Joined: July 2004
||Posted: 24 April 2019,10:25
|Quote (lutonlagerlout @ 12 April 2019,20:39)|
|they currently work on 1 M3 of crates for every 15M2 of drive or roof|
That seems excessive, but then it may be that there is really poor ground permeability where you are, Tone.
It all gets very complicated, trying to determine how big a soakaway is required, but the key is that ground permeability. I keep trying to write a simple explanation of how to do a basic 'back of a fag packet' calculation for crate requirements, but it always ends up with me getting dizzy and having to lie down in a dark room.
As a very, very, very rough guide, I've been working on the principle that, if a 300x300x300mm trial hole formed at invert level of the intended soakaway (so that means this 300x300x300mm hole would lie underneath the base of the lowest crate)...if such a hole is filled to the top with water and that water drops by 150mm or more overnight or in 24 hrs, then use 1 crate per 15m² which is equivalent to 1m³ of crates per 60m² of roof or paving.
Obviously, if the local BCO have published guidance, that would supercede anything I suggest, and it's often worth giving them a call to check if they do have any guidance, and if so, what they would suggest, as they, better than almost anyone else, would know what's what locally when it comes to groundwater drainage.
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