Numerical modelling in tunnels

Transcription

1 ITA - AITES WORLD TUNNEL CONGRESS 007 PRAGUE The rd Training course TUNNELLING IN URBAN AREA Prague, - th May 007 TRAINING MATERIAL PREPARED BY Ing Radko Bucek Ph.D. (Mott MacDonald, Czech Republic)

2 Introduction Chapter 1 - Sequential excavation tunnel support structural elements Index Chapter - Numerical models of tunnels and reality constitutive laws Chapter - Settlement above shallow tunnels Conclusions /0

3 Introduction Shotcrete does not mean NATM /0

4 Selection of tunnel support structural elements Introduction ground excavation method demand for control of deformation - settlement /0

5 Ground Introduction Soils R.M. with less than systems of discont. R.M. with more than systems of discont. Continuum Numerical methods Discontinuum Numerical methods + Structural analysis!! Continuum Numerical methods /0 0

6 Excavation method Introduction Segment lining Perforex Shotcrete TBM Perforex NATM 6/0

7 Control of deformation σ (MPa) Ground reaction curve GCR δ rad Introduction A Stiff support Optimum deformation Deformable support δ (mm) rad 7/0

8 Introduction Timing of support installation 8/0

9 Chapter 1 Sequential excavation tunnel support structural elements shotcrete rock bolts 9/0

10 Shotcrete membrane effect Chapter 1 Rock How do mass mechanical deforms into properties the opening, of the rock and cosequently, mass in the vicinity in case of an circular opening or eliptical change?????????? shape of the opening, radial discontinuities and cracks tend to close. Stocking effect Výrub Tunnel Výrub Tunnel Tunnel Tunnel 10/0

11 Shotcrete wedge effect wedges Chapter 1 Tunnel Shotcrete 11/0

12 Shotcrete shear strength and the strength of adhesion Chapter 1 shotcrete Loose block Magnitude of adhesion is estimated to be close to MPa Detail T opening Tlou Shotcrete šťka stříkaného thickness betonu <cm < cm Shotcrete thickness >cm 1/0

13 Rock bolts US Tunnel engineering handbook Chapter 1 Rock bolt is the general term that includes rock bolts, rock dowels and cable tendons. 1/0

14 Pevnost 1 Rock bolts Zatížení Load ( σ1) Chapter 1 Shear strength Odpor proti boční deformaci ( ) Confinement σ P σ Obálka pevnosti Rock arch formed by the rock bolts- rock mass interaction. σ σ σ1 σ1 Napětí stress 1/0

15 Shotcrete and rock bolts Chapter 1 span Rozpětí span Rozpětí 1/0 0

16 Shotcrete and rock bolts Chapter 1 shotcrete 16/0

17 Dulles international airport Chapter 1 17/0

18 8/0

19 Dulles static calculation Chapter 1 I II 19/0

20 1 Perforex tunnels Chapter 1 0/0

21 Perforex static calculation Chapter 1 I II 1/0

22 Chapter 1 Which is better OK Claystone OK+ OK Clay xxxxxxxxx /0

23 Deformation and mobilized strength Chapter 1 τ peak τ f OC clay NC clay residual τ r Δl /0

24 Chapter 1 Mobilised strength Claystone Short def. path All components together Rock self supporting Footing bearing capacity sufficient Clay Long def.path Components gradually Time dependent loading Non of the components itself sufficient /0

25 Potential collapse Chapter 1 /0 0

26 Chapter 1 Bearing capacity of the support 6/0

27 Chapter 1 Which is better 7/0

28 Chapter Numerical models of tunnels and reality - constitutive laws constitutive laws Shotcrete rockbolts 8/0

29 Chapter Do numerical models provide us with information about: immediate crown stability during excavation? immediate face stability during excavation? loads that the support shall be dimensioned for? deformations that should be expected? 9/0

30 Chapter Constitutive laws 0/0

31 Constitutive laws σ Linear elasticity σ Non-linear elasticity Chapter ε σ Elastoplasticity ε ε 1/0

32 Chapter Elastoplasticity σ Strain hardening σ Strain softening σ Perfectly plastic ε σ ε Strain hardening Strain softening Perfectly plastic ε ε /0

33 Does rock change in mud in yielding zones??? No!!! Chapter Yielding zones only signal locations where the strength of the material, mostly calculated as shear strength, became lower than acting stresses. All deformations calculated as yielding are always questionable and should be taken with caution. However, extensive existence of large yielding zones signal certainly problems in numerical Model, and might signal also problems in reality. /0

34 Chapter Elastoplasticity with Mohr Coulomb Elastoplasticity with Hoek and Brown Cam clay E μ φ c E μ m s M Γ κ λ /0

35 Cam-Clay Chapter CSL NCL λ C κ C = c /.0 = r /.0 N N Γ NCL CSL NCL CSL M κ 1 1 l λ 1 1 p'=1 p'=1 p'=1 ( p'= 1/( σ1 + σ) ) /0 0

36 Chapter Po σ t σ t Po σ r σ r Increase of stiffness Increase of strength From the characteristics Is that always true? of rock mass to characteristics that are close to intact rock sample 6/0

37 7/0 1 Tunnel Dobrovského in Brno Chapter

38 Chapter Deformation/time E=80MPa 10 days HL-HP HL HP HL-PS HP-PS PS deformace [mm] Mrázovka E=0MPa 10 months Dobrovského HL - PS HP - PS HL - HP zahájení správy štol oprava bodů 8/0

39 Chapter Creep in clays deformace [mm] HL - PS HP - PS HL - HP zahájení správy štol oprava bodů Rock, Clays sand, time gravel dependant behavior 9/0

40 Result of creep Chapter Elasto-plasticity creep influence σ yin Situ = 60 kpa σ y = 0 kpa σ y = 80 kpa 0/0

41 Chapter Settlement above shallow tunnels 1/0

42 Deformation ahead of the face beyond Deformation the face Face deformation Lining instalation Face deformation Excavation without support Lining instalation Poklesová kotlina settlement Convergence Lining Lining deformation rock bolts lining Deformation response to the excavation Chapter 1. Rock deformation in front of the face. Rock deformation between face and installed lining. Closing of discontinuities around opening due to radial movements. Rock lining interaction. Elastic part of deformation 6. Plastic part of deformation Deformace p ř ed č elbou Deformation ahead of the face Deformation beyond the face Settlement /0

43 Settlement trough Chapter /0

44 /0 1 Effect of tunnel excavation on surface structures

45 Chapter /0 0

46 Terminology Chapter 6/0

47 Surface structures damage Chapter shear mechanisms tension 1. shape of s.t.. extent of s.t. rel. defl.- sagging rel. defl.- hogging 7/0

48 Criteria for analyzing damage 8/0

49 Prague metro line C Chapter Vs1=Vs 9/0

50 Conclusions What is the value of a numerical model? Technical value of a numerical model is directly proportional to the professional skills of the engineer working with the model, his ability to use the software, and his understanding of all aspects of the technical problem under consideration. 0/0