| In this paper, finite element analysis software Midas GTS and the finite difference software FLAC3 D are used as a main platform, Midas and FLAC3 D are used to develop the numerical model of the interaction between soil-underground structure, and then the numerical model is embedded into FLAC3 D to analyze the seismic effects of the soil moisture content on dynamic seismic responses of underground structure and the effect of the groundwater level change on dynamic response of soil and underground structure. Finally, effect of different factors on dynamic seismic responses of underground structure in liquefiable soil is analyzed, and some conclusions are reached. The main research results can be summarized in the following:1. In the first part of this thesis, the effect of moisture content of soil on elasticity modulus, cohesion, internal friction angle and density of soil is summarized. Given compactness of soil, several mechanical parameters of soil will have “peak value” effect at the optimum moisture content. In this part simulation and analysis on dynamic responses of unsaturated soil under seismic excitations by using Flac3 D finite difference software are carried out, and the effect of moisture content on dynamic responses of underground structure under seismic excitations is investigated. Analysis results may be concluded as follows:(1)Properties of soil at the optimum water content are optimal for the seismic responses of underground structures, because in this case the internal forces achieve the minimum values;(2)The relative horizontal displacement of top and bottom slabs changed insignificantly, and the displacement gradually decreases with the increase of water content until the optimum water content is reached;(3)So do the maximum accelerations of soil and structure with the increase of water content.2. In the second part of this thesis, FLAC3 D software is used to model nonlinear soil-underground structure dynamic interaction by 2D finite element method. Mohr- Coulomb soil constitutive model is used to simulate the dynamic behavior of soils above the groundwater level, and the Finn constitutive model is used to simulate the development of pore water pressure in soil. Several cases of the interaction between soil-underground structure under seismic excitations are analyzed. The results of analysis show that:(1)With the increase of water level pore water pressure and pore pressure ratio increase, and the soil around the structure is easy to be liquefied.(2)Acceleration at top and bottom slaps and mid-pillar achieve maximum at the same time, and the change of the groundwater level has insignificant effect on acceleration at top and bottom slaps and mid-pillar.(3)The stresses at bottom slap’s corners are greater than that at the mid-pillar, and the principal stresses at bottom slap increase with the increase of groundwater level.3. In the third part of this thesis, three factors affecting the dynamic response of the underground structure: different forms of structural section, combined action of horizontal and vertical seismic waves and different inputting seismic wave form have been investigated. The results show that:(1)The stress distributions and the most adverse location of arch and rectangular cross section structure in the liquefiable soil under seismic action are addressed.(2) Models under transverse, longitudinal seismic actions, separately and jointly, are studied. It is shown that the amplitude of pore pressure ratio under the combined horizontal and vertical seismic action is greater.(3) Different seismic waves forms have little influence on the stress distributions of structure. But the acceleration of structure varies with different seismic waves remarkably.4. In the forth part, it summarizes the research results and points out the problems to be solved in the future and some ideas and methods for solving these problems are suggested by the author. |
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