Analysis Of Dynamic Response Of Inhomogeneous Unsaturated Soil Under A Moving Load

As the high-speed railroad network is interwoven,the transportation is in the fast lane of high-quality development.The foundation vibration problem caused by the development of high-speed railroads and automobile traffic,etc.is attracting increasing attention from the society,so it is more theoretical value to study the dynamic response of foundation under the action of moving load.In the past,many important results have been achieved in the analysis of dynamic response of single-phase elastic foundation and saturated ground foundation,however,most of the soil is a complex medium composed of three phases,and most of the buildings in construction projects are carried on unsaturated soil.The current research on the dynamic response of foundations is mainly based on the assumption that the soil is isotropic and homogeneous,etc.However,due to the sedimentary effect of geology,most foundations are composed of layered foundations with different parameters and have layered non-homogeneous,and there is multiphase coupling under the action of moving loads,which makes the dynamic response analysis more complicated.Therefore,in this thesis,based on the theory of unsaturated porous media,a mathematical model of the problem under moving load is established and the dynamic response law of inhomogeneous unsaturated soil under moving load is studied.The main work is as follows:(1)Based on the research results of unsaturated porous media theory,the dynamic control equations of unsaturated soil are derived by considering the compressibility of soil particles,pore fluid and the viscous and inertial coupling effects between each phase.With the combination of coordinate transformation,Fourier transform and Helmholtz vector decomposition principle,the dynamic response solutions of unsaturated soil displacement,pore water pressure and pore air pressure in the frequency domain are obtained.The numerical solutions of displacement,stress and pore pressure in unsaturated soil were obtained by Fourier inversion.(2)The foundation model of unsaturated soil under moving load is established,and the dynamic response law of unsaturated ground foundation under moving load is studied.By numerical calculation,the influence law of load moving speed,saturation and other factors on the dynamic response of unsaturated ground foundation was analyzed.The results show that the vertical displacement of the ground surface increases with the increase of saturation degree and load moving speed;while the pore water pressure and pore air pressure increase first and then decrease along the depth direction.(3)The model of non-homogeneous unsaturated ground foundation under moving load was established.By considering that the physical and mechanical properties of the unsaturated ground foundation vary along the depth direction according to the power function,the gradient is introduced to characterize the non-homogeneous degree of the foundation,and the dynamic response of the non-homogeneous foundation under moving load is studied by using the reverberation ray matrix method(RRMM).The influence law of non-homogeneous degree of foundation and load moving speed on the dynamic response of non-homogeneous foundation is discussed and analyzed.The results show that the horizontal and vertical displacements of the ground surface decrease with the increase of the gradient factor,while the pore water pressure and pore air pressure increase and then decrease.The surface horizontal displacement,vertical displacement,pore water pressure and pore air pressure all increase with the increase of moving speed.(4)The computational model of two-dimensional layered unsaturated foundation is established to study the dynamic response of layered unsaturated foundation under the action of moving load.The stiffness matrix of the laminated unsaturated foundation is obtained by using the transfer matrix method with the boundary and interlayer continuity conditions,and the numerical solution of the layered unsaturated foundation in the frequency domain is solved.The effects of load movement velocity,shear modulus of topsoil and saturation on the dynamic response of two typical layered foundations,namely,upper-soft and lower-hard,and upper-hard and lower-soft,are investigated respectively.The results of the study show that: when the load movement velocity is close to the shear wave velocity in the unsaturated foundation,the resonance of the soil body is caused and the vertical displacement of the surface increases rapidly to the peak;the order of the soil layers in the layered unsaturated foundation has a significant effect on the surface displacement,and the vertical displacement of the surface in the upper-soft foundation is larger than that in the upper-hard foundation;the saturation degree has a significant effect on the dynamic response of the layered unsaturated foundation,and the vertical displacement of the surface in the upper-soft foundation is larger than that in the upper-hard foundation.The saturation degree has a significant effect on the dynamic response of the layered unsaturated foundation,and the surface vertical displacement increases with the increase of the saturation degree of the surface soil in both the upper-soft and lower-hard foundation and the upper-hard and lower-soft foundation.(5)The computational model of two-dimensional layered unsaturated soil foundation was developed and the transmission-reflection matrix method(TRM)was used to study the dynamic response of layered unsaturated soil under the action of moving loads.The effects of load movement velocity,soil shear modulus,saturation and load frequency on the dynamic response of three types of layered foundations,namely,homogeneous soil,soft interlayer and hard interlayer foundation are discussed.The results of the study show that: when the load movement velocity is close to the Rayleigh wave velocity in the unsaturated foundation,the soil resonates and the surface vertical displacement increases rapidly to the peak;the arrangement order of soil layers in the layered unsaturated foundation has a significant effect on the surface displacement,compared with the homogeneous foundation,the surface vertical displacement of the hard interlayer foundation is large,while the surface vertical displacement of the soft interlayer foundation is small The saturation has a significant effect on the dynamic response of the layered unsaturated foundation;with the increase of the loading frequency,the displacements of the three layered foundations show obvious fluctuation along the horizontal distance direction.