1. The document summarizes a lecture on underwater concrete floors (UCFs), their uses, design rules, and innovations. 2. UCFs are commonly used in the Netherlands for sub-surface construction in soft soils below the groundwater level, serving functions like retaining water, distributing horizontal and vertical forces. 3. Design rules are provided in CUR77, which was revised in 2014 to comply with Eurocodes. The rules cover modeling, dimensioning, and detailing of unreinforced UCFs. 4. Steel fiber reinforcement of UCFs improves cracking behavior and allows the UCF to serve both temporary and permanent structural functions. Several innovative applications in the Netherlands were highlighted.

1. Lecture CiTG
Underwater concrete floors
ir. Ruud Arkesteijn
29th of September 2015

2. Content
1st hour:
• Use and functions of UCF’s
• Distribution of forces
2nd hour:
• Design-rules (CUR77)
• Case: guidelines for preliminary design
Extra:
• Steel fibre reinforced UCF’s
• Projects
• Innovations

3. Use of UCF’s
Conditions for application in building pits:
1. sub-surface construction in ‘soft soils’…
2. below the groundwater level…
3. especially in permeable soils.
Typical Delta/Dutch conditions!

4. Bouwput en fasering

5. Bouwput en fasering

6. Functions of UCF’s
1. Water retaining layer
2. Horizontal force equilibrium (strut)
3. Vertical force equilibrium (up burst / heave)
Often a combination of the above!

7. Bouwput en fasering

8. Distribution of forces
4 mechanisms:
• Boundary-disturbance à “Randstoringseffect”
• Arching à “Boogwerking”
• Membrane-effect à “Membraanwerking”
• Re-distribution of forces à “Krachtenherverdeling”

9. Boundary-disturbance à “Randstoringseffect”

10. Arching à “Boogwerking”

11. Membrane-effect à “Membraanwerking”

12. Arching & membrane-effect

13. Re-distribution of forces à “Krachtenherverdeling”

14. Ultimate limit states
1) Bending moments (tension)
2) Bending moments in arch (compression)
3) Shear failure (near retaining wall)
4) Failure or slipping at retaining wall
5) Pull-out of retaining wall (geotechnical failure)
6) Failure of connection with tension piles (punching shear)
7) Pull-out of tension piles (structural or geotechnical failure)

15. Design rules (CUR77)
CUR77 provides
guidelines for design
of unreinforced UCF’s
with respect to:
• Schematisation
• Modelling
• Dimensioning
• Detailing
Revision in 2014!
Demand is to comply with Eurocodes (0, 2 & 7)!

16. • Longitudinal (“lange richting”):
à no boundary-disturbance
à no initial normal forces
à membrane-effect is big!
• Cross-sectional (“korte richting”):
à boundary-disturbance is critical
à normal forces present (strut-function)
à limited membrane-effect
Focus in CUR77 is on the cross-sectional
direction. Longitudinal direction is not
critical under the assumption of:
Schematisation #1
“lange” richting
“korte” richting
onderwaterbetonvloer
damwand
palen
Ly
Lx
Ly ≤ Lx
CUR77:2001+2014

17. à hgem = average height (minimum 800mm?)
à tolerances on floor thickness
à calculate stresses with:
hmin = hgem - √(tolonder
2+ tolboven
2)
Schematisation #2
Guidelines:
tolonder à 250 mm for peat/clay
à 150 mm for sand/gravel
tolboven à 75 mm for hob-dobber
à higher for slopes?

18. Modelling
à beam-model of cross-section

19. Longitudinal:
à
Serviceability Limit State (SLS)
à dry building pit
à discrete cracking (minimal compression-zone)
2
, ,
1
(without N')
8
s rep y r repq L M£× ×
Cross-sectional:
à uncracked
or with arching
or with arching + re-dristribution of forces
, ,mod , (with N')s rep el r repM M£

20. Ultimate Limit State (ULS)
à structural safety
à incl. material and load factors
Longitudinal:
à no check because of membrane-effect!
Cross sectional:
à uncracked
or with arching and infinite re-distribution of forces (local):
, ,mod , (with N' )s d el r d dM M£
2
, ,
1
8
s d s d xM q L= × ×

