Underground Structures In Liquafiable Ground: Seismic Response And Numerical Analysis Method

The seismic response of underground structures in liquefiable ground is an important and challenging topic in the field of geotechnical earthquake engineering.However,the existing research on underground structures in liquefiable ground have mostly been conducted in assumed homogeneous soil profiles,without efficiently modelling of non-linear dynamic properties of reinforced concrete components,and the seismic response and failure mechanism of underground structures in different types of liquefiable ground remain unrevealed.In this research,a new combined structure element modelling technique was presented,based on which a 2D and 3D dynamic finite element analysis method for underground structures in liquefiable ground was developed.The seismic response and failure mechanism of underground structures in different types of liquefiable ground were revealed,and their three-dimensional effects were analyzed.In addition,an anti-seismic-floating checking method and an evaluation method for anti-floating measures were developed.The main achievements are concluded as follows:1.A new combined structure element modelling method of high efficiengy was formulated for modelling of non-linear dynamic properties of reinforced concrete components.It was validated by simulating monotonic and cyclic loading tests,as well as dynamic centrifugal model tests.The dynamic finite element analysis method for underground structures in liquefiable ground was then developed.2.The seismic response and failure mechanism in the cross-section of underground structures situated in liquefiable ground were revealed based on a series of 2D dynamic analyses,and the distribution of inertial force in underground structures was found to be important for the seismic response of underground structures in liquefiable ground.With liquefiable soil around the bottom part of the underground structure,the uplift failure could be induced more easily.With liquefiable interlayer passing through the structure sidewall,the shear failure would be more prone to occur in the cross section.3.The three-dimensional effects of seismic responses and failures of underground structures in spacial non-homogeneous liquefiable ground were investigated based on a series of 3D dynamic analyses,and the condition for simplifying to 2D analysis was preliminarily defined.With homogeneous liquefiable soil in the long direction of the underground structure line,the uplift failure or the shear failure could occur more easily in the cross section.With limited liquefiable zone around the underground structure in the line direction,the shear failure could be more prone to induce between the cross sections near the interface of two different soil layers.When the length of liquefiable zone in the long direction of the underground structure is longer than 4 times of the span length,it can be simplified as a two-dimensional analysis to reflect shearing action in the middle section.4.Both vertical and horizontal dynamic behaviours of underground structures in liquefiable ground were examined.Related closely to the relative spatial distribution of liquefiable soil and underground structures,four different types of failures were proposed,including the three shear failures in cross section and between the cross sections(vertical and horizontal)as well as the uplift failure.Several main factors governing the seismic responses of underground structures in liquefiable ground were investigated comprehensively and comparatively,including the position,thickness and inclination of liquefiable ground,the water level,the density of the structure,the multidirectional shaking and the seismic intensity.5.A practical calculation and evaluation method for the anti-seismic-floating checking of underground structure in liquefiable soil layer is proposed,and its rationality is preliminarily verified.Based on the analysis of structural displacement,deformation and internal force,the anti-floating effect from underground continuous wall,backfill to gravel drainage method is reduced successively.