Theoretical Research On The Dynamic Response Of Soil And Tunnnel Subjected To Underground Trains

Although the traffic pressure in cities can be relieved greatly by the subway,the environmental vibration problem induced by the underground trains has received growing concerns.This ground-borne vibration is essentially a result of waves generated by the inner train loads propagating in the underground structures and its surrounding soil.By establishing several different models,the ground vibration subjected to the underground moving loads and the transmission and attenuation of waves in the soil are studied in many aspects.The details are as follows:(1)Based on the Lame-Navier equation of the elastic medium,the solutions for the dynamic response of the three-dimensional viscoelastic half-space under the embedded moving load are obtained by using the Fourier integral transform.The time histories?frequency spectrum and spatial distribution of the ground vibrations are presented.Meanwhile,the influences of the embedded depth?velocity and frequency of the load on the vibration are also investigated.(2)A plane-strain tunnel-saturated soil model with a unit harmonic load acting on the tunnel invert is established.The motion equations of the thin-walled cylindrical shell and the wave equations of the Biot's saturated soil are solved in the polar coordinate system by using the Fourier transform.The spatial distribution of radial and circumferential displacements?normal stress and pore water pressure in the soil are presented.A parametric analysis including the soil permeability,load frequency and soil damping is conducted to investigate the vibration propagation in the saturated soil.(3)A tunnel-grouting layer-saturated soil coupled model is established by treating the grouting layer as a homogeneous?isochoric layer surrounding the tunnel lining.The influences of the grouting layer on the steady-state response in the saturated soil are studied by numerical examples.(4)By simplifying the tunnel as an infinite long Euler-Bernoulli beam,a two-dimensional tunnel-layered saturated soil model in the longitudinal section is established.Based on Biot's saturated poroelastic theory,the solutions for the dynamic response of the saturated layered ground subjected to a moving load are obtained by applying the TRM method.By establishing three different soil cases,the effect of a soft/hard interlayer on the ground vibration is investigated.(5)A beam-spring-damper model is adopted to simulate the floating-slab-track(FST)system.The track system is coupled with the tunnel-soil model according to the interaction force between the track system and tunnel.The vibration isolation effect of the FST system under moving loads with different velocities and frequencies are studied.The ground vibration generated by the underground railways is studied mathematically by establishing several different models in this dissertation.In these models,parameters about the soil,the grouting layer,underground structures and dynamic loads are all considered trying to investigate the vibration propagation more comprehensively.The conclusions obtained can provide useful results and a reference for the ground vibration prediction and control in the design and operation stages of a subway.