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AS_NZS2566 Presentation.pptx
- 1. Flexible Pipe Design Brad Rudsits | Principal Engineer
- 2. NZS2566.1 Buried Flexible Pipe Overview Presentation will cover the following: Structural design of flexible pipelines using NZS2566.1 • Why? • Definition of flexible pipe • Trench and pipe design • Soils + Dead loads • Live Loads • Gravity + Pressure applications • Tips and tricks • Larger diameters
- 3. NZS2566.1 Buried Flexible Pipe NZS 2566.1 • AS/NZS 2566.1 – Part 1: Structural Design – 30 Pages • AS/NZS 2566.1 – Supplement 1 Part 1: Structural Design - Commentary – 38 Pages • AS/NZS 2566.2 – Part 2: Installation – 85 Pages – Appendices A – O – Appendix M Hydrostatic Field Testing for Pressure Pipelines • Other methods of analysis: • ATV127 / AWWA M45 • EN BS 1295-1
- 4. NZS2566.1 Buried Flexible Pipe Flexible Pipes • Plastic pipes – ABS (Acrylonitrile butadiene styrene) – GRP/FRP (Glass/Fibre reinforced plastic) – PVC (Poly vinyl chloride) – PE (Polyethylene) – PP (Polypropylene) • Metal pipes – DI (Ductile iron) – Steel
- 5. NZS2566.1 Buried Flexible Pipe Why flexible pipes need structural design Flexible pipelines rely on trench side support to resist vertical loads • Vertical force transferred through pipe to the surrounding bedding/soil
- 6. NZS2566.1 Buried Flexible Pipe Failure Modes • Deflection • Buckling • Strain
- 7. NZS2566.1 Buried Flexible Pipe Trench and pipe design
- 8. NZS2566.1 Buried Flexible Pipe Pipe Properties continued Ring Bending Stiffness 𝑆𝐷𝐼 = 𝐸𝑏𝐼 𝐷3 𝑠𝐷𝐿 = 𝐸𝑏𝐿𝐼 𝐷3 Initial Long term Where 𝐸𝑏 𝑎𝑛𝑑 𝐸𝑏𝐿 are defined as per Table 2.1 Sometimes only 𝑆𝐷𝐼 provided by suppliers – but 𝑠𝐷𝐿 used in analysis 𝑠𝐷𝐿 can be 2 year or 50 year value (check ground conditions) Examples DN300 SN8 DN150 SN16 = 8000 and 16 000 N/m/m
- 9. NZS2566.1 Buried Flexible Pipe Pipe Properties Refer to Table 2.1 but…
- 10. NZS2566.1 Buried Flexible Pipe Soils and moduli Soil modulus = “measure of resistance of the soil to deformation” NZS 2566.1 uses Leonhardt equation to determine effective soil modulus of both native soil and embedment. Originally derived from European soil bearing plate tests
- 11. NZS2566.1 Buried Flexible Pipe Soils and moduli
- 12. NZS2566.1 Buried Flexible Pipe Soils and moduli
- 13. NZS2566.1 Buried Flexible Pipe Effective Soil Modulus Based on Leonhardt Correction factors • Developed to model the interaction of embedment modulus with native soil modulus • Trench width, relative pipe diameter influences the factor
- 14. NZS2566.1 Buried Flexible Pipe Dead and live loads
- 15. NZS2566.1 Buried Flexible Pipe Soil loads; and Superimposed dead loads include: • Building Foundations • Bridge Supports • Excess spoil Dead Load = Wg + Wgs Dead Load
- 16. NZS2566.1 Buried Flexible Pipe The working loads due to road vehicle loading is as per the Transit New Zealand Bridge Manual and includes the following vehicle loadings: -0.85 (HN) (Lightly Trafficked Rural) Loading -HN (Normal) Loading -HO (Overweight) Loading Also need to consider construction loads – short term loading Live Loads
- 17. NZS2566.1 Buried Flexible Pipe Live Loads If height of fill is < 0.4 m, a wheel load is considered to act at the top of the pipe If height of fill is > 0.4 m, a wheel load is considered to be distributed as per the diagrams Live Loads = Wq Distribution of Road Traffic Loads
- 18. NZS2566.1 Buried Flexible Pipe Live Loads If height of fill is < 0.4 m, a wheel load is considered to act at the top of the pipe If height of fill is > 0.4 m, a wheel load is considered to be distributed as per the diagrams Live Loads = Wq Distribution of Road Traffic Loads
- 19. NZS2566.1 Buried Flexible Pipe Design Analysis – Deflection (%) From Table 2.1 Function: Dead and live loads (Wg Wgs Wq) Ring bending stiffness (SDL) Effective soil modulus (E`)
