Foundation Shuttering for Drainage

[RobboBCFC]

Hi guys hoping if someone can shed some light on a problem I have.

Currently have an extension being built.
The foundations have been poured but I'm getting paranoid about how the concrete was shuttered off to solve the problem of drainage running through foundations. The plan is shuttering the concrete and using 2 concrete lintels on top to bridge over.

The drainage is currently at a depth 900mm from ground level. Foundations have been dug to below invert level of said pipe. With a gap of 150MM+ either side of the 110mm drainage.

Whats worrying me is how it's been done means theres two seperate sections of foundation (see picture attached - sorry those are my best paint skills).

1. Would this method cause differential movement between the two sections?

and/or

2. Is how its been done an accepted and valid method?

Thanks for any advice guys, been getting worried about this!

Rob.

 

[^woody^]

It's not right. The pipe should have been bridged as close to the pipe as possible , allowing a gap for settlement , so about 50-100mm above the pipe.

It will likely pass building control inspection, but what you have now is increased risk of differential initial settlement, and differential movement longer term.

Surely that is not how it was detailed on the approved drawings?

 

[RobboBCFC]

Thanks for the quick reply.

Is there anything at this point that can be done to remedy this problem?

 

[frutbunn]

It's not right. The pipe should have been bridged as close to the pipe as possible , allowing a gap for settlement , so about 50-100mm above the pipe.

It will likely pass building control inspection, but what you have now is increased risk of differential initial settlement, and differential movement longer term.

Surely that is not how it was detailed on the approved drawings?

Not sure how it would have passed B Regs, I certainly wouldn't of. The foundation should have been stepped under the pipe.
As for being detailed on the plan, more often than not the majority of plan drawers don't even lift IC covers, some even show the IC in different positions to reality to get the plans approved. Quite a few plan drawers these days don't even do B Reg drawings in any case.
Have you submitted B Regs and were the excavations inspected?

 

[Alastairreid]

My Bco wont sign off unless the foundation runs under the pipe is built up to and linteled over.

 

[RobboBCFC]

They were submitted and passed off.
However cant find on the drawings this method that has been done.

At this point, is there anything I can do to fix this problem?

Can rebar be drilled into either side of foundation fixed chemically and a new pour of concrete to join them together?

 

[frutbunn]

They were submitted and passed off.
However cant find on the drawings this method that has been done.

At this point, is there anything I can do to fix this problem?

Can rebar be drilled into either side of foundation fixed chemically and a new pour of concrete to join them together?

As you have some deep foundations then I would probably accept that as long as the rebar is continuous over the opening so either overlap the bars from either face to be drilled or wire another bar to the ends fixed into the founds.

 

[RobboBCFC]

Thanks for the reply!

What size rebar and how many would you use if Im going to drill either side and have them overlapped and tied together?

I'd talk this over with builder but looks like Im getting rid.

Thanks for the help

 

[frutbunn]

Thanks for the reply!

What size rebar and how many would you use if Im going to drill either side and have them overlapped and tied together?

I'd talk this over with builder but looks like Im getting rid.

Thanks for the help

I'd probably go for 4no 12mm+ bars.

 

[Notch7]

Whats worrying me is how it's been done means theres two seperate sections of foundation

what sort of muppet does that?

Id be seriously worried about allowing the builders to continue TBH.

 

[RobboBCFC]

So to clarify is this how you would go about it now?

doesn't there need to be a bridge of concrete underneath the pipe to?

Excuse the paint drawings:

 

[frutbunn]

So to clarify is this how you would go about it now?

doesn't there need to be a bridge of concrete underneath the pipe to?

Excuse the paint drawings:
View attachment 197496

That looks OK.

 

[RobboBCFC]

Thanks for the reply. There isn't a requirement for concrete to run underneath? and it's fine for the hole to be square around drain?