Study On Dynamic Characteristics Of Saturated Sand Under Complex Stress Condition

The action forms of deep and shallow earthquakes on soil layer are different.It is generally considered that deep source seismic waves have only horizontal dynamic shear effect on soil layer,and shallow seismic waves have the coupling dynamic effect of vertical and horizontal shear.Therefore,when analyzing the dynamic effect of seismic wave on soil,it is necessary to study the two dynamic forms respectively.Before bearing seismic load,the actual foundation is usually in the complex initial stress state with different triaxial principal stress,and the dynamic characteristics of soil are significantly different because of the different initial stress state.It is particularly important to simulate the three-way unequal state and explore the influence of the initial consolidation parameters on the dynamic characteristics of soil.In this paper,a series of dynamic tests for saturated Fujian standard sand were carried out by using hollow cylinder torsional shear instrument to simulate deep source earthquake with cyclic torsional shear dynamic load and shallow source earthquake by axial torsional coupled dynamic load.The main research contents and results are as follows:(1)First,the effects of initial principal stress coefficient,initial deflection stress and initial average consolidation stress on dynamic shear modulus and damping ratio of saturated sand were studied by cyclic torsional shear tests with small stress amplitude to simulate shear wave of deep source earthquake.(2)Secondly,the cyclic torsional shear tests with large stress amplitude were carried out to simulate the shear wave of deep source earthquake,and the influences of the initial consolidation parameters on the cumulative deformation and pore pressure development of saturated sand were studied.At the same time,the development model of comprehensive cumulative strain with vibration frequency was established,and the relationship between pore pressure and comprehensive cumulative strain was derived by combining the single exponential relationship between pore pressure and vibration number.(3)Finally,the coupling dynamic test of large stress amplitude was carried out to simulate shallow seismic waves,and the effects of coupling phase difference of axial dynamic stress and horizontal dynamic shear stress on dynamic deformation,dynamic pore pressure and liquefaction resistance of saturated sand were obtained.The attenuation model of dynamic modulus of saturated sand with vibration times was established,and the dynamic shear expansion characteristics of saturated sand under deep and shallow earthquakes were compared.