2. Limitations of AS/NZ2566.1 For The Trenchless Technology Industry Dr Ian Bateman Director Interflow Pty Ltd

4. too conservativeConclusions and recommendations

6. Assumes existing pipe has no strength

9. Overview of AS/NZ2566.1 AS/NZ2566.1 is designed to cover - installation of a flexible pipe into a trench - takes into consideration - pipe characteristics (stiffness and material properties) - embedment characteristics - design loads - prescribes a method of performing a design

10. Design Method Calculate Applied Loads - Soil load - External hydrostatic load - Internal pressure - Dead loads - Live loads (eg traffic) Check the following - Deflection - Strain - Buckling

11. Buckling Condition In most applications the governing equation is (Applied Loads) x FOS = (St)1/3 x (E’)2/3 St = Pipe ring stiffness E’=Modulus of Soil Reactivity

12. In Other Words … The applied loads need to be resisted by The ring stiffness of the pipe (liner) The surrounding soil But, the effect of the soil is much more dominant

13. AS/NZ2566.1 In Our Trenchless Industry Used successfully for more than a decade Hundreds of thousands of pipes re-lined Industry provides cost effective solutions Installers have effective and practical systems Suppliers are able to produce products for nearly all situations So, what’s the problem?

14. Potential Problems As the industry develops … We are faced with ever more challenging situations Suppliers develop more and more sophisticated products Fall outside of the intent of AS/NZ2566.1

16. RING STIFFNESS is a function of

17. The modulus of the material

19. High Modulus Thin Walled Liners This is reasonable if the liner of perfectly circular cross section Implicit in AS/NZ2566.1 is that pipes are supplied to site free of defects (then buried) In a trenchless application the pipe (liner) is formed inside a deteriorated host pipe The final shape of the liner is influenced by the shape of the deteriorated host pipe

20. High Modulus Thin Walled Liners Liners can contain IMPERFECTIONS x

21. Effect of Imperfections On Liner Stiffness Phenomenon is well studied (Moore,I et al) Effect on liner stiffness is a function of Liner Thickness Size of the Imperfection

22. With Typical Liner Materials

23. With A High Modulus Liner

24. Summarising… With a high modulus material, a 150mm liner has almost zero stiffness with a 15mm imperfection The effect is far less severe with traditional materials The effect reduces as the diameter increases Looking at this another way…

25. Theoretical Thickness With High Modulus Material Theoretical Thickness

26. Theoretical Thickness With Traditional Materials Theoretical Thickness

27. How Deal With This Issue Options Set a minimum liner thickness of (say) 4mm Use an equation to de-rate the actual stiffness and compensate for imperfections of a given size Calculate theoretical thickness and add a constant (say) 2mm

30. Example Stiffness required to re-line a pipe 5m below surface assuming constant E’=4 ** Long Term Stiffness

32. Flexible pipes with a long term stiffness of >8,000N/m/m do not exist

33. Furthermore the reason for the stiffness is due to installation damage not deflection over time

35. With E’=14 instead of E’=4 E’=4 E’=14 Changing the value of E’ has a major affect on what is possible

36. …. Even more dramatic effect on required stiffness E’=4 E’=14

37. How Is E’ Determined Selecting a realistic value of E’ has a huge bearing on the solution (and economics) AS/NZ2566.1 provides the following table But there are other methods

39. AS/NZ2566.1 and E’ Suggests a range of values between 1 and 20 Suggests the values are conservative Suggests with cover heights greater than 10m higher values should be used Shows that the value increases as greater compaction occurs BUT, Trenchless Industry tends to use values of between 2 and 5 WHY?

40. Selection of E’ Estimating E’ is difficult and time consuming We often do not know what occurred during initial pipe construction We don’t know what has happened to the soil during its lifetime Cannot ensure 100% uniform support of the liner by the host pipe and/or soil The cost involved in estimating the actual E’ outweighs the cost of installing a stiffer liner – in smaller diameter pipes.

41. Estimating E’ … but in large diameter pipelines this is probably not true. Estimating an appropriate value for E’ will have a significant bearing on the overall economics Not understanding the condition of the soil in large diameter pipelines can lead to serious consequences Above a certain diameter it is worth determining a realistic value of E’

42. Silo Reduction Factors AS/NZ2566.1 allows the use of silo reduction factors when the depth of cover exceeds 10 times the diameter For small diameter pipes this seems reasonable At large diameters this becomes very conservative Silo effects actually occur at much lower cover heights ALSO, E’ has been shown to be related to depth

43. AS/NZ256.1 For Large Diameters Using a constant AND/OR low values of E’ Not applying silo reduction factors to soil loads until 10 x D VERY CONSERVATIVE EXPENSIVE NOT POSSIBLE

44. How To Deal With This Issue Suggestions Continue to apply the current approach up to a diameter that provides cost effective outcomes Above this diameter, establish more information about the condition of the soil (E’) Allow silo reduction factors below 10 times D

45. Alternatively… If we don’t then we will have to … Ensure that large diameter pipelines are rehabilitated before they reach the fully deteriorated condition Use a different design method at large diameters (not AS/NZ2566.1)

46. Conclusions The design approach borrowed from AS/NZ2566.1 has served the industry very well As products and the industry have evolved some limitations of this approach have arisen As these situations present themselves specifications should be enhanced with specific guidelines