Pile Tunnel Interaction During Mechanized Tunnelling

Transcription

1 Pile Tunnel Interaction During Mechanized Tunnelling Tiago Dias, PhD Adam Bezuijen, PhD Laboratory of Geotechnics, Ghent University, Belgium 9 th IS - Underground Constructions in Soft Ground São Paulo,

2 Before Now Introduction Piles and tunnels are now close enough for their interaction to be significant

3 Introduction First attempts to define the pile settlement based on the relative position to the tunnel Zt -Zp Kaalberg et al. (25) Selemetas et al. (25) 2. Dt C B A B C D C B A Jacobsz et al. (22) B C 45º 45º+φ cv/2 D δp>2cm δp<2cm Ld Dt 5 δp/ δs <.5 (b).5-1 >1

4 Introduction ØTunnelling degrades the pile base capacity q Higher mobilization of shaft friction ØGround settlements induce negative friction q Higher mobilization of toe capacity S+T S T S+T S T

5 So what was necessary? ØAn accessible method for pile analysis that could react to ground settlements Modified Load Transfer Method q Include unloading paths for the load mobilization q Mobilization = f ( relative pile-soil settlements ) i δ p i σ z i t= i δ p i δ s i > τ γ p Pile Soil = δ p δ s i+1 δ p i+1 σ 1 = z i+ t Δ δ i+1 < i+1 δ p i+ 1 δ s

6 Mobilization Functions = f( ) Shaft Friction Tri-linear (bi-directional) mobilization function Toe Force Exponential loading ; Proportional unloading (Rebound) τ/ τmax +1 τep 1 cv 2 cv q b q b max Rb. 1 t= max Rb. 4 t= max 4 t 5 s2 s1 t 1 -τep t 4 t 2 s2 t s3 2,3 1 t= max 5 4 t= max T

7 Pile Loading Cycle Settlement (mm) Forces (MPa) Normalized Depth Axial Load (MPa) Mobilized Shaft Friction Load Shaft Toe Loading Unloading

8 Pile Equilibrium with Ground Displacements. Axial Stress (kpa) m long friction pile Displacements (mm) Shear Mobilization Relative pile depth Before After Before Difference P P PDP PD P+PD Before Before After

9 Tunnelling Settlements ØNumerical solution of the equilibrium equations based on the (stress) boundary conditions at the excavation perimeter q Boundary Conditions = f ( Physical Process ) ØTail Void Grout q The injected grout pressure dissipates as the Zt grout flows between the lining and the soil A B C B D A dl dh p = f (soil-lining gap) τ g p = p. dl γ. dh B A g gap excavated boundary gap front shield C Lining back shield (Rigid Buoyant Element) lining ext Excavated Boundary (Deformable) Grout (Bingham Plastic) Injection Nozzle

10 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 { σ } = λ. { σ} { σ} = f ( TBM ) Tunnel, Soil and Grout Parameters Soil-Lining GAP Grout Pressure s Simulatio n Script

11 Tunnelling Settlements ØDiameter of 1m, centred at a depth of 3m q Initial soil-lining gap of 15cm ØHardening Soil model q Empirical correlations with RD ØGrout Properties q Yield stress of.5 kpa; γ = 2 kn/m³ ØInjection Strategy q Grout p. at the tunnel roof.5 and 1.% volume loss around the tunnel

12 Tunnelling Settlements Zt-Zp Dt 1. A B C -1 Distance from tunnel centre (m) Settlements (mm) A Ld. Dt Settlements (mm) -3 Depht (m) A1. B.5 B1. C.5 C TBM_.5 TBM_1. -5

13 Example Piles ØPiles 22.5 m / D = 1 m / E = 1 GPa / γ=25 kn/m3 ØShaft Linear increase q S1 = S3 =.3 / S2 = / τep = 1 ØToe Max. mobilization at 1 mm q 1% rebound ØPile Capacity 1.5 MN q 1% Shaft (T) q 5% Shaft and 5% Toe (T5) ØInitial Loading State FS=2 Depth (m) Axi al Stress (kpa) σ T σ T5 δ T δ T Settl ements (mm)

14 Examples of Pile Tunnel Interaction ØFriction pile q Settlements - δp/dp x δp/δs - o =.5% x = 1.% q Shear Mobilization ( negative shear - δs > δp ) q Increment of Axial Stress ( decrease at A, but increased at B and C ) Pile / Surface Settlements δp/δs.5 δp/δs 1. δp/dp 1. δp/dp.5 9% 6% 3%. % Lateral Distance / Tunnel Diameter Pi l e Settlements / Diameter Depth (m) Shear Mobilization Initial A.5 A1. B.5 B1. C. 5 C1. Depth (m) Increment of Axi al Stress (kpa) A.5 A1. 5 B.5 B1. C. 5 1 C

15 Examples of Pile Tunnel Interaction ØShaft and Toe Capacities (5 / 5%) q Settlements Higher than T q Shear Mobilization forces can be transferred to the toe q Increment of Axial Stress ( decrease at A, but increase at B and C ) Pile / Surface Settlements δp/δs.5 δp/δs 1. δp/dp 1. δp/dp.5 9% 6% 3%. % Lateral Distance / Tunnel Diameter Pi l e Settlements / Diameter Depth (m) Shear Mobilization Initial A.5 A1. B.5 B1. C. 5 C1. Depth (m) Increment of Axi al Stress (kpa) A.5 A1. 5 B.5 B1. C. 5 1 C

16 Conclusion ØA modified version of the load transfer method can be used to predict how a single pile reacts when subjected to ground displacements, such as the ones induced during a mechanized excavation ØPile settlements decrease with Ld, but increase with the tunnel VL q Between 6.5 and 1.3% of the pile diameter. ØThe ratio between the pile and the surface settlements (δp/δs): q >1 for a pile located above the tunnel q <1 for Ld larger than one tunnel diameter. ØAxial forces decrease when the pile is directly above the tunnel, but increase otherwise

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