control of the ground during shield tunneling - … · control of the ground during shield...
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Control of the ground during shield tunneling
Los Angeles December 16, 2011
Edward J. Cording Professor emeritus University of Illinois at Urbana-Champaign
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Figure 1-1
London, 1818
• In patent application: Marc Isambard Brunel describes objective of
his tunnel shield…
to “open… the ground in such a manner that no more earth shall be displaced than is to be filled by the shell or body of the tunnel.”
1825 – 1841: Thames River: First subaqueous
shield tunnel Brunel made soundings & borings (sand lenses under blanket
of clay), designed tunnel, obtained financing, built the shield, directed construction, recovered from seven floodings, rebuilt the shield under the river, re-financed the project, …. and, in 1841, was knighted by Queen Victoria.
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Figure 1-1
London, 2011
• Thames Tunnel still in operation on London Underground
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Control of the ground during shield tunneling
• 1841: Thames Tunnel: 40-ft-wide box • 1940: Chicago Subway 20 – 25 feet • 1972: Washington DC Metro • 2000: Evanston IL (12-ft) • 1990: Metro Red Line under Jewelry Mart
• 2006: Metro Gold Line Eastside Extension • 2011: Sound Transit U Link, Capitol Hill • 2008: Barcelona Line 9 40-ft-dia. • 2011: Alaskan Way Viaduct Replacement 56- ft-dia.
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5 FIGURE 2-1
Primary objective:
Relate tunnel
construction…
Chicago Subway,
1938-1941
Karl Terzaghi and Ralph Peck
Soft Chicago Clay
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6 FIGURE 2-2
… to settlement at the surface
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Squeeze tests: to measure ground
movement into face, crown & walls
Rods embedded into clay; ends of rods
were surveyed,
Displacement was correlated with
excavation sequences...
Monkey drift with
wall plate added , to support arch
Result: Excavation sequence was changed
Surface Settlements
reduced:
4” 2”
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Hansmire, Cording 8
1/4 inch
DEEP SETTLEMENT
POINT
(1.5’ above crown)
1972 Washington DC Metro, Lafayette Square, Alluvial sand, clay
Locate and evaluate source of ground loss
13 inches
Deep settlement point – extensometer
Shield
Deep
Settlement
Point
6 inches
Inclinometer: measure
lateral displacement into
tunnel face
Surface Settlement
Monitor every shove of the shield
Used to determine source of ground
loss around shield
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Result
• Shield hood rebuilt for second tunnel
• Settlements reduced from 6 to 2 inches
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Control Sources of Ground Loss
– F: FACE
– O: OVERCUT
– S: SHIELD
– T: TAIL
– L: LINING
F
L O S T
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Test Section 4Vertical ground movements with Face Advance
Distance to the Shield Face (ft)
-100 -80 -60 -40 -20 0 20 40 60 80 100
Settle
ment (in)
-4
-3
-2
-1
0
D4
Surface point
Deep point
18.8 ft
12 ft66.7 ft
½ “
1 ½”
½”
Deep Settlement point
Annulus: ¼” ¾” ¼”
2000 Evanston, IL: Soft Chicago Clay McNally Construction
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1990, Metro Red line, Segment 1, Alluvium Shank - Ohbayashi
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Chemical grouting ahead of face, compaction grouting as shield passed
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Pressurized face shields
Recommended for projects in Los Angeles ECIS and NEIS
Metro Gold Line Eastside Extension
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Pressurized & conditioned muck (foam & polymer) in
chamber supports face
Screw removes conditioned muck & provides back pressure
Lining erected in tail of shield
Grout placed through tail as shield is shoved
Earth Pressure Balance Shield
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Typical Mining Cycle – 5 ft
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Typical Mining Cycle – 5 ft
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2006, Metro Gold Line Eastside Extension
1.7 miles: Traylor Frontier Kemper JV
Earth Pressure Balance Shields Monitoring of ground movement 75 Extensometers &
Surface settlement cross-sections Tunnel centerline settlement points Building settlement points
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West bound
East bound
0.3” 50’
SLOPE: 1/2000 = 0.5 x 10-3
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Angular Distortion, (x10-3
)
0 1 2 3 4 5 6 7
Late
ral S
train
,
L (x10
-3)
0
1
2
3
4
Col 36 vs Col 37 Col 39 vs Col 40
Col 48 vs Col 49
NEGL.
