Today we have dug out new trenches ready for redirected a 11KV cable. We are only rerouting half of the cable, so we started at one end and made our way to where the joint was going to made off.
When we were digging out the existing cable we hit a concrete bed. This concrete bed was covering the existing cable, with a width of about 1 Metre.
Out of curiosity and confusion, we unearthed the cable at several locations and found that cable was covered with concrete there too.
Has anybody else experienced this kind of protection over a buried cable?

Note: - the cable is at least 30 years old, maybe 40

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Fail to prepare...Prepare to fail!

Adam

Not uncommon - a lean mix dropped into the trench after stonedust or sand partial backfill was a quick and cheap method of providing what in this case is a continuous cable "tile".

concrete was a specification requirement in some arenas for protection against digging, sometimes as a protection against terrorism and sometimes just becasue that's what the electrical engineer always did

regards

OMS

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Failure is always an option

So from your experience,

What would you estimate the depth of this concreate?

Or is this a stupid question???

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Fail to prepare...Prepare to fail!

Adam

Normally 4" of 1:3:9 of OPC, sand and aggregate (ie a lean mix) - but it could be anything at that age - I've seen it with 200mm+ of gen 2 mix and reinforcing mesh in before - just because they had some "spare"

Good luck - breaking out concrete around cables if it isn't on proper bedding is a right bitch

regards

OMS

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Failure is always an option

It would be interesting to read your risk assessment. Assuming that the cable is still live, digging through concrete towards a known 11kV cable is a high risk scenario if you don't know the depth of the concrete or the depth of the cable! The safest option is to isolate it while the cable depth / concrete depth is determined. The safe option is to leave the cable off until the concrete has been removed.

Regards,

Alan.

Alan,

The other option could be to get someone to hit it with a digger and the resulting blast may clear the concrete if the protection doesn't operate fast enough.

Can't see the RAMS beginning signed off for it though


Stu

The cable can be made dead to remove the concrete, or dig down away from the cable, then undermine the concrete (assuming the cable is not encased all the way around).

Simon

I'm sure there are plenty of digger drivers that will give it a go if there's an offer of free fish and chips or if you just tell him you have to find the cable asap and its "job and knock"

Just make sure the RAMS mention wearing ear muffs

Hi Alan,

I wouldn't even entertain the idea of keeping the cable live, whilst trying to uncover the the concrete pad.

This job will now be done in the next shut down and removed once all power is off.

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Fail to prepare...Prepare to fail!

Adam

Sounds like we have an intresting task infront of us then,

I will let you know the results of the depth, once discovered

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Fail to prepare...Prepare to fail!

Adam