Lecture 4. Tunneling Through Fault Zones and Melanges

Transcription

1 Lecture 4 Tunneling Through Fault Zones and Melanges BIMROCKS SHORT COURSE Dr. Edmund Medley Consulting Geological Engineer, Belmont, California, USA [email protected] Geological Engineering Department, Haceteppe Univ, Ankara June 22 and 23, 2004

2 Much of this lecture is possible thanks to the use of slides and photographs permitted by: Gruppe Geotechnik Graz, Austria Prof. Dick Goodman Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer 2

3 BIG CONCLUSION 1: Remember this picture!!! Matrix Proposed Tunnel Blocks, inclusions, lenses, etc Scale: 1:?????? Matrix Actual Distribution of Blocks Medley, 2000

4 BIG CONCLUSION 2: Remember this picture as well!!! Matrix Proposed Tunnel Matrix Apparent Distribution of Blocks Willis, 2000

5 Tunneling failures can occur in relatively coherent rock-masses Photo: courtesy Prof. R. Goodman Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer 5

6 Some Rock Mass BEHAVIOUR TYPES Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer 6

7 Tunneling in in fault rocks and melanges can result in in failures Collapsed Tunnel M2, Egnatia Motorway, Greece Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer 7

8 Tunnel Collapse in in unexpected bimrock Galgenberg Tunnel, Austria Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer 8

9 Example Case Hepp Study Kavsak of of Geotechnical (Turkey) Hazard Assessment Project Data Upgrading of the river for energy production. Headrace tunnel (length 9km, diameter 9,0m Power house Tasks Geotechnical hazard assessment and optimization of design prior to construction Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer 9

10 Geotechnical Longitudinal Section for for the the Tender Design faulted Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer 10

11 Site mapping in in faulted rocks Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer 11

12 Site mapping Geotechnical Hazard Assessment Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer 12

13 Site mapping of of geological structures Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer 13

14 Site mapping of of bimrock... Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer 14

15 Revised Geotechnical Longitudinal Section Fault zones with bimrocks Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer 15

16 Geotechnical Longitudinal Section for for the the Tender Design faulted Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer 16

17 BIMROCK EFFECTS in in TUNNELS Mixed face conditions require different excavation methods on the same section Strong variation of rock mass quality Stress redistribution and deformations extremely influenced by arrangement of blocks and matrix Prediction of displacements and lining utilization extremely difficult Danger of brittle failures in blocks Difficulty of determination of proper support Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer 17

18 BIMROCK EFFECTS PROBLEMS of DISPLACEMENTS IN MATRIX IN RELATION TO BLOCK DISTANCE Displacements depend on the length of the weak zone between two stiff blocks ,20-0,25-0,30-0,35-0,40 Δr 5 length of 20 weak zone 40 m 75 m Δr -0,45 Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer [email protected] 18

19 BIMROCK EFFECTS DISPLACEMENTS Final displacements influenced by zone length and stiffness contrast between blocks and matrix ,20-0,30-0,40-0,50-0,60-0,70-0,80 E 1 /E 2 = 1,5 E 1 /E 2 = 2,0 E 1 /E 2 = 4,0-0,90-1,00-1,10 Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer [email protected] 19

20 BIMROCK EFFECTS STRESS DISTRIBUTION Stress concentration in blocks depend on stiffness contrast and distance between blocks σ1/p1 40,0 50,0 60,0 70,0 80,0 90,0 100,0 110,0 120,0 130,0 140,0 150,0 160,0 170,0 180,0 2,70 2,60 2,50 2,40 2,30 2,20 2,10 2,00 1,90 1,80 F 1,5 / Var 8 F 2,0 / Var 8 F 4,0 / Var 8 Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer [email protected] 20

21 BIMROCK EFFECTS STRESS CONCENTRATIONS Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer 21

22 BIMROCK EFFECTS MODEL 1.1 STIFF advance SOFT STIFF STIFF-SOFT-STIFF FINAL SETTLEMENTS FINAL STRESSES NORMALISED σ Z / σ [-] V,PRIM settlement [m] stress σz / σv,prim [-] normal chainage [D] 2/3 E stiff 1/2 E stiff 1/4 E stiff Relative stress increase in stiff material Relative stress decrease in soft material Trough shaped displacement chainage [D] VECTOR ORIENTATION TREND +1/2 D verctor orientation [ ] normal Change of displacement vector orientation near transition Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer [email protected] 22 chainage [D]

23 BIMROCK EFFECTS BLOCK REINFORCEMENT Stress concentrations can cause brittle failure in stiff blocks Resulting stress redistribution leads to additional displacements in the matrix material Knowledge of the spatial distribution of blocks and matrix essential to properly estimate stress situation Short term prediction and prediction of displacements extremely important Support / reinforcement of blocks necessary to avoid brittle failure and long term stress redistribution, frequently mistaken for creeping Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer [email protected] 23

24 BIMROCK EFFECTS CASE STUDIES Location Map Tunnel Spital, Austria Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer 24

25 BIMROCK EFFECTS: Case Study Project data : Tunnel Spital, Austria Twin 2,2 km long freeway tunnels in the Semmering region, eastern Austria Alignment along a major fault zone Excavation area m2 Underpass of a railway line and built up area average overburden 30 m, maximum 80 m Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer [email protected] 25

26 BIMROCK EFFECTS CASE STUDY Tunnel Spital, Austria Geological overview Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer 26

27 BIMROCK EFFECTS CASE STUDY Geological sections at tunnel faces at various tunnel locations Tunnel Spital, Austria Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer 27

28 BIMROCK EFFECTS CASY STUDY Geological overview Nord tube: m South tube: m Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer 28

29 BIMROCK EFFECTS Case study Heterogeneity - Displacements Tunnel Spital, Austria Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer [email protected] 29

30 BIMROCK EFFECTS CASE STUDY Block effect on displacement settlement crown / top heading Block Tunnel Spital, Austria Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer [email protected] 30

31 BIMROCK EFFECTS: COLLAPSE at at GALGENBERG TUNNEL, AUSTRIA A fatal collapse July 1994 at station 1330 m. Eight meters of heavily supported tunnel section collapsed at the face. A miner, and equipment was buried Redesign and maintenance work lasted for two months. Collapse caused by brittle failure of stiff rock outside of excavation Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer [email protected] 31

32 BIG CONCLUSION 1: Remember this picture!!! Matrix Proposed Tunnel Blocks, inclusions, lenses, etc Scale: 1:?????? Matrix Actual Distribution of Blocks Medley, 2000

33 BIG CONCLUSION 2: Remember this picture as well!!! Matrix Proposed Tunnel Matrix Apparent Distribution of Blocks Willis, 2000

34 Copyright: Dr. Edmund Medley, PE CEG Consulting Geological Engineer 34

35 ex po po nent (ik-spo nent) n. 1. One who expounds or interprets.