- 20. NZS2566.1 Buried Flexible Pipe Design Analysis – Ring Bending Strain (m/m) Function: Deflection ( Δ𝑦 𝐷 ) Ring bending stiffness (SDL) Effective soil modulus (E`) From Table 2.1
- 21. NZS2566.1 Buried Flexible Pipe Design Analysis – Combined Loading Function: Strain (𝜀𝑏) Internal working pressure (Pw) From Table 2.1
- 22. NZS2566.1 Buried Flexible Pipe Design Analysis – Allowable Buckling (kPa) Function: Ring bending stiffness (SDL) Effective soil modulus (E`) Poissons ratio (𝜈) Steel/GRP (𝜈 = 0.3) ->26.3 HPDE (𝜈 = 0.45) ->30.1
- 23. NZS2566.1 Buried Flexible Pipe Design Analysis – Buckling (kPa) Function: Overlaying soil density (𝛾) Dead and live loads (Wg Wgs Wq) Depth of cover (H) Depth of water table (Hw) For H > Hw 𝛾(H-Hw) + (𝛾L + 𝛾sub)( 𝐷𝑒 2 + Hw) + Wgs + Wq + qv 𝛾sub= 𝜌𝑠 - 1 𝛾 𝜌𝑠 < qall qall, where qall is the greater of qall1 and qall2
- 24. NZS2566.1 Buried Flexible Pipe Design Analysis – Buckling (kPa) Function: Overlaying soil density (𝛾) Dead and live loads (Wg Wgs Wq) Depth of cover (H) Depth of water table (Hw) For Hw > H (ie in flood plain) 𝛾L( 𝐷𝑒 2 + Hw) + 𝛾sub( 𝐷𝑒 2 + H) + Wgs + Wq + qv < qall 𝛾sub= 𝜌𝑠 - 1 𝛾 𝜌𝑠 qall, where qall is the greater of qall1 and qall2
- 25. NZS2566.1 Buried Flexible Pipe How to do analysis…. • Unfortunately no software covering all material types • Iplex Australia – Structural Calculator • Excel = Good
- 26. NZS2566.1 Buried Flexible Pipe Large Diameter Considerations • For polyethylene need to watch out for factors like pipe string length and changes to SDR. • Some iterations required for HPDE analysis. • GRP type = CC or FW • NZS only applies for pipes with OD > 75 mm Need to consider buoyancy and minimum cover requirements
- 27. NZS2566.1 Buried Flexible Pipe Tips and Tricks • Pipe embedment and compaction requirements o Helps to know what likely construction machinery could be. • Embedment material, grading curves, fine movement if below true D85 fine < 0.2 D15 Coarse (Native) (Embedment) • Worked examples = NZS2566.1 Supplementary 1
- 28. NZS2566.1 Buried Flexible Pipe Project Example – Grading Curves
- 29. NZS2566.1 Buried Flexible Pipe Tips and Tricks • Trench geometry – increase trench size (B) for smaller diameters • Soft ground conditions = foundation requirements 4.914 4.919 4.924 4.929 4.934 4.939 4.944 4.949 4.954 4.959 870.616 880.616 890.616 900.616 Elevation (RL) Chainage Baseline Survey IL (20th Nov 14) Comparative Survey IL (19th DEC 14) Comparative Survey IL (12th JAN 15) Design IL Design IL +10mm Design IL -10mm
- 30. NZS2566.1 Buried Flexible Pipe Other Design Aspects - Cyclical Loading • Applies to: PVC, PE, Polypropylene (Plastic) • Does not apply to FRP Source: PIPA POP001
- 31. NZS2566.1 Buried Flexible Pipe Other Design Aspects - Cyclical Loading • Determine number of cycles (per day) • Determine Fatigue Load Factor • Pressure Range / Fatigue Load Factor = Minimum Pressure Class
- 32. NZS2566.1 Buried Flexible Pipe Other Design Aspects – Temperature • Applies to: PVC, PE, Polypropylene (Plastic) • FRP only good upto 30°C
- 33. NZS2566.1 Buried Flexible Pipe Other Resources • Tyco Steel Manual – Design of all things related to steel pipe • PIPA (www.pipa.com.au) – Technical references and industry guidelines • HOBAS TextBook / Flowtite Engineering Design Guidelines • Marley – PVC & PE Pressure Technical Manual • James Hardie/Iplex Design Manual (Hardcopy), or • Iplex Australia Website
- 34. NZS2566.1 Buried Flexible Pipe www.ghd.com
Editor's Notes
- Summary list covering what you need to know for pipe structural design using NZS2566.1
- ATV127 + AWWA M45 – GRP pipes
- Flexible pipes could also be considered thin walled pipes Also includes metal pipe which might seem counter intuitive but they can be considered thin walled. Materials can either homogenous or composite (eg CLMS) Plain walled or structured wall (PVC and PP) Steel pipe excludes corrugated steel pipe Also excludes bored, HDD installations
