Dynamic Responses Of A Twin-tunnel Subjected To Moving Loads In The Saturated Soil

With the fast development of urban metro lines in China,subways have gradually become a popular means of transportation for daily travel of urban residents In the meantime,the environmental vibration problems caused by subways have received increasing attention.The subway operation will generate a certain amount of noise which is harmful to the health of the residents living along the subway line.Meanwhile,the environmental vibration induced by the subways will also affect some precision instruments.It is a common practice to construct underground railway lines in pairs.And the influence of adjacent tunnels on the dynamic response of subway operations cannot be ignored.Therefore,an investigation on ground vibrations induced by subways in the context of twin tunnels is necessary and desirableIn this paper,a three-dimensional finite element model is established to study the dynamic response of soil and lining caused by the loads moving in twin tunnels.In addition,considering the high groundwater level in the southeast coastal area,based on the Biot's porous media theory,the soil around the tunnel is simulated as the saturated soil.The subway load is simplified to a moving point which is applied to the invert to represent the subway excitation.A three-dimensional finite element dynamic analysis program TSSVP and the the MTF artificial boundary are used to solve the dynamic problems in this paper.And the dynamic response of a twin tunnel embedded in a half-space saturated soil caused by subways is studiedFirstly,this paper introduces the three-dimensional dynamic finite element analysis program TSSVP,which uses a unique stiffness matrix storage method to greatly improve the computational efficiency and is able to simulate the elements of saturated soils.At the same time,to suppress spurious reflections at the truncation boundaries,an artificial boundary condition named the multi-transmitting formula(MTF)is applied to transmit the out-going waves in the saturated soil medium.In addition,this analysis program is verified by comparing the transient response caused by the radial load applied to the surface of the circular cavity with the existing analytical solutionsThen,a twin tunnel model embedded in a homogeneous saturated soil is established to compare the differences in the dynamic response of the following model group:the single tunnel and the twin tunnel,the saturated soil and the single-phase soil,the single load and the double loads,and the same or different direction of the double loads.Also,the parametric studies have been performed for investigating the effects of the load velocity,the burying depth of tunnel,the tunnel spacing and the Young's modulus of soil on the prediction results.Computed results showed that the dynamic response of the twin-tunnel model is greater than that of the single tunnel model.And the spacing between two tunnels,tunnel buried depth,load moving speed and the Young's modulus of soil are the essential parameters to determine the dynamic response of the tunnel and soil.There is a critical speed,when the moving speed of the load approaches it,the dynamic response of the soil and the tunnel will be amplified.Finally,based on the original model,a twin tunnel model buried in a double-layer saturated soil was established.It divides the soil into two layers of equal height.And the effects of the different distribution of soil layers,the relative modulus of two soil layers and the relative position of layer boundary and tunnel on the dynamic results have been discussed.Studies have shown that the distribution of the soil layer has a certain effect on the dynamic response of the soil and lining caused by the moving load.The critical velocity of the tunnel-soil system is determined by the property of the soil below the twin tunnel.The relative position of layer boundary and tunnel will also affect the interaction between the soil and the tunnel.