Control of the ground during shield tunneling

Los Angeles December 16, 2011

Edward J. Cording Professor emeritus University of Illinois at Urbana-Champaign

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.

Figure 1-1

London, 2011

• Thames Tunnel still in operation on London Underground

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.

5 FIGURE 2-1

Primary objective:

Relate tunnel

construction…

Chicago Subway,

1938-1941

Karl Terzaghi and Ralph Peck

Soft Chicago Clay

6 FIGURE 2-2

… to settlement at the surface

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”

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

Result

• Shield hood rebuilt for second tunnel

• Settlements reduced from 6 to 2 inches

Control Sources of Ground Loss

– F: FACE

– O: OVERCUT

– S: SHIELD

– T: TAIL

– L: LINING

F

L O S T

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

1990, Metro Red line, Segment 1, Alluvium Shank - Ohbayashi

Chemical grouting ahead of face, compaction grouting as shield passed

Pressurized face shields

Recommended for projects in Los Angeles ECIS and NEIS

Metro Gold Line Eastside Extension

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

Typical Mining Cycle – 5 ft

Typical Mining Cycle – 5 ft

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

West bound

East bound

0.3” 50’

SLOPE: 1/2000 = 0.5 x 10-3

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

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:

Robinson, Bragard, 2007

2006, Metro Gold Line Eastside Extension

Robinson, Bragard, 2007

72-inch hard fan line 100,000 cfm 200 feet: 3 section

Screw Conveyor

2006, Metro Gold Line Eastside Extension

• 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

2011 Sound Transit Jay Dee/ Coluccio/ Michels Ulink JV Glacial till, outwash, lake clays

Capitol Hill Launch

Capitol Hill Trailing Gear

Test Sections: Piezometer & Extensometer Continuously monitored

Diponio, et al 2011, in press

Pressurized, conditioned muck fills overcut

Grout injected through tail under pressure

Co

nd

ito

ne

d m

uck

u

nd

er

pre

ssu

re

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

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

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

2008: I2-m-diameter

earth pressure balance shield

In erection bay,

Line 9, Barcelona

Control

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

Alaskan Way Viaduct Replacement Glacial soils

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

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.”