Calculation of Face Stability for EPB

Course in Tunnelling and Tunnel Boring Machine Kurs w zakresie drążenia tuneli oraz maszyny drążącej

CALCULATION OF FACE STABILITY FOR EPB MACHINE MODEL OF ANAGNOSTOU & KOVARI (1996) Design Abacus

Prof. Eng. Daniele PEILA

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Calculation model

HORN’S MODEL (1961) 1

Calculation model Drained conditions:

> 10-7 ÷ 10-6 m/s

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Soil permeability

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Excavation advancing ratio

≤ 0.1 ÷ 1 m/h

Strenght parameters to use: DRAINED for sands and gravels. For the clay only in machine stop conditions.

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Calculation model The pressure must be applied in terms of EFFECTIVE stresses. Contact “grain-grain” of the soil The water pressures into the bulk chamber affect the presence of the seepage forces.

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Calculation model Acting forces on the soil wedge: 1. The submerged weight G’ 2. The vertical force V’ 3. The seepage forces Fx e Fz 4. The pressure applied on the tunnel face S’ 5. The ortoghonal force on the inclined surface N’ 6. The orizontal ortoghonal to the surface

forces lateral

7. The shear forces that developes at the interfaces 4

Calculation model

Boundary conditions for the seepage forces:

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constant permeability

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pressure inside the tunnel hf ≤ h0

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constant underground water height

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Calculation model Calculation procedure for the stability analysis of the tunnel face:

1. Numerical modelling of the flow field 2. Calculation of the forces acting on the soil wedge with the sliding geometry assumption 3. Calculation of the force that must be applied on the tunnel face

Choice of the critical sliding surface by the iteration of steps 2 and 3.

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Calculation of the effective pressure thet must be applied on the tunnel face The pressure that must be applied is affected by different parameters:

s’= f(D, H, hf, h0, c, j, g’, gd)

By a dimensional analysis has been obtained the following formulation:

∆h s' = F0 γ' D − F1c + F2 γ' ∆h − F3c D 7

Effective pressure calculation that must be applied at the tunnel face

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Effective pressure calculation that must be applied at the tunnel face

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Effective pressure calculation that must be applied at the tunnel face

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Effective pressure calculation that must be applied at the tunnel face

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Example of calculation

Great Belt Project (Denmark): Data: D=7m H = 30 m h0 ≈ 47 m

ϕ = 32,5° γ’ = 13 kN/m3

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Example of calculation

F F00 == 0.2 0.2 13

Example of calculation

F F11 == 22 14

Example of calculation

F F22 == 0.43 0.43 15

Example of calculation

F F33 == 0.108 0.108 16

Example of calculation Obtained values using the abacus:

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F0 = 0,2

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F1 = 2

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F2 = 0,43

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F3 = 0,108

Obtaining: s’= 18 –2c+5,6(h0 – hf) – 0,016c(h0 – hf)

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Example of calculation

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Observations on the obtained results and on the applicative aspects Important observations:

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Static equivalence of different technological solutions.

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Importance of the water pressure into the bulk chamber (calculation of the pressure in the soli pores without tunnel face pressure).

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Problems due to high effective pressures into the bulk chamber.

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Observations on the obtained results and on the applicative aspects

Possible problems with high effective pressure into the bulk chamber.

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