Investigation of hydromechanical interactions at the tail void of bored tunnels due to grouting

Transcription

1 RUHR-UNIVERSITÄT BOCHUM Investigation of hydromechanical interactions at the tail void of bored tunnels due to grouting Arash Lavasan Tom Schanz Presented by: Zdenek Zizka Chair of Foundation Engineering, Soil and Rock Mechanics Faculty of Civil and Environemntal Engineering Ruhr-Universität Bochum SFB 837 9th International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground Sao Paulo

2 Motivation and Challenges Subsystems: Ø Progressive excavation Ø Face support Ø Volume loss due to overcutting and conicity Ø Grouting at TBM tail Ø Lining installation Excess pp around TBM Main Challenges in numerical simulations: Ø Adequate constitutive model for soil Ø Adequate simulation of subsystems: Ø Hydromechanical interactions around TBM Ø Consolidation in grout and subsoil Ø Time dependent mechanical behavior of grout 2

3 Objectives The main objective is to study the influence of different strategies for numerical simulation of HM process around TBM on: Ø Settlement trough Ø Excess pore pressure generation and dissipation at the tail of TBM Ø Structural forces in lining element The numerical simulation accounts for: Ø Stress redistribution & volume loss around the TBM Ø Mechanical / Hydromechanical grouting pressure Ø Degradation of permeability in subsoil due to Ø Time dependent evolution of the stiffness in grout (in one scenario) 3

4 Assumptions Type of the soil: Ø Soft to medium dense normally consolidated Clay with very low permeability Type of constitutive model for soil: Ø Hardening soil model ABCD ABCDABCDABCD Properties of structural lining elements: Ø Linear elastic ABCD ABCD ABCDABCD. ABCDABCDABCD ABCD ABCD ABCD ABCD ABCDABCD m φ ψ ABCD Ø 2D 1 plate element E Ø Lining thickness: 2 cm ABCD ABCD ABCD ABCDABCD (MPa) (-) (deg.) (m/sec) (-) (kn/m 2 ) (-) ABCD ABCD ABCD ABCD 4

5 Assumptions Tunnel Geometry Ø Tunnel diameter (D=8 m) Ø Overburden (1.D=12 m) Ø Target volume loss:. % Tunnel-lining likely configurations: Ø Upward arrangement Ø Centered arranegment Ø Downward arrangment Time dependent grout properties: Ø Stiffness (deformability) Ø Poisson s ratio (compressibility) Ø Properties chosen to highlight the Stiffness (MPa) lower grouting pressure higher grouting pressure influence of, Stiffness Poisson's ratio, Time (hour),,4,4,3,3 Poisson's ratio

6 Simulation Scenarios (undrained+) #1 Stress release method: Stage 1 Stage 2 Stage 3 γ * γ #2 Soil stiffness reduction method: Stage 1 Stage 2 Stage 3 E * E E #3 Mechanical pressure boundary on drilled zone: Stage 1 Stage 2 Stage 3 p g Stage 2: undrained Stage 3: undrained + p g =2 kpa (uniform) In-situe stress at tunnel crown p =2 kpa 6

7 Simulation Scenarios (undrained+) #4 Deformation release (predefined contraction): Stage 1 Stage 2 Stage 3 ε r # Hydrostatic pressure boundary on cavity and lining: Stage 1 Stage 2 Stage 3 p g #6 Reduced lining stiffness method: Stage 2: undrained Stage 3: undrained + p g =2 kpa (uniform) In-situe stress at tunnel crown p =2 kpa Stage 1 Stage 2 Stage 3 EA * EI * EA EI 7

8 Simulation Scenarios (staged construction) #7 Time dependent HM pressure boundary : E grout (t) ν grout (t) Hydraulic pressure In grout for 2 hr To generate excess pore pressure in grout Stage 1 Stage 2 Closed hydraulic boundary for 1 hr Note: these 7 scenarios are defined in a manner to have identical volume loss around the TBM =. % E grout Fully (t) coupled ν grout hydromechanical (t) analysis Stage 3 Pressure (kpa) Grout pressure Excess PP Time (hour) 8

9 Results and conclusion (settlement trough) Distance from tunnel centre (m) construction construction Stress release γ * #1 Soil stiffness release E * #2 Mechanical pressure Hydrostatic pressure # Distance from tunnel centre (m) -1 construction -1 Lining stiffness reduction #6 p g EA * EI * construction - -1 construction construction p g ε r #3 Deformation release #4 Time dependent HM E grout (t) ν grout (t) # Distance from tunnel centre (m) construction 9

10 RUHR-UNIVERSITÄT BOCHUM Results and conclusion (lining def. & pore pres.) Stress release Hydrostatic pressure - γ* #1 # pg - Soil stiffness reduction - - EA* EI* - #3 - Undeformed tunnel εr Time dependent HM Egrout(t) νgrout(t) Deformation release #6 #7 - pg Lining stiffness reduction Mechanical pressure E* #2 #4 Deformed tunnel after construction (scale factor: 1) Deformed tunnel after (scale factor: 1) 1

11 Results and conclusion (lining force) RUHR-UNIVERSITÄT BOCHUM Scenario N max_constructio n (kn/m) N max_consolidation (kn/m) # # # #4 14.7* 1.9** # # # Scenario M max_construction (kn.m/m) M max_consolidatio n (kn.m/m) # # # # # # # * tension is developed at the tunnel crown kn/m ** tension is developed at the tunnel crown 9.1 kn/m Soil stiffness release E * Stress release γ * Mechanical pressure p g Deformation release ε r Hydrostatic pressure p g Lining stiffness red. EA * EI * Time dependent HM E grout (t) ν grout (t) #1 #2 #3 #4 # #6 #7 11

12 Thank you for your attention 12