One-pass and Two-pass Precast Segmental Linings Wern-ping (Nick) Chen Jacobs
Applicable to: Tunnel Boring Machine (TBM) tunneling
Not for: Hand mining, such as drilled and blast or excavation by roadheader or other mechanized means
UT Austin Seminar, April 4, 2007 Presentation starts from big questions and narrows down to details
Outline 1. Definitions 2. Factors that drive the use of segmental lining 3. Tunnel alignments 4. Rationale for choosing one or the other 5. Types of precast segmental linings/Material 6. Geometries 7. Segment joints 8. Segment construction tolerance 9. Design/Modeling 10. Construction considerations 11. References 12. 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
1. Definitions
Secondary/final lining
One-pass lining
• Tunnel support or lining installed following and independent of excavation to satisfy user/function requirement • Normally it is cast-inplace concrete
• Lining used as both initial support and final lining of a tunnel; normally it is precast segmental lining
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1. Definitions
1. Definitions
Two-pass lining
Two-pass Segmental lining
•
•
With primary/initial support installed as temporary ground support and followed by an insitu final concrete lining
1. Definitions
Use segmental lining as initial ground support and cast-inplace (CIP) concrete as final tunnel lining
Segment, Open Face, Single Shield
TBM Shield/Segment
TBM Shield/
1. Cutterhead 2. Shield 3. Articulation (option) 4.Thrust ram 5. Segment erector 6. Muck extraction conveyor 7. Muck transfer Conveyor 8. Gathering arm 9. Muck hopper 10. Motor 11. Tailskin articulation (option) 12. Thrust ring
Schematic Earth Pressure Balance Machine (EPBM)
Schematic Slurry Shield Machine
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Open Gripper TBMs
1. Definitions Main Beam TBM • • •
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 kelly 5. Outer kelly in two positions with grippers and telescope jacks 6. Push jacks 7. Cutter head drive 8. Rear support 9. Belt conveyer 10. Roof bolting drill 11. Probe drill
2. Factors that drive the use of segmental lining •
• •
Ground stability during tunneling 1. Soft ground tunneling 2. 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 infiltration
2. Factors that drive the use of segmental lining Case Study - Upper Rouge Tunnel Project Limy Shale – Fissile (disking) behavior; 30 ft ID
Notes: • 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 onepass 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
4. Rationale for choosing one or the other
3. Tunnel alignments • Horizontal – public right of way; geological
One-pass Segment Advantages:
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 Diameter of TBM (D) in meters
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)
Minimum Radius of curvature in meters
10
400
7
300
4
80
4. Rationale for choosing one or the other
4. Rationale for choosing one or the other
One-pass Segment Disadvantages
One-pass Segment Disadvantages
• • • • •
•
Higher cost Tight alignment tolerance/control Difficult to repair Difficult interface design and construction Relatively delayed initial support
• • • • •
•
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
Gasket Precast Segment
Radial Joint Detail
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4. Rationale for choosing one or the other Two-pass Segment Advantages
Two-pass Segment Advantages •
Pattern Dowels
Less stringent construction tolerance; easy for erecting Easier alignment control Highest TBM production rate
• •
4. Rationale for choosing one or the other
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•
•
Two-pass - Dowels & Rib
•
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
•
5. Types of precast segmental linings/Material
Two-pass Rib only
2 1.8 1.6 1.4 1.2 1 0.8
Two-pass Segment Disadvantages •
URT South Tunnel Cost Analysis
One-pass segment
Robust initial ground support Easier alignment control Less joints in final lining Easier interface design and construction
Two-pass ExpandedSegment
• • • •
4. Rationale for choosing one or the other
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 • 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)
(RC/FRC)
Cross Section of Segments
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5. Types of precast segmental linings/Material
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
Segment Components
5. Types of precast segmental
5. Types of precast segmental linings/Material
linings/Material
Spalling of joints
Welding a segment cage for a large diameter highway tunnel
Cracking and splaaing during erection
6. Geometries
Cross Section
Segment cage for a large diameter highway tunnel
6. Geometries
Side View
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
6. Geometries • αl - based on construction consideration; the length of the shield; and the length of the segment; normally from 17 -20o • αl = 0o
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 • Shape and width of segments normally based on handling and transportation considerations
Section a-a
