Analysis Of Ground Seismic Characteristics And Pile Foundation Dynamic Response In Permafrost Site In The Cold Region Of The Northwest

There is much permafrost in the northwestern part of China,and with the development of the northwest economy,implementation of the Belt and Road policy,the transportation infrastructure is gradually strengthening.Because the mechanical properties of frozen soil change with temperature and are extremely unstable,pile foundations are often used in transportation infrastructure,which has good stability.The northwestern region is also a region with frequent earthquakes.Therefore,for the safety and durability of the transportation infrastructure,it is of great practical significance to conduct seismic analysis of the permafrost field and pile foundation system in the permafrost environment.It also provides a reference for the seismic design of the cold regions in the northwest.In order to analyze the seismic response of the permafrost field and pile foundation system in the cold area,the dynamic characteristics of the frozen soil should be studied first.Therefore,the dynamic triaxial test was carried out on the frozen silty clay,analysis the dynamic stress strain,dynamic elastic modulus and damping ratio of frozen soil,it is concluded that the dynamic stress-strain curve conforms to the Hardin-Drnevich hyperbolic model;the dynamic elastic modulus decreases with increasing temperature,the influence of confining pressure on the dynamic elastic modulus depends on the temperature,the dynamic elastic modulus decreases first and then increases as the water content increases;damping ratio increases with increasing temperature.Secondly,establishing a finite element model for frozen soil sites and non-frozen soil sites,the seismic response of frozen soil sites and non-frozen soil sites is compared to analyze the impact of frozen soil changes on seismic response.it is concluded that frozen soil will have a certain inhibition on seismic response under seismic P wave.Under the seismic S wave,the lateral acceleration of the frozen soil site is larger than that of the unfrozen soil,the lateral displacement is larger than that of the unfrozen soil in the early stage of the earthquake,when the seismic load is large,the unfrozen soil field has large cumulative deformation due to its small intensity.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.