Study On Mechanical Behavior Of Super Large Diameter Shield Tunnel In Shallow Covered Soil In Offshore Area

At present,the shield method has been received more and more attention and development in the development and application of underground space.Tunnels built in the offshore area,due to the complex water environment,the shield crosses the stratum with large differences,and the structural characteristics of the structure are still unclear.For example,the drag force generated by the water flow on the sediment particles will cause the riverbed to wash away too much.It seriously affects the stability of structural forces.Secondly,the external load received by frequent tunnels changes continuously.How to determine the dynamic response characteristics of tunnel external loads,and correctly evaluate the mechanical effects of tunnels has become the top priority of research problems.In view of this,using literature research,theoretical analysis,numerical simulation and other methods,the mechanical behavior of the tunnel under extreme scouring,the dynamic response characteristics of the external shield under the tidal action and the mechanical behavior of the tunnel under the tidal action are carried out.The research finally formed the research results of the mechanical behavior of the super-large diameter shield tunnel in the shallow overburden soil in the offshore area.The main conclusions of the paper are as follows:(1)It is proved that the whole section of the Maliuzhou tunnel is dominated by scouring,and the calculation formula suitable for predicting the extreme scouring depth is derived.The long-term extreme scouring depth of the Maliuzhou waterway is predicted to be 4.8m,and the influence of the scouring depth is discussed.Several parameters,finally calculated and analyzed the mechanical effects of the tunnel lining structure during the tunnel scouring process.(2)Based on the principle of stress seepage coupling,the calculation formula for calculating the depth of influence of excess pore water pressure under wave action is derived.According to the relationship between depth of tunnel and depth of excess pore water pressure,the external load of tunnel under tidal action is proposed.Different dynamic response modes were combined with field measured data to verify the conclusions.(3)Based on the principle of impervious characteristics of soil layer,the impervious design model is proposed,and the relevant parameters of the model are modified with the field measured data.Finally,the finite element analysis software is used under the premise of considering the longitudinal mechanical effect of the tunnel.There is a large three-dimensional refined model(inter-ring: segment-bolt,longitudinal: segment-shear pin)Established by MIDAS/GTS NX,and analyzed the mechanical characteristics of the whole ring segment,shear pin and bolt under the action of tides.