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Limitations of AS/NZ2566.1 For The Trenchless Technology Industry<br />Dr Ian Bateman<br />Director<br />Interflow Pty Ltd...
Outline<br />Use of AS/NZ2566.1<br />Examples where AS/NZ2566.1 is <br /><ul><li>not conservative enough
too conservative</li></ul>Conclusions and recommendations<br />
Design in AUS/NZ Trenchless Industry<br />There is no specific design standard<br />We borrow aspects from other standards...
 Assumes existing pipe has no strength
 Assumes liner acts like a buried flexible pipe</li></ul>In Tact<br /><ul><li> Borrow from ASTM F1216
 Assume existing pipe acts to enhance the liner strength</li></li></ul><li>Overview of AS/NZ2566.1<br />Scope<br />“This S...
Overview of AS/NZ2566.1<br />AS/NZ2566.1 is designed to cover<br />	- installation of a flexible pipe into a trench<br />	...
Design Method<br />Calculate Applied Loads<br />	- Soil load<br />	- External hydrostatic load<br />	- Internal pressure<b...
Buckling Condition<br />In most applications the governing equation is<br />	(Applied Loads) x FOS = (St)1/3 x (E’)2/3<br ...
In Other Words … <br />The applied loads need to be resisted by<br />The ring stiffness of the pipe (liner)<br />The surro...
AS/NZ2566.1 In Our Trenchless Industry<br />Used successfully for more than a decade<br />Hundreds of thousands of pipes r...
Potential Problems<br />As the industry develops …<br />We are faced with ever more challenging situations<br />Suppliers ...
AS/NZ2566.1 – Not Conservative Enough<br />High Modulus Thin Walled Liners<br /><ul><li>AS/NZ2566.1 allows us to determine...
RING STIFFNESS is a function of
The modulus of the material
The thickness of the material</li></li></ul><li>High Modulus Thin Walled Liners<br />Example<br /><ul><li>To achieve a des...
High Modulus Thin Walled Liners<br />This is reasonable if the liner of perfectly circular cross section<br />Implicit in ...
High Modulus Thin Walled Liners<br />Liners can contain IMPERFECTIONS<br />x<br />
Effect of Imperfections On Liner Stiffness<br />Phenomenon is well studied (Moore,I et al)<br />Effect on liner stiffness ...
With Typical Liner Materials<br />
With A High Modulus Liner<br />
Summarising…<br />With a high modulus material, a 150mm liner has almost zero stiffness with a 15mm imperfection<br />The ...
Theoretical <br />Thickness<br />With High Modulus Material<br />Theoretical <br />Thickness<br />
Theoretical <br />Thickness<br />With Traditional Materials<br />Theoretical <br />Thickness<br />
How Deal With This Issue<br />Options<br />Set a minimum liner thickness of (say) 4mm<br />Use an equation to de-rate the ...
AS/NZ2566.1 – Too Conservative?<br />Large Diameter Lining<br /><ul><li>By number,  >95% of all pipes rehabilitated are at...
By dollar, ~60 -70% </li></li></ul><li>Returning to Our Design Equation…<br />(Applied Loads) x FOS = (St)1/3 x (E’)2/3<br...
Example<br />Stiffness required to re-line a pipe 5m below surface assuming constant E’=4<br />** Long Term Stiffness<br />
A Perspective On Pipe Stiffness<br /><ul><li>Most large diameter plastic sewer and stormwater pipes will have LT Stiffness...
Flexible pipes with a long term stiffness of >8,000N/m/m do not exist
Furthermore the reason for the stiffness is due to installation damage not deflection over time
Flexible plastic pipes are commonly made up to 2,400mm diameter (LT stiffness~1,500 N/m/m)</li></li></ul><li>Using a Typic...
With E’=14 instead of E’=4<br />E’=4<br />E’=14<br />Changing the value of E’ has a major affect on what is possible<br />
…. Even more dramatic effect on required stiffness<br />E’=4<br />E’=14<br />
How Is E’ Determined<br />Selecting a realistic value of E’ has a huge bearing on the solution (and economics)<br />AS/NZ2...
AS/NZ2566.1 and E’<br />Suggests a range of values between 1 and 20<br />Suggests the values are conservative<br />Suggest...
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Limitations of AS/NZ2566.1 For The Trenchless Technology Industry

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Transcript of "Limitations of AS/NZ2566.1 For The Trenchless Technology Industry"

  1. 1.
