Digging foundations and raising ground level

[Neo Cortex]

Dear forum,

I am about to start digging the foundations for a building (7m x 9m) and could do with some advice on what to do with the soil that is dug out.

The location makes it very difficult to get rid of the soil.

We had to raise the height of the garden by about 8 inches in order to keep the soil pipe underground in order to accommodate the drop. So the area that the building will go onto is actually 8 inches lower than the rest of the garden.

Seems like the obvious thing to do is to spread out the soil evenly across the area to level the ground and also raise it by the 8 inches.

I have zero experience with this sort of thing so interested to hear if this is a normal thing to do or what, if any problems it may cause?

Appreciate your assistance

 

[oldbutnotdead]

Depends on your ground. Up here there's usually a foot or so of earth, then you hit clay. Spreading the earth around the garden is fine (up to you whether you riddle it to get stones and pebbles out), if you are building up ground level next to other buildings make sure you aren't compromising dpc, air bricks etc. The clay - don't try spreading that around, you'll end up with a claggy undrainable mess of a garden.
Also don't try and cheat pd requirements by lifting ground level so your building can be higher.

 

[noseall]

Dear forum,

I am about to start digging the foundations for a building (7m x 9m) and could do with some advice on what to do with the soil that is dug out.

The location makes it very difficult to get rid of the soil.

We had to raise the height of the garden by about 8 inches in order to keep the soil pipe underground in order to accommodate the drop. So the area that the building will go onto is actually 8 inches lower than the rest of the garden.

Seems like the obvious thing to do is to spread out the soil evenly across the area to level the ground and also raise it by the 8 inches.

I have zero experience with this sort of thing so interested to hear if this is a normal thing to do or what, if any problems it may cause?

Appreciate your assistance

We just completed a dig for a small extension (5.5m wide x 2.8m out). The spoil covered 10 no, 1200 x 2400mm ply sheets with two foot of earth.
You deffo don't want clay.

 

[oldbutnotdead]

Yerse, as above digging 700mm footings trench and scraping topsoil for my garage (10m x 7m) took 3 8 cube skips. Mostly clay with easy access.
You're going to have a significant volume to deal with, if you can't shift it immediately it'll cost you time and money working round it. Time to explore options- it could become a significant budget element in your plan if (for instance) you need to crane skips over your house!

 

[Neo Cortex]

I haven't decided if I want the surrounding ground to be turfed or paved yet. Most likely will do a small area as turf and rest paved.

Yep. Once you get a about a foot down it becomes clay.

Surely the clay is OK to go in the middle of the foundation rectangle?

There will be a pathway going around two of the perimiter edges so any rock or stone that comes out will get put onto the path as a foundation for the MOT to go on top of.

 

[oldbutnotdead]

Why are you digging the clay out of the middle? Usually stripping the topsoil give you enough depth for your floor.

 

[Neo Cortex]

No, I am saying the clay that will come out of the foundations will be safe to put into the center section of the foundations. The bit that will be under the floor. The inspector hasn't been round to look yet but the pilot hole will be 1m deep so I am assuming thats how deep the rest will be. Thats deep enough to hit the clay level.

 

[oldbutnotdead]

Depth depends on local conditions - up here its typically 700mm (into the firm clay and below the frost line).

If you're having a suspended floor and you have the space to build up ground level under what will be the floor then yes if you must. If you're doing a slab then beware- backfilling under it would be made ground and unwise. Either way it would be unwise to pile the clay up round open trenches- you'd really want your founds to be out of the ground before piling a load of clay on.
If you are doing strip founds and blocks you can use the clay as backfill round the blocks as well.

 

[noseall]

No, I am saying the clay that will come out of the foundations will be safe to put into the center section of the foundations. The bit that will be under the floor.

Noooooooooooooooooooo......!

 

[noseall]

Once you get a about a foot down it becomes clay.

Are there any trees or shrubs nearby?