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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.
