Influence of Upward Cavities on the Stability of Deeply Buried Mega-section Tunnels and Its Safety Distance
In order to investigate the influence of upward-facing caverns on the stability and safety distances of deeply buried weak and fragmented peripheral rock tunnels with large cross sections,a numerical simulation method was employed.The study the effects of cavern diameter(8 m,10 m,12 m)and spacing between the caverns and tunnels(3 m,4m,5 m,6m)on tunnel stability and safe-ty distances was examined.The findings are as follows.When the diameter of the karst cave remains constant,the settlement of the dome decreases as the distance between the cave and the tunnel increases,and the vertical pressure on the dome decreases with the in-crease of distance.When the distance between the tunnel and the karst cave remains constant,the settlement of the dome increases with the increase of the diameter of the cave,and the pressure on the tunnel's dome is not significantly affected by the changes in the diameter of the cave.The presence of uplifted caverns has no significant impact on horizontal convergence and horizontal pressure at the arch girdle,as well as uplift and vertical pressure at the arch base of deeply buried tunnels.When the diameter of the cavern is not greater than 8 m and the distance between the cavern and the tunnel is less than 3 m,the tunnel is in an unstable state with a safety distance of 3 m.When the diameter of the cavern is between 8～10 m and the distance between the cavern and the tunnel is less than 5 m,the cavern is in an unstable state with a safety distance of 5 m.When the diameter of the cavern is between 10～12 m and the distance between the cavern and the tunnel is less than 6 m,the tunnel is in an unstable state with a safety distance of 6 m under these conditions.It was found that when the cavern is located above the tunnel and the cavern is not considered to be filled with water,the most dangerous location of the tunnel is not located at the minimum distance between the tunnel and the cavern,but below the edge of the cavern.
frail and brokenlarge cross-sectionstabilitycritical thicknessShangvu Cave
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