Bridging utility cable laying foundations

[walkern]

He'll,
Need a bit of advice. I'm building a porch (well doing some of the donkey work to save money). I've gone down 900mm, but about 20cm from the bottom the electric cable runs thought it perpendicular at the front of what will be the porch.

My builder friend says dig a few extra inches down, about a foot wide, around the cable, get the concrete people to fill the whole trench to just below the pipe, then shutter an inch to each side and continue filling. Then fill the gap with sand and the bricks will bridge over the top.

This means my foundations are in two pieces essentially. Would it not be better to somehow cover the top of the pipe and then fill it all? Or am I over thinking this as a problem...

Thanks.

 

[garyo]

I agree - do it in one pour.

I'd shutter it off with some osb/ply boxing, embedded in the sides of the trench a bit so that it won't go anywhere, filled with pea shingle so it won't try to float away in the concrete, and then wrap some dpm/gaffer around to stop concrete ingress.

You could use an offcut of soil pipe too if you think you can make it work.

 

[oldbutnotdead]

Not sure exactly what building regs has to say on the subject- me I'd be getting a bit of 50mm ducting or 70mm gutter pipe, slitting it, putting it over the cable, pack gap between cable and inside of duct with expanding foam (try and keep cable in the centre of the duct) then pour the concrete over the whole lot (make your bit of duct long enough that the trench sides shutter it).

Or if you go for your solution, if you've got 200mm below the cable then that's plenty- you could be putting blocks on top of that 200mm so shuttering round the cable would work fine. But you won't get a huge amount of time to muck about if you're getting Readymix or whatever in

 

[walkern]

So, this is what he's proposing I think

 

[bernardgreen]

Assuming this is the cable that serves only your house and not the cable along the street. If it serves other houses then the District Network Operator ( DNO )has to be involved.

Assuming it is naked cable and not cable already is a duct. What diameter is the cable ?

If it is naked cable then as mentioned

Use duct split to fit on the cable and bound in place with tape.

Allow the cable to be a loose fit in the duct in case you ever have to have it replaced.

Take care not to damage the cable,

If it is plastic cable then reasonable care should be OK. if it not plastic then it might be brittle and easily damaged, in which case get advice from your DNO who may decide to replace it if it is very old cable.

 

[walkern]

Hello,
Thanks. It's just my house. It's bare cable, probably from the late 50s. It's about just under two inches bendy with a slight braid on it.

Do you mean put some drain pipe around it, tape it up then just let the concrete flood the whole area? Should i support the duct underneath before filling? That's better than my original shuttering solution?

 

[Ian H]

I'd get a piece of 4" pipe and cut it a bit wider than your trench, slit it so you can pop it over the pipe. Make sure the concrete can't get inside it then pour.

 

[walkern]

That's what I've done, thanks. Took some doing opening the pipe wide enough

But I spoke to my builder friend a bit ago and he said no matter what I still need to shutter around the pipe as concrete cannot lie on top because if there's any movement in the foundations or ground it'll take the pipe with it...

 

[Ian H]

But you would have 50mm space for any up/down movement.

 

[noseall]

Burying it under the concrete wouldn't make a jot of difference.
However, just sleeve it with some slit gutter down pipe. Plug the ends with insulation then tape the DP with some duct tape.

 

[walkern]

I made a nice loose box to go round the duct.

 

[walkern]

I also made some shuttering just in case