A small construction site just opened up fairly nearby to me – they’re building a few 2-3 bed bungalows on a site which lies right next to the main road out of town. What’s the gert big ****-off hole half-filled with the plastic crates for? Is it going to be a water drainage soakaway or similar?
https://www.geograph.org.uk/photo/6917099

Soak away for the water off the building. Saves all the water rushing off into local drains and creates a lag between peak rainfall and discharge.

Yeh it’s a soakaway, the crates create a much larger storage volume than the old fashioned method of filling the hole with rubble, so the hole can be smaller.

If you get your drive resurfaced and it’s not permeable, you should be getting a few of these dug in to prevent rainwater running into the street/drains to prevent flooding.

Cheers guys, I guessed as much. Is there a better technical term for them than ‘crates’?

SUDS init!

Attenuation Crates if you want to be fancy, but still crates

Of course, got it now…. ‘SUDS Attenuation Crates’, so I’ve updated the description on Geograph accordingly.
Well done, STW never fails

The crates get wrapped in the white permeable geotextile you can see in the photo, this stops long term silting up.

https://skyplastics.co.uk/500x400x1000mm-40t-modular-water-storage-crate.html?gclid=CjwKCAjwxo6IBhBKEiwAXSYBs7OYPrdlOYjdSQ-0ZXnp6asuv7wkv-S5EhvNy6vX86r9vs12TxOl0RoCOb8QAvD_BwE

*Pedant mode* Could be soakaway or could be an attenuation tank to temporarily store water and release it in a controlled manner into a watercourse or existing sewer via a control structure.

The crates themselves just create the void, what it’s wrapped in determines what they’re building. Based on the the earth looking clayey as **** I’d guess attenuation tank and the white wrap is actually impermeabl.

The actual technical term would be geocellular storage.

I thought they were traps for underground lobsters

If you get any brown trout in them someone hooked up the wrong pipe.

*double pedant mode*… sorry but filter geotextiles are most definitely permeable, it would be a very inefficent soakaway if wrapped in an impermeable membrane.

https://www.surescape.co.uk/drainage-geotextile-fabric-2m-x-25m-roll-121-p.asp?gclid=CjwKCAjwxo6IBhBKEiwAXSYBswEgVkytTuOACORPC_v43eoJuZh8r-A77S8kwnVVlRZuXwLBWDb2GRoCXKoQAvD_BwE

https://www.sure-green.com/geotextiles-2m-x-25m.html?gclid=CjwKCAjwxo6IBhBKEiwAXSYBs-ZYwzYwwdw-BWNmeoPByCVm3iBKGgDx7abpbjfDcjVzs1l1uQigphoCDlkQAvD_BwE

Very interesting.

But why dig such a gert big hole and not fill it with the crates?

Skoolday!!

But why dig such a gert big hole and not fill it with the crates?

You mean why are the crates there at all? Stops the hole collapsing and a bit of grass over the top looks nicer than a sink hole 🙂

*Triple Pedant mode*

*double pedant mode*… sorry but filter geotextiles are most definitely permeable, it would be a very inefficent soakaway if wrapped in an impermeable membrane.

Eh… That’s what I said. It’s not necessarily a soakaway. You don’t generally built a soakaway where the permeability of the subsoil is so low that it won’t actually soak away. What you do in those circumstances is wrap in an impermeable membrane and have a control structure such as a weir or a hydro brake in a manhole that either connects it back into the sewer or to a watercourse.

You absolutely do wrap it in permeable membrane if you want it to soakaway.

So when you design one you typically need the infiltration rate of the underlying geology by doing a soakaway test and the hydrology of the site. If it soaks away you would then have to size it to provide the storage needed to allow the time required to soakaway (reservoir routing calculation) either in excel or in software like micro drainage.

If you go down the release to watercourse or sewer you would need the discharge rate permissable and size the tank and control structure to achieve that.

I can send you the Suds Manual Ciria report C753 if you don’t believe me.

But why dig such a gert big hole and not fill it with the crates?

Might not be finished yet. If it’s been designed properly they need an inlet structure (manhole with a pipe or a set of crates connecting it to the main tank should also have a silt trap of some description) and also the bottom rows should have jetting locations which is a pipe connected to an inspection chamber (each row needs its own).

It also easier to back fill if you have enough space to compact it properly.