VSL
SLIGHTDAMAGE
MODERATE TOSEVERE DAMAGE
SEVERE TO VERY SEVERE DAMAGE
Figure 25 Damage level estimation and observed damage level
* The results of two field cases and one numerical test
are out of range
( ) - Damage level based on
maximum crack width
(Burland et al., 1977)
[ ] - Damage level based on
field observation
(Boscarding and Cording, 1989)
(N) - Negligible
(VSL) - Very slight
(SL) - Slight
(M) - Moderate
(SE) - Severe
(VSE) - Very severe
[N] - Negligible
[VS] - Very slight
[SL] - Slight
[M] - Moderate
[SE] - Severe
[VSE] - Very severe
Numerical tests
Field cases
MODERATE DAMAGE
Constant Principal
Extension Strain
FIGURE 4-1
Angular Distortion, ( x 10 - 3 )
1/1000 1/500 1/200 1/100
after Boscardin & Cording, 1989
Damage criterion based on state of strain at a point
Grade beam & floors tied to bearing walls
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Control of gas during construction
• Pressurized face
– Inflow of water and gas prevented into face
– Volume of gas limited to volume in pore space in the excavated muck
– Robust ventilation
• Gasketed lining installed immediately:
– Inflow of water and gas prevented over length of tunnel:
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Robinson, Bragard, 2007
2006, Metro Gold Line Eastside Extension
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Robinson, Bragard, 2007
72-inch hard fan line 100,000 cfm 200 feet: 3 section
Screw Conveyor
2006, Metro Gold Line Eastside Extension
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• Double protection against leakage of gas & water
• 2nd gasket serves as bulkhead for grouting between gaskets to seal leaks
• Proposed: Cross gasket to confine leakage & grout to area between 2 adjacent rings
Precast concrete segments with double gasket
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2011 Sound Transit Jay Dee/ Coluccio/ Michels Ulink JV Glacial till, outwash, lake clays
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Capitol Hill Launch
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Capitol Hill Trailing Gear
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Test Sections: Piezometer & Extensometer Continuously monitored
Diponio, et al 2011, in press
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Pressurized, conditioned muck fills overcut
Grout injected through tail under pressure
Co
nd
ito
ne
d m
uck
u
nd
er
pre
ssu
re
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Grout injected through tail under pressure
Co
nd
ito
ne
d m
uck
u
nd
r p
ress
ure
Pressurized, conditioned muck fills overcut
0 Deep Settlement
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Regular Ground Losses at Shield – F: Face
• Pressurized closed-face mode: maintain face pressure with conditioned muck • Reduce risk of large ground loss • Reduce ‘elastic’ face displacement: More critical for large-diameter shields
– O: Overcutter annulus
• Annulus aids steering, reduces shove forces, reduces wear • Reduce annulus or • Fill annulus with conditioned muck or inject bentonite around shield
– S: Steerable shield – short (L/D) or articulated • Minimizes required overcut to negotiate turn • Minimizes plowing and yawing
– T: Tail gap • Grout through tail skin during shove • Improved grouting procedures such as two component grout, accelerated set • Control grout volume & injection pressures • Adequate tail seals & grease injection ports
– L: Lining deflection:
• Adequate lining installation & tail grouting
F
L O S T
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Monitoring and Control
• Continuous readout of machine parameters – Face pressure – Pressure around shield – Grout pressure, volume – Belt scale weight of muck excavated
• Continuous monitoring of ground behavior as shield passes test section – Deep settlements – Surface settlements – Piezometric levels in groundwater
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2008: I2-m-diameter
earth pressure balance shield
In erection bay,
Line 9, Barcelona
Control
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Example of Reference, Warning, & Alert Levels Bono et al, 2008: Barcelona, P.K. 2+400 to 2+600
Parameter Reference Warning Alert
Face pressure, crown 1.75 bar, per ring & 2 hours
<1.5 bar >2.0 bar
<1.3 bar, >2.3 bar During 15 min.
Pressure gradient 1.7 t/m2
<1.6, t/m2
>1.8 t/m2
Face pressure, axis 2.45 bar <2.0, >3.0
Tail grout injection pressure, lines B1-10
2.3 bar (0.5-1 bar> face pressure
<1.2 bar >2.8 bar
Depending on injection volume
Tail grout injection volume
6.5 m3/ml <5.5 m3/ml >8.8 m3/ml
<5.2 m3/ml >10.3 m3/ml
FIR, foam injection ratio Min 25
FER, foam expansion ratio Min 20
Max penetration 60 mm/rev < 20 mm/rev < 3mm/rev
Weight of muck on belt scale
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Alaskan Way Viaduct Replacement Glacial soils
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Control of the ground
• Open shields – Difficult to control all ground conditions
• Reliance on stand-up time of the ground
• Pressurized face machines: – Ability to control the ground
• Understanding, monitoring, and controlling key operational parameters in real time – Ensure control of the ground
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1818: Marc Isambard Brunel’s objective:
to “open… the ground in such a manner that no more earth shall be displaced than is to be filled by the shell or body of the tunnel.”