simon
New Member
Posts: 19
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Post by simon on Oct 1, 2018 11:06:35 GMT 12
Hi,
I'm trying to find reference to the above in 1547, I can only find a requirement for topsoil to be added to the ground surface to increase distance to ground water to minimum required. From experience must it be top soil or can the same soils from site (or local) be placed to form the raised bed and then covered again with topsoil. I would specify that only track rolling be done, site is flat so no stability issues. This design would require around 150m3 of soils to be added.
What do people think?
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Post by techworks on Oct 1, 2018 13:55:10 GMT 12
Hi Simon
Can you give a bit more info:
-Whats your soil category?
-what is the depth to ground water?
-Does the relevant Regional Council set a minimum clearance to ground water?
Here is my take on this situation:
1547: Appendix M
CM1 states:"Topsoil should be of good quality, rich in humus, and free of non-topsoil material"
and CM7.1 states: "The natural soil into which irrigation lines are installed should consist of a minimum depth of 150 mm (for subsoil categories 3 to 5) and 250 mm (for subsoil categories 1, 2, and 6) of good quality topsoil"
M3.1 states: "Shallow subsurface drip systems shall be installed at a 100 – 150 mm depth into 150 to 250 mm of topsoil in grassed or other suitably vegetated areas."
M6.1 states: "All irrigation systems shall be designed to ensure that effluent is not applied at rates which exceed the absorption capacity of the soil.", and table M1 specifies loading rates depending on soil cat, so as long as your loading rate is matched to the most limiting soil category (be it the fill material used to provide additional clearance to ground water or the underlying soil) then I dont believe you have to use topsoil to raise the area to provide adequate clearance to ground water level. If fact too much good quality topsoil could be undesirable as it could hold too much moisture and be difficult to mow/maintain.
Be interested to hear others thoughts.
Cheers
Grant
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simon
New Member
Posts: 19
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Post by simon on Oct 1, 2018 14:16:34 GMT 12
Thanks Grant,
I would have thought as you say that the limiting factor is the underlying soil type however AS1547 mentions building up with topsoil in Table R1 and just soil in Table K2 (and TP58 mentions Topsoil) so was wanting opinions. Thanks for yours. It was Cat 4 soils, 400 deep water table (winter) and 600mm required setback.
Regards
Simon
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Post by techworks on Oct 1, 2018 15:34:15 GMT 12
Yeah, I'm guessing the different terminology ("topsoil" versus "soil') between R1 and K2 is not intentional, otherwise they should have qualify a max depth of topsoil that is allowable to be used to raise the ground level.
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