Unexpected High Boundary Displacement in Tunnel Excavation Analysis

1

Dear All,

I am modeling a tunnel under the water table. The analysis includes the hydrostatic solution without water flow analysis. So, I considered the water table and its density in the model without CONFIG FLUID and put the other commands like a dry analysis with Mohr Model. However, when I controlled the contour of the displacement after 1m of the excavation, the displacement in the tunnel’s boundary was considerably high in comparison to the zones which located immediately behind the boundary (maybe 2000 mm to 10 mm). How can I fix this problem?

Thanks

image
image1116×710 109 KB

Figure 1: Pore Pressure as a fixed pressure

image
image1108×699 77 KB

Figure 2: Displacement in z Direction

2

I have used only two commands for pore pressure (without applying ‘Config Fluid’)

  1. zone water plane origin 0 0 12.13 normal 0 0 -1
  2. zone water density 1000

The walls of the tunnel and the face include the stabilizations like the shotcrete, beam, bolts and forpoles. In other words, the floor of the tunnel doesn’t have any measures.

Thanks

3

how deep is your tunnel? probably the pore pressures on the tunel faces are bigger than what the support you instaled there is able to manage … may be an option is set to 0 de pore pressures in the first zones of the tunnel:

image
image689×434 89.6 KB

4

Thanks for your response. The depth of the tunnel is 35m andthe water elevation is 12m above the tunnel crown. I used Beam and Shell Elements for stablizing the tunnel walls and Cables for the Face. However, there is no any measures for the floor. Under dry condition, the displacement of the tunnel’s floor was arount 5 cm. But by applying the pore pressure, this parameter is dramatically high and uncontrolable! I initilaized the pore pressure inside the tunnel including the boundary as 0 due to excavation. Anyhow, if I also considered the fix pore pressure (Hydrostatical condition), The displacements are even high!