Research On Seismic Damage Characteristics And Seismic Reinforcement Method Of Pile Foundation Pier Considering Seasonal Freeze-thaw Effect Of Soil

In order to explore the seismic behavior of pile-based piers considering seasonal freeze-thaw effect of soil mass and the influence of different parameters on the seismic behavior of pile-based piers under the influence of frozen soil,the quasi-static loading test of railway pile-based pier specimens in seasonal frozen soil area is carried out in this paper,based on the material test data of concrete and steel bars.The pier model of pile foundation in seasonal frozen soil area under the coupled action of thermal-mechanical sequence and the results of quasi-static test are compared and validated,and then an analysis model with different parameters is established to study the influence of different parameters on the seismic behavior of pile foundation pier under the influence of frozen soil.At the same time,thermal-mechanical sequential coupling method is used to analyze the seismic performance of pile foundation pier under different freeze-thaw cycles.According to the particularity of seasonal frozen soil area and the failure characteristics of test model,BFRP material is used to reinforce the pile foundation pier and the reinforcement effects of different reinforcement methods are compared and analyzed.The main research work is as follows:(1)Quasi-static test is carried out on the pier model of pile foundation in seasonal frozen soil area,and the seismic behavior of pile foundation pier in seasonal frozen soil area is analyzed from the aspects of test phenomena,hysteresis characteristics,energy dissipation capacity and rigidity degradation.With the increase of loading displacement,octagonal cracks appear in the soil mass on the north and south sides of the cap,two main cracks appear in the pier body and the pier bottom and penetrate.When loading to 55 mm,the pier is destroyed and micro-cracks appear on the pile.(2)A thermo-mechanical sequential coupled finite element model based on ABAQUS is proposed,which can effectively simulate the temperature field distribution of pile foundation pier in seasonal frozen soil area and the mechanical behavior of railway gravity pile foundation pier under horizontal repeated load,and then the changes of seismic performance of pile-soil-pier system affected by various parameters are analyzed and compared.The changes of thickness of frozen soil layer,melting depth of surface layer,axial compression ratio and shear-span ratio have significant effects on seismic behavior of pile-foundation pier in seasonal frozen soil area,while other parameters have relatively weak effects.(3)Pile-soil-pier finite element model under freeze-thaw cycle is established.The freezing depth of soil gradually increases with the number of freeze-thaw cycles,but its change is almost invisible after three times.At the same time,with the increase of the number of freeze-thaw cycles,the seismic performance of the pile-soil-pier system is decreasing continuously,and the seismic performance of the pile-soil-pier system after the first freeze-thaw cycle decreases the most.(4)Three different reinforcing methods of pile-foundation pier in seasonal frozen soil area are selected and their reinforcing effects on seismic performance of pile-foundation pier in seasonal frozen soil area are compared and analyzed.The seismic performance of pile-soil-pier system strengthened by different reinforcing methods will be increased to some extent.The overall anti-seismic performance will be improved to some extent after the reinforcement with fiber cloth.The improvement of embedded reinforcement on lateral deformation capacity is the most obvious,while the lateral ultimate load of composite reinforcement on pile-soil-pier system is the largest.