Soakaway fill material

[newbuild upnorth]

this is just a thought I had so anybodies experience or thoughts are welcome.

 

im not far away from digging my Soakaway - for rainwater - all the calculations have been done and I need 3600 litres of storage capacity in the Soakaway for roof runoff, the details give a typical Soakaway detail using crushed rock as the fill with only a 40% void ratio, it then occurred to me to explore crates - 95% + void ratio.

for our own scenario, space isn't an issue, and the ground is pretty forgiving so we can have long / shallow / deep / wide / trenches it doesnt matter really.

 

if im doing the work myself there won't be much difference in cost, crates will be dearer but smaller hole, rock will be slightly cheaper but bigger hole and more work.

 

I can't see anything that is a hard and fast rule for what you can and can't use, everything refers to BRE365 which again isn't particularly specific, the rest of the internet by and large has it one or the other, rocks or crates.

 

what if we could easily / cheaply get another material for fill, up here there is a huge quantity of used MDPE pipe from salmon cages, people use it for various things but it doesnt really have any value so it is often seen as an opportunity to recycle.

im thinking that if short sections of this were used as fill it would easily be up in the 90% void range, its as tough as can be and MDPE is what they use for civils so its proven not to degrade or leech.

common sizes are 90mm OD so it this was roughly cut into 100mm / 150mm / sections and just thrown in randomly as you would with rock I dont see how this wouldn't work, plenty void for storage and easy for the water to makes it way around and through. I wouldn't try it under a driveway but down the side of a field I dont see how it would be much different in settlement or compressive strength than crates.

 

any thoughts or experience in not using crates or rocks? or why the MDPE pipe as fill wouldn't work?

 

 

Edited Thursday at 07:43 by newbuild upnorth
spelling

[nod]

I’d check with BC first They normally dictate what is to be done 

Crates seem to be the preferred choice 

[kandgmitchell]

I'd run it past BC first but I can't see why it wouldn't work. The purpose of the rocks/hardcore is to fill the hole so the surface doesn't fall in but leave voids for the rainwater to be held whilst soaking into the sub-strata. If you have another material that can perform both those functions then where's the problem? The one issue may be how strong the filled ground would be, but down the side of a field does it matter? Getting a handle of the void volume in such a scenario may be an issue but be a bit conservative and propose it to BC.

[JohnMo]

I would be careful your scheme is or should be an approved scheme by SEPA.  So they will have reviewed the design and approved it. Changing without prior consent would negate your certification. It is also subject to a building warrant and is likely to reviewed by building control or at least a photo trail.

[torre]

Interesting idea but don't you need around 3600 cut lengths of pipe that size? If it's not available cut then I can't see it's worthwhile cutting pipes yourself. The compressive strength may well be questioned by BC.

 

Maybe this would work better with pipes the length of your soakaway all laid the same way creating a stable honeycomb shape like you'll see when pipes are stored in a builders yard? (Around 100 pipes of 3.6m length)

 

Either way you'll still need the whole thing wrapped in a membrane.

[newbuild upnorth]

2 hours ago, JohnMo said:

I would be careful your scheme is or should be an approved scheme by SEPA.  So they will have reviewed the design and approved it. Changing without prior consent would negate your certification. It is also subject to a building warrant and is likely to reviewed by building control or at least a photo trail.

its just an idea, ive not decided on it, I dont think sepa has anything to do with suds though, certainly not for my building warrant, calculated by calculators and stamped by building control, its only for the rainwater not for sewage. and its very vague, perhaps because of where it is and how readily the ground takes the water, it isn't like its designed, just example Soakaways and required volumes.

[newbuild upnorth]

1 hour ago, torre said:

1 hour ago, torre said:

The compressive strength may well be questioned by BC.

 

this is something that may open up a whole line of questioning, I see that all the baskets for sale have a rating of 20 ton or 40 ton so this may be impossible to prove.

[Kelvin]

1 hour ago, newbuild upnorth said:

its just an idea, ive not decided on it, I dont think sepa has anything to do with suds though, certainly not for my building warrant, calculated by calculators and stamped by building control, its only for the rainwater not for sewage. and its very vague, perhaps because of where it is and how readily the ground takes the water, it isn't like its designed, just example Soakaways and required volumes.

