Study On Simplified Artificial Boundary And The Influence Of Gravity In Seismic Analysis Of Underground Structures

According to the current seismic intensity zoning map of China,many underground structures are constructed in high-intensity seismic regions,especially urban rail transit underground structures,pipe corridors,tunnels,and underground shopping malls.Due to the functional limitations of these underground structures and the lagging nature of urban activity surveys,more and more underground structures cannot effectively avoid or stay away from seismic regions.The seismic problem of underground structures has become increasingly prominent.Therefore,the study of underground structures under earthquake has become one of the hot topics.Numerical analysis is used as the main research method.Firstly,the problem of selecting soil damping in nonlinear calculation is studied.Secondly,a simple lateral boundary treatment method is proposed in seismic calculation of underground structures,and it is also related to the viscoelastic boundary.Accuracy verification was performed to verify the influence of the soil damping ratio,structure scale,and seismic wave characteristics on the value of the lateral horizontal calculation scale.Finally,a reasonable case of gravity application in the seismic analysis of the underground structure was obtained through typical case analysis,verification and the influence of gravity on the seismic analysis of underground structures.The specific research content are as follows:(1)Firstly,the nonlinearity of soil is introduced from the three aspects of the basic characteristics of the dynamic stress-dynamic strain relation of soil and the dynamic stress-dynamic strain of the combined element.Secondly,the nonlinear dynamic constitutive theory of one-dimensional soil is introduced.On the basis of this,the nonlinear dynamic constitutive model of 2D and 3D soils is extended.Finally,the problem of soil damping selection in nonlinear seismic calculation is presented,and the correct use method of soil damping ratio curve is proposed.The method is verified by typical cases.(2)Introduces the theory of viscous boundary,viscoelastic boundary and free field boundary that are commonly used in dynamic calculations.Based on the above dynamic boundary theory,a simple lateral boundary treatment method is proposed,namely,the roller boundary and viscoelastic boundary.Comparing the accuracy,the influence of the damping ratio,the structure dimension and the seismic wave characteristics of the soil on the value of the lateral boundary width was verified by examples of different soil layers and different boundary widths.Finally,the design value of the lateral width of the project was given.(3)Firstly,the influence of gravity on soil properties and the influence of gravity on seismic response are analyzed theoretically.The existing initial stress treatment methods are introduced.Finally,the most reasonable gravity application during seismic analysis is obtained through comparison of different working conditions.On the basis of the above research,linear and nonlinear conditions are calculated by selecting different sites and ground motion peaks.Through the analysis of the calculation results,the influence of gravity on seismic calculations in the process of linear and nonlinear seismic calculation is discussed.Finally,the full text is summarized,and the direction of further work is briefly discussed.