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- 1. Precast Segmental Lining Design W.K. Kong (2007)
- 2. Overview <ul><li>Concept of Shield Tunnel Design </li></ul><ul><li>Design standard and Specification </li></ul><ul><li>Segmental Lining Design </li></ul><ul><li>- Segmental lining geometry </li></ul><ul><li>- Calculation of internal forces </li></ul><ul><li>Bolt design </li></ul><ul><li>Segment manufacture </li></ul><ul><li>Waterproofing design </li></ul><ul><li>TBM introduction </li></ul>
- 3. Concept of Shield Tunnel Design <ul><li>For Soft Ground tunnels, principle issues are: </li></ul><ul><li>a) TBM/shield selection; </li></ul><ul><li>b) Segmental lining design; and </li></ul><ul><li>c) Ground movement induced </li></ul><ul><li>They are inter-related! </li></ul>
- 4. Design Standard and Specification <ul><li>General Design Guidance </li></ul><ul><li>AFTE – Recommendation for design, sizing and constructiuon of precast concrete segments installed at the rear of a tunnel broing machine(TBM) 1997. </li></ul><ul><li>Guildnace for the design of Shield Tunnel Lining – Working Group No. 2 International Tunnelling Association 2000. </li></ul><ul><li>Code of Practice </li></ul><ul><li>Reinforced concrete design for segmental lining – relevant code of practice I.e. BS8110 in HK </li></ul><ul><li>Steel Design – relevant code of practice I.e. DS 5950 in HK </li></ul><ul><li>Specification of Segment manufacturing and final products </li></ul><ul><li>Model Specification for tunnelling: Thomas Telford, London 1997 </li></ul><ul><li>Railways Cooperation – Standard Specification of Civil Engineering Works </li></ul>
- 5. Segmental Lining Design – Lining Geometry <ul><li>Basic ring geometry: </li></ul>Tunnel advance Leading edge Trailing edge Circumferential joint Radial joint Key block
- 6. Segmental Lining Design – Lining Geometry <ul><li>Basic ring geometry: </li></ul>Universal Taper Ring Left Hand Taper Ring Left Hand Taper Ring
- 7. Segmental Lining Design – Lining Geometry <ul><li>Basic ring geometry: </li></ul>Bolt hole Segment plate arrangement and number of bolts are critical for: a) Alignment control b) Practical handling ring build R – Rectangular T – Trapezoidal K – Key block R R R T T K
- 8. Segmental Lining Design – Lining Geometry <ul><li>Basic ring geometry: </li></ul>
- 9. Segmental Lining Design – Lining Geometry <ul><li>Basic ring geometry: Useful rules </li></ul><ul><li>a) Segment thickness = Diameter/ 22 </li></ul><ul><li>b) No segments = Even Number plus Key block, 2 of which are trapezoidal, others rectangular </li></ul><ul><li>c) No bolts = Even number of bolts, minimum 3 per plate circumferential joint </li></ul><ul><li>d) Segment length depends on practical handling restrictions, tunnel alignment and limitation of reinforcement </li></ul>
- 10. Segmental Lining Design – Lining Geometry Key block design Principle issues: a) Limiting obliqueness of angle (as surface becomes twisted) b) Ensuring can be inserted by TBM segment erector
- 11. Segmental Lining Design – Lining Geometry Key block design Principle issues: a) Limiting obliqueness of angle (as surface becomes twisted) b) Ensuring can be inserted by TBM segment erector
- 12. Segmental Lining Design – Lining Geometry
- 13. Segmental Lining Design – Calculation of Internal Forces <ul><li>Load cases to consider are: </li></ul><ul><li>Ground and Groundwater loads </li></ul><ul><li>Loads induced by maximum desirable deflection </li></ul><ul><li>TBM propulsion jacking loads </li></ul><ul><li>Grouting loads (annulus and secondary grouting) </li></ul><ul><li>Seismic loading </li></ul><ul><li>Handling and stacking loads </li></ul>
