Study On The Propagation Characteristics Of Body Waves In Heterogeneous Unsaturated Soils

The geotechnical medium fluctuation problem is a key scientific problem to solve various geotechnical seismic hazards and has been widely concerned by the mechanics and engineering communities.Geotechnical medium is the most widely existed engineering material in nature,and it is a typical porous multiphase medium.Studying the wave problem of geotechnical medium is not only the improvement and development of the wave theory of geotechnical medium,but also the application value of practical engineering.Most of the previous researches on the fluctuation of rock and soil media simply regard the soil mass as single-phase elastic medium and two-phase saturated soil medium,while the soil mass in nature is generally a porous multiphase medium composed of three-phase media(solid,liquid and gas phases).The researches and tests of some scholars have shown that the wave propagation characteristics are affected by the presence of trace bubbles in the soil mass.The propagation characteristics of elastic waves in unsaturated soils are obviously different from those in single-phase and twophase saturated soils.In addition,most of the researches on wave wave are based on the assumption that soil is isotropic and uniform,while the actual soil layer is usually non-uniform.So far,there are few researches on the propagation characteristics of body wave in non-uniform unsaturated soil based on the theory of porous media,considering that non-uniformity is a major feature of soil formation.Therefore,it is of practical significance to study the propagation characteristics of body waves in heterogeneous unsaturated soil.In this paper,based on the theory of wave propagation in unsaturated porous media,the fluctuation equation of unsaturated soil is obtained,and the dispersion equation of the body wave fluctuation problem in non-uniform unsaturated soil is established based on the Helmholtz vector decomposition principle,considering the non-uniformity of non-saturated soil media,while the parameters such as dynamic shear modulus are considered to be modified with the change of saturation and the gradient non-uniform unsaturated soil foundation,layered The influence law of body wave propagation characteristics in non-homogeneous unsaturated land and layered unsaturated land is systematically studied.The main work of this paper has the following aspects:(1)To study the propagation characteristics of body waves in homogeneous unsaturated ground.Based on the theory of porous media mixture,the fluctuation control equation of three-phase unsaturated soil is obtained.Based on the Helmholtz vector decomposition principle,the dispersion characteristic equation of the body wave in unsaturated soil is derived by rewriting the fluctuation equation and assuming the form of the solution of the fluctuation equation.By expanding the characteristic equations of P-wave and S-wave,three kinds of compressional waves and one kind of shear waves can be found in the unsaturated porous medium.Then the effects of saturation,frequency,and the intrinsic permeability coefficient on the wave velocity and attenuation coefficient of body waves in unsaturated soil are discussed by numerical simulation.The calculated results show that,with the exception of P1 and S wave velocities,the wave velocities and attenuation coefficients of the four body waves are clearly influenced by frequency,saturation,and intrinsic permeability coefficient.(2)The propagation characteristics of body waves in a gradient,non-uniform,unsaturated soil foundation are studied.According to the wave governing equation of unsaturated soil,considering the non-uniformity of unsaturated soil medium,considering the non-uniformity of non-saturated soil medium,and assuming that the physical and mechanical properties of the soil medium vary by power function along the depth direction,using the Return ray matrix method.The influence of the gradient factor,i.e.,soil non-uniformity,on the propagation characteristics of body waves in unsaturated soil is studied.The results show that the non-uniformity of unsaturated soil has a significant effect on the wave velocity and attenuation coefficient of body waves,and the greater the heterogeneity of soil,the greater the variation amplitude of the velocity and attenuation coefficient of body wave with each parameter.The effect of soil non-uniformity on wave velocity and attenuation coefficient decreases gradually with the increase in depth.(3)The propagation characteristics of body waves in a layered unsaturated soil foundation are studied.According to the governing equation of wave motion of unsaturated soil,the solution of wave motion problem in layered unsaturated soil foundation is solved by the transfer matrix method combined with boundary and interlayer continuity conditions.The influence of parameters such as the shear modulus of the surface layer,the saturation of the surface layer,the thickness of the surface soil,and the frequency on the propagation characteristics of body waves in unsaturated soil in a typical layered foundation with soft upper and hard lower layers is analyzed.The results show that the variation of each parameter of the surface soil has a large effect on the P1,S-wave velocity,and attenuation coefficient.Except for the saturation and frequency of the surface layer,all other parameters have no effect on P2 and P3 waves.The larger the difference of shear modulus between upper and lower soil layers,the larger the variation amplitude of body wave velocity and attenuation coefficient with each parameter.