Numerical Simulation Analysis Of A Excavation Connected Aisle In Metro With Fluid-structure Interaction

As the urban population rapidly increases,the pressure of ground transportation increases,traffic congestion has become a common phenomenon in densely populated cities.Therefore,it was inevitabled to accelerate the development of urban underground rail transit.At present,the construction of subway has been launched successively in densely populated cities in China.As a connected aisle connecting the left and right tunnels,connected aisle plays an important role in ensuring the safety of passenger evacuation in the event of a sudden disaster.The connected aisle with the pump house was also responsibled for the collection and drainage of the tunnel in the subway operation and the risks and counter measures of the connected aisle with the pump house in the process of construction have been increasingly attracted public attention.During the construction of the subway connected aisle,when the groundwater level of connected aisle was relatively high,the excavation of rock and soil mass will inevitably lead to the secondary distribution of the internal stress of rock and soil mass,the seepage field will change with the stress field and the seepage field will affect the stress field.Therefore,stress field and seepage field will affect and restrict each other,so that the problem of fluid-structure interaction in the construction of connected aisle also arises.Thus,based on the case of a subway connected aisle engineering,this paper uses the finite element method to carry out fluid-structure interaction numerical simulation for the excavation process of the subway connected aisle,and the research on the influences left on the displacement field and the stress field after the excavation of connected aisle under seepage field;based on the monitoring results,it analyses the laws of surface subsidence and surface building displacement;finally,compared with the the numerical and monitoring results,get some reliable conclusions.There are the research contents and conclusions of this paper:(1)The study summarized existing construction methods,the scope of application,the advantages and disadvantages of the subway connected aisle,and made a detailed comparison of the characteristics of common construction methods,economic indicators,construction period,risks,and the degree of impact on the environment.(2)The deformation and stress characteristics of the subway connected aisle with the consideration of the fluid-structure interaction or not were simulated and analyzed,and the two simulation results were compared,it was concluded that the settlements at the ground surface,when without considering the fluid-solid interaction,were all smaller than those with the fluid-solid interaction,the surface subsidence and tunnel vault settlement with effect of the fluid-solid interaction were 165%and 137%respectively,compared with those with the fluid-solid interaction;the horizontal displacement in the cave and the bottom uplift of the pump house were both greater than those with considering the fluid-solid interaction;the effective stress of rock and soil mass and the internal force of the initial branch sprayed and mixed structure were respectively greater than those with considered the fluid-solid interaction.(3)Based on the analysis of the surface subsidence and surface building settlement from the monitoring results,and the comparison of the two numerical simulation methods in which whether the fluid-structure interaction was adopted or not,the conclusion was reached that the variation trend in three monitoring spot located in the surface of the connected aisle was very similar.As the time passing by,the accumulated sedimentation rates gradually increased.The initial branch of the complement grouting work was completed,which had a significant effect on reducing the subsidence of the surface building.According to the two longitudinal sections of surface subsidence diagram shown,the variation trends of the three curves were basically the same,the amount of surface subsidence was the largest in the range of about 15m from the center-line of the connected aisle;as the sedimentation ratio being considered the fluid-structure interaction effect was larger than those without adopting the methods of the fluid-structure interaction and the monitoring results,it accounts for that the simulation results with the fluid-structure interaction effect tend to be more safe.Therefore,it was proved that the simulation method adopted in this paper was reliabled in dealing with the fluid-structure interaction problem in the construction of the subway connected aisle.