Raft foundation or potentially something else?

[asnoop20]

I couldn't really get a definitive answer on Google.

Does the picture confirm it's a raft foundation or is there any other foundation that uses a poured concrete outer?

All my ground floors are concrete. One I drilled got soft at roughly 20cm.

 

[stevie888]

It could be a raft. It could be a ground beam sitting on piles it could even be a conventional trench fill where shuttering has been used.

You need to dig down and find the bottom.

 

[asnoop20]

If it were a trench fill that wouldn't fill the inner though right?, or might you pour concrete in later on, in which case it almost becomes a raft foundation?

Edit - raft has a steel mesh in the middle (so reenforced concrete)? Metal detector over a wide area of the floor?

 

[noseall]

If it were a trench fill that wouldn't fill the inner though right?, or might you pour concrete in later on, in which case it almost becomes a raft foundation?

You need to dig a bigger, deeper hole and expose more of the concrete, as said above.

A 'raft' foundation is a steel reinforced engineered structure with a distinct design, often with a 'toe' (but not always) protruding beyond the masonry.
You may just have a concrete slab.

 

[asnoop20]

I'll be digging in a bit, how deep is enough, until I strike oil?

 

[noseall]

I'll be digging in a bit, how deep is enough, until I strike oil?

Find the conc' bottom and scratch a bit of earth from beneath to confirm.

 

[^woody^]

Is it a council estate, with system built houses?

The probability of a raft is often tied to the ground geology and type of house.

 

[asnoop20]

What's the difference though between it being a raft and trench fill, both are going to look the same at the bottom? I read a raft will go to the frost line, usually 900mm, and a trench might go further, but it also might not?

It's not a council estate, year is 1984 but close to a river where the ground might be unstable. The builders (or rather the desperate miners that Thatcher made redundant) will have used the cheapest method they could get away with. Trust me on this it's a shocking build.

However I must 100% confirm it, no guessing, because weight will be placed on the 'raft' if it is one. If it's not a raft probably the house will collapse on one side. I can't take any chances.

 

[martygturner]

Seeing as you live close to a river its more than likely a trench fill to get over the water table. The bit of the river you see is not the extent of the river underground, the river channel is the lowest point. Basically its really the only option to build cost effectively in a river.... which is what the flood plain is, its part of the river.

 

[asnoop20]

Back of house is probably 50-70m from edge of river, and perhaps 10m up, roughly.

If it is a raft it probably doesn't go down that far, so someone else said? I'm continuing to dig...

 

[asnoop20]

Let's see if I've done enough...

There's 7 layer of standard concrete brick and then I hit concrete (doesn't seem that even). There's a black thing to the side which chips away easily (the wood shutter turned to charcoal?).

So it's not a raft, right?

 

[martygturner]

correct

 

[asnoop20]

It is enough to know that. Thanks all.

 

[stevie888]

Let's see if I've done enough...

There's 7 layer of standard concrete brick and then I hit concrete (doesn't seem that even). There's a black thing to the side which chips away easily (the wood shutter turned to charcoal?).

So it's not a raft, right?

It's looking like a traditional strip foundation, typically 200 or so thick.

If it is vital to know what you have then you need to find the bottom of the concrete. If you're talking about adding substantial loads then you need an SE's input anyway.

 

[^woody^]

Seeing as you live close to a river its more than likely a trench fill to get over the water table.

If that was the case, more likely a raft to deal with any poor load bearing, or piles.