Study On The Effect Of Non-rock Site On Seismic Behavior Of Safety-related Nuclear Structure

It is scare for the bed rock site which is better for the nuclear power plant construction,The non-rock site have to kept in reserve,for the rapidly development of nuclear power plant,Earthquake is one of the major external threats which could influence the safe operation of nuclear power plants,the study always focus on the seismic ability of nuclear power plants.Compared with the bed rock site,there have many unknown in the seismic response of safety-related nuclear structure on non-rock site account for more uncertainties.Therefore,studies on the dynamic response and evaluation seismic safety are critical issues for the safety-related nuclear structure on non-rock site.The input motions for use in the seismic design,seismic response behaviors of safety-related nuclear structure on non-rock site,the effect of the soil dynamic properties,embedment effect,lateral backfill soil dynamic effect,separating soil and structure at the upper layers,have been investigated,The replacement treatment for the soil layers not satisfying the foundation design requirements are studied,in order to systematically solve the critical issues and technique problems of the safety-related nuclear structure,some conclusions with scientific and engineering practical value are obtained.The research contents and achievement of this paper are as following:(1)The latest seismic analysis standards and guides for the safety-related nuclear structure are introduced,,and the input motion location for the soil-structure interaction analysis are confirmed,the seismic response of safety-related nuclear structure on non-rock site are compared with on the bed rock site,and the seismic response behaviors and rules are revealed,Seismic analysis are performed for three components,it is concluded the two horizontal components of input motion have significant effect on the vertical seismic response of structure.The seismic response behaviors of safety-related nuclear structure on non-rock site have more sensitivity to the soil dynamic properties and soil layer construction.(2)The influences of different shear wave velocities and soil layer thickness on the seismic response behaviors of safety-related nuclear structure are discussed.The sensitivity results show with the increasing of shear wave velocities,the foundation rigidity and the soil –structure system rigidity are also increasing,the frequency corresponding to the peak of the acceleration spectrum shifts toward higher frequency;for the same shear wave velocity,with the increasing of soil layer thickness,the frequency corresponding to the peak of the acceleration spectrum shifts toward lower frequency,the soil –structure system rigidity are decreasing.Soil layer thickness exhibit amplifications in the peak of the acceleration spectrum and zero-period acceleration,but when the soil layer thickness exceeds a certain critical value,the peak of the acceleration spectrum begin to decrease with the increasing of soil layer thickness,only the soft soil with more depth can exhibit seismic isolation effect in the high-frequency range.(3)The input motions of the embedded structure are analyzed.The effects of embedment soil layers,different depth and separating upper soil from building on seismic response of safety-related nuclear structure are studied,which are compared with the results of the surface structure.The structure model with lateral backfill is established and validated,the effect of different lateral backfill on structural seismic response behaviors is evaluated,the following is presented,the energy transfer and dynamic interaction exist in the upper structure,the soil layers below the foundation and the surround embedded soil,which compose a coupled soil-structural system.The seismic response behaviors of safety-related nuclear structure depend on the system damping ratio and the system rigidity.The suggestion is proposed that when a structure is analyzed as a deeply embedded structure,separating upper soil from building should be considered.The backfill dynamic effects impacts severely on the seismic SSI responses,depending on the backfill soil properties and sizes(4)The foundation input response spectra from two methods are compared,the reason of the non-rock site amplifications on the foundation input response spectra and floor response spectra are analyzed.The numerical models for replacement treatment soil layers is established and plain concrete replacement is verified as the rock in the soil-structure interaction analysis,the seismic response analysis of safety-related nuclear structure with graded sand gravel foundation conditions and plain concrete is carried out.It is concluded that the graded sand gravel foundation is feasible and reliable.The size of replacement soil has little effect on the seismic response of structure.