- Vertical force from dead and live loads conveyed to surrounding soil through the pipe – pipe designed to deflect/deform within prescribed limits Pipe not required to resist all the vertical force, not like a concrete pipe Vertical force causes decrease in vertical diameter and increase in horizontal diameter (elliptical)
- Deflection = circumferential, not longitudinal . Can also be considered measure of how elliptical the pipe is. Out of round Buckling = whether the pipe has sufficient stiffness to prevent collapse under the vertical loading. Ability to transfer vertical loads to horizontal. Strain = important in consideration of potential for pipe creep (plastics this is very important) – feeds into equation for long term and short term analysis The analysis as per NZS2566.1 considers all the above, as depending on whether it is short term or long term scenario's, load cases, different failure modes might be critical Metallic pipes – generally deflection is critical to limit any liner damage Plastic – can handle high strains, so generally deflection or buckling critical GRP – low strain properties, so generally strain is critical
- The diameter term is the at the neutral axis, which is a function of wall thickness. Manufacturers can sometimes select D that suits calculations in material provided. Tolerances in manufacturing mean wall thickness and internal diameter change. Long term refers to 50 year design life. But standard allows the use of 2yr moduli values – assumption that most plastic pipes reach stable condition after 2 years in ground. But if weak native soils, high groundwater or poor embedment, use 50yr Testing for stiffness can done using AS 3572.8 (2 yr stiffness 50yr stiffness) or ISO 9967 and 9969 NZS2566.1 only suitable for pipes with 𝑆 𝐷𝐼 > 1250 N/m/m and 𝑠 𝐷𝐿 > 625 N/m/m Need to check the SN values of selected pipes – generally they are all for the Initial stiffness ( 𝑠 𝐷𝐿 ) GRP manufacturers always seem to have values for SDI and SDL hidden away (Filament Wound = 𝑠 𝐷𝐿 = 60% 𝑆 𝐷𝐼 ; CC = 𝑠 𝐷𝐿 = 40 to 65% 𝑆 𝐷𝐼 )
- Table 2.1 contains majority of pipe properties for most common pipes – ring bending moduli (long and short term), factor of safety’s, allowable limits. But need to refer to manufacturers information for GRP, polypropylene pipes, profile walled pipes etc GRP pipes have different values depending on if they are centrifugally cast (Hobas) or Filament wound (Maskell/Flowtite) Polyethylene pipe info – Graeme Dick is the best person in GHD. Profile walled pipes can be difficult to assess speak with manufacturers directly (ie Frank PKS ribbed PE pipe)
- Geotech engineers typically get asked what the value of soil moduli would be for both native and embedment material. Not to be confused with bulk modulus, Youngs or Elasticity modulus Usually assessed with shear vane testing (NZ) But NZS 2566.1 considers Standard Penetration Tests Originally derived from European design practice using soil bearing plate tests. These moduli are generally about 50% of deformation moduli from tri-axial tests Using allowable foundation bearing pressures, it is possible to derive the plate load or pipe design soil moduli from the Boussinesq’s plate bearing theory for an elastic, homogenous, isotropic solid. That is for a rigid plate and a soil Poisson’s ratio of 0.5
- The table that Geotechs hate – asked to recommend a value based on limited data and knowledge. Do not always have SPT’s, so have to guess based on “firm” stiff” descriptors and soil classification. Lot of NZ applications around silts and clays. However if in river plains (Canterbury etc) then can be in top half of soil classification. If in the very fine grained and very plastic materials, get specialist geotech advice (probably very bad ground conditions). Can then get specialist analysis (ie FEM) – see Razel Ramilo (Wellington) Table 3.2 also important for definition of the embedment compaction standards required.
