Excavating Basement

[Pappa]

Hi guys

 

My structural engineer has given me his blessing to excavate a basement under my house (clay and silt).

I'm thinking of sending rain water down there, in to a controlled hole, to suspend the clay. A dirty pump would then send the slurry up in to settling tanks.

I want to do it in the most eco friendly and passive way, not necessarily the fastest.

My idea is to filter the clay and pass it on to local schools etc if it saves it going to landfill.

 

Could this work?

 

Thanks

 

P

[MikeSharp01]

Sounds like fun and a recipe for disaster unless you can seriously control that hole - pile round the internal perimeter, and so stop the  scheme undermining your foundations. Still what do I know, a soil mechanic / ground works expert will be along shortly and will hopefully tell me I am talking tosh! 

[SteamyTea]

7 hours ago, Pappa said:

My idea is to filter the clay and pass it on to local schools

Do they want it, or you going to fly tip it.

(We are constantly fighting a battle with fly tipping, disadvantage of a free carpark and a tennent that never locks the gate when they leave)

[saveasteading]

9 hours ago, Pappa said:

thinking of sending rain water down there, 

Sounds awful. The last thing I'd want in a basement excavation is water.*

Can you explain more? What does suspending clay mean?

How do you intend to excavate?

How are you stopping the building collapsing?

 

*second last thing, after rubble from above.

 

 

[Nickfromwales]

9 hours ago, Pappa said:

Hi guys

 

My structural engineer has given me his blessing to excavate a basement under my house (clay and silt).

I'm thinking of sending rain water down there, in to a controlled hole, to suspend the clay. A dirty pump would then send the slurry up in to settling tanks.

I want to do it in the most eco friendly and passive way, not necessarily the fastest.

My idea is to filter the clay and pass it on to local schools etc if it saves it going to landfill.

 

Could this work?

 

Thanks

 

P

Please set up a Timelapse camera so we can sit with your SE, popcorn in hand, and watch your house slowly disappear.

 

I very much doubt you’ll be in any kind of ‘control’ here, and this method sounds crazily indiscriminate to me, but I’m no basement expert.

 

I hope your pockets are as deep as your basement, and also that you have certification for this methodology and that your SE’s PI insurance allows them to advise you to do this; also that it would pay out if it ‘accidentally’ undermines your current homes foundations / underlaying ground.

 

Sounds to me like a slow, risky, impractical and non passive way to do this as it’ll need huge amounts of electricity, a recirculating filtration system (which will need near constant caretaking), and your time to monitor and control.

 

I do love a basement, but this sounds like a ‘less than good’ idea to me, sorry.

 

16 minutes ago, saveasteading said:

What does suspending clay mean?

Suspending it in the water so it can be exported through the pump as a slurry. 

[saveasteading]

39 minutes ago, Nickfromwales said:

Timelapse camera 

To watch the faces of contractors and insurers as you explain this proposal to them.

 

A retrofit basement is surely only justifiable in a very expensive city centre where land and m2 is worth a fortune.

 

Unless it is a relatively small hole in the middle of a big space. Basically a service pit, or a wine cellar.

[Pappa]

Thanks for the comments guys.

I might just take a wide berth around this one then.

 

I got the idea from excavation companies who offer this as a service. They basically come in with a jet wash and a powerful pump. They claim the holes are dug cheaper, and more neatly. Granted, their main clientelle are those who don't want to accidently damage underground services with sharp spades.

 

I'm wondering if my basement could be dug out without breaking my back and easier and cheaper and with a nice purified byproduct too that doesn't go in the skip/landfill. This could be done in a completely passive way as I'm not pressed for time. The system would only be switched on when I'm close enough to keep an eye on it.

 

Thanks again

P

[Nickfromwales]

1 minute ago, Pappa said:

They basically come in with a jet wash and a powerful pump. They claim the holes are dug cheaper, and more neatly.

Yes, and there’s your problem….. “they” not “me”   

 

“They” will be certified and insured, “me”, not so.

 

So can’t be DIY’d afaic.

 

38 minutes ago, saveasteading said:

To watch the faces of contractors and insurers as you explain this proposal to them.

And your mortgage supplier. 

[ProDave]

As above, a basement under an existing building is NOT in any way a DIY job.

[Pappa]

Thanks guys.

I'll keep water out of my basement.

 

Excavating foundations for a new outhouse away from the existing house and other foundations...

Could this work here?

Thanks again

P

[SteamyTea]

37 minutes ago, Pappa said:

I'll keep water out of my basement.

I worked on a basement swimming pool in a hotel once, as the pool was being enlarged, an underground stream was breached.

I have never seen a project go so seriously over budget.

Edited Thursday at 10:40 by SteamyTea

[saveasteading]

I suspect thd jetting process needs an enormous stillage pond.

Then the clay and silt will sink slowly and form new strata. 

 

Are you willing to tell us why the basement is appealing and if the existing walls are adjacent?  OK to say no.

[Pappa]

5 minutes ago, saveasteading said:

I suspect thd jetting process needs an enormous stillage pond.

Then the clay and silt will sink slowly and form new strata. 

 

Are you willing to tell us why the basement is appealing and if the existing walls are adjacent?  OK to say no.

 

The key when settling small particles is to have multiple stratifying tanks, smaller containers but many of them is more efficient. I've got a near unlimited supply of these.

 

My brother dug out his basement about 20 years ago and he swears by it. Its been a play room for his kids, then they grew up and it became a study, then a warehouse for when he ran an ebay shop, then an office when he was WFH +- a place to dump extra storage and bulky appliances - washer/dryer/chest freezer/boiler etc.
My neighbour did the same thing. He doesn't need the space but he's making £800 pcm in rental income.
 

There is already a basement underneath half of the house, but I need to excavate down by 500mm to give me a comfortable 2.4m head height + tanking/insulating the floor.

I'm thinking if I'm excavating that, I might as well excavate the other half of the house and underpin it as per SE spec.

 

In terms of the economics, houses sell for 2.5k per sq m at the moment where I live. The quotes given by builders/architect/SE makes me think I will recoup the cost of the basement dig out and make a profit when I sell +- appreciation.

 

The basement is 50 sq m and almost a perfect square. Until you guys advised me against the idea, I was going to make the controlled hole for my water pit slap bang in the middle so its away from the foundations. I'll stick to spade and wheelbarrow for now though.

This project will be a slow burner - a weekend project for me and my son.

 

Thanks again

 

P

 

 

[Big Jimbo]

I know that there are companies out there who use some sort of water jet machine, to cut a slot alongside a tree line. i think they go 2.4 m deep. They then put ridgid plastic in the seam to stop the encroachment of roots. It must be some serious pressure they use, as it cuts through tree roots etc. There was also a granite company i used to use, that cut granite using a water jet.

I very much doubt you could do something similar on a DIY basis.

I used to know the owner of the Biggest basement company in London. `They used to dig a meter wide hole in the front garden. Take out a portion of the footing. send in a micro digger, and would underpin in 1 meter sections as they excavated. Always had a conveyor, and a couple of guys with picks and shovels for the bits that the digger could not reach.

It was mind blowing expensive, but all around Kensington and Chelsea and the square m price around there was £20k at the time.