Study On Seismic Response Laws And Seismic Design Methods Of Underground Structures

Along with increasingly expanding construction of urban rail transit system, especially subway system, urban rail transit system safety has become a priority. To ensure the safety of subway system in a very long operation cycle, good seismic performance is necessary. For seismic problems of underground structures, model testing and numerical caculation are two essential means; a reasonable and simple seismic design method is the purpose; and nonlinear dynamic constitutive model of soil surrounding underground structures is the difficulty. In this paper, thorough study on seismic response laws and seismic design methods of Underground Structures was carried out, and the following findings were made:1. constitutive model of soilAccording to Hardin Curve of soil’s dynamic stress-strain relationship and Pyke’s Revise for irregular cyclic loading, combined with boundary theory proposed by Dafilias and Popov, a boundary surface constitutive model of soil based on Hardin Curve was constructed, while this constitutive model was implemented by customizing the secondary development of materials in Finite Element Method software ADINA.2. 2-Dimensional finite element dynamic analysisNonlinear dynamic finite element analysis on seismic responses of saturated sand site was executed by Opensees, and soil property, amplitude, duration, frequency of earthquake were changed to analyze the influences of these factors; then dynamic numerical simulation was carried out to calculate the seismic responses of box tunnel with mid column in saturated sand when seismic waves of different amplitudes were input, and afterwards acceleration responses and spectral properties of ground and structures, permanent deformation of ground, aftershock displacement of tunnel, the internal force distribution of tunnel were analyzed, while seismic response laws and damage mechanism of underground structures in liquefiable soil layer were revealed.3. Shaking table test on seismic responses of underground structure in saturated sandShaking table test on seismic responses of underground structure in saturated sand was carried out; then the test results were analyzed in aspects of pore pressure, soil layer acceleration & spectrum, undergroud structure acceleration & spectrum, dynamic soil pressure and underground structure strain, while seismic response laws of saturated sand site and the underground structure buried in were studied.4. 3-Dimensional finite element dynamic analysisThe 3-D finite element model of box tunnel across the interface between saturated sand and clay was established in Opensees and dynamic numerical caculation was carried out; seismic responses of layer and tunnel at both sides of interface were contrasted, while the distributions of ground surface vertical displacement, tunnel deformation and internal forces longitudinally along the tunnel were also analyzed; different effects of saturated sand and clay on tunnel were revealed; seismic response laws and damage mechanism of tunnel across the interface between saturated sand and clay were probed, which made significant sense to seismic research of this kind of tunnel in practical engineering.5. Cross-section seismic design methods of underground structuresPrinciples and details of response displacement method were exhaustively introduced, and the results of several valuation methods for ground spring were compared in accuracy, taking the result of dynamic calculation as a reference; nonlinear revise of valuation methods for ground spring under severe earthquake was proposed based on response displacement method, and the results were verified; furthermore simple pushover analysis method based on response displacement method was proposed, and the results were verified.6. Longitudinal seismic design methods of subway tunnelSeveral common longitudinal seismic design methods of subway tunnel were introduced, such as BART method, mass-spring model method and response displacement method; then with p-y curve spring of pile-soil interaction introduced into longitudinal seismic design methods of subway tunnel, the p-y curve spring model of long tunnel-soil interaction was established, and a longitudinal elastoplastic design method of tunnel was proposed by Pushover analysis of this model; finally according to dynamic numerical calculation of the long tunnel-soil interaction p-y curve spring model in multi-point excitation, several laws of internal forces and deformation longitudinally along the tunnel were obtained.