Grout pressure distribution during TBM tunnelling

Transcription

1 Grout pressure distribution during TBM tunnelling Tiago Dias, PhD Adam Bezuijen, PhD Laboratory of Geotechnics, Ghent University, Belgium 9 th IS - Underground Constructions in Soft Ground São Paulo,

2 Introduction ØWe have been able to control the occurrence of settlements around TBM s q Face pressure, tail-void grouting ØBut 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 { } λ. { σ} 0 σ = { σ} = f ( TBM )

3 Introduction Soil deformable Fluid (bentonite, grout) viscous Face Shield Tail/Lining Structure (shield, lining) rigid? Pieces of the TBM Puzzle

4 Grout Injection The injected grout pressure dissipates as the grout flows between the lining and the soil Zt B dl dh p = f (soil-lining gap) A τ g p = p. dl γ. dh B A g gap Excavated Boundary (Deformable) Grout (Bingham Plastic) C Lining (Rigid Buoyant Element) Injection Nozzle gap

5 Grout Injection ØHow 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 Simulatio n Script

6 Grout Consolidation ØWater pressure gradient (outflow) ØBoundary pressure = f (convergence) k. ( GP( dr) Uw) ( n ) i n f. dt = dx x ( 1 n ) i slurry grout V0 ni slurry grout Vg(t) filtered grout Vfg(t) ni nf filtered grout Vfg(t= ) nf Vw-out(t) Vw-out(t= )

7 Grout Consolidation Ø Consolidation q Think of a balloon. volume Local water outflow Variation in q Local reaction x Closed system same as the pressure is deformation monitored so is the that the deformation total

8 Simulation Routine (Python) ØFEA Calculation: Creates a phase with the new grout pressures q The displacements around the tunnel are imported from the Output software. ØIterative Grout Pressure: Uses the 1 st 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) ØGrout Consolidation: Calculate average contraction due to consolidation q Root finding scheme (using 2 nd routine) for the grout pressure at the tunnel roof to cause an average boundary contraction that is equivalent to the consolidation contraction

9 Example Calculation q Empirical correlations with RD Ø Grout Properties Yield stress of 0.5 kpa ; γ = 20 kn q ni = 0.4, nf = 0.3; /m³ ØInjection q 400 Strategy kfg = m/s kpa at the Roof x 560 kpa q 400 kpa at the Roof x 560 kpa at the Invert

10 Example Calculation ØGrout Injection Grout Pressure x Soil Deformability Normalized Tunnel Height 1.0 Top Bottom Grout Pressure (kpa) Settl ements (mm) Soil-lining gap (cm) Di stance from tunnel alignment (m) Top Bottom Top Bottom

11 Example Calculation ØGrout Consolidation Pressure drop x Gap variation Hei ght above invert / diameter min 30 min UW Grout Pressure (kpa) Roof Invert Mid-Height dgap Average Contraction (cm) Grout Pressures (kpa) Time (min) 0.0

12 Example Calculation ØGrout Consolidation Soil deformations Soil-lining gap (cm) 0 Di stance from the tunnel centre (m) min 30 min Settl ements (mm) min 15 min 30 min

13 Conclusion associated with a finite element model to calculate the Ø processes in interaction with the induced soil displacements Injection The position of the Consolidation s around the tunnel can have a major influence Continuity the for final the pressure tunnel boundary distribution as and a whole the displacements q Ø very The fast reaction dissipation, of the tunnel causing invert a is distribution very stiff of A grout local model pressures would violating predict a Output = f (input) but the point here is that within an objective and

14 THANK YOU FOR YOUR ATTENTION Tiago Dias, PhD Adam Bezuijen, PhD Tiago Dias Ghent University, Belgium Contact: Tiago_Dias/ 9 th IS - Underground Constructions in Soft Ground São Paulo,