herrenknecht ag softground tbms > 40 ft - SCATnow

MIXSHIELDS PART 2
Operating pressure during advance [bar]
15.0
12.5
10.0
7.5
5.0
2.5
2.5
Mülheim
ø 6.9m
sandstone,
mudstone
Grauholz
ø 11.6m
sand, gravel
molasse
HERA
ø 5.95m
sand, gravel
3.5 3.5
Sydney
ø 10.4m
sandstone, clay
0.0
1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2000 2003
While it is possible to accomplish the
required shield thrust by changing the
number or diameter of the thrust cylinders,
far more sophisticated technical solutions are
required for seal systems. This is especially
true of the main bearing seal system, which is
one of the most sensitive design elements in
high-pressure applications. For support
pressures beyond 4 bar, pre-stressed
cascade systems are used with the individual
cascade chamber pressures automatically
following the face pressure.
Westerschelde
ø 11.34m
sand, clay
Wesertunnel
ø 11.67m
gravel, clay, boulders
4. Elbröhre
ø 14.2m
gravel, clay, boulders
Above: Fig 9 - Operating pressure of Herrenknecht Mixshields
Torque main drive [kNm]
40,000
35,000
30,000
25,000
20,000
15,000
10,000
5,000
0
Design Mixshield [kNm]
Design EPB [kNm]
4.0
5.5
7.5
Hallandsas
ø 10.53m
design pressure
13.0
Diver assignment cutting tool change
Hallandsas
Grauholz
SMART
Chongming,
Nanjing
4. Elbröhre
2 4 6 8 10 12 14 16
Shield diameter [m]
H8
H3/4
Zürich-Thalwil
Above: Fig 10 - Torque comparison of cutterhead drives (Mixshield vs EPB-shield)
Below: Fig 11 - Chongming alignment
Tunnel
9km
Elevated highway
6.5km
A86
Bridge
10km
Shanghai Changxing Chongming
Island
These systems can handle pressures far
beyond 10 bar for an extended period of
time in dynamic mode without the risk of
overloading the individual lip seals. Longterm
field experience with large diameter
drive systems (bearing diameter range of
6m) with face pressures of 7 bar to 10 bar
already exist and full scale workshop and
commissioning test programmes with
pressures of 15 bar have been performed
successfully. In emergencies or extended
stoppages (long-term static mode),
additional inflatable seals are included.
While it is now possible to address highpressure
operations by using appropriately
designed equipment, the key questions
relate more to the potential and the
limitations for chamber access under
hyperbaric conditions.
Technical solutions to reduce the need
for man access to the excavation chamber
are available and currently include:
• Accessible cutterheads for atmospheric
cutter tool change (larger machines only)
• Remotely activated standby cutter tools
• Load detection and wear sensor systems
However, these technical features will not
totally eliminate the need for a “Plan B” for
manual intervention to cover unforeseen
conditions or worst-case scenarios.
Based on the system of excavation and
face support, a Mixshield requires lower
cutterhead torque compared with an EPB
shield (figure 10), as the cutterhead is only
excavating the ground at the tunnel face
into the suspension-filled excavation
chamber. The excavated soil sinks towards
the submerged wall opening in the invert
due to gravity, assisted by the flow direction
of the circulated slurry, and is carried to the
suction pipe after clearing the rock crusher
and suction grille.
An EPB shield requires a comparatively
high torque at the cutterhead because, in
addition to the soil excavation, the
cutterhead itself acts as a mixing tool inside
the excavation chamber, which is
completely filled with muck.
Therefore by adopting high torque EPB
drive systems that have been developed for
large diameter machines, such as that used
on the M30 project, in Madrid (with
125,000kNm), there is huge potential for the
development of larger diameter Mixshield
machines.
Examples of projects
The following presentation of the
Chongming and A86 tunnel projects
demonstrates the efficiency of current
Mixshields and the value of development.
Mixshield used as a shield with slurry
supported face – Chongming, China: A
twin tube road tunnel is currently being built
beneath the Yangtze River in the city of
Shanghai, comprising two 7160m-long bores
with three lanes each. The tunnel, along with
a new bridge, will link the islands of
Changxing and Chongming to the freeway
system and city. The geology of the tunnel is
defined by its position in the river delta,
consisting of soft clay deposits and thin sand
layers. The tunnel has an outside diameter of
15m. The pre-cast concrete ring consists of
9+1 segments with a length of 2m. The
segments are 640mm thick and weigh up to
16.7 tons. The basic concept of the two
Mixshield machines for the project is based
on experiences from the Mixshield used at
32 Tunnels & Tunnelling International JUNE 2008