- More information about soil moduli – source = Iplex Australia (http://www.iplex.com.au/iplex.php?page=lib&lib=26&sec=176&chap=236)
- Leonhardt developed effective soil modulus in early 80’s. Wider the trench, more the pipe wall will be interacting with the embedment with no side support from native material. This results in a higher effective soil modulus – if soft conditions, easier to dig it out and replace with competent material.
- Need to specify the unit weight of soil/backfill above the pipe Normal fill = 20 kN/m³ Crushed rock = 24 kN/m³ Need to consider any hydrostatic loads as well – for example pipes in flood plain with additional weight of water on them (buckling checks) Wg = trench fil load Wgs = uniformly distributed dead load
- For short term construction loading use stiffness as per 2/50 year values to be more conservative), but if that is critical loading scenario then check with the initial stiffness to see if pipe would be overdesigned.
- If <0.4 m then wheel load acts on area as per the contact area of wheel/tyre/track Can have wheel loads acting on the pipe, even if wheel path is not directly over the pipe. Ie pipe in shoulder of the carriageway No consideration of concentration of loads at prism overlaps Note that NZS2566.1 does not consider multiple axles, or load prisms overlapping from multiple axles
- If <0.4 m then wheel load acts on area as per the contact area of wheel/tyre/track Can have wheel loads acting on the pipe, even if wheel path is not directly over the pipe. Ie pipe in shoulder of the carriageway No consideration of concentration of loads at prism overlaps Note that NZS2566.1 does not consider multiple axles, or load prisms overlapping from multiple axles
- Deflection is managed by combination of both pipe stiffness and effective soil modulus If one is insufficient then the other needs to increase to meet the deflection limit
- Deflection is already known from previous calculations Df is the shape factor. As Stiffness reduces, or effective soil modulus increases then Df increases. This models the deformation of the pipe relative to the surrounding bedding. Higher the shape factor, more deformation, more strain. Strain failure occurs from outside of pipe wall to inside.
- Strain is already known from previous calculations Internal working pressure = normal pressure in the pipe (ie design pressure) and not the maximum allowable pressure For gravity pipe Pw = 0, so strain is only factor relevant. Rc = re-rounding coefficient. An internal pressure helps to keep the pipe ‘in round’ and is a function of the working pressure. Not applicable for pressures over ~300m ( 3.0 Mpa) Units are dimensionless
- Fs = Factor of safety = 2.5 unless reason to change otherwise. v = Poissons ratio Poissons ratio is the relationship between pipe length (longitude) and pipe diameter (circumferential) Increasing internal pressure will increase diameter (plastic pipes) and therefore pipeline will shorten. Pipes with higher Poisson ratio (but same stiffness) will have greater buckling capacity qall1 used when cover <0.5 m – soil is not providing any support, and only pipe wall thickness is resisting buckling. Poissons effects in pipes important for thrust restraint (separate subject)
- The first two terms represent Wg (Dead load) for when water table below cover level) 𝛾L Unit weight of water (10 kN/m3) 𝛾sub = Submerged unit weight of soil Ps = Specific gravity of soil (2.65 unless noted otherwise) Wgs = Superimposed dead load Wq = live loads (wheel loads etc) qv = vacuum (where applicable) qall1 and qall2 calculated on previous slide Bucklign failure occurs generally from inside of pipe wall to outside.
