Northern Sewerage Project: Lining Selection in a Corrosive Environment

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  • The Northern Sewerage Project is currently under construction in the northern suburbs of Melbourne. Melbourne Water and Yarra Valley Water are joint clients. John Holland is the main contractor. Design was undertaken by Sinclair Knight Merz and Jacobs Associates. I [mark] will describe the tunnelling and geology and how it affected the lining selection Doug will discuss the sewer issues, concrete corrosion mechanism and risks affecting liner selection.
  • The Northern Sewerage Project is proceeding because: Melbourne’s original sewers were constructed over a century ago. During wet weather, many of these ageing sewers overflow. The photo gives you an idea on the size, form of construction and condition of the aging system Photo of Gary Griffioen in the Hobson’s Bay Main Sewer about 1990 (taken taken by Doug)
  • The current project is part of a strategy that was developed in 1973 by the Melbourne and Metropolitan Board of Works. The strategy split Melbourne into western and eastern zones It envisaged an intercepting sewer extending from Werribee to Bundoora. The Northern Sewerage Project is an extension of the Western Trunk and North Western Sewers built by Melbourne Water in the 1980’s and 1990’s
  • [Describe location using maps] NSP is located in the northern suburbs of Melbourne – The main site office is in Coburg North. In total 7 tunnel sections and 8 access shafts will be constructed [point out NSP1, NSP2 and shaft locations]
  • Slide illustrates the density of the residential housing along most of the NSP1 alignment. This particular photo is along MPIS (NSP1) – Tunnel is about 30m deep at chainage.
  • A significant length of the proposed sewer is located in the Moonee Ponds and Merri Creek valleys. Old, under-capacity sewers overflow into these waterways.
  • The geology along the NSP tunnels will be predominately Silurian (interrbedded siltstone/sandstone) and Basalt. NSP1 tunnels will main be trough Silurian (5 to 85 MPA – fresh and extremely weather average strengths typically 30 to 40MPa) NSP2 will be predominately Basalt with strengths general ranging from 60 to 190 MPa. There is a short section of tunnel (~500m) in NIS 1 (southern section) which is anticipated to be the ex weathered siltstone and recent alluvium mat’l.
  • The geology along the NSP tunnels will be predominately Silurian (interrbedded siltstone/sandstone) and Basalt. NSP1 tunnels will main be trough Silurian (5 to 85 MPA – fresh and extremely weather average strengths typically 30 to 40MPa) NSP2 will be predominately Basalt with strengths general ranging from 60 to 190 MPa. There is a short section of tunnel (~500m) in NIS 1 (southern section) which is anticipated to be the ex weathered siltstone and recent alluvium mat’l.
  • Much of the investigation effort was aimed at optimising conditions for tunnelling. The NDS2 will be one of the more difficult drives due to the paleovalley (Basalt average 100-MPa).
  • 3 TBMs will be used on NSP. Two earth Pressure Balance Machines and one shielded hard rock machine. 3-m EPM will do 4.7km of tunnel, 4-m EPB 4km and the hard rock about 3.2km JH, working with the SKM/JA indicated that 3m was the minimum cut diameter if a manned TBM was to be used. Pipe jacking was eliminated in the CD phase due to the depth, number shafts required and residential area.
  • All 4 Tunnel Sections on NSP-1 will use precast bolted and gasketed segments. The NSP1 segments (both 2.4m and 3.4m diameter) will provide primary and secondary support. 100 yr design life (including watertightness). NSP2 will use similar precast segments to NSP1 in the short soft ground section (500m). But for the basalt reaches [next slide]
  • shotcrete, rock bolts and possibly steel sets will be used to support the ground behind the hard rock TBM. JH can either use slick lines to backfill the pipes in-place or grout thru pre-installed grout ports.
