The Research Of Influence And Control Measures For Ground Settlement Of Xi'an Metro Tunnel Construction

Xi'an is located in the typical loess area.As the starting point of the onshore Silk Road in the “One Belt,One Road” national development strategy,Xi'an is about to embark on a faster development track.Urban underground traffic track is an important symbol of urban development.It has the advantages of small footprint,high space utilization,fast running speed and convenient ground connection.However,the construction of underground rail transit in loess area will be special due to the mechanical properties of loess.Sexuality and surface subsidence affect the safety of subway construction and operation,and it is necessary to study it.Based on the YCK20+623~YCK21+799 tunnel engineering research project of Xi'an Line 2,through the data collection,theoretical analysis and calculation,on-site monitoring,numerical simulation and other technical means,the ground settlement caused by shallow buried tunnel construction and its control The measures were studied and the construction control method for the post-construction settlement of the Yellow Earth iron tunnel was put forward,and the following knowledge was obtained:(1)Using stochastic medium theory to theoretically defer surface subsidence,using Matlab software to select different buried depths(12m,9m,6m,3m)for verification,the main factors affecting tunnel surface settlement are two points: Under the influence of the buried depth of the tunnel,the surface settlement decreases with the increase of the buried depth of the tunnel;the second is the nature of the loess itself.(2)The maximum settlement of the surface monitored by surface subsidence is 31.5mm,and the surface settlement to the left and right sides is gradually reduced.After more than 3 times the hole diameter range,the sinking amount of the measuring point is rapidly reduced.The convergence of surrounding rock deformation mainly occurred on the first day,then the convergence gradually decreased,and began to develop toward a stable trend after 12 days,indicating that the deformation of the loess tunnel has certain rheological characteristics.(3)Through the numerical calculation results,the ground subsidence has a small distribution law on the large sides of the tunnel center.The shape of the settlement tank is similar to the normal distribution curve in the probability theory proposed by Peck(1969).The vertical stress of the soil is characterized by the large size of the middle and small ends.The farther away from the center line,the smaller the vertical stress.With the excavation of the tunnel,the vertical stress of the soil within the span of the tunnel continues to decrease,and the lateral pressure coefficient of the soil increases with the depth.(4)Surrounding rock reinforcement plays an important role in controlling surface settlement.The surrounding surrounding rock reinforcement should be selected preferentially.Under the premise that the settlement requirements are not met,the face surface grouting reinforcement can be carried out,and the grouting reinforcement effect on the face is very significant.In the future,we should pay attention to the grouting reinforcement of the face,in order to improve the strength and stability of the core soil ahead of the face,and ensure the safe and smooth excavation.