Segment inserted in longitudinal direction
6. Geometries Shape and dimensions of steel segment (in mm)
• The thickness is normally determined from design requirements
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 •
6. Geometries
Tapered ring – to accommodate curved tunnel alignment/or alignment adjustment
6. Geometries
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7. Segment Joints
7. Segment Joints
Circumferential Joints Radial Joints
Curve bolt (out of date)
Dowell
7. Segment Joints
Straight bolt and sleeve
Shear Cone
7. Segment Joints
Connection by drifting
Dowell
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
7. Segment Joints – Gasket Seal
T configuration testing
Elastomeric gasket Typical pressure curve for a given displacement
7. Segment Joints – Gasket Seal •
Typical load deflection curve
8. Segment Construction Tolerance
The selected gasket must meet watertightness rating and tolerance specified
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
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:
Solid beam with full or partial bending rigidity
Ring with hinges
Ring with shear and rotational springs
9. Design/Modeling
• •
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 Stacking load
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9. Design/Modeling – construction loads
9. Design/Modeling – construction loads
Lift/Grout socket
Lifting load Contact grout
9. Design/Modeling –
9. Design/Modeling – construction loads
construction loads
Ring erector
Jacking load
10. Construction Considerations –
9. Design/Modeling – construction loads
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.
EPDM (Ethylene Propylene Diene Monomer) gasket compression
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10. Construction Considerations
10. Construction Considerations – Work Shaft Length of tail section
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Work Shaft Length (L) to Diameter (D) Ratio
L/D
Cutter outside diameter (mm)
10. Construction Considerations –
10. Construction Considerations – lining match mark
lining placement Lifting lug
Match Marks
10. Construction Considerations
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Contact Grout
Segment ID
10. Construction Considerations
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Contact Grout
Grouting Criteria – by refusal or by volume Removable Lifting Insert Grout Tube
Non Return Valve
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10. Construction Considerations
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Tunnel Break-in
10. Construction Considerations
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Tunnel Break-in (launching pit and cradle)
Mostly required in soft ground tunnelling
10. Construction Considerations – Break-in, TBM Jacking Frame
10. Construction Considerations – Break-in, TBM Jacking Frame
Front/Middle/ Tail shields with Jacking Frame
TBM Tail Initial Lining
10. Construction Considerations
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Tunnel Break-in (w/o ground modification)
10. Construction Considerations
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Tunnel Break-out
Mostly required in soft ground tunnelling
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10. Construction Considerations
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Tunnel Break-out
10. Construction Considerations
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Tunnel Break-out
Receiving Pit
10. Construction Considerations
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Tunnel Break-out
10. Construction Considerations Tunnel Break-out
10. Construction Considerations
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Tunnel Break-out
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10. Construction Considerations
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Tunnel Break-out (w/o ground modification)
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10. Construction Considerations
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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. 2. 3. 4. 5.
6. 7. 8. 9.
Design Philosophy of Concrete Linings for tunnels in soft soils by C.B.M. Blom, 2002. Gijsberg, F.B.J., Hordijk, D.A., 1997, “Experimenteel onderzoek naar het afschuifgedrag von ringvoegen”,TNO-rapport COB K111 ITA Guidelines for the Design of Tunnels, in Tunnelling and Underground Space Technology, 1988 ITA Guidelines for the Design of Shield Tunnel Lining, in Tunnelling and Underground Space Technology, 2000 Janssen, P., 1983, "Tragverhalten von Tunnelausbauten mit Gelenktübbings", Report-No. 83-41 University of Department of civil engineering, Institute for structural analysis. Japan Society of Civil Engineer 1996. Japanese Standard for Shield Tunneling. Muir Wood, A.M., 1975, "The circular tunnel in elastic ground", Géotechnique 25(1) Tunnel Boring Machines, Trends in Design & Construction of Mechanized Tunnelling. 1996 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
[email protected]
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