Post on 02-Apr-2015
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One-pass and Two-pass Precast Segmental Linings
Wern-ping (Nick) Chen
Jacobs
UT Austin Seminar, April 4, 2007
Applicable to:Tunnel Boring Machine (TBM) tunneling
Not for:Hand mining, such as drilled and blast or excavation
by roadheader or other mechanized means
Presentation starts from big questions and narrows down to details
Outline
1. Definitions2. Factors that drive the use of segmental
lining3. Tunnel alignments4. Rationale for choosing one or the other5. Types of precast segmental linings/Material6. Geometries7. Segment joints8. Segment construction tolerance9. Design/Modeling10. Construction considerations11. References12. Q/A
1. Definitions
Primary/initial lining
• The ground support installed immediately after the excavation
• It is a temporary structure for safety and operation during tunneling
• Normally in associated with hard rock tunneling
• Examples are rock dowels, steel set, or shotcrete
1. Definitions
Secondary/final lining
• Tunnel support or lining installed following and independent of excavation to satisfy user/function requirement
• Normally it is cast-in-place concrete
1. Definitions
One-pass lining
• Lining used as both initial support and final lining of a tunnel; normally it is precast segmental lining
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1. Definitions
Two-pass lining
• With primary/initial support installed as temporary ground support and followed by an in-situ final concrete lining
1. Definitions
Two-pass Segmental lining
• Use segmental lining as initial ground support and cast-in-place (CIP) concrete as final tunnel lining
1. Definitions
TBM Shield/Segment
TBM Shield/
Segment, Open Face, Single Shield
1. Cutterhead 2. Shield 3. Articulation (option) 4.Thrust ram5. Segment erector 6. Muck extraction conveyor 7. Muck transfer Conveyor8. Gathering arm 9. Muck hopper 10. Motor11. Tailskin articulation (option) 12. Thrust ring
Schematic Earth Pressure Balance Machine (EPBM)
Schematic Slurry Shield Machine
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• The family of open TBMs is developed for excavating in rock.• The thrusting force is obtained by reacting on the grippers.• The head is equipped with cutting disks.
1. Cutter head 2. Cutter head shield 3. Erector to place rib and mesh 4. Inner kelly5. Outer kelly in two positions with grippers and telescope jacks 6. Push jacks 7. Cutter head drive8. Rear support 9. Belt conveyer 10. Roof bolting drill 11. Probe drill
Main Beam TBM
1. Definitions
Open Gripper TBMs
2. Factors that drive the use of
segmental lining
• Ground stability during tunneling1. Soft ground tunneling2. Adverse geological condition in hard rock
tunneling; such as in laminated shale, embedded with clay
• Construction schedule – pending on the contractor, the construction schedule may be reduced
• Potential of excessive groundwater infiltrationNotes:• To be cost effective of employing a TBM, the length of the tunnel shall
be roughly greater than 1.2 miles (2 Kilometer) long• Generally speaking, the cost of a two-pass lining is lower than the one-
pass segmental lining
Case Study - Upper Rouge Tunnel ProjectLimy Shale – Fissile (disking) behavior; 30 ft ID
2. Factors that drive the use of
segmental lining
2. Factors that drive the use of
segmental lining
URT case study
• Original design – Rock dowel and steel rib as initial ground support with CIP concrete final lining
• Final design – Revised to one-pass or two-pass segmental lining
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URT – Shallow cover tunnel in Antrim Shale
3. Tunnel alignments
804
3007
40010
Minimum Radius of curvature in meters
Diameter of TBM (D) in meters
• Horizontal – public right of way; geological features; 3rd party issues (transportation and muck handling); distance/function
• Vertical – cover above tunnel crown; 1 to 2 D, pending on ground condition (design issue); function/operation; geological condition
• Radius of curvature of tunnel
4. Rationale for choosing one or the other
One-pass Segment Advantages:
• Smaller excavation diameter• Better concrete quality control (precast)• May shorten tunnel total construction schedule (but longer mucking duration)
• Robust – designed for the worst ground condition• Less water treatment required (TSS &Ph)
4. Rationale for choosing one or the other
One-pass Segment Disadvantages
• Higher cost• Tight alignment tolerance/control• Difficult to repair• Difficult interface design and construction• Relatively delayed initial support
4. Rationale for choosing one or the other
One-pass Segment Disadvantages
• Quality of installed bolted/gasketed system
• Tight segment construction & installation tolerance
• Need to patch bolt pockets and caulking groves (water/wastewater tunnel)
