IL FUTURO DI SELI

Condivisione di obiettivi e traguardi

TBM EXCAVATION AND TUNNEL DESIGN FOR ROCK

TUNNELS UNDER HIGH COVER IN CRITICAL

GEOLOGICAL CONDITIONS

Remo Grandori_Swiss Tunnel Society – September 2010

TBM TUNNELING SCIENCE TECHNOLOGY AND ART

Soft ground TBM tunnelling

Rock TBM tunnelling

SOFT GROUND TUNNELINGMix 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

ROCK TUNNELINGTechnology, 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

EXAMPLE OF EXTREME EVENT IN ROCK TUNNELLING

The GIBE II CASE

Tab.1 Water Conveyance project main data

PURPOSE HPP (432MW)

TUNNEL LENGHT 25,8 km

EXCAVTION DIAMETER 7,0 m

DESIGN DISCHARGE 100 m3/s

DESIGN INTERNAL PRESSURE min.2 bar max.7 bar

Tab.2 Lining geometrical characteristics

SEGMENT TYPE 4 HEXAGONAL

SEGMENT THICKNESS 25 cm

SEGMENTAL LINING OUTSIDE DIAMETER 6.800 mm

SEGMENTAL LINING FINAL INTERNAL 6.300 mm

SEGMENT WIDTH 1.600 mm

The Gilgel Gibe II Hydro-Power Plant 240km from Addis Ababa, in Ethiopia, between Gibe and Omo Rivers.

Figure 1. Typical lining section

EVENT AT THE CHAINAGE 4+196 FROM INTAKE HEADING

The tunnel face moved towards and pushed back the TBM at 40-60 mm/hour.

The measured pressure of mud was 40 bars

TBM SHIELD DEFORMED

LINING DAMAGED

BORE HOLES FOUND MUD AT 40 BAR AND OVER 40c°

Figure 6. Mud poured out from one of the borehole

BACK – CHAMBER DESIGN (BY LOMBARDI ENGINEERS)

BY PASS TUNNEL AND BACK CHAMBER

MUD EXTRUDED AND FLOWING INSIDE THE LEFT BY PASS TUNNEL

Extruding mud in the Exploratory Adit

Figure 12. Extruding mud in the Exploratory Adit

Figure 13. Extruding mud at the Adit Portal

Extruded mud at the Adit Portal

Extruded mud in the Power Tunnel

Consolidated mud filling the Power Tunnel

Water pressure (manometer BH n°2 Back Chamber)

0,0

2,0

4,0

6,0

8,0

10,0

12,0

14,0

16,0

18,0

20,0

22,0

24,0

26,0

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

19/1

0

29/1

0

8/11

18/1

128

/11

8/12

18/1

2

28/1

2

7/1

17/1

27/1

days

p [b

ar]

2nd Event

BH-SM-1

3th Event

1st Event

4th Event

BH-SM-3

BH-SM-9

BH-SM-11 BH-SM-15

BH-SM-17-18

FOR N.3 TIMES THE LEFT ADIT AND THE TUNNEL WERE FLOODED BY THE MUD

Pressure variation measured in the Back Chamber

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)

RIGHT END SIDE BY PASS

Rescue Chamber to recover the TBM

BY PASS TUNNEL SCHEME

Concrete Plug

By pass tunnelTBM ri-assembly tunnel Fault

PRODUCTION AFTER RESTART OF EXCAVATION.

Figure 28. TBM production chart after the excavation resuming

The Tunnel excavation completed on June 6th

2009, the two TBMs meet at the ch.: 8+520,8

EVENT OCCURRED AFTER START OF OPERATION

Remo Grandori

ALMOST 10.000 CM OF MUD, SAND, BOULDERS AND BLOCKS ENTERED THE TUNNEL

Remo Grandori

FROM A SECTION OF 10 – 15 m OF TUNNEL

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

SIX MONTH AFTER...ALMOST OUT

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

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

DOUBLE SHIELD DESIGN EVOLUTION

• 1983- 1993 - Increase capacity in Hard Rock boring

• 1995- Increase Torque and Auxiliary Thrust

• 2001-2005 New DSU TBM design

• 2005-2010 – Dual mode EPB DSU

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

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.