Study On Mechanical Properties Of Metro Lining In Coastal Composite Strata During The Operation Period

The development focus of subway tunnels in China has changed from construction to operation.The tunnel operation period is long,the load is complex and variable,and the groundwater level changes dynamically.Therefore,the structural mechanic’s performance and damage law of tunnel lining during the operation period should be focused on to ensure the safe operation of the tunnel.During the operation period,human exploitation and use of groundwater as well as the construction of the project,groundwater level changes show different patterns of decline.Due to the production or construction process stage problems,the lining structure will appear initial cracks,under the action of fluid-solid coupling,the lining structure stress,displacement changes,lining initial cracks further expansion,so the study of the mechanical properties of the tunnel lining in the operational period under the action of the falling water table and train load and the crack expansion law is particularly important.This study is based on the Dalian Metro Line 4 project and utilizes ABAQUS numerical analysis software to analyze the stress and displacement changes and crack propagation patterns of tunnel lining structures under the fluid solid coupling effect of stress and seepage fields.This study considers factors such as train speed,different water level drop modes,and the location and number of cracks,and couples multiple influencing factors to study their effects on the stress and displacement changes of tunnel lining.The main research contents are as follows:(1)Using ABAQUS simulation software,the shield tunnel model was numerically simulated under the action of stress field and seepage field by setting different water level drop modes according to the actual working conditions of the shield tunnel dimensions and the composite stratigraphic parameters of Dalian Metro Line 4,to study the stress and displacement law of the tunnel lining at each monitoring point under different water level drop modes;the initial single and double cracks were set at different locations of the lining structure,and the extended finite element method was used to study the crack expansion law of the lining structure under different water level drop modes.(2)Set different train operating speeds,calculate the dynamic load functions below different train speeds,and study the stress displacement variation law of each monitoring point of tunnel lining under different train speeds;The initial single crack and double crack were set at different positions of the lining structure to study the crack growth law of the lining structure at different train speeds.(3)Set different drainage boundary conditions,train load adopts different train travel speeds,establish crack-free models,single crack models and double crack models respectively,and study the changes of lining stress distribution,displacement deformation and crack propagation under different groundwater level drop patterns and train travel speeds.(4)The three-dimensional tunnel lining structure finite element model was set up to study the crack expansion law according to the combination of the falling water table pattern,train operation speed,and cracks,which have the greatest influence on the mechanical properties of the lining structure.