Analysis Of Pile Foundation Dynamic Response Under Earthquake Load In The High-frozen Area

In recent years,with the promotion of national policies on the Belt and Road Initiative,a large amount of infrastructure has begun to be constructed in the northwestern region.Due to the severe cold climate in the northwest,there is a vast area of permafrost,and railway and highway projects need to pass through a long section of high frozen frozen soil.Taking into account the frost heave and thaw settlement of the building roadbed as a result of climate change and engineering thermal disturbance,the traffic foundation Most of the facilities adopt the engineering structure of "bridges instead of roads".At the same time,the northwest region is also an earthquake-prone area.Therefore,for the safety and durability of the traffic foundation,the seismic response analysis of the pile foundation in the high-frozen soil area is of great practical significance,and it also provides a certain degree for the seismic design of the northwest cold region.Reference.To analyze the seismic response of the pile foundation system in the high-content frozen soil area,the dynamic characteristics of the high-content frozen soil should be studied first.Therefore,indoor dynamic triaxial tests were carried out on three types of frozen silty subclays with ice content of 30%,50%,and 75%.The dynamic stress-strain relationship and dynamic elastic modulus of frozen soil were analyzed,and the dynamic stress-strain curve conformed to Hardin-In the Drnevich hyperbolic model,the dynamic elastic modulus decreases with increasing temperature.The influence of confining pressure on the dynamic elastic modulus depends on temperature.For frozen soil with high ice content,the dynamic elastic modulus first decreases with the increase of water content.Increase,that is,there is a worst water content,and its dynamic elastic modulus will be the smallest.With the increase of dynamic load frequency,the dynamic elastic modulus of frozen soil gradually increases,and the dynamic elastic modulus of high temperature frozen soil is less affected by frequency,and high temperature frozen soil has a vibration reduction effect.Establish a finite element model of the frozen soil-pile-cap system to analyze the seismic responses of single-pile foundations and single-row double-pile foundations under different frozen soil sites,and study the changes of different frost heave rates,different frozen soil depths,and different The influence of pile layout on seismic response.It is concluded that under the vertical seismic wave load,the vertical displacement of the platform under the high frost heave rate frozen soil site is greater,the vertical acceleration of the platform is greater,and the maximum vertical stress of the pile body is distributed in the frozen soil layer;The depth of the frozen soil layer will cause the vertical displacement and acceleration of the platform to increase.Under transverse seismic wave load,the lateral displacement of the platform under different frost heave rates is not much different,and the lateral acceleration of the platform under high frost heave rate is smaller,indicating that the environment of high frost heave and frozen soil is more conducive to the lateral pile foundation.Seismic stability: The greater the depth of frozen soil,the smaller the response of lateral seismic acceleration of the cap,which is more favorable for earthquake resistance.The maximum contact force between pile and soil will change with the increase of frozen depth.The displacement and acceleration of the single-row double-piles under vertical and lateral seismic loads are smaller than those of the single-pile system,indicating that the double-pile foundation is more conducive to earthquake resistance than the single-pile.Finally,the seismic response analysis of the frozen soil-pile-cap system is carried out to analyze the stress,displacement and relative displacement of the pile foundation system under different temperatures of frozen soil environment.Under the seismic P wave,in the-6 °C frozen soil environment,although the pile foundation system will generate large stress,the vertical displacement of the cap will be smaller,and from the displacement growth rate,the higher the temperature,the more the displacement growth rate fast.Therefore,for the seismic design of P wave,attention should be given to the temperature in the frozen soil environment above-1 °C.Under the seismic S wave,the stress and displacement of the pile foundation system differ greatly at different temperatures,pile and frozen soil will produce slip phenomenon at-1 °C,the cap will have a large lateral displacement at-6 °C.Therefore,for the seismic design of S waves,temperature factors should be considered.