TBM EXCAVATION AND TUNNEL DESIGN FOR ROCK TUNNELS UNDER HIGH COVER IN CRITICAL GEOLOGICAL CONDITIONS

Transcription

1 TBM EXCAVATION AND TUNNEL DESIGN FOR ROCK TUNNELS UNDER HIGH COVER IN CRITICAL IL FUTURO DI SELI GEOLOGICAL CONDITIONS Condivisione di obiettivi e traguardi Remo Grandori_Swiss Tunnel Society September 2010

2 TBM TUNNELING SCIENCE TECHNOLOGY AND ART Soft ground TBM tunnelling Rock TBM tunnelling

3 SOFT GROUND TUNNELING Mix of science and technology Ground normally homogeneous Shallow cover and water pressure Risks more predictable, limited to man made actions/objects Procedures and discipline in operation and maintenance

4 ROCK TUNNELING Technology, art and small science No homogeneous (Rock to mud) High cover and water pressure Risks difficult to be predicted (poor science) Force of nature may become impressive, normally were not expected

5 EXAMPLE OF EXTREME EVENT IN ROCK TUNNELLING The GIBE II CASE

6 The Gilgel Gibe II Hydro-Power Plant 240km from Addis Ababa, in Ethiopia, between Gibe and Omo Rivers. PURPOSE TUNNEL LENGHT EXCAVTION DIAMETER Tab.1 Water Conveyance project main data HPP (432MW) 25,8 km 7,0 m DESIGN DISCHARGE 100 m 3 /s DESIGN INTERNAL PRESSURE SEGMENT TYPE min.2 bar max.7 bar Tab.2 Lining geometrical characteristics 4 HEXAGONAL SEGMENT THICKNESS SEGMENTAL LINING OUTSIDE DIAMETER SEGMENTAL LINING FINAL INTERNAL SEGMENT WIDTH 25 cm mm mm mm

7 Figure 1. Typical lining section

8 EVENT AT THE CHAINAGE FROM INTAKE HEADING The tunnel face moved towards and pushed back the TBM at mm/hour. The measured pressure of mud was 40 bars

9 TBM SHIELD DEFORMED

10 LINING DAMAGED

11 BORE HOLES FOUND MUD AT 40 BAR AND OVER 40c Figure 6. Mud poured out from one of the borehole

12 BACK CHAMBER DESIGN (BY LOMBARDI ENGINEERS)

13 BY PASS TUNNEL AND BACK CHAMBER

14 MUD EXTRUDED AND FLOWING INSIDE THE LEFT BY PASS TUNNEL

15 Extruding mud in the Exploratory Adit

16 Figure 12. Extruding mud in the Exploratory Adit

17 Figure 13. Extruding mud at the Adit Portal

18 Extruded mud at the Adit Portal

19 Extruded mud in the Power Tunnel

20 Consolidated mud filling the Power Tunnel

21 FOR N.3 TIMES THE LEFT ADIT AND THE TUNNEL WERE FLOODED BY THE MUD Water pressure (manometer BH n 2 Back Chamber) 26,0 p [bar] 24,0 22,0 20,0 18,0 16,0 14,0 12,0 1st Event BH-SM-1 BH-SM-3 BH-SM-9 BH-SM-11 BH-SM-15 BH-SM ,0 8,0 6,0 2nd Event 4,0 2,0 3th Event 0,0 12/5 22/5 1/6 11/6 21/6 1/7 11/7 21/7 31/7 10/8 20/8 30/8 9/9 19/9 29/9 9/10 19/10 29/10 8/11 18/11 28/11 8/12 18/12 28/12 7/1 17/1 27/1 4th Event days Pressure variation measured in the Back Chamber

22 A NEW STRATEGY WAS DEFINED the mud was removed from tunnel the Back-Up was extracted to portal new drainage drilling performed Exploratory Adit on the Right side (40m behind)

23 RIGHT END SIDE BY PASS

24 Rescue Chamber to recover the TBM

25 BY PASS TUNNEL SCHEME Fault TBM ri-assembly tunnel By pass tunnel Concrete Plug

26 PRODUCTION AFTER RESTART OF EXCAVATION. Figure 28. TBM production chart after the excavation resuming

27 The Tunnel excavation completed on June 6 th 2009, the two TBMs meet at the ch.: 8+520,8

28 EVENT OCCURRED AFTER START OF OPERATION Remo Grandori

29 ALMOST CM OF MUD, SAND, BOULDERS AND BLOCKS ENTERED THE TUNNEL Remo Grandori

30 FROM A SECTION OF m OF TUNNEL

31 SO WE WERE AGAIN IN THE...TO THE NECK

32 SIX MONTH AFTER...ALMOST OUT

33 NEVER GIVE UP EVEN THE WORSE SITUATIONS CAN BE OVERCOME BY ENGINEERING SPECIAL MEASURES AND DEDICATED EXPERT CREWS THIS IS WHAT MAKES TUNNELLING SUCH A WONDERFUL WORK

34 DON T STOP TBM DESIGN PROGRES THE PROGRESS IN TBM DESIGN WILL MORE AND MORE LIMITS THE NECESSITY OF SPECIAL MEASURES TO VERY EXTREME A ND RARE EVENTS

35 DOUBLE SHIELD DESIGN EVOLUTION Increase capacity in Hard Rock boring Increase Torque and Auxiliary Thrust New DSU TBM design Dual mode EPB DSU

36 TODAY STATE IN ROCK TBM DESIGN Short shields Conical shields Extended overboring & overcutting Extended ground and face treatment Torque and thrust same of EPB TBMs Double mode capacity (with no stand by time) were required Improve cutterhead design to cope with widest range of geological applications

37 TUNNEL DESIGN The fact that TBMs are and will be more and more capable to bore trough extremely bad ground under high cover and water pressure will move the criticality to tunnel lining and support design.