- 14. Segmental Lining Design – Calculation of Internal Forces <ul><li>Load cases to consider are: </li></ul><ul><li>Ground and Groundwater loads </li></ul><ul><li>Loads induced by maximum desirable deflection </li></ul><ul><li>TBM propulsion jacking loads </li></ul><ul><li>Grouting loads (annulus and secondary grouting) </li></ul><ul><li>Seismic loading </li></ul><ul><li>Handling and stacking loads </li></ul>Ultimate Limit State: Check against failure Max. Bending moment/min. thrust couple
- 15. Segmental Lining Design – Calculation of Internal Forces <ul><li>Load cases to consider are: </li></ul><ul><li>Ground and Groundwater loads </li></ul><ul><li>Loads induced by maximum desirable deflection </li></ul><ul><li>TBM propulsion jacking loads </li></ul><ul><li>Grouting loads (annulus and secondary grouting) </li></ul><ul><li>Seismic loading </li></ul><ul><li>Handling and stacking loads </li></ul>Serviceability Limit State: Check against cracking Max. Bending moment/min. thrust couple
- 16. Segmental Lining Design – Calculation of Internal Forces <ul><li>Ground and Groundwater loading </li></ul><ul><li>Main methods of calculation: </li></ul><ul><li>Elastic analysis (Curtis/Muir Wood 1976, Einstein/Swartz 1979) </li></ul><ul><li>Finite Element Numerical Analysis (FLAC, PLAXIS, etc) </li></ul>Example: 6m diameter tunnel 20m deep Lining = 250mm segmental Stiff Clay – E = 100MPa Ko = 0.8
- 17. Segmental Lining Design – Calculation of Internal Forces <ul><li>Ground and Groundwater loading </li></ul><ul><li>Critical design parameters - soil: </li></ul><ul><li>Elastic modulus of soils (E) </li></ul><ul><li>Earth pressure at rest (K o ) </li></ul><ul><li>Shear strength (c u or c’, ’) [to determine soil-lining slippage] </li></ul><ul><li>Critical design parameters - lining: </li></ul><ul><li>Concrete properties (E, f cu ) </li></ul><ul><li>Lining thickness & Number of joints (to determine Moment of Inertia) </li></ul><ul><li>Use of staggered ring joints or cruciform joints </li></ul>
- 18. Segmental Lining Design – Calculation of Internal Forces <ul><li>Ground and Groundwater loading </li></ul>Curtis/Muir Wood (1976) Method Elastic continuum analysis for cases in soil or rock Worst Case
- 19. Segmental Lining Design – Calculation of Internal Forces <ul><li>Loads induced by maximum desirable deflection: </li></ul>Assessed using methods of Morgan (1961) to derive bending moment due to distortion coupled with minimum thrust value: a) deflection checking at maximum allowable deflection of 1% internal diameter; b) future development load case: distortion of 25mm. For assumed jointed and un-jointed lining, where Moment of Inertia derived from Muir Wood (1975).
- 20. Segmental Lining Design – Calculation of Internal Forces Effects of Poor Ring Build
- 21. Segmental Lining Design – Calculation of Internal Forces Effects of Poor Ring Build
- 22. Segmental Lining Design – Calculation of Internal Forces Effects of Poor Ring Build
- 23. Segmental Lining Design – Calculation of Internal Forces Grouting loads (annulus and secondary grouting): Assessment: a) Determine grout for Annulus Primary and Secondary Grouting; b) Check using Muir-Wood (1976) – Stage 1 will give Big Thrust, Zero Moment, Stage 2 will give Small Thrust, Large Moment
- 24. Segmental Lining Design – Calculation of Internal Forces <ul><li>Significant load case, must be developed with the TBM manufacturer and Contractor. </li></ul><ul><li>Assessment of tensile stress / bending moment by: </li></ul><ul><li>Elastic analysis </li></ul>Analysis of effects of eccentric ram loads TBM propulsion jacking loads:
- 25. Segmental Lining Design – Calculation of Internal Forces TBM propulsion jacking loads: Assessed using Guyon (1972)
- 26. Segmental Lining Design – Calculation of Internal Forces Seismic Design – Use method of Wang (1991) Assess impact of: a) Axial deformation along tunnel b) Curvature deformation along tunnel c) Ovaling of tunnel profile Normally, no special joints are required, more reinforcement may be needed.
