Posted By Drew Shaw
Hi. First time post and hoping for some guidance.

Basically, we are about to repair a high voltage cable and whilst we've taken all necessary electrical precautions, we're a bit unsure as to when we need to look at shoring up a trench.

I've looked at HSE's guidance and it seems they (on purpose ?) don't mention a depth at which a trench should be shored up, which tends to lead you along the path of having to risk assess each individual instance on it's own merits.

I'm just wondering, is there a rule of thumb for trench depth ? Our trench (we think) will be around 1000mm - 1200mm deep and, maybe significantly, the guys who will be in the trench working, will be kneeling to make the new joints.

Cheers in advance.

Drew

Posted By Jerry Lucey
Goodmorning Drew,

If your trench is between 1m and 1.2m you will need to take precautions. Excavations in excess of 1.2m require the appropriate inspection regime and sign offs. Fatalities can occur in excavation collapses in excavations of less than 1.2m and precautions should be taken with all excavations.

Even where ground looks sound this may not be the case and other factors such as weather conditions can play a part.

The precautions would consist of;

(1) implementing trench control, if this option is taken please ensure that trench control is adequate.

(2) the second option would be to have the excavation battered at 45degress which will eliminate the risk.

(3) all excavations should be protected to safeguard third parties e.g. members of the public.

I would tend to go for option 2 if you are unsure as you can easily inspect if the measures taken are adequate. The key however is to appoint a competent contractor to carry out the work.

Hope this helps.

Posted By Frank Hallett
Hi Drew

I must agree with the first 2 respondants.

There are a range of training schemes out there that will provide various degrees of competence on many different types of trench shoring methods and one or more of those may be what you need.

If you cannot find anything directly suited to your type of trenching needs please feel able to contact me direct as I have recently been involved in putting a comprehensive trench shoring course together.

Frank Hallett

Posted By Drew Shaw
Thanks to everyone for your views.

Since I posted this morning, we've been on site with our contractor and we're pretty comfortable about way forward. Got to say, it was good that the guy who'll be in charge of the dig brought up info that concurred with what you guys raised.

Turns out that he's going to grade the trench at 45 degress where the cable jointers will be working and cordon off either end to stop the jointers walking into the part of the trench which hasn't been graded. It's an MOD site within a secure fenceline so we dont need to worry about the public falling in but we're going to barrier tape along the full length on either side anyway as MOD police sometimes patrol nearby.

Cheers again.

Drew

Posted By Drew Shaw
Salus,

First time doing this job so don't worry, we've not been doing repairs of this nature without giving due consideration for potential for collapse.

Yes we've a safety officer but whilst she's a safety professional, she (like most if not all safety officers) isn't a specialist in every single field and she'd have to go looking for the info. That's the reason I thought I'd get a jump and put up a post to get a few quick opinions. As it happens, it worked a treat ... within an hour or two I had a few sound bits of info, which when you consider we're hardly talking rocket science here, were more than sufficient for this particular task.

Cheers for your post.

Drew