SEPA didn’t have any involvement with ours but building standards wanted an engineered design. Ours is 14m x1m trench with 110mm perforated pipe in pea shingle and permeable membrane. Silt trap where all the pipes meet  then down into an inspection chamber. 

Edited Thursday at 15:23 by Kelvin

[saveasteading]

10 hours ago, newbuild upnorth said:

used MDPE pipe from salmon cages

great idea. if you were to band them together and wrap in membrane then it would be a recognisable 'thing'.

I would propose it to the bco first, but seriously expect approval or else ask why not, and argue as long as it took.

 

Reasons not to? 

Strength. Crates can carry loads. does yours need to?

Fills with muck? so wrap it in membrane, as you would a crate anyway.

Not perforated so acts as long pipes....so cut them or perforate them.

 

Advantages, other than cost,

reusing waste product.

Linear if you so choose.

 

If you have the choice, then a long trench arrangement will often work better than the design implies.

By exposing more ground surface to the water there is more soakage. plus there is much more chance of exposing a more

permeable bit of ground, perhaps broken up by roots.

 

I've considered doing this, and if old pipes are not available then using cheap perforated land drain  pipe, banded together.

 

What else might be cheap as void fillers for those of us without salmon frames nearby?

(What are those pipes anyway and why are they available?) 

errmmm. Traffic cones. Plastic drums after the liquid is used....make holes in them. Vegetable crates   Ideas please.

 

 

[newbuild upnorth]

@saveasteading the salmon cages start off as big floating cages for rearing farmed salmon, when they reach the end of their useful life they get taken ashore and cut up.

people use the mdpe pipe for all sorts around here as far as I know the companies give it away to save on paying to dispose of it as it would probably end up in a landfill.

they fill them with concrete and use them for fencing, cut them in half and use them for animal feeding troughs, road crossing pipes, ducts, all sorts.

 

the absolute best thing they are repurposed for is a community run company which uses the 90mm pipe for the frames of bombproof polytunnels, they have been designed and certified and you see them everywhere now, I even saw they were ordered for the Falkland Islands - proven to stand up to over 100mph wind in shetland. they are called polycrub and have a Facebook / website, worth a look as it is brilliant.

 

 

im going to look into using the pipe as some sort of fill or attenuation a bit more, I think you are right about being better used in length with a lot of holes in it.

 

 

[saveasteading]

Very interesting. Absolutely, prepare a sketch, make it look technical, and propose it.  

Does the pipe come to you curved? What lengths? I'd cut it into 1m or so and band it into bundles of 4 (square) or 5 ((round, and better?). Perhaps have 10mm  holes drilled in every pipe???

Then wrap in non-woven geomembrane and band that too. 

These then get laid along the trench or piled in a hole in a gravel surround.

Name it the Shetland Sustainable Soakaway.

[Mulberry View]

Anecdotally, if anyone is feeling frustrated by the amount of work needed for a Soakaway, know that this is what we had to have for our modest (200m2) 4-Bedroom house. 96 standard sized crates in 2 layers (though these are larger crates so there are *only* 60). Just under 20,000 litres. LOL.

 

Edited Friday at 12:13 by Mulberry View

[Kelvin]

Yes I was surprised at how big a hole we were going to need if using crates. The problem we had was we are on a considerable slope so digging said big hole into the side of the hole wasn’t going to be easy or practical. I suggested terracing the slope into three wide terraces primarily to give us a bit more useable garden area which also afforded the long trench way of doing it in the middle terrace. 

[markc]

2 hours ago, Mulberry View said:

Anecdotally, if anyone is feeling frustrated by the amount of work needed for a Soakaway, know that this is what we had to have for our modest (200m2) 4-Bedroom house. 96 standard sized crates in 2 layers (though these are larger crates so there are *only* 60). Just under 20,000 litres. LOL.

 

200 sqm house so maybe 150sqm of roof including a garage? How did you end up at 20 cube of soak away?

[Mulberry View]

6 minutes ago, markc said:

200 sqm house so maybe 150sqm of roof including a garage? How did you end up at 20 cube of soak away?

 

Because we're founded on hard chalk. Made for great foundations, but less so for water infiltration.

 

 

The bottom of this hole is like a bathtub, the soakaway was designed to potentially be half-full most of the time.

[saveasteading]

1 hour ago, markc said:

How did you end up at 20 cube 

20m3 / 200m2.   100mm of rain. Best stay indoors.