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Posted: Wed Jul 25, 2012 7:11 pm
by Rick
I posted a separate Q on soakaway crate ... and will backfill around these with 100mm sharp sand.
Q is on the land drainage trenches these are ~400 x 400 with an 80mm perforated pipe.
2 Q's ...
Is it best to have pipe in the centre of the material .. i.e. 150 below pipe 150 above ?
Second Q ... I have bought a couple of 1 tonne bags of 30mm clean stone for this ...intended putting this in fully wrapped in Geotex.
As some have mentioned using shingle ... is clean stone not suitable ? or do I need to add some small stone to this ... or even sand ... that would fill the voids.
Posted: Wed Jul 25, 2012 8:49 pm
by msh paving
who told you to back fill around the crates with sand?Totally silly idea,19mm or even 40 mm stone is ideal,
pipe need to sit on some gravel to keep the slight fall,50-100mm below rest above,make shure the geo textile is water permable, i would not put geo textile in a land drain trench, you never see land drain companys do it in fields
no sand to fill voids this will clog up the shingle, voids is what you need to collect water
MSH 
Posted: Wed Jul 25, 2012 10:42 pm
by Rick
msh paving wrote:who told you to back fill around the crates with sand?Totally silly idea,19mm or even 40 mm stone is ideal,
It is the spec stated in Polypipe Tech manual ...>
.Polystorm Tech Manual
I did phone them ... they said it had to be 100mm sand base and at least 100mm on all sides & top)
I have bought 30mm stone chippings ... so if this is usual, then I'll use it for crates & trenches.
Just a further Q ... if you don't Geotex wrap the fill, surely with rain it will wash silt into stones fillimng the voids and eventually it will stop working ?
Just a thought that is all.
Posted: Thu Jul 26, 2012 8:35 am
by seanandruby
what size is your stone? 20mlish will be fine. line your trench with a geo texti'le like terran, make sure you leave enough to cover the stone/shingle. Place 100 ml of stone in trench place wrapped pipe, top up with 100 ml of shingle/stone pull the two excess pieces of terran over the shingle overlapping one with the other by at least 200ml , lay your subase, or backfill taking care not to lift the material.
Posted: Thu Jul 26, 2012 9:49 pm
by Dave_L
You would only sand around a wrapped rainwater attentuation cell, not a soakaway.
Posted: Thu Jul 26, 2012 10:39 pm
by Rick
I have 30mm stone.
I asked neighbour who was local BCO.
He advises 100mm sand in base, lay in non woven geotex.
Set in boxes, wrap in geotex.
Attach pipes..also encased in stone & grouted wrapped.
Backfill with 30mm stone, and at least 150mm top cover.
Then overlay this with geotex, with at least 200 extra all round ....then backfill with soil.
The top sheet is important in his view, otherwise soil will simply migrate down into voids and block the drainage function.
Posted: Fri Jul 27, 2012 6:47 am
by Dave_L
All looks good to me but I wouldn't wrap the bottom of the soakaway, give the water the best shot at migrating away from the soakaway quickly and efficiently.
I don't sand the bottom of them, use 100mm or so of 20mm chipping.
Posted: Fri Jul 27, 2012 11:59 am
by Rick
Dave_L wrote:All looks good to me but I wouldn't wrap the bottom of the soakaway, give the water the best shot at migrating away from the soakaway quickly and efficiently.
Do you just have it hanging loose down sides, or do you have it tucked under base ... but not covering ?
>>>
I don't sand the bottom of them, use 100mm or so of 20mm chipping.
>>
I have bought the 30mm chippings so it's either sand or those ... or I suppose I could do a mix ?
Posted: Fri Jul 27, 2012 8:37 pm
by Dave_L
Personally I'd just use the chipping but mixing it won't hurt I guess.
Posted: Fri Jul 27, 2012 9:48 pm
by Rick
Dave_L wrote:
what about the other Q ... do you just leave Geotex hanging loose down sides of crates ?
or have an overlap under crate but not fully covered ?
Posted: Fri Jul 27, 2012 9:57 pm
by Dave_L
Tucked nicely down the sides then carefully filled with single size stone.