On the use of Z and U piles Bruk av Z eller U profiler

1. On the use of Z and U pilesBruk av Z eller U profiler Arjen Kort Norwegian Geotechnical Institute NSF – NGF meeting October 20 2004

2. On the use of Z and U piles • Use of sheet piles worldwide • Characteristics of Z and U piles • Oblique bending of double U piles • Drivability • Case • Discussion

3. Use of Z and U piles worldwide • Norway: Mostly Z piles • USA: Mostly Z piles • Germany: Both Z piles and U piles • the Netherlands: Both Z piles and U piles • France: Mostly U piles • UK: Mostly U piles • Japan: Only U piles

4. I = 100% I = 10 to 15% Characteristics of Z piles bending axis = wall’s axis

5. Characteristics of U-piles Continuous wall (I = 100%) Single U-piles (I = 30 to 50%) Double U-piles (I = 60 to 80%) Triple U-piles (I = 95 to 100%)

6. F Oblique BendingBending in 2 Directions

7. Oblique BendingBending in 2 Directions Distance to outermost fibre decreases: Loss of strength and stiffness Reduction factors bI and bW to account for losses: Ieff = bI I and Weff = bW W

8. Reduction factors in CUR 166 top bottom

9. Reduction factors in first version of Eurocode 3 part 5

10. Filling in missing knowledge on oblique bending • Effect of structural measures by numerical modelling • Laboratory testing (bending tests and interlock friction tests) • Field test in Rotterdam

11. Numerical ModellingStructural measures to reduce oblique bending Capping beam Free oblique bending Horizontal fixation Welded interlock

12. Numericalmodelling

13. Reduction factors bI;0 = 0.49

14. Important • The loss of strength and stiffness of U piles is in practice not so drastic as is suggested by the theoretical value following from the cross-section • This is due to the soil structure interaction

15. RotterdamSheet Pile Wall Field Test

16. Instrumentation

17. Strain distributionin various test stages

18. Reduction Factors for Stiffness Short-Term Dry excavation Excavation under water Lowering water level Long-Term End of long-term test Final measurement Just before plastic hinge H2 H4 H5 H6 0.60 1.00 0.97 1.00 --- 0.74 0.68 1.00 0.57 0.68 0.68 0.76 0.56 0.70 0.69 --- 0.58 0.72 0.71 0.80

19. Drivability

20. e Declutching… Less chance of declutching Zones suffering from driving

21. General Dutch Experiences • Consultants prefer Z piles • More stiffness and strength with less kilos of steel • No discussion about oblique bending • Contractors prefer U piles • Better drivability and less damage due to installation • Second-hand piles are of better quality • Anchor connections are easier • Not everybody ”believes” in oblique bending

22. Case: Parking Garage Delft

23. Pressing Z sheet piles Historic building on a vulnerable raft foundation Driving Pressing Z piles with length 20 m

24. Sheet piles declutched at 13 locationsDamage repaired with a jetgrout screen

25. I = 100% I = 10 to 15% Pressing single Z piles Fb h Euler: Fb = EI / h2

26. Summary • Single and double U piles involve loss of strength and stiffness • Hot discussions going on regarding reduction factors for oblique bending • U piles have less risk of declutching • Pressing single Z piles can be riskful because of its weak stiffness properties

27. Takk for oppmerksomhet!

28. Straight Web Piling Combi Walls U Piling Z Piling

29. Case: Service Tunnel Amsterdam Vibrodriving was not allowed by the client

30. Case: Service Tunnel Amsterdam • Pressing Z piles of 12 m • Piles designed for vertical • bearing capacity • No U piles because of low • bending stiffness • No U piles because of soil • plugging in trough of SPW

31. New method

32. Advantages of U piles • Wide range of sections • The combination of great wave depth with important flange thickness giving excellent statical properties? • Re-usability • Better installation quality and performance • Easy fixing of horizontal support devices • Good corrosion resistance

33. Skewwall

34. Advantages of Z piles • an extremely competitive relation section modulus/mass • an increased inertia reducing the deflection, allowing the choice of high yield steel grades for the most economical solution • large width resulting in high installation performance

35. But we want this easy: with General differential equations

37. Influence of Sheet Pile Driving on bI 0.6 < bI < 0.8

38. Interlock shift with rulers Double piles: 4 mm Single piles: 8 mm

39. Measurements in Schiedam

40. Design Rule(Kort, 2002) bI;0 Plus the sum of: • Soil shear resistance: DbI = 0 to 0.05 • Transverse supports: DbI = 0 to 0.10 Plus one of: • Soil in interlock: DbI = 0 to 0.05 • Treatment of interlocks: DbI = 0 to 0.20 • Driving effects: DbI = 0 to 0.10

41. Design Rule(Kort, 2002) bW;0 Plus the sum of: • Soil shear resistance: DbW = 0 to 0.10 • Transverse supports: DbW = 0 to 0.05 Plus one of: • Soil in interlock: DbW = 0 to 0.05 • Treatment of interlocks: DbW = 0 to 0.20 • Driving effects: DbW = 0 to 0.15

42. Design Rule(Kort, 2002)

43. Lohmeyer (1934) = + + y c T M•y T T•c •y s(y) = - - I A I Wrong!

45. Use = + + y c T M•y T T•y0 •y s(y) = - - I A I

46. Progress on Interlock Friction • We have an interlock spring model for double U piles • We can build an interlock spring model for single U piles • We can derive spring parameters from field measurements on single U piles (literature) • We can substitute those spring parameters into the model for double U piles

47. Available Case Histories • Hebert et al. (1978) • Gigan (1984) • Williams and Little (1992) • ……….

48. Oblique Bending in London Clay(reliable?) g = 17 kN/m3 cu = 55+8z kPa 10 m 15 m PU 16

49. Oblique Bending in London Clay(reliable?) No conclusions possible until results have been verified to 3D FE calculations!

50. FJ/YG 08121999 2248