- 27. Segmental Lining Design – Calculation of Internal Forces <ul><li>Stacking of segments – Assessed as static load case </li></ul>Handling and stacking loads Normally, check reinforcement capacity derived for other reasons, against stacking loads
- 28. Segmental Lining Design – Calculation of Internal Forces <ul><li>Handling of segments in installation – Dynamic load case (use factor of 3) </li></ul>Handling and stacking loads Normally, check reinforcement capacity derived for other reasons, against handling loads
- 29. Segmental Lining Design – Calculation of Internal Forces Reinforcement Design:
- 30. Segmental Lining Design – Calculation of Internal Forces Reinforcement Design Design of reinforcing quantity and layout needs to accommodate: a) Design loading; b) Distribution to limit crack widths and cover for durability; c) Limit damage (accidental or under loading) around bolt pockets, lifting socket, segment corners, etc).
- 31. Segmental Lining Design – Calculation of Internal Forces Reinforcement Design:
- 32. Segmental Lining Design – Calculation of Internal Forces <ul><li>Based on Short Column capacity </li></ul>Reinforcement Design – Circumferential bars:
- 33. Bolt Design Design principles: Bolts are intended to: a) Aid ring build quality b) Compress gaskets c) Provide safety prior to annulus grout hardening Bolts can be curved or straight (steel or plastics). Bolts and washer assemblies do not need waterproofing
- 34. Segment Manufacture Documentation required: a) Segment design drawings; b) Segment mould shop drawings; c) Specification on casting, concrete mix, steel fixing, etc. d) Tolerances for mould, steel fixing, etc.
- 35. Waterproofing Design Main waterproofing elements: a) Gaskets on all joints with hydrophilic inserts in gaskets b) Use of hydrophilic strips c) Provision of caulking groove Soil side Drive direction
- 36. Waterproofing Design Gasket design: Need to check against poor ring build and bolt capacity
- 37. TBM Introduction Type of TBM ( (According AFTES Association) Ground support Main TBM Types None Beam TBM Road Header With Shied Support only Open Shield Machine With Shield and Front support Earth pressure balance Machine Slurry Machine Compressed air shield
- 38. TBM with no shield and frontal support Main Beam and Reamer Beam Machine Road Header
- 39. TBM with open shield Double Shield TBM Single Shield TBM
- 40. Closed Shield TBM – Slurry Machine Confinement is achieved by pressurizing boring fluid inside the cutterhead chamber
- 41. Slurry Machine/ AIR BUBBLE TECHNOLOGY <ul><li>Cutting Wheel </li></ul><ul><li>Pressure Bulkhead </li></ul><ul><li>Air Cushion </li></ul><ul><li>Submerged Wall </li></ul><ul><li>Slurry Line </li></ul><ul><li>Stone Crusher </li></ul><ul><li>Feed Line </li></ul><ul><li>Erector </li></ul>1 2 3 4 5 6 7 8
- 42. Slurry Machine / AIR BUBBLE TECHNOLOGY <ul><li>Submerged Wall </li></ul><ul><li>Excavation Chamber </li></ul><ul><li>Regulation Chamber </li></ul><ul><li>Air Cushion </li></ul><ul><li>Pressure Bulkhead </li></ul>3 1 4 5 2
- 43. Closed Shield TBM – EPBM Shield Tail skin Mucking and support functions trailing Ring building and annulus grouting Propulsion / steerage Excavation Active pre-cast concrete tunnel lining support
- 44. Mix Shield Machine <ul><li>Switching between EPBM and Slurry Mode </li></ul>
- 45. TBM OPERATION – Erecting for launch Launching shaft prepared Lower part of shield, bulkhead and drive rams Installing main drive
- 46. TBM OPERATION – Erecting for launch Upper shield and drive rams Lower part of tail-skin Ring erector installed Cutter-head installed
- 47. TBM OPERATION – Erecting Al Bugeisha for launch Completed shield and tail-skin Prepared launching eye with seals
- 48. TBM OPERATION – Segmental tunnel lining Stack of 3 test rings Ring placed in TBM tail skin Ground is not exposed Segment casting Soil Annulus grout Key block
- 49. PORE WATER PRESSURE IN SCREW Soil conditioning improves hydraulic gradient in screw TBM OPERATION – Application of EPB face pressure h o h 1 Ratio of h 1 /h o is linearly proportional to achievable effective face pressure h 2 Second screw is a risk mitigation measure Soil conditioning = higher effective face pressure