• Segment flotation during construction• Bolt corrosion (water/wastewater tunnel)• Design consideration for internal pressure at gaskets (water/wastewater tunnel)
• Maintenance
Radial Joint Detail
Gasket
Precast
Segment
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4. Rationale for choosing one or the other
Two-pass Segment Advantages
• Robust initial ground support• Easier alignment control• Less joints in final lining• Easier interface design and construction Pattern Dowels
4. Rationale for choosing one or the other
Two-pass Segment Advantages
• Less stringent construction tolerance; easy for erecting
• Easier alignment control• Highest TBM production rate
4. Rationale for choosing one or the other
Two-pass Segment Disadvantages
• High cost if not using “junk” segment
• Design the worst ground condition for initial support ($)
• Few, about four (4) in the US, contractors have done junk segment
• The largest expanded segment in the US is NBC of 26’ ID tunnel
• Required more contact grout
URT South Tunnel Cost Analysis
0.8
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1.2
1.4
1.6
1.8
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Two-pass - Dowels
& Rib
Two-pass -
ExpandedSegment
One-pass segment
Two-pass Rib only
• South Tunnel Baseline - 30-ft ID; 19,000 ft long; 20% steel rib + 6” shotcrete ; 20% 16’ pattern dowels with mesh; 12’ dowels and mesh for the rest of the tunnel
5. Types of precast segmental
linings/Material
Cross Section of Segments
(RC/FRC)
5. Types of precast segmental
linings/Material
• Selection of segment type to suit the tunnel usage, ground condition, construction methods, and cost.
• For present time in US, concrete segment is the most popular one (highest compression capacity, but is the heaviest for handling)
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5. Types of precast segmental
linings/Material
Segment Components
5. Types of precast segmental
linings/Material
• As light (thin) as possible
• High strength concrete (> 6,000 psi) to accommodate shear force
• Low W/C ration (>0.4; 0.35 is normal); Adding silica film or fly ash, as cementitious replacement to Portland cement, to reduce permeability; however, with the consequence of excessive spalling in a fire event
• Small rebar cover to avoid spalling and chipping during erection (1 to 11/2” cover)
• Consider fiber to prevent cracking
5. Types of precast segmental linings/Material
Spalling of joints
Cracking and splaaing during erection
5. Types of precast segmental linings/Material
Welding a segment cage for a large diameter highway tunnel
Segment cage for a large diameter highway tunnel
6. Geometries
Cross Section
Side View
6. Geometries
K segment inserted in radial direction
K segment inserted in longitudinal direction
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6. Geometries
• αr = θk /2 + θω• θω - determined based on workability and design to transmit thrust; as small as possible; it is about 2 -5o; 3o is recommended
Segment inserted in radial direction
6. Geometries
• αl - based on construction consideration; the length of the shield; and the length of the segment; normally from 17 -20o
• αl = 0o
Segment inserted in longitudinal direction
Section a-a
6. Geometries
• Shape and width of segments normally based on handling and transportation considerations
• The thickness is normally determined from design requirements
6. Geometries
Shape and dimensions of steel segment (in mm)
6. Geometries
Shape and dimensions of concrete segment (in mm)
6. Geometries
Case 1 - key segment inserted in radial direction
Thickness is based on security load case
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6. Geometries 6. Geometries
Case 2 - key segment inserted in longitudinal direction
6. Geometries 6. Geometries
• Tapered ring – to accommodate curved tunnel alignment/or alignment adjustment
6. Geometries 6. Geometries
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7. Segment Joints
Radial Joints
Circumferential Joints
7. Segment Joints
Curve bolt (out of date)
Dowell
Straight bolt and sleeve
Shear Cone
7. Segment Joints
Dowell
Connection by drifting
7. Segment Joints
Radial joint by bolt and sleeve
Circumferential joint by dowel
7. Segment Joints
Radial joint by rod
7. Segment Joints
Circumferential joint by cone
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7. Segment Joints – Gasket Seal
Elastomeric gasket
7. Segment Joints – Gasket Seal
T configuration testing
Typical pressure curve for a given displacement
Typical load deflection curve
7. Segment Joints – Gasket Seal
• The selected gasket must meet watertightness rating and tolerance specified
8. Segment Construction Tolerance
8. Segment Construction Tolerance 8. Segment Construction Tolerance
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8. Segment Construction Tolerance 8. Segment Construction Tolerance