  • The cut diameter was based on John Holland’s recommendation. 3m and 4m were picked for the tunnels. The spatial constraints played a major role in the lining selection specifically when it came to the pipe joints. NSP1 open in-wall joints (bell and spigot would not fit) have been proposed. A drain system was used on NSP1 as the segments will provide the structural support and watertightness. ON NPS2 the system is designed as a sealed system . Therefore the final lining provides both long-term ground and groundwater support. Segements are used on in the short soft ground section but they are only designed for short-term groundwater support. These segments will provide long term ground support. HAND OVER TO DOUG
  • Is a corrosion lining required? This photo shows a concrete sewer suffering the effects of corrosion after only 4 years in service.
  • Is a corrosion lining required? This photo shows the Merri Creek Main sewer in the same general area as the proposed NSP2 (50-80 years old here??).
  • Is a corrosion lining required? This photo shows a concrete sewer pipe in the NSP2 (I.e. further upstream) catchment showing some slime growth.
  • Is a corrosion lining required? This photo shows a concrete sewer pipe which is a tributary of NSP2.
  • Is a corrosion lining required? Also a tributary, but further upstream.
  • Is a corrosion lining required? MCM123 showing about 10mm corrosion after 30 years service. 0.0 to 0.1 mm/year between Jukes Road and LE Cotchin Reserve Shafts (NIS Section 3); 0.1 to 1.0 mm/year between Newlands Road and Jukes Road Shafts (NIS Section 2); and 0.2 to 1.5 mm/year between Carr Street and Newlands Road Shafts (NIS Section 1).
  • Is a corrosion lining required? Many contemporary sewers have been constructed with protective liners.
  • Is a corrosion lining required? The root cause is bacteria in the slime on the sewer walls. The bacteria convert hydrogen-sulphide gas into sulphuric acid The pH of sewer walls can be as low as zero Sulphide model was done to predict corrosion rates along NSP.
  • Is a corrosion liner required? Investigations included: Sampling of sewage, chemical analysis and predictive spreadsheet modelling were undertaken to determine the need for a non-corrosive liner. Inspection of nearby sewers was undertaken to gather representative data on concrete corrosion rates. Sewage quality, hydraulics, turbulence were reviewed. Advice was obtained from concrete technologists and materials specialists. Risk and the preferences of each client were taken into account. The answer is yes, in all but the upstream end of NSP2 The result was independently reviewed.
  • What type of corrosion liner is appropriate? Many options were investigated, ranging from the simple allowance of an extra thickness of concrete to hi-tech materials. NSP1 Considered a very wide range of options (see figure) NSP2 Considered a smaller range of options 1 RCP (with sacrificial concrete) 2 RCP+PE 3 CIP(not considered further) 4 FRPP 5 Polycrete®
  • GRP liner pipes are light but flexible This photo (courtesy of John Holland) shows a GRP liner being being lowered into the Perth Main Sewer.
  • Concrete pipes with a plastic sheet liner are often used for pipe-jacking This photo shows the jacking pipes used in the Brown’s Bay sewer in Auckland NZ Note the lines indicating the extrusions providing the anchorage
  • This photo shows a sample of plastic sheet (PVC or PE typically) with anchors that are cast into concrete
  • Two entirely separate teams were required by the Clients The corrosion issue was analysed, data was gathered, a wide range of options were considered, risks were assessed, preferences considered and recommendations made. The potential for precipitation (or 'scaling‘) due to minerals in the ground water is indicated by the Langelier Saturation Index (LSI). If ground water infiltrated through cement based grout, its pH would increase and its LSI would increase. Groundwater with an elevated Langelier Saturation Index (LSI) could deposit minerals between RCP and a PE membrane. A Langelier Saturation Index with a strong tendency to deposit calcium carbonate (CaCO3) was considered possible for NSP2.
