Shallow trenching for fibre ducts

As part of discussion on fibre installation last year I posted that our crumbling footways were being cut up yet again by a ducting contractor, and expressed surprise that the ducts were only 300mm down.

Our roadway and footways are now being resurfaced for the first time in 26 years, and a digger is used to lift the old blacktop from the footways. You can guess the rest

300mm that is deep.

When one of the VM predecessors laid their fibre here it was literally 50mm (max) below the finish. And across the road, where fibre was laid for one particular customer, it is much teh same, so when anoth contractor arrived to dig a trench for 66kV they carfeull marked te locations in green, then took a 100mm deep scoop and yes, straight into the ducting.

I have been watching the contractors do the electrical work, and their work is extremely good - no corners cut, proberly down 800mm or more, protected, marked, covered, vibro-compacted, and then tarmac. Overall a very, very good job.

Virgin shallow trenching in my manor is shockingly bad.

I'm amazed that the OP's pavements are being dug out to about a foot depth!

Unless they are shrinking them to widen the road.

In reply to a post by partial:

Virgin shallow trenching in my manor is shockingly bad.

That 50mm above the 350mm Openreach depth must make all the difference.

300mm is how deep it's supposed to be. I have no idea why resurfacing, the clue is in the name, requires excavation that deep.

The correct depth for Telecoms duct is 350mm of cover in a carriageway, footpath or verge and 600mm for road crossings

Electric is 450mm (LV) to 1200mm (HV)

VM installation in my street today using microduct for FTTP.

https://imagizer.imageshack.com/img923/6936/xZcVjb.jpg

I wasn't at home when the trench was open but it looks more like 300mm deep, rather than 500mm.
When the cabinet plinths were installed, the elbows for the approx 76mm duct into the cabinet were set at around 300mm deep.

Unconnected work last year to repair the 3 phase power cable, exposed the 1970s unducted, wire armoured OR telephone cables - and they were only around 150mm deep, literally just beneath the sub-base of the pavement.

https://imagizer.imageshack.com/img923/7983/CyhL6z.jpg

If you look carefully at the left of the trench in the centre, there is a dark patch in the chalk, within that is the elbow from the stop tap of a blue polythene water pipe.

I think someone has posted on here before, the OR guide which shows utilities placement in pavements, both laterally from the kerb and depth. Telecoms are always near the top, gas, water and particularly HV electricity (> 450v ac) are much deeper.

Edited by sidef (Mon 20-May-19 18:49:22)

In reply to a post by TechServ:

The correct depth for Telecoms duct is 350mm of cover in a carriageway, footpath or verge and 600mm for road crossings

Electric is 450mm (LV) to 1200mm (HV)

No. Cable is permitted 250mm cover in footway, 450mm in carriageway. 350mm applies to Openreach.

If pavement resurfacing is cutting Virgin shallow trenched, unprotected, directly buried fibre tubes one of two things is happening.

Either Virgin shallow trenched, unprotected, directly buried fibre tubes are much more shallow than the armchair expert's book says.

Or the subby doing the resurfacing is digging down way. way deeper than they need to, maybe as a public spirited gesture to ensure that their resurfacing is much better than the council has specified.

My money is on the former.