21. New in revised CUR77 (v2014):
1. Revised according to Eurocode 2 (NEN-EN1992)
2. No design rules for SLS in cross sectional direction
3. Optimization of arch-height (z) in ULS
4. Check on shear forces near retaining wall
5. Safety check considering slipping of UCF at retaining wall
6. Adjustments for disc-shape-connections (micro piles):
- extra safety factor kr for punching shear
- increased capacity of concrete compression strength under discs
7. Calculation of axial stiffness piles based on secant-value
à according to CUR236:Anchor-piles
8. Calculation method for optimization with membrane force
9. Guidelines for use of 2D calculation models
Latest developments have been published
in Cement 2013/3 and Cement 2015/5

22. Not in CUR77…
Hydration of concrete produces heat à temp. in UCF to 30-45oC
Cooling after heating à shrinkage
Strength of concrete at 50% à sensitive for cracking
Thermal shrinkage of concrete:
à In relatively big building pits the risk of water-conducting
cracks to occur is high even before pumping out the water !

23. Verificatie en toepasbaarheid

24. Case
à Use CUR77:2001 (on Blackboard)
à Consider an unreinforced UCF (no addition of steel fibres)
Make a preliminary design for a deep building pit:
à Modelling a beam-model is not necessary
à Do not check SLS in cross-sectional direction!
à Only check:
SLS longitudinal direction
ULS punching shear
ULS equilibrium in arch

25. Case: guidelines for preliminary design of UCF
1. Choose concrete strength class B25 (nowadays C20/25):
à tensional strength fb = 1,15 N/mm2
à compression strength f’b = 18,0 N/mm2
2. Determine Ly using SLS check in longitudinal direction (CUR77).
Choose Lx ≤ Ly
(for edge piles distance to retaining wall Lx,edge < Lx )
LxLx,edge

26. Case: guidelines for preliminary design of UCF
3. Determine effective load on piles based on:
Lx * Ly * Pwater pressure–weight of UCF (incl. load factors)
4. Check punching shear (CUR77).
Adjust hgem or Lx if needed/possible.

27. Case: guidelines for preliminary design of UCF
5. Determine normal forces in UCF (with D-Sheet Piling):
à suggested modelling:

28. Case: guidelines for preliminary design of UCF
6. Check safety in arching-mechanism (ULS cross-sectional direction)

29. Steel fibre reinforced UCF
First use:
Potsdammer Platz Berlijn
(1997)
In the Netherlands:
• Heinoseweg Zwolle
(1998)
• Betuweroute
(1999-2002)
• multiple others…
2014:
• Mauritshuis (The Hague)
• Groninger Forum

30. “After-crack-behaviour”
à Tensional strength ≈
à Early tensional strength
à Tensional strength after crack
à Re-distribution of forces
à Moment capacity
Effect on force distribution
tension:
bending:
à limits shrinkage-cracks-widths
à limited crack-depth

31. Moment capacity for UCF with steelfibres
à example for UCF with hmin = 700 mm and N’ = 200 kN/m’
à 30 kg/m3 of steelfibres
0
100
200
300
400
0,0 2,0 4,0 6,0 8,0 10,0
momentcapaciteitMRd[kNm/m']
kromming κ [mrad] *10-6
M-N-κ diagram
SVB (UGT)
C25/30 (UGT)
fctd,pl
εUGT = 0,1%:
MRd = 380 [kNm/m']
Egescheurd = 4.664 [MPa]

32. Projects
Groninger Forum

33. Projects
Groninger Forum

34. Link to video (dutch) of the process of
pooring the UCF with steel fibres for
project Groninger Forum:
https://vimeo.com/89189883
Lecture CiTG

35. Projects
Mauritshuis (The Hague)

36. Mauritshuis (The Hague)

37. Mauritshuis

38. Link to video (dutch) with animations
made by diving company C.O.W.:
https://vimeo.com/24826624
Lecture CiTG

39. Innovations…
“Traditional building method”:
- Unreinforced UCF with
temporary function
- Reinforced concrete floor
has permanent function
“Integrated floor”:
- Steelfibre reinforced UCF
- For the permament
function the UCF is
collaborating with a
(traditional) reinforced
concrete floor
“Permanent UCF”:
- Steelfibre reinforced UCF
has a temporary and a
permament function

40. Lecture CiTG 29th of September 2015