  2. 2. Limitations of AS/NZ2566.1 For The Trenchless Technology Industry<br />Dr Ian Bateman<br />Director<br />Interflow Pty Ltd <br />
  3. 3. Outline<br />Use of AS/NZ2566.1<br />Examples where AS/NZ2566.1 is <br /><ul><li>not conservative enough
  4. 4. too conservative</li></ul>Conclusions and recommendations<br />
  5. 5. Design in AUS/NZ Trenchless Industry<br />There is no specific design standard<br />We borrow aspects from other standards<br />Fully Deteriorated<br /><ul><li> Borrow from AS/NZ2566.1
  6. 6. Assumes existing pipe has no strength
  7. 7. Assumes liner acts like a buried flexible pipe</li></ul>In Tact<br /><ul><li> Borrow from ASTM F1216
  8. 8. Assume existing pipe acts to enhance the liner strength</li></li></ul><li>Overview of AS/NZ2566.1<br />Scope<br />“This Standard sets out a practice for the structural design of buried flexible pipelines which rely primarily upon side support to resist vertical loads without excessive deformation. The interactive pipe/embedment structure is considered only in the transverse direction. Structural performance is predicted in the long-term for pipes in trenches and embankments but not for jacked or bored lines.”<br />
  9. 9. Overview of AS/NZ2566.1<br />AS/NZ2566.1 is designed to cover<br /> - installation of a flexible pipe into a trench<br /> - takes into consideration<br /> - pipe characteristics (stiffness and material properties)<br /> - embedment characteristics<br /> - design loads<br /> - prescribes a method of performing a design<br />
  10. 10. Design Method<br />Calculate Applied Loads<br /> - Soil load<br /> - External hydrostatic load<br /> - Internal pressure<br /> - Dead loads<br /> - Live loads (eg traffic)<br />Check the following<br /> - Deflection<br /> - Strain<br /> - Buckling<br />
  11. 11. Buckling Condition<br />In most applications the governing equation is<br /> (Applied Loads) x FOS = (St)1/3 x (E’)2/3<br />St = Pipe ring stiffness<br />E’=Modulus of Soil Reactivity<br />
  12. 12. In Other Words … <br />The applied loads need to be resisted by<br />The ring stiffness of the pipe (liner)<br />The surrounding soil<br />But, the effect of the soil is much more dominant<br />
  13. 13. AS/NZ2566.1 In Our Trenchless Industry<br />Used successfully for more than a decade<br />Hundreds of thousands of pipes re-lined<br />Industry provides cost effective solutions<br />Installers have effective and practical systems<br />Suppliers are able to produce products for nearly all situations<br />So, what’s the problem?<br />
  14. 14. Potential Problems<br />As the industry develops …<br />We are faced with ever more challenging situations<br />Suppliers develop more and more sophisticated products<br />Fall outside of the intent of AS/NZ2566.1<br />
  15. 15. AS/NZ2566.1 – Not Conservative Enough<br />High Modulus Thin Walled Liners<br /><ul><li>AS/NZ2566.1 allows us to determine the RING STIFFNESS of a liner that is needed
  16. 16. RING STIFFNESS is a function of
  17. 17. The modulus of the material
  18. 18. The thickness of the material</li></li></ul><li>High Modulus Thin Walled Liners<br />Example<br /><ul><li>To achieve a desired RING STIFFNESS of 1,000 N/m/m</li></ul>Can achieve desire stiffness using thin, high modulus materials<br />
  19. 19. High Modulus Thin Walled Liners<br />This is reasonable if the liner of perfectly circular cross section<br />Implicit in AS/NZ2566.1 is that pipes are supplied to site free of defects (then buried)<br />In a trenchless application the pipe (liner) is formed inside a deteriorated host pipe<br />The final shape of the liner is influenced by the shape of the deteriorated host pipe<br />
  20. 20. High Modulus Thin Walled Liners<br />Liners can contain IMPERFECTIONS<br />x<br />
  21. 21. Effect of Imperfections On Liner Stiffness<br />Phenomenon is well studied (Moore,I et al)<br />Effect on liner stiffness is a function of<br />Liner Thickness<br />Size of the Imperfection<br />
  22. 22. With Typical Liner Materials<br />
  23. 23. With A High Modulus Liner<br />
  24. 24. Summarising…<br />With a high modulus material, a 150mm liner has almost zero stiffness with a 15mm imperfection<br />The effect is far less severe with traditional materials<br />The effect reduces as the diameter increases<br />Looking at this another way…<br />
  25. 25. Theoretical <br />Thickness<br />With High Modulus Material<br />Theoretical <br />Thickness<br />
  26. 26. Theoretical <br />Thickness<br />With Traditional Materials<br />Theoretical <br />Thickness<br />
