Spatio-temporal Effect of Long-span Loess Tunnel Surrounding Rock Deformation
The tunnel surrounding rock deformation is mainly influenced by the construction,time,and space.Understanding the surrounding rock deformation characteristics varying with time and space is crucial for summarizing the surrounding rock deformation rule,and determining the reasonable support timing.Based on the Shenmu-Fugu expressway project,combined with two working conditions of normal excavation and shutdown,the statistical analysis of on-site monitoring data was conducted.The surrounding rock deformation rule shows that the tunnel vault settlement is closely related to time,develops slowly with time,and eventually tends to be stable.While the net clearance convergence deformation is mainly affected by the construction procedures.During the construction on middle and lower steps,the net clearance convergence value accounts for about 95.2%of the total deformation.The convergence deformation quickly tends to stable after the inverted arch excavation and backfill.It is found that there is a certain spatial constraint effect of tunnel face on the surrounding rock deformation,through the data analysis on vault subsidence at site shutdown section.As the distance to tunnel face increases,the constraint effect gradually decreases.When the distance to tunnel face is greater than three times of the tunnel excavation span,the constraint effect basically disappears.The three-dimensional numerical simulation analysis was conducted on the tunnel support excavation process,considering the loess creep characteristics.It is found that the soil disturbance radius in front of excavation face is about 1.5 times of the tunnel excavation span by using the three-step starting excavation method.The initial displacement at tunnel vault caused by excavation is about 5%of the total deformation.To make reasonable use of the tunnel face spatial constraint effect and reduce the surrounding rock deformation,for the deep-buried section of surrounding rock grade V in long-span loess tunnels,the inverted arch excavation and backfill should be completed within 3 times the tunnel excavation span from tunnel face.
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万方数据
