Study On Operation Settlement Control Of Subway Tunnel In Loess Area

With the rapid development of China’s economy and the further improvement of China’s infrastructure construction.As the main means of alleviating traffic congestion and developing urban economy,the construction of urban subway tunnels is constantly increasing.However,the vibration load generated during subway operation will not only affect the soil around the tunnel and cause uneven settlement,but also affect the road surface or adjacent buildings above the tunnel.As of March 2020,there are a total of 12 lines under construction in Xi’an Metro.It is expected that a metro network of 12 lines with a total length of 425 kilometers will be formed by 2025.Loess is widely distributed in my country,and its structural,underpressure and collapsible characteristics are outstanding.Under the action of vibration load,the large and medium pores of the loess may collapse,resulting in the continuous increase of the residual strain of the loess,which is macroscopically represented by the vibration or settlement of the foundation.Different from earthquake load and impact load,the subway train’s small amplitude cyclic dynamic load can easily cause soil settlement under long-term action..Therefore,in order to ensure the long-term driving safety of the subway tunnel and reduce the impact on the surrounding buildings,it is of great scientific significance to carry out research on the long-term settlement of the subway tunnel in the loess area and the control measures for settlement.This paper mainly takes Xi’an Metro Line 2 and Line 4 as the engineering background to study the problem of tunnel-stratigraphic dynamic response under cyclic loading.The tunnel-stratigraphic physical model test with a geometric ratio of 1:30 was used to explore the long-term settlement of the tunnel under the action of cyclic load;the optimal treatment plan,treatment scope,treatment depth and other issues of tunnelreinforcement and uplift were discussed through numerical simulation.The main research results are as follows:(1)Based on the established tunnel-stratumphysical model test,the settlement law of metro tunnel under long-term vibration load was studied,and the effects of vibration frequency,peak vibration load and cycle number on the long-term settlement of the tunnel were discussed and analyzed.(2)Through literature research and engineering actual conditions,it was determined that the grouting reinforcement method was used to deal with the settlement during the operation period.The numerical simulation software FLAC 3D was used to simulate and analyze the optimal disposal plan,the optimal disposal scope and disposal depth,and the The effect was calculated and verified.(3)Using the Chai model in the empirical model method to calculate the long-term settlement of the tunnel,the 5-year cumulative settlement value is very similar to the model test settlement value,thus verifying the correctness of the model test.The long-term settlement of the subway tunnel after grouting reinforcement and uplifting is calculated,and the effect of different treatment time on the long-term settlement is obtained.