1. Structural Slab Analysis
Design Assumptions
Loadings
Proposed Slab Options

2. Structural Slab Analysis
Assumptions
Check whether 300mm thick slab is sufficient in temporary and permanent conditions.
For the time being, assume there are not hazards in the tunnel (e.g. spillage of aggressive chemicals, stray current corrosion etc.)
In the permanent case, Vibration Loading from dipole is not considered.
Accidental Loading (e.g. fire only, helium release event not considered)
Design according to the EuroCodes
Durability checks according to EC2 e.g. standard crack width criteria (0.3mm)
All factors as recommended by general EuroCodes (not National Annexes)
Max speed of the vehicles < 10km/h (Temporary Case)

3. Structural Slab Analysis
Fire Design Assumptions
Fire characteristic curve: ISO 834
Requested fire resistance: Class R60
Tabular method for the definition of the minimum thickness of the concrete structures and the minimum rebar cover.

4. Structural Slab Analysis
Loading Parameters
Indicative layout from ILC TDR

5. Loadings

6. Loadings

7. Option 1a: Cast In-situ Concrete
Proposed Construction Sequence:
Step 1:
Fix rebars in both walls
Install movable shutter
Concrete
Step 2:
Fix rebars in the slab 2 1 1
This Option To Be Analysed

8. Option 1a: Cast In-Situ Concrete
Worked examples:
Barcelona Metro (Spain)
Type 1
Cross section with cast in-situ mass concrete
Gantry on rollers (Crossrail)
Concreting on site
Movable shutter

9. Option 1b: Cast In-situ Mass Concrete and Pre-stressed Slab Unit
Proposed Construction Sequence:
Step 1:
Fix rebars in the thick wall
Install movable shutter
Fix bars in hollow concrete units
Concrete
Step 2:
Install pre-stressed slab panels
Fix connection rebars
Concrete the topping 2 1 1

10. Option 1b: Cast In-situ Concrete Slab
Worked examples:
Over-head crane to lift pre-stressed units
Barcelona Metro (Spain)
Type 1
Mortarless Concrete Block Wall
Concreting on site
Movable shutter

11. Option 1c: Cast In-situ Mass Concrete and Pre-stressed Slab Unit
Proposed Construction Sequence:
Step 1:
Fix rebars in thick wall
Install movable shutter
Fix bars in hollow concrete units
Concrete
Step 2:
Fix corbel bars
Cast concrete 3 2 1 1
Step 3:
Install pre-stressed slab panel
Fix connection rebars
Concrete the topping
Worked examples as for Solution 1b

12. Summary on Options 1a, 1b, and 1c
Pros:
Robust mass concrete under Dipole prevents vibration issues
Especially for Solution 1c, where the safe area envelope is shifted
Typical RC-concrete
Not innovative material = reasonable price
Good fire performance of RC-elements
Individually designed passive resistance of concrete (cover, polyfibres).
Gantry directly behind the TBM including:
Formwork on rails/rollers
Crane for lifting pre-cast units
Cons:
Thick Elements
Rebars due to Thermal Cracking
Slow construction progress due to on-site concreting
For Options 1b and 1c, the process accelerated by providing pre-stressed units
Corbel construction

13. Solution 1d: Pre-fabricated Concrete Units

14. Solution 1d: Pre-fabricated Concrete Units
(Slow Construction)
Worked examples:
SMART tunnel (Malaysia)
Airport Link tunnel (Australia)

15. Solution 1d: Pre-fabricated Concrete Units
(Slow Construction)
Pros:
Typical pre-stressed RC-units
Not innovative material = reasonable cheap
Good fire performance of RC-elements
Culvert-laying gantry directly behind the TBM
Cons:
Thick Elements
Multiple Short Spans
Slow construction progress due to cast in-situ topping
Corbel construction

16. The following options are for information only since they don’t meet the key objective of providing stiff, robust and vibration-free support for the dipole.
However, they present innovative techniques and some individual ideas can be implemented into the final solution.

17. Option 2: Steel or Pre-stress Frames
(Moderately Quick Construction)

18. Option 2: Steel or Pre-stress Frames
(Moderately Quick Construction)
Worked Example:
Intermediate pre-stressed concrete slab units
Barcelona Metro (Spain)
Section Type 2
Over-head crane lifting the units

19. Option 2: Steel or Pre-stress Frames
(Moderately Quick Construction)
Pros:
Quick construction
Frames assembled in a factory
Long span of the main frames
Optimised usage of steel
Simple connections (i.e. pinned)
Limited zones of mass fillings
By both sides of the frame only
Limited areas of concrete mass fill
Easy to construct concrete block walls
No shutter needed
Cons:
A lot of concreting on site
Slab toppings and mass concrete
Slow construction progress
Fire protection layer needs to be sprayed/cast
Temporary bracing (if steel frames used)

20. Option 3: UHPFRC* Slab Units
(Quick Construction)
* Ultra-High Performance Fibre-Reinforced Concrete

21. Option 3: UHPFRC* Slab Units
(Quick Construction)
Worked Example:
Airport Link tunnel (Australia)
Separated culvert-laying gantry from the TBM backup

22. Option 3: UHPFRC* Slab Units
(Quick Construction)
Pros:
Quick construction
Prefabricated units “ready-to-use”
Small amount of concreting on site
In the joints only
Long span of the main frames
Optimised usage of concrete
Thin units due to very strong concrete
Simple connections (i.e. pinned)
Limited zones of mass fillings
On side only
Limited areas of concrete mass fill
Easy to construct concrete block walls
No shutter needed
Cons:
Very expensive material
Fireproofing tests need to be done
Individual design approach
Full scale fire tests
Very smooth top surface
Wearing Surface material to be installed
Corbel Construction
* Ultra-High Performance Fibre-Reinforced Concrete

23. Option 3: UHPFRC* Slab Units
Very high compressive strength MPa
Examples:
Steel fibres added to achieve ductile behaviour
Low W/C ratio
Available on French market
(DUCTAL, BSI/CERACEM, BCV)
Comparison of a UHPFRC slab and a conventional concrete slab
Physical and mechanical characteristics UHPFRC (example)
UHPFRC slab (example)
* Ultra-High Performance Fibre-Reinforced Concrete