- The first two terms represent Wg (Dead load) including mass of water above the pipeline 𝛾L Unit weight of water (10 kN/m3) 𝛾sub = Submerged unit weight of soil Ps = Specific gravity of soil (2.65 unless noted otherwise) Wgs = Superimposed dead load Wq = live loads (wheel loads etc) qv = vacuum (where applicable) qall1 and qall2 calculated on previous slide
- No PipeClass equivalent Iplex calculator needs registration form and then need ITS to install the software Excel is the best tool, cause you can use features like goal-seek and scenario manager to assess a whole range of variables. Some “pro-forma” spreadsheets existing – see Brad Rudsits
- Pipe string length – how much needs to be moved at any one time, and what stresses that induces in pipe (outside the NZS) For HPDE can end up chasing wall thickness to achieve structural design but maybe another material might be better. To many changes to SDR (wall thickness) can change the hydraulic design (adversely). Very different values for allowable long term ring bending strain for centrifugal cast (0.6%) and filament wound (0.2%) FW always seems to be cheaper but CC handles strain better. Buoyancy is a separate subject not covered by the standard
- Can go for higher spec embedment with high compaction load (95% MDD) but what happens if they use large compaction wheel on digger etc. Can lead to ovality issues during final inspection – Wallan Branch Sewer, out of round. Movement of fines through the trench occurs if 20% of diameter of 15% percentile of coarse material is greater than diameter of 85% percentile of native material Foundation requirements – may need to consider specifying minimum bearing capacity requirements (undercuttin) Worked examples present a range of different scenarios for pipe materials and ground conditions, provide good reference. Access through Standards NZ – have requested it to be added our online portfolio
- Notes included a limitation on the construction loads Offered three options for embedment material to suit contractors plant equipment etc. If doing contract admin, get recent grading certificate from quarry/supplier. Had ca ontractor provide a certificate that was 2+ years old. Migration of fines was a concern (native soils were river sediments, very alluvial) so we added grading curves to drawing.
- Numerous equations are a function of trench width and diameter. For smaller pipes < 200mm, can achieve a higher effective soil modulus by increasing the trench width B. Easy to justify if large machinery/bucket size being used. Example from NYM project – contract didn’t undertake required foundation works, sections of settlement. Original design was for 12.0m lengths to reduce number of joints. Contractor said they needed to use 3.0m lengths for OHS reasons.
- When used under cyclic loading conditions such as for sewage rising main, then over life time of the pipe it will have a reduced pressure value. Need to de-rate the pipe due the cyclic loadings. Most manufacturers have some information but refer to the Plastic Industry Pipe Association of Australia (PIPA) for analysis for PVC types, and PE.
- Need to be careful with sewage rising mains – ie based on average of 8 starts per hour = 192 per day = 7 Million cycles. Fatigue Load factor of 0.71 = Increase to pressure range of 40%
- Temperature de rating important if doing anything with Trade Wastes, or Industrial Water, as these tend to have elevated temperatures. For PVC, PE the design life is reduced along with the maximum allowable pressure rating. Generally do not have 100yr design life for pipes with trade or industrial wastes. Not practical for $. Can get FRP/GRP with epoxy liners or different ester combinations, but need to reduce allowable stiffness to 60-70% of original value ie SN 10 000 to SN 6 000 Prolonged exposure to elevated temperatures can reduce the pressure and stiffness capabilities.