Soakaway Back Fill

[Digger1]

When installing soakaway crates can you use MOT Type1 as backfill around and on top or does it have to be pea gravel?

Thanks

[JohnMo]

Would MOT type 1 just block everything up as it has lots of fines in the mix. 

 

Gravel or pea would be my thoughts 

[markc]

Type1 used where you want it to compact and become almost a solid lump so definitely not good for a soak away, screened (washed) railway ballast, pebbles, crushed concrete etc.

[Canski]

He did say around and on top not inside. 

[Temp]

Some MOT type 1 is considered impermeable to water so definitly not a good idea to use any old MOT 1.  

 

MOT type 3 is meant to be permeable but as @JohnMosaid, I'd use pea gravel.

 

 

[JohnMo]

45 minutes ago, Canski said:

He did say around and on top not inside. 

Wrap a soakaway in an impermeable material, you no longer have a soakaway, you have a bucket with stones in it.

[Digger1]

Just to be more clear. The crates will be wrapped in geo membrane.  I have some crushed hardcore. Its probably bigger than Type1, 60mm-30mm. Would this be ok to put down the sides?  The bottom will have sand/sharp sand.

[nod]

The 60 / 30 is ok around the crates 

The previous posters are pointing out that mot is designed to do the opposite to what you are trying to achieve The big clean stuff around the crates will help it stay clear 

[Digger1]

A question about wrapping of the permeable geo membrane. Is the idea that this is wrapped around perfectly to really contain most of the water or is its purpose to keep soil from getting in?  
stuggling to see how i can wrap the crates perfectly enough to create a semi water tight void.

[joe90]

58 minutes ago, Digger1 said:

its purpose to keep soil from getting in?

Yes.

[Carrerahill]

17 hours ago, Digger1 said:

When installing soakaway crates can you use MOT Type1 as backfill around and on top or does it have to be pea gravel?

Thanks

They are doing a big attenuation system round the corner from my office under the roads, they put in the crate boxes into a membrane lined pit, then they used washed 40-50mm drainage stone (granite usually) also known as clean gravel. Type 1 has too much whin dust and other fines in it. The stuff was dumped on the road and left almost no dust marks it was clearly the right stuff.

 

Even washed pea is not that clean and being round rather than angular creates less voids between the stone, big angular stone creates larger and more voids between the stone. 

 

To be fair, at a push, Type 1 would be fine, but it is not actually the right stuff. 

 

Clean 3" crusher run of recyclables would be good and cheaper. 

Edited July 14, 2022 by Carrerahill

[JohnMo]

But small bear to use the correct backfill material, in the grand scheme of things.