Burying gas and electric services in concrete.

[David W.E. Roberts]

Hi,

Having just passed the BCO inspection for my new drains I am about to fill up the trench in my drive with concrete.

When digging it out I unearthed (unconcreted) the gas and electricity supplies.

Quite fun really, seeing the gas main appear about 5mm from the tip of the concrete breaker.......

I am now going to re-bury them and wondered if there was anything special I should do when encasing them in concrete.

For instance I could put some plastic pipe around them so the next poor sucker has a bit more warning.

I could wrap them in plastic to keep the new raw concrete away from them.

I intend to write in the new concrete warning where the mains are.

The gas pipe especially has a bitumen-ish covering over metal, and some of this has come away with the removal of the old concrete.

Should I paint the pipe with a bitumen sealant to protect the metal, or should it be O.K.?

Looked in my DIY manual but the chapter on digging up and reburying gas mains seems to have been missed out :-)

TIA Dave R

[wanderer]

I'd try 'phoning your gas and leccy companies first, tell them you've found their services in the trench you've excavated and ask if they can supply some split ducts to put around the services before you re-concrete. In my day (leccy) we'd supply some ducts FOC for you to put around the service.

If they don't want to play ball, or want lots of money, try your local Builder's Merchant for some 100mm/4" split ducts.

You'll need to hand dig on the services to undercut the sides of the trench by just a few inches, then sort of work the ducts into the soil each side of the trench, so the concrete won't run into the ends of the ducts.

Not quite sure how the ducts come these days, you may actually have a solid duct with a line down each side. Rest them on a bed of sand and gently *tap* down the line with a brick, hammer, whatever. Do one side then the other, you should suddenly hear the note change as the duct starts to split lengthways down the line. Refit the ducts around the services, wrapping the two halves together with some wire or similar. You might find it easier to part fill the trench almost upto the services then fit the ducts so the bottom piece is supported by the concrete.

Could be a bit dodgy, if someone digs down on a plastic pipe in several years time and thinks it's a piece of soil pipe, hacksaws into it, and...... .

Nah, get some denso tape or similar from the Builder's Merchant. This is a fabric tape that's *very* heavily impregnated with a greenish waxy paste. It's a lovely mucky job wrapping it on, really squishes between the fingers. :))

[David W.E. Roberts]

Thanks for that - some things I didn't make clear:

(1) The services run lengthways along the drive from road to garage and are embedded in concrete all the way from the road to the point where they enter the garage, where my trench also meets the right angle join between house and garage and exposes the last bit of the pipe run. So hand digging at either end of the exposed pipe is not an option because one end disappears into the garage wall and the other disappears into concrete. I am also not too worried about the concrete getting to the pipes - the rest is already buried - more concerned about someone digging up the drains and blowing themselves up with a gas/electric double whammy.

(2) I will try to find split pipe but 100mm/4" (roughly the same as soil pipe) does not seem to be an option because (a) there is less than 4" between the two services at some points (b) there is less than 2" between the services and the top of the drive at some points. I am trying to visualise putting two lengths of soil pipe across the line of the trench and I think that this would leave all pipe and no concrete. [The shallow run is what gave me the scary moment; I knew there were services under there but had no idea they were so near the surface.]

The compromise I am considering it to put the services in split white plastic waste pipe and put a warning in the concrete. This is not ideal, but in future someone would hit the white plastic and hopefully pause for thought, instead of blasting straight into the gas or electric supply. I read elsewhere about hazard warning tape being buried in shingle above a run of oil pipe - presumably so that anyone digging would realise there was a hazard below. Is there not hazard warning pipe or similar that can be buried in concrete to warn that you are approaching dangerous services? Even a flat sheet of plastic or similar would do - this would appear as you broke your way through the concrete and warn you to go carefully.

Thanks for the tip about the 'denso' tape - will talk to my B&PM.

Cheers Dave R

[wanderer]

Given what you've clarified, I think I'd not bother at all. I was thinking about how the services could be replaced in the event of a fault, but from what you're saying, it rather seems as though the utilities would need to go for a different route altogether. It might be prudent if there's enough space to lay concrete, then just a little soft sand around the services then concrete up to the top. What you need to try and prevent is a sharp edge from one of the bits of the ballast coming into permanent contact with either of the services.

You can get gas and electric warning tape, try the electrical wholesalers or BM's.