Study On Elastoplastic Method To Seismic Response Analysis Of Soft Soil Sites

Soft soil is widely distributed in China,but it is weak in mechanical properties.The study of soft soil seismic subsidence has been a difficulty in the field of soil dynamics for many years,but the traditional equivalent linearization method is not suitable for the seismic response analysis of soft soil.Meanwhile,no systematic and reliable theory or method of soft soil site seismic response analysis has appeared.Therefore,this paper studies the seismic response analysis method of soft soil site based on elastoplastic calculation.In order to discuss the elastoplastic method to seismic response analysis of soft soil sites completely in the paper,the advantages and disadvantages of the traditional equivalent linearization method are summarized,many soft soil geotechnical tests are carried out,and the elastoplastic constitutive model and mechanical characteristics are analyzed.Meanwhile,the elastoplastic seismic response analysis of soft soil site under multiple input ground motion amplitudes based on finite element method calculation is completed,while the elastoplastic seismic response analysis results and equivalent linear results of soft soil sites are compared and analyzed.The main contents and conclusions of the paper are as follows:1.A large number of geotechnical tests show that the soft soil in the sampling site is a sort of saturated organic mucky clay with strong structure,strong compressibility,low permeability and stable critical state line.2.The equivalent linearization method is not suitable for the calculation and analysis of soft soil site,though the method is simple and straightforward in principle,minor in calculation and is easy to obtain the parameters that it needs.3.The Transformation Stress-Cyclic Mobility(TS-CM)constitutive model is introduced and a complete set of parameters in TS-CM constitutive model is obtained.4.Simulations are accomplished using the TS-CM constitutive model,while comparative verifications are made between the simulation results and the mechanical test results.The results of comparative verifications show that the TS-CM constitutive model is suitable for the saturated organic mucky clay which is used in the research,and the effect of the simulation is ideal.Meanwhile,the parameters used in the constitutive model are accurate.5.The analysis show that the results obtained by the elastoplastic calculation method are more consistent with the cognition of soft soil site's seismic response,and are closer to the results of real site.Relatively reasonable solution can be obtained by the elastoplastic method even when the input amplitude of ground motion is large.When using the elastoplastic method,the effective stress,stiffness characteristics and deformation of any point in soil in real time can be reflected,and the final residual deformation can be obtained,but the equivalent linearization method can hardly dothese.It can be concluded that the elastoplastic method is more suitable for the seismic response analysis of soft soil site than the equivalent linearization method.