Land Development Engineering

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  • 1.  Flexible joints outside manholes?

    Posted 06-05-2016 09:10

    I am currently being questioned by a developer with regards to the requirement for flexible joints outside manholes.

    PNCC's engineering standards require double flexible joints upstream and downstream for wastewater manholes and single flexible joints upstream and downstream for stormwater manholes.

    I have checked some standards from other LA's around NZ and there seems to be some inconsistency.

    I would appreciate any feedback on what your requirements are?

    Kind Regards

    Tony

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    Tony McGlynn
    Developments Team Leader
    Palmerston North City Council
    Palmerston North
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  • 2.  RE: Flexible joints outside manholes?

    Posted 09-05-2016 09:18

    In Central Queensland,

    We follows CMDG guideline which states, for sewer 2 flexible joints are required please refer below.

    "Where pipelines are connected to large structures (e.g. sewage pump stations or 1500mm diameter Access Chambers) or where excessive differential movement might occur, then connection by means of 600mm long pipes and two flexible joints is required. The first joint being at or within 150mm of the face of the structure. Where flexible joints cannot be made with cut pipes, the Contractor shall select pipes from the various lengths provided in order to make the second joint within 300mm of the position shown on the drawings. Foam cores shall be provided for future connections."

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    Madhav Karki
    Livingstone Shire Council
    YEPPOON QLD

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  • 3.  RE: Flexible joints outside manholes?

    Posted 11-05-2016 09:15

    Hi Tony,

    James is correct. The reason for having two flexible joints means that any un-even settlement of pipe bedding etc does not crack or damage in/outgoing pipes. The pumpstation or manhole chambers do not usually settle much, whereas the pipe can settle more.

    This was a common occurance on clay pipes but not so much of an issue on PVC pipes that allow a certain amount of movement.

    However, that said, it is in my opinion that it is good practice to still install these flexible joints as PVC can also crack.

    Mike 

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    Michael Kulpa
    Land Development Engineer
    Waikato District Council
    Ngaruawahia

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  • 4.  RE: Flexible joints outside manholes?

    Posted 09-05-2016 09:22

    Hello Tony

    In a past life when I was inspecting / asset collecting stormwater lines, circumferential cracks in the pipes just upstream and downstream of pits was common.  Probably due to the pit being on more compact bedding than the pipes.

    Based on the number of cracks, I would recommend the flexible joints, unless the developers can show a way where they will annually inspect the pipes for say 1 or 2 m from the pit / maintenance hole and replace any pipes with any cracking within 3 months of the inspection.  The duration of the annual inspections is to be at least half the design life of the pipe system.

    If the developers don't want to construct to your standards, then the developers can undertake the maintenance that you are designing out by having flexible joints.

    Developer often tell me similar things, such as you don't need expansion joints in concrete slabs or the other Council's don't require full depth expansion, or some other detail that aids longevity buts takes a bit of extra effort during construction.  I ask them if they are including maintenance in their price if they leave that out. 

    Thanks

    Jim

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    JimTurner
    Team Leader Design Projects
    GORDON NSW

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  • 5.  RE: Flexible joints outside manholes?

    Posted 10-05-2016 09:26

    Hi

    The 1981 and 2010 NZS4404 documents require/d two flexible joints for wastewater pipes.  

    Auckland's Watercare standards (online & current) require one flexible joint at both the inlet and outlet within 600mm of manhole connecting to an approved manhole connector (PE/MDPE/PVC) which I suspect gives a little more flexibility compared to old earthenware pipes with concrete joint to MH.

    Auckland's Stormwater standards require one flexible joint at both inlet and outlet where the pipe is less than or equal to 600mm diameter with the joints within 600mm of the MH riser, Pipes greater than 600mm do not require flexible joints.

    It should be remembered there is an expectation on a solid base and Auckland's soils are relatively firm with limited settlement expected. Where settlement may occur in weaker soils (even when a larger base is proposed) two flexible joints may at least better protect the connection to the manhole.

    Will be interesting to read what others do and why.

    Regards

    Glenn

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    Glenn Broadbent
    Auckland Council
    Auckland

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  • 6.  RE: Flexible joints outside manholes?

    Posted 17-05-2016 09:21

    The requirement for rocker pipes are covered in WSAA Gravity Sewerage Code of Australia WSA 02 -2014 Version 3.1

    " Extract from WSA 02 Clause 7.6.4.3 Rocker pipes

    A flexible joint at the interface of the MH connection with a second flexible joint in close proximity, achieved through the use of a rocker pipe, is generally sufficient to alleviate differential settlement induced pipeline failure.

    Rocker pipes shall be provided at entry to, and exits from, an MH when PVC-U, VC, GRP, RC and DI pipes are used. Their length shall be as shown in Table 7.3.

    PE and PP pipes may generally be connected to rigid structures without the use of short rocker pipes or MH couplings. PE and PP pipes have sufficient flexibility and strain tolerance to accommodate differential settlement at the interface.

    Major pipeline infrastructure shall be designed with the assistance of comprehensive ground investigations and methods of analysing settlement.

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    Carl Radford
    Water Services Association of Australia
    Docklands VIC

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  • 7.  RE: Flexible joints outside manholes?

    Posted 19-05-2016 09:32

    Our specifications are available on our website.

    Subdivisions Supplement to NZS4404

    Whanganui remove preview
    Subdivisions Supplement to NZS4404
    ​​​​​​​The following document provides details of Whanganui District Council's subdivision and land development engineering standards, aligned to NZS4404. NZS4404 is available from Standards New Zealand. The Council's supplement document has been divided into sections for ease of use. Registers (all PDF) Documents (all PDF) Page reviewed: 01 Dec 2015 5:41pm
    View this on Whanganui >
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    Damien Wood
    Development Engineer
    Whanganui District Council
    Whanganui

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