  • Northern Sewerage Project: Lining Selection in a Corrosive Environment

    1. 1. Northern Sewerage Project: Lining Selection in a Corrosive Environment
    2. 2. Old Brick Sewers
    3. 3. Long Time Coming
    4. 4. Location
    5. 5. Residential Section along MPIS
    6. 6. Environmental Concerns
    7. 7. NSP1 Geology Weathered Silurian along NDS Section 2 (NSP-1) <ul><li>Melbourne Formation (Silurian Age) </li></ul>
    8. 8. NSP2 Geology <ul><li>New Volcanics (Basalt) </li></ul>Massive Basalt NIS Section 2 (NSP2)
    9. 9. Long Section NSP1 – NDS 2
    10. 10. Excavation Methods (photo courtesy of John Holland/Melbourne Water) <ul><li>Tunneling (3 TBMs): </li></ul><ul><ul><li>EPB 3-meter dia. = 4,700m </li></ul></ul><ul><ul><li>EPB 4-meter dia. = 3950m </li></ul></ul><ul><ul><li>Main Beam 3-meter dia. = 3190m </li></ul></ul>
    11. 11. Primary and Secondary Support 2400 I.D Test Ring (photo courtesy of John Holland) <ul><li>5 SEGMENTS PLUS A KEY </li></ul><ul><li>RIGHT, LEFT AND STRAIGHT RINGS </li></ul>
    12. 12. Primary and Secondary Support INITIAL SUPPORT (Rock Bolts) Final Lining (RCP w/ Sac. Concrete, or FRPP) 1800 R 1500 Heavy Support Light Support TIMBER BLOCKING RING BEAM BACKFILL GROUT
    13. 13. Spatial Constraints NSP Stage 2 Support Types
    14. 14. Lining Required?
    15. 15. Lining Required?
    16. 16. Lining Required?
    17. 17. Lining Required?
    18. 18. Lining Required?
    19. 19. Lining Required?
    20. 20. Similar Projects <ul><li>Singapore DTSS </li></ul><ul><li>Pantai Trunk Sewer, Kuala Lumpur </li></ul><ul><li>Perth Main Sewer </li></ul><ul><li>S1 Sewer, Brisbane </li></ul><ul><li>Hallam Valley Main Sewer, Melbourne </li></ul>
    21. 21. Corrosion - Sulphide Sulphate, SO 4 Sulphide, S 2- Hydrogen Sulphide, H 2 S [aq] Hydrogen Sulphide, H 2 S [g] Sulphuric Acid, H 2 SO4 Moisture on walls Prevent sulphate reducing to sulphide - add oxygen, nitrate, reduce temperature, BOD, sulphate Prevent sulphide converting to aqueous hydrogen sulphide - increase pH Minimise turbulence to prevent hydrogen sulphide in liquid releasing to sewer atmosphere. Ventilate to prevent hydrogen sulphide converting to sulphuric acid on walls Liner impervious to sulphuric acid, Control exits and treat odours.
    22. 22. Investigation
    23. 23. Lining Options
    24. 24. Durability
    25. 25. Durability
    26. 26. Durability
    27. 27. Groundwater
    28. 28. Groundwater
    29. 29. Final Lining Selection <ul><li>MWC team </li></ul><ul><li>industrial catchment </li></ul><ul><li>deeper sewer </li></ul><ul><li>sedimentary </li></ul><ul><li>residential route </li></ul><ul><li>groundwater excluded </li></ul><ul><li>more $ in BG segments </li></ul><ul><li>more sewer drops </li></ul><ul><li>higher risk of H 2 S corrosion </li></ul><ul><li>required 100% liner </li></ul><ul><li>PE sheet </li></ul><ul><li>YVW team </li></ul><ul><li>domestic catchment </li></ul><ul><li>shallower sewer </li></ul><ul><li>basalt </li></ul><ul><li>creek valley route </li></ul><ul><li>groundwater infiltration </li></ul><ul><li>less $ on segments </li></ul><ul><li>fewer sewer drops </li></ul><ul><li>accepted shaft risk, avoided tunnel risk </li></ul><ul><li>preferred robust liner </li></ul><ul><li>GRP pipe </li></ul>
    30. 30. <ul><li>QUESTIONS? </li></ul>

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