Grout pressure distribution during TBM tunnelling

9th IS - Underground Constructions in Soft Ground São Paulo, April, 2017

Tiago Dias, PhD

Adam Bezuijen, PhD

Laboratory of Geotechnics, Ghent University, Belgium

Introduction

Ø We have been able to control the occurrence of settlements around TBM’s

q   Face pressure, tail-void grouting

Ø But we still struggle to predict these settlements accurately

Numerical models will never be accurate if their boundary conditions do not reflect the real stresses around a TBM

{ } { }0.σλσ = { } ( )TBMf=σ

Introduction

Soil – deformable Fluid (bentonite, grout) –

viscous Structure (shield, lining) –

rigid?

Face Shield Tail/Lining Pieces of

the TBM Puzzle

Grout Injection

The injected grout pressure dissipates as the grout flows between the lining and the

soil

p = f (soil-lining gap)

Zt

Excavated Boundary(Deformable)

Grout (Bingham Plastic)

Lining(Rigid Buoyant Element)

Injection Nozzle

A

B

C

dl dh

gap

dhdlgap

pp gg

AB .. γτ

−−=

Grout Injection

Ø How can we model that realistically? q   Traditional approach = The imposed pressure is constant

q   Iterative calculation = The pressures depend on the ground deformations

Tunnel, Soil and Grout

Parameters

Soil-Lining GAP

Grout Pressure

s

Simulation Script

Grout Consolidation

Ø Water pressure gradient (outflow) Ø Boundary pressure = f (convergence)

slurry groutV0

slurry groutVg(t)

filtered groutVfg(t)

filtered groutVfg(t=∞ )

ni nf

Vw-out(t) Vw-out(t=∞ )

ni

nf

( )( ) ( )( )i

fi

nnn

dxdtxUwdrGPk

−

−=

−

1..

Grout Consolidation Grout Consolidation

Consolidation Ø 

Think of a balloon…. q  

Local water outflow Variation in volume

q  

Local reaction x Closed system

deformationpressure is monitored so that the is the total deformation

same as the

δ = q

Simulation Routine (Python)

Ø FEA Calculation: Creates a phase with the new grout pressures q   The displacements around the tunnel are imported from the Output software.

Ø Iterative Grout Pressure: Uses the 1st routine iteratively until equilibrium between grout pressures and tunnel contraction is achieved

q   f (Fixed grout pressure at the tunnel roof, and an initial soil lining gap)

Ø Grout Consolidation: Calculate average contraction due to consolidation q   Root finding scheme (using 2nd routine) for the grout pressure at the tunnel

roof to cause an average boundary contraction that is equivalent to the consolidation contraction

Example Calculation

Empirical correlations with RD Ø 

Grout Properties q  

Yield stress of 0.5 kPa

; γ = 20 kN

/m³ q   ni = 0.4, nf = 0.3;

kfg = 2 × 10-8 m/s Ø Injection Strategy q   400 kPa at the Roof x 560 kPa

at the Invert q   400 kPa at the Roof x 560 kPa at the Invert

Example Calculation

Ø Grout Injection Grout Pressure x Soil Deformability

0.0

0.2

0.4

0.6

0.8

1.0

200 300 400 500 600

Nor

mal

ized

Tun

nel H

eigh

t

Grout Pressure (kPa)

Top

Bottom

0

5

10

15

20 Soil-lining gap (cm)

Top Bottom-60

-50

-40

-30

-20

-10

00 20 40 60

Settl

emen

ts (m

m)

Distance from tunnel alignment (m)

Top

Bottom

Example Calculation

Ø Grout Consolidation Pressure drop x Gap variation

0.0

0.2

0.4

0.6

0.8

1.0

250 350 450 550 650

Hei

ght a

bove

inve

rt /

diam

eter

Grout Pressures (kPa)

0 min30 minUW

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

350

400

450

500

550

600

0 5 10 15 20 25 30

Aver

age

Cont

ract

ion

(cm

)

Gro

ut P

ress

ure

(kPa

)Time (min)

Roof Mid-HeightInvert dGap

Example Calculation

Ø Grout Consolidation Soil deformations

0

5

10

15

20

0 min 30 min

Soil-lining gap (cm)

-35

-30

-25

-20

-15

-10

-5

00 20 40 60

Settl

emen

ts (m

m)

Distance from the tunnel centre (m)

0 min

15 min

30 min

Conclusion

associated with a finite element model to calculate the processes in interaction with the induced soil displacements Ø 

Injection The position of the s around the tunnel can Consolidation s around the tunnel can

Continuityhave a major influence on the final pressure distribution and the for the tunnel boundary as a whole q  displacements The reaction of the tunnel invert is very stiff A local model would predict a Ø very fast dissipation, causing a distribution of grout pressures violating

Output = f (input) but the point here is that within an objective and accessible framework, any condition can be processed and the results evaluated

Contact: tgsdias@gmail.com www.researchgate.net/profile/Tiago_Dias/

THANK YOU FOR YOUR ATTENTION

9th IS - Underground Constructions in Soft Ground São Paulo, April, 2017

Tiago Dias, PhD

Adam Bezuijen, PhD Tiago DiasGhent University, Belgium