Sample ring built (normally without gasket)
9. Design/Modeling – Beam/FEM
Solid beam with full or partial bending rigidity
Ring with hinges Ring with shear and
rotational springs
9. Design/Modeling
Radial joint model:• Empirical formula by Allan Muir-Wood (1975) -homogenous rigid ring by reducing the bending
• I = IS + In • (4 / m)²
• I … reduced area-wise moment
• IS… area-wise moment of the force transmission zone
• In… area-wise moment of complete section
• m … number of segments (small key-segment not counted)
Other joint simulations:• Radial – Janssen (1983)
• Circumferential - Gijsbers and Hordijk (1997)
9. Design/Modeling
Design Loads:• Ground load – soil, long term rock, rock wedge…
• Hydrostatic pressure
• Functional – vehicular (highway, transit), surge (water/wastewater), insert support (M&E, Utility…)
• Contact grouting pressure - > 30 psi net (offset the groundwater pressure)
• Construction loads – stacking, lifting/transportation, jacking, gasket compression…
Moment distribution because of the joints
9. Design/Modeling
Stacking load
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9. Design/Modeling – construction loads
Lifting load
9. Design/Modeling – construction loads
Contact grout
Lift/Grout socket
9. Design/Modeling – construction loads
Ring erector
9. Design/Modeling – construction loads
Jacking load
9. Design/Modeling – construction loads
EPDM (Ethylene Propylene Diene Monomer) gasket compression
10. Construction Considerations –Work Shaft
• Work shafts – shaft size to accommodate TBM access and exist, specifically considering the shield size and its interaction with vent duct, convey belt, and other utilities in the shaft during construction.
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10. Construction Considerations –Work Shaft
Length of tail section
Cutter outside diameter (mm)
L/D
Length (L) to Diameter (D) Ratio
10. Construction Considerations –
Work Shaft
10. Construction Considerations –lining placement
Lifting lug
Match Marks Segment ID
10. Construction Considerations –lining match mark
10. Construction Considerations –
Contact Grout
RemovableLifting Insert
Grout Tube
Non Return Valve
Grouting Criteria – by refusal or by volume
10. Construction Considerations –
Contact Grout
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10. Construction Considerations –
Tunnel Break-in
Mostly required in soft ground tunnelling
10. Construction Considerations –
Tunnel Break-in (launching pit and cradle)
Front/Middle/Tail shieldswith JackingFrame
10. Construction Considerations –Break-in, TBM Jacking Frame
TBM Tail Initial Lining
10. Construction Considerations –Break-in, TBM Jacking Frame
10. Construction Considerations –
Tunnel Break-in (w/o ground modification)
10. Construction Considerations –
Tunnel Break-out
Mostly required in soft ground tunnelling
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Receiving Pit
10. Construction Considerations –
Tunnel Break-out
10. Construction Considerations –
Tunnel Break-out
10. Construction Considerations –
Tunnel Break-out
10. Construction Considerations –
Tunnel Break-out
10. Construction Considerations –
Tunnel Break-out
10. Construction Considerations –
Tunnel Break-out (w/o ground modification)
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10. Construction Considerations –
Tunnel Break-out (w/o ground modification)
10. Construction Considerations
• Obstructions – headache to the shield tunneling in soft ground; identified and removed as soon as possible or baselined
• Contract documents
• Specifications – GC; DRB, VECP, EBD, Division 1, technical specifications, measurement and payment
• Drawings
• GBR – baseline for DSC
• GDR
• Alternative Bid concept
11. Reference
1. Design Philosophy of Concrete Linings for tunnels in soft soils by C.B.M.
Blom, 2002.
2. Gijsberg, F.B.J., Hordijk, D.A., 1997, “Experimenteel onderzoek naar het
afschuifgedrag von ringvoegen”,TNO-rapport COB K111
3. ITA Guidelines for the Design of Tunnels, in Tunnelling and Underground
Space Technology, 1988
4. ITA Guidelines for the Design of Shield Tunnel Lining, in Tunnelling and
Underground Space Technology, 2000
5. Janssen, P., 1983, "Tragverhalten von Tunnelausbauten mit
Gelenktübbings", Report-No. 83-41 University of Department of civil
engineering, Institute for structural analysis.
6. Japan Society of Civil Engineer 1996. Japanese Standard for Shield
Tunneling.
7. Muir Wood, A.M., 1975, "The circular tunnel in elastic ground",
Géotechnique 25(1)
8. Tunnel Boring Machines, Trends in Design & Construction of Mechanized
Tunnelling. 1996
9. Specification and Guidelines for the use of Specialist Products in
Mechanized Tunnelling (TBM) in Soft Ground and Hard Rock, EFNARC,
April 2005.
Q and A
Nick.Chen@Jacobs.com