Study On The Constitutive Relationship Of Soil In Ground Fissure Site Under Seismic Load

As a non-seismogenic tectonic plane,ground fissures are produced by the internal structure of geological environment,combined with human activities and engineering construction.At present,on the basis of shaking table test of ground fissure site,a lot of research on dynamic response law of ground fissure site has been carried out,but in the process of dynamic numerical simulation analysis,because of the lack of systematic research on dynamic constitutive relationship,most of them are still static soil constitutive models.However,the static constitutive model can not reflect the dynamic characteristics of soil,which makes the analysis results unreliable.Therefore,it is of great practical value to study the dynamic constitutive law of ground fissure site soil.Taking Xi'an f₄ ground fissure site as the main research object,based on the similarity theory and using layered shear soil box,the dynamic response shaking table test of ground fissure site is carried out in this paper.According to the results of shaking table test and numerical simulation,the dynamic constitutive model of soil suitable for ground fissures is found,and several factors affecting the hanging wall and footwall effect and the numerical size of amplification effect on the ground fissure site are explored.Its main tasks are:Firstly,based on shaking table test of Xi'an f₄ ground fissure site,the filtering effect of ground fissure site soil on seismic wave is studied,and the effect of soil on filtering high frequency and retaining low frequency of input seismic wave is obtained.Through MATLAB software,the first natural frequencies of test models under different ground motion intensities are obtained,and the damping ratios of different layers of soils are calculated by half-broadband method.It shows that the first natural frequencies decrease and the damping ratios increase with the increase of ground motion intensity.According to the experimental data,the peak amplification coefficient of seismic wave acceleration of each measuring point is greater than 1 when the height change along the soil is obtained,and the closer the surface amplification coefficient is.Secondly,the FORTRAN language subroutine of equivalent linearization model and boundary surface model is written by means of programming software Microsoft Visual Studio2012 and Inter Visual Fortran2013 which can be associated with ABAQUS.The constitutive model of soil and its own soil constitutive model in ABAQUS are analyzed numerically,and compared with the experimental results,the boundary surface model is determined as the dynamic constitutive model of ground fracture site soil.Finally,using the definite boundary surface model,the ground fissure site model and the common site model with different soil layers are established.The numerical simulation is carried out by ABAQUS finite element analysis software,and the main factors affecting the floor and floor effect and amplification effect of the ground fissure site are found.The influence range of the floor and floor effect is obtained,with the hanging wall being 11.0 m and the footwall being 9.0 m.