How to fill a ditch to build on.

[FingersAndThumbs]

Hi,

 

I have an area of garden that for historic reasons is about a metre below the level of the rest of the garden and of course, this is where I'd like to build a garage.

 

What steps would I have to take to bring that part of the garden up to the same level? I'm guessing that if I just fill it with earth then it will need time to settle? Could I fill with rubble first and then a layer of top soil?

 

The size of garage I have in mind is something in the region of 10m x 6m.

 

The ditch/channel is around 20m long, 6 to 8m wide and 1 to 1.5m deep.

 

All advice greatly appreciated.

 

Thanks.

 

[Temp]

 

11 minutes ago, FingersAndThumbs said:

The ditch/channel is around 20m long, 6 to 8m wide and 1 to 1.5m deep.

 

That's quite a lot of hardcore infill. I make it over 100 cubic meters, possibly as much as 140/50.  Does it ever get water in it?

 

Once its filled I think there are two methods for the foundations...

 

* A reinforced raft (So if anything moves it all moves together).

* A piled foundation (Extends foundation down to solid ground).

 

Our site was flat but there was evidence of a pond years ago where we wanted our garage. Builder opted for piled foundations. Sorry not sure about the cost as some years ago now..

 

 

[FingersAndThumbs]

Thanks Temp,

 

It doesn't get water in it, just a nuisance that it's at a different height.

 

Agree it's sizable amount of infill. Would another approach be to put the foundations at the lower height and then build up, do you think?

[markc]

1 minute ago, FingersAndThumbs said:

Thanks Temp,

 

It doesn't get water in it, just a nuisance that it's at a different height.

 

Agree it's sizable amount of infill. Would another approach be to put the foundations at the lower height and then build up, do you think?

This would probably work out cheaper unless you are looking at very heavy vehicles or point loads in the garage. Plus you could end up with useful storage underneath

[ProDave]

You are looking at this the wrong way.  You don' fill in the ditch and build on it.  You dig the foundations, e.g. strip foundations into the present ground at it's present height.  You then build up the walls from that.  The foundations will be deep with respect to finished raised ground level, but probably not especially deep with respect to existing ground level.  Then you infill the area inside the garage with hard inert infill compacted in layers and pour the concrete slab on that.  the ground outside the garage area if you want to raise that as well can be infilled with anything, e.g all the soil you stripped off the build area and what you dug out for the foundation trenches.

[Iceverge]

+1 to @ProDaves suggestion. 

 

it might be worth tieing the garage floor into the rising walls with some poured concrete and rebar. 

 

Alternatively forget about filling and just do a concrete suspended floor with precast planks. £2k ish should see you most of the way there

[FingersAndThumbs]

Thanks all. Building up is the way to go!

 

Precast planks sound interesting and £2k seems reasonable. At that kind of cost, would it support the weight of car?

 

Doing that would mean there'd be space underneath for storage, as markc suggests.

[Iceverge]

Yup if you get it specced properly. You might need a structural screed. 

 

Storage underneath might be damp and difficult to access .