and its influence on the stability of the cooling tower,and to provide scientific basis and technical guidance for the design and construction of cooling towers.This thesis takes the loess in the Huangfan area of Shandong as the research object,and obtains the basic physical parameters through conventional geotechnical tests and static triaxial tests.The liquefaction resistance characteristics of saturated loess in the Huangfan area under cyclic loading are analyzed through dynamic triaxial tests.The UBC3D-PLM model is used to simulate and verify the classic LEAP-UCD-2017 centrifuge test and the dynamic centrifuge model test of single pile foundation in liquefiable ground.Based on the results of triaxial tests,the model parameters of loess and sand in the Huangfan area are fitted.The seismic response of two different liquefaction sites is analyzed and compared using the Plaxis3 D finite element numerical software,which has important significance for guiding anti-seismic protection measures and coping with earthquake disasters in the Huangfan area,and provides a quantitative analysis basis for practical engineering.The main research content of this thesis includes:(1)The physical and mechanical characteristics of loess and sand in the Huangfan area are tested through conventional geotechnical tests and static triaxial tests,and the basic physical parameters are obtained.The dynamic characteristics of loess in the Huangfan area are summarized by dynamic triaxial tests,and a dynamic database is constructed for validation.The test results show that the strain accumulation rate of soil samples increases with the increase of dynamic stress amplitude;the development rate of pore water pressure increases with the increase of dynamic stress amplitude and decreases with the increase of dry density;confining pressure,deviator stress,initial dry density,and initial relative density can significantly improve the dynamic strength of the soil.(2)The UBC3D-PLM model is used to simulate and verify the dynamic centrifuge test and single pile foundation test in liquefiable ground,and the model’s ability to simulate dynamic centrifuge tests and single pile foundation tests is verified.The dynamic constitutive model parameters applicable to loess and sand in the Huangfan area are obtained by fitting the results of triaxial tests using finite element software.(3)Based on finite element numerical simulation software,the dynamic response of rigid pile composite foundation and different protective pile types under earthquake load in actual engineering is simulated,and the anti-liquefaction characteristics under different liquefaction layers and protective pile schemes are explored.The calculation results show that sand in the Huangfan area is more prone to liquefaction under seismic load than loess,and the outer protective pile can constrain the liquefaction range of the surface liquefiable soil,improve the anti-liquefaction ability of the soil in the pile foundation reinforcement zone,and reduce the surface settlement of the foundation to a certain extent.In addition,protective piles have a certain marginal effect,and the long-short pile type is the most beneficial type in all calculation conditions. |
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