Analysis Of Surface Settlement In Double-Line Shield Tunnel Construction In Coastal Water-Rich Soft Soil Considering Fluid-Solid Coupling Effect

In the construction of metro tunnels in coastal cities,it is often necessary to cross the water-rich soft soil zone.Due to the complex and varied geological conditions and other factors such as groundwater or surface water,it will inevitably disturb the surrounding soil and cause soil settlement.This can cause adverse effects on traffic,surrounding buildings and underground pipelines,and even cause ground collapse in severe cases.Therefore,it is of great significance to research the problem of surface settlement in this metro construction area.This paper takes the Qingdao Metro Line 8 Citizen Health Center Station-Citizen Fitness Center Station as the engineering background,and used the combination of FLAC3 D numerical simulation and on-site monitoring to studied the surface settlement in the construction of shield double-line tunnel in the coastal water-rich soft soil layer.The feasibility and superiority of simulation considering fluid-solid coupling effect are verified,and the influencing factors of surface settlement are analyzed.The main research contents and conclusions are as follows:(1)Through the on-site monitoring,simulation considering the fluid-solid coupling effect,and simulation without considering the fluid-solid coupling effect,the law of surface settlement caused by the construction of shield double-line tunnel in the coastal water-rich soft soil layer is studied.The comprehensive analysis shows that: the horizontal settlement tank of the surface shows a “W” shape distribution,and the surface settlement value and its influence range have obvious superposition effect;the maximum horizontal settlement of the surface occurs above the centerline of the right-line tunnel,and the maximum value is in the range of 16.32?16.52mm;the main affected area of the horizontal settlement is within 25?30m outside the center of the two tunnels;the longitudinal settlement curve of monitoring center point with the advancing of the working surface shows a stretching "Z" shape;When the working surface is 10 ? 15 m away from the monitoring center point,the settlement of the monitoring center starts to develop gradually.When it reaches the vicinity of the monitoring center point,it develops the fastest.After passing through the monitoring center point 20 ? 30 m,the settlement gradually becomes stable;after the completion of double-line tunnel excavation,the surface settlement of the later tunnel is larger than that of the first tunnel,and the later tunnel excavation will have a lasting impact on the first tunnel,resulting in a certain increase in the surface settlement of the first tunnel;in the process of shield excavation,the surface settlement behind the working face is obviously larger than that in the front,with the advancement of the shield,the surface settlement in front of the face begins to increase,and then gradually stabilizes.(2)Comparative analysis of surface settlement results obtained by on-site monitoring,simulation considering fluid-solid coupling effect,and simulation without considering fluidsolid coupling effect.The research shows that: The basic laws of surface settlement change and development can be reflected by simulation considering fluid-solid coupling effect and simulation without considering fluid-solid coupling effect.However,there is a great difference in numerical value between simulation considering fluid-solid coupling effect and simulation without considering fluid-solid coupling effect.The simulation considering fluidsolid coupling effect can more realistic response to the size and regularity of surface settlement caused by shield excavation.It is an effective research method.(3)By using numerical simulation considering fluid-solid coupling effect,this paper studies the influence of net distance of tunnel,tunnel diameter,groundwater and surface water on surface settlement,and puts forward the corresponding control measures for surface settlement in the design and construction of metro tunnel.The results show that: within a certain range,with the increase of the net spacing between the two tunnels,the shape of the surface settlement trough has a tendency to change from “V” shape to “pan” shape to “W” shape,and the maximum of monitoring cross-section surface settlement has the rule of decreasing first and then increasing,therefore,in the actual design of metro engineering,it is most reasonable that the net spacing of double-line tunnels is taken near the minimum point of the maximum curve of surface settlement;with the increase of tunnel diameter,the value of surface settlement is increasing,and the increasing range is becoming larger,therefore,in the actual design of metro engineering,the tunnel diameter should be reduced as much as possible under the necessary traffic conditions;the groundwater has a great influence on surface settlement during shield tunneling,and the influence of surface water is relatively weak,therefore,in the actual metro construction,the content of groundwater in soil can be reduced by some drainage measures and ground treatment methods,so that the soil can be drained and consolidated in advance,if the tunnel is inevitably going through large rivers and lakes,the corresponding reinforcement and protection measures should be taken.