  27. 27. How Deal With This Issue<br />Options<br />Set a minimum liner thickness of (say) 4mm<br />Use an equation to de-rate the actual stiffness and compensate for imperfections of a given size<br />Calculate theoretical thickness and add a constant (say) 2mm<br />
  28. 28. AS/NZ2566.1 – Too Conservative?<br />Large Diameter Lining<br /><ul><li>By number, >95% of all pipes rehabilitated are at diameters of 1,000mm or below
  29. 29. By dollar, ~60 -70% </li></li></ul><li>Returning to Our Design Equation…<br />(Applied Loads) x FOS = (St)1/3 x (E’)2/3<br />St = Pipe ring stiffness<br />E’=Modulus of Soil Reactivity<br />The industry’s default approach has been<br /> - Use values of E’ of between 2 and 5 MPa<br /> - Design a liner with sufficient Stiffness<br />
  30. 30. Example<br />Stiffness required to re-line a pipe 5m below surface assuming constant E’=4<br />** Long Term Stiffness<br />
  31. 31. A Perspective On Pipe Stiffness<br /><ul><li>Most large diameter plastic sewer and stormwater pipes will have LT Stiffness of less than 3,300N/m/m
  32. 32. Flexible pipes with a long term stiffness of >8,000N/m/m do not exist
  33. 33. Furthermore the reason for the stiffness is due to installation damage not deflection over time
  34. 34. Flexible plastic pipes are commonly made up to 2,400mm diameter (LT stiffness~1,500 N/m/m)</li></li></ul><li>Using a Typical Liner Material…<br />~10% Diameter Loss<br />3000mm<br />2700mm<br />2400mm<br />2100mm<br />1800mm<br />1500mm<br />1200mm<br />900mm<br />600mm<br />300mm<br />At large diameters a solution would be not be possible and/or would be very expensive<br />
  35. 35. With E’=14 instead of E’=4<br />E’=4<br />E’=14<br />Changing the value of E’ has a major affect on what is possible<br />
  36. 36. …. Even more dramatic effect on required stiffness<br />E’=4<br />E’=14<br />
  37. 37. How Is E’ Determined<br />Selecting a realistic value of E’ has a huge bearing on the solution (and economics)<br />AS/NZ2566.1 provides the following table<br />But there are other methods<br />
  38. 38.
  39. 39. AS/NZ2566.1 and E’<br />Suggests a range of values between 1 and 20<br />Suggests the values are conservative<br />Suggests with cover heights greater than 10m higher values should be used<br />Shows that the value increases as greater compaction occurs<br />BUT, Trenchless Industry tends to use values of between 2 and 5<br />WHY?<br />
  40. 40. Selection of E’<br />Estimating E’ is difficult and time consuming<br />We often do not know what occurred during initial pipe construction<br />We don’t know what has happened to the soil during its lifetime<br />Cannot ensure 100% uniform support of the liner by the host pipe and/or soil<br />The cost involved in estimating the actual E’ outweighs the cost of installing a stiffer liner – in smaller diameter pipes.<br />
  41. 41. Estimating E’<br />… but in large diameter pipelines this is probably not true.<br />Estimating an appropriate value for E’ will have a significant bearing on the overall economics<br />Not understanding the condition of the soil in large diameter pipelines can lead to serious consequences<br />Above a certain diameter it is worth determining a realistic value of E’<br />
  42. 42. Silo Reduction Factors<br />AS/NZ2566.1 allows the use of silo reduction factors when the depth of cover exceeds 10 times the diameter<br />For small diameter pipes this seems reasonable<br />At large diameters this becomes very conservative<br />Silo effects actually occur at much lower cover heights<br />ALSO, E’ has been shown to be related to depth<br />
  43. 43. AS/NZ256.1 For Large Diameters<br />Using a constant AND/OR low values of E’<br />Not applying silo reduction factors to soil loads until 10 x D<br /> VERY CONSERVATIVE<br /> EXPENSIVE<br />NOT POSSIBLE<br />
  44. 44. How To Deal With This Issue<br />Suggestions<br />Continue to apply the current approach up to a diameter that provides cost effective outcomes<br />Above this diameter, establish more information about the condition of the soil (E’)<br />Allow silo reduction factors below 10 times D<br />
  45. 45. Alternatively…<br />If we don’t then we will have to …<br />Ensure that large diameter pipelines are rehabilitated before they reach the fully deteriorated condition<br />Use a different design method at large diameters (not AS/NZ2566.1)<br />
  46. 46. Conclusions<br />The design approach borrowed from AS/NZ2566.1 has served the industry very well<br />As products and the industry have evolved some limitations of this approach have arisen<br />As these situations present themselves specifications should be enhanced with specific guidelines<br />
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