It’s a gravel pit*, for all those bikes of said name once they go the way of the fat bike.

*Check out my…

I thought they were traps for underground lobsters

Graboids?

@joshvegas We’re on pretty permeable geology around here for the most part, New Red Sandstone, albeit with a bit of glacial boulder clay on top in places. But on that basis, I’m going with ‘probably a soakaway’. Thanks all round.

@joshvegas clearly no impermeable membrane present in the op’s photo, only a non-woven geotextile. The impermeable membrane would be between the crates and the non-woven geotextile. My money is on primary role being a soak away and not an attenuation tank. That said, and as you’ve mentioned, they are not necessarily exclusive, it could also have a high level outlet to allow discharge during abnormally high flows when capacity is reached. So soak away during normal conditions and attention during flood.

Soil looks sandy to me, excavation could easily be confused with clay from the colour but the spoil heap in the background gives it away.

Thats an impressive angle of repose for sand though. Probably Sandy clay, or clayey sand.

Thats an impressive angle of repose for sand though. Probably Sandy clay, or clayey sand.

there are largish cubes of material beside the excavation that look as-dug – i`d guess a sandstone. so it standing up is probably fine. you sometimes need a breaker to excavate into a sandstone as the usual JCB machine will refuse.

I’m more worried teh crates seem to be stacked in vertical piles and not in a brick fashion (as normally specified) and the top isnt flush which means the block ties may not be present- still if its in a landscaped area it might be alright. I’ve only seen one collapse in a landscaped area.

The impermeable membrane would be between the crates and the non-woven geotextile.

@wibble – this isnt true for mant cases – most crate manufacturers would specify a protection fleece between the crate and the impermeable liner to stop you poking holes in the liner.

Some impressive SUDS knowledge in here!!!

Well you learn something new every day.

I gathered that to help control flooding most new builds had to have soak aways, but I didn’t realise that they were filled with large lumps of plastic. Not very eco is it !

I gathered that to help control flooding most new builds had to have soak aways, but I didn’t realise that they were filled with large lumps of plastic. Not very eco is it !

In Scotland Wales and Northern Ireland it’s a requirement to include Suds it won’t get through planning without out them. There’s a lot of additional Suds systems not just soakaway. The concept is very simple. Water is a resource keeping it where it lands is generally a good thing.

As for the plastic… Tricky.

Its about 98% void and the crates weigh around 400grams and will sit under a car park. That’s a very very efficient hole in the ground compared to a hole filled with gravel. Gravel which needs to be round (biggest void ratio) so… River gravel that’s got to be dug somewhere, not good for the environment. By machines, not good for the environment. And lugged around the country, not good for the environment. And placed by machine, again… Bad. And when it silts up which it will you have to dig it out.

Compared to a plastic crate which can be placed by hand very quickly. Is designed to be jetted to remove silt. Plastic in this regard is a good choice.

tthew
Full Member
Very interesting.

But why dig such a gert big hole and not fill it with the crates?

Posted 3 days ago

Depth will depend on the drainage invert levels and the area around it is for working space

Two types of these things – attenuation to store water and combined with a flow control device..limits / controls flow into the existing network / rivers (stpos flash flooding) – and soakaway style

Its rare for us to do a housing esate nowadays without these

That’s the remains of the most recent site party drinking fancy lager.

A large hole has appeared at a local building site. Police are looking into it.

Some impressive SUDS knowledge in here!!!

Especially when you consider half of them are skiving off work to post long messages clearly related to their work!

Don’t know what you mean…

@VanHalen Fair enough, I’ve personally never had to do a geotextile, membrane, geotextile sandwich but could easily be systems out there that require it. I’ve only ever had to do crate, membrane, geotextile, backfill. Though my experience is only with Polypipe, Wavin and SDS systems.

Especially when you consider half of them are skiving off work to post long messages clearly related to their work!

Noooo, we wouldn’t do something like that…

I didn’t realise that they were filled with large lumps of plastic. Not very eco is it !

If you think about it the reason people get upset about plastic in the environment is exactly the reason these are good materials for this sort of task. It will last a very long time and not breakdown. Whilst lots of plastic in the environment is a bad thing, it’s misleading to jump to the conclusion that all plastic is bad for all purposes.

You would say that poly…

You would say that poly…