- 50. TBM OPERATION – Alignment control Use of ring taper on curves <ul><li>PHYSICAL STEERING: </li></ul><ul><li>Preferential loading or rams </li></ul><ul><li>Overcutting using protruding bit </li></ul><ul><li>Shield articulation to accommodate curves </li></ul><ul><li>Segment taper using ring rotation </li></ul><ul><li>SURVEY CONTROL: </li></ul><ul><li>Optical targetting using TBM specific guidance system </li></ul><ul><li>Regular total station survey checks </li></ul><ul><li>Final wriggle survey </li></ul>
- 51. TBM OPERATION – Measures to limit settlement risk AVOIDANCE OF OVER-EXCAVATION: If results indicate over-excavation: <ul><li>Review to check if increased muck volume is due to the change of ground conditions </li></ul><ul><li>Review the face pressure design </li></ul>Cut soil: Volume = 109m 3 /ring Mass = approx. 212T/ring Spoil from advance: Volume =F.109m 3 /ring Mass = f.212T/ring Muck volume compared to theoretical volume, by means of: <ul><li>Laser scanner (volume) </li></ul><ul><li>Load cell (weight) </li></ul>Volume m 3 /m Advance (m)
- 52. TBM Selection <ul><li>Main Constraints </li></ul><ul><li>Length of tunnel and Alignment (radius) </li></ul><ul><li>Hydrogeology Condition I.e. water pressure and water bearing Ground </li></ul><ul><li>Geology (Type of material boring through) </li></ul><ul><li>Existing Structures </li></ul><ul><li>Tunnel Crown Cover </li></ul><ul><li>Sizes of Tunnel </li></ul>
- 53. TBM Selection – Face stability Yoshikowa et al (1980) Requires measures to maintain slurry pressure Slurry TBM requires heavy de-siltation facilities Slurry requires secondary separation treatment High risk of blockages particularly when N>15 APPLICABILITY OF SLURRY TBM FOR COMPARISON
- 54. TBM Selection Geological Profiles
- 55. TBM Selection <ul><li>Comparison of twin and single bored options </li></ul><ul><li>Disadvantages of Large diameter single bore </li></ul><ul><li>TBM cost more </li></ul><ul><li>Result in higher settlement and hence deeper tunnel </li></ul><ul><li>Higher net cross sectional area per track </li></ul><ul><li>Advantages of large diameter single bore </li></ul><ul><li>Possible saving in construction programme </li></ul><ul><li>Elimination of lining interaction for twin bored tunnel </li></ul><ul><li>Possible advantages in relation to alignment design </li></ul>
- 56. TBM Selection <ul><li>EPBM </li></ul><ul><li>Large diameter single bored (11.5m ID) </li></ul><ul><li>Loss of face pressure due to cobbles and gravels at the western side of the river crossing </li></ul><ul><li>High Torque required for large diameter bore </li></ul><ul><li>Twin bored smaller diameter tunnel (5.5m ID) </li></ul><ul><li>Loss of face pressure due to cobbles and gravels at the western side of the river crossing </li></ul><ul><li>Higher risk of pressure loss than large diameter TBM with same cobbles and gravels </li></ul><ul><li>Boulders clasher required for both cases </li></ul>
- 57. TBM Selection <ul><li>Slurry Machine </li></ul><ul><li>Twin and single bore </li></ul><ul><li>More Suitable than EPBM for gravel and cobbles ground </li></ul><ul><li>Often adopted for permeable ground </li></ul><ul><li>Heavy de-silting facilities required for boring through silt and clay layers </li></ul>
- 58. TBM Selection <ul><li>Discussion </li></ul><ul><li>Risk of EPBM through gravel and cobbles within water bearing ground. Might be feasible with present techniques requiring checking with TBM manufacturer </li></ul><ul><li>Slurry Machine have less risk for boring through gravels and cobbles but when boring through clay requiring de-silting facilities </li></ul><ul><li>Mix shield (EPBM and Slurry) could be adopted involving changing mode for appropriate ground condition. Size of tunnel for twin bores might be a restriction for mix shield </li></ul><ul><li>Details need confirmation from TBM manufacturers I.e. Herrenknecht etc. </li></ul>

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