Design of An Immersed Tube Tunnel

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A full original (hypothetical) design and detail of an Immersed Tube Tunnel for the Passage West region, Cork, Ireland.

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Design of An Immersed Tube Tunnel

  1. 1. Design of an Immersed Tube Tunnel
  2. 2. Project Objectives <ul><li>Design of a suitable underwater tunnel </li></ul><ul><li>Passage West – Cobh </li></ul><ul><li>Alleviate traffic from Jack Lynch Tunnel </li></ul>
  3. 3. Immersed tube tunnel <ul><li>Type of underwater tunnel construction </li></ul><ul><li>100 – 120m long elements </li></ul><ul><li>Cast in a casting basin </li></ul><ul><li>Floated and transported to site </li></ul><ul><li>Immersed into dredged channel on seabed </li></ul><ul><li>Elements joined and sealed </li></ul><ul><li>underwater </li></ul>
  4. 4. Tunnel Geometry <ul><li>Reinforced concrete 16.66m x 8.2m x 100m elements </li></ul><ul><li>Two bore (single lane bore) with central service shaft </li></ul>
  5. 5. Bore Detail <ul><li>4.3 x 4.9m traffic envelope </li></ul><ul><li>4.9m clear height </li></ul><ul><li>1m footpath </li></ul>
  6. 6. Loading <ul><li>Primary Loads </li></ul><ul><li>Self Weight </li></ul><ul><li>Hyrostatic pressure </li></ul><ul><li>Backfill/sedimentation </li></ul><ul><li>Traffic loads (10%) </li></ul><ul><li>Secondary Loads </li></ul><ul><li>Wave </li></ul><ul><li>Dropping Anchor </li></ul><ul><li>Ship loading </li></ul><ul><li>Temperature differential </li></ul>
  7. 7. Structural Analysis <ul><li>a) Design calculations </li></ul><ul><li>Excel spreadsheets </li></ul><ul><li>`` </li></ul><ul><li>b) Numerical model with simulation </li></ul><ul><li>LUSAS( London University Stress Analysis Software) </li></ul>
  8. 8. <ul><li>Transverse Analysis </li></ul>Portal Frame Model <ul><li>Simple portal frame </li></ul><ul><li>Max hogging/sagging moments </li></ul>
  9. 9. Single Box Model
  10. 10. Final cross-section Accuracy of Results 1943 1933.8 Max Hog Moment (KN/m) 1315 1322.5 Max Shear (KN) 979.2 981 Max Sag Moment (KN/m) LUSAS Design Calculations Entity
  11. 11. Longitudinal Analysis <ul><li>Complex analysis – bending of tunnel cross section longitudinally </li></ul><ul><li>2 stages: Placement & Settlement </li></ul><ul><li>Placement </li></ul><ul><li>Element rested on jacks and shear keys </li></ul><ul><li>Simply supported beam – 100m span </li></ul><ul><li>Submerged weight of tunnel element (6%) </li></ul><ul><li>Settlement </li></ul><ul><li>100m elements - divided into five 20m semi flexible segments </li></ul><ul><li>Beams on elastic foundation – 20m span </li></ul>
  12. 12. Placement Design Calculations LUSAS Results R = 2193.4 KN M max = 6583 KN/m Results R = 2073 KN M max ~ 1000 KN <ul><li>Simple/conservative slab span </li></ul><ul><li>WL 2 /8 </li></ul><ul><li>Complex – stiffness of cross section </li></ul>
  13. 13. Settlement <ul><li>Design Calculations </li></ul>LUSAS <ul><li>Beam on elastic foundation </li></ul><ul><li>K = 10,000 KN/m 2 Δ = F/K = 25mm </li></ul><ul><li>Total load on foundation = 250KN/m 2 </li></ul><ul><li>M max = (1/10)(w)(L 2 ) = 1250 KN/m </li></ul><ul><li> 8 </li></ul><ul><li>More realsitic – stiffness of cross section </li></ul><ul><li>Max moment = 942 KN/m </li></ul>
  14. 14. Casting Basin & Construction <ul><li>Casting basin – sheet piled and excavated. </li></ul><ul><li>Elements constucted inside basin </li></ul><ul><li>Travelling formwork casts 20m segements – construction/expansion joints </li></ul><ul><li>Cracking of concrete </li></ul><ul><li>Elements sealed – steel bulkheads </li></ul><ul><li>Basin flooded – element transported to immersion site </li></ul>Oresund Link Tunnel
  15. 15. Transportation & Immersion <ul><li>Post tensioning </li></ul><ul><li>Tug boats transport elements </li></ul><ul><li>Cranes on floating pontoons </li></ul><ul><li>Temporary ballast water tanks </li></ul><ul><li>Stay ties – horizontal alignment </li></ul>
  16. 16. Foundations <ul><li>Dredging </li></ul><ul><li>Cutter/suction head </li></ul><ul><li>Channel dimensions – soil stability </li></ul><ul><li>Tunnel Foundation </li></ul><ul><li>Sand flowing method </li></ul>
  17. 17. Element Joints
  18. 18. <ul><li>Any Questions? </li></ul>

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