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.

In reply to a post by partial:

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.

?????? What the heck are you on about posting that in response to my post, which was entirely about the OP? You can't even claim the lame excuse of laziness and just replying to the latest post. It stinks of your persistent previous trolling of me on this site. Please stop it.

There is no mention of Virgin by the OP, so you either got confused by other posts in the thread or found it from his opening post in this thread, where the 300mm is also given. So it isn't a typo.

300mm = 30cm = 11.8 inches. In green tubing and with green warning tape above it. No protection against the digger one assumes, but the question is why it is digging that deep. Which is precisely what my post was about.

You were putting your money on a dead horse. Not a good idea.

Not just resurfacing, the road and footways are being re-kerbed as well. The dropped kerbs at each junction require at least 350mm for bedding. The contractor has uncovered bundles of 8mm ducts, one for each house I presume; they aren't even in tubing and the bundles have become filled with little stones between them. Glad I don't rely on this job.

Edited by Malwaremike (Tue 21-May-19 15:29:55)

Utilities, including VM, should have been given a heads up so that they could lower their plant. It's what happened here when works were done that would have impacted them.

The microducts are okay on their own. They are not held by larger ducts and are supposed to be okay to bury. It's not direct burying they are ducts and that's how they are intended to be used.

Contrary to what some may say it's not the same as directly burying cables. A directly buried cable breaks it has to be replaced in full, fibre can be reblown down the microduct if need be.

Oh well.

So VM can expect to redig all their trenches after less than two years? Two ducts across our driveway have been severed at a point only 200mm below the blacktop surface. Contractor tells me on his last job the ducting contractor had made two cuts in the blacktop, scraped a groove with a shovel, then asphalted directly onto the ducts. The resurfacing contractor found the hot asphalt had fused the plastic ducts into a solid sheet which came up on the first bucketful. Our job is now in limbo while they work out a repair scheme, but better now than having to carve up our nice new entrance.

In reply to a post by Malwaremike:

So VM can expect to redig all their trenches after less than two years?

Yep.

Exactly - they should have been laid correctly at day one.

Virgin's shoddy build of shallow trenched, unprotected, directly buried fibre tubes has an immediate impact when they are cut by unsuspecting streetworks contractors.

But perhaps in the longer term minor, unreported damage by contractors to the shallow unprotected tubes will hit as the tubes become water filled.

In reply to a post by MHC:

Exactly - they should have been laid correctly at day one.

Sometimes operators have to move or lower ducting. That's life. If they had the 250mm of cover, which OP informed they did, they were installed correctly.

VM had to lower ducts near here to accommodate others' works. They were installed correctly.

Backing up what Ignition has advised here is a diagram straight from the horses mouth (Virgin Media) on their new build requirements. 250mm min.

VM New Build Ducting

Gary's diagram specs a 96mm duct with 250mm cover on top. Installation around here is 8mm microducts laid in a 300mm deep trench cut along the footways and crucially under my driveway and that of my neighbour. The ducts were severed when the resurfacing contractor was excavating for a dropped kerb at the edge of my driveway. Virgin worked until 2145 that night to restore service.

One of the breaks may have been caused by a sharp stone, forced through the bedding by the increasing number of LGVs which use the footway as a convenient loading bay or to take phone calls etc. As Partial says, further damage to the network is to be expected ...

The diagram I placed is for full HFC rather than fibre.

On a FTTH (as Virgin Media call it) to HFC the 96mm pipe could be substitated for multi-duct or micro-duct bundles, however this would still need to be at a minimum of 250mm (260mm Scotland).

Edited by gary333 (Fri 24-May-19 16:37:12)

In reply to a post by partial:

Virgin's shoddy build of shallow trenched, unprotected, directly buried fibre tubes has an immediate impact when they are cut by unsuspecting streetworks contractors.

But perhaps in the longer term minor, unreported damage by contractors to the shallow unprotected tubes will hit as the tubes become water filled.

Water wouldn�t cause a problem if it�s FTTP though.

I�m not sure I see the problem anyway really. If the ducts are damaged, causing s blockage when Virgin try and push something through it then they�d just do a dog to locate the blockage. Or am I missing something?

I suppose they must do a downward dog.

In reply to a post by Icaras:

Water wouldn�t cause a problem if it�s FTTP though.

I�m not sure I see the problem anyway really. If the ducts are damaged, causing s blockage when Virgin try and push something through it then they�d just do a dog to locate the blockage. Or am I missing something?

Nah. The error was by the contractor who hit VM's plant. Had they done their job properly they'd have had the VM plant marked up and, if hitting it unavoidable, have informed VM and paid for VM to lower the plant to ensure safety and compliance.

There's nothing wrong with use of microduct - VM didn't randomly decide this was how they were going to deploy, the process was recommended and implemented with the assistance of Huawei and indeed is how networks are built now.

Water isn't a problem. The plant isn't copper and doesn't need pressurising to prevent water ingress. Things move on from the requirements BT set and had. BT themselves are playing with bundles of microducts.

BT only pressurised the E-side network anyway. But yes Openreach use micro ducts for FTTP. Along with a tonne of overhead when they could get away with it.

The Wallasey FTTP build in Wirral is very heavy on overhead, going forward though micro ducts will be more common as more overhead has proved controversial for Openreach. Remember when they had to rip all those new poles out of the road when they�d just gone in? That�s been replaced by micro ducts.

In reply to a post by Icaras:

BT only pressurised the E-side network anyway. But yes Openreach use micro ducts for FTTP. Along with a tonne of overhead when they could get away with it.

The Wallasey FTTP build in Wirral is very heavy on overhead, going forward though micro ducts will be more common as more overhead has proved controversial for Openreach. Remember when they had to rip all those new poles out of the road when they�d just gone in? That�s been replaced by micro ducts.

Curious: are BT using them in a similar manner to others so, in their case, connectorised fibre block then a microduct from block to each property with lateral cuts from a spine cut?

I'm wondering as the alternative suppliers are using cabinets where a bunch of subscribers terminate and a dedicated microduct from there to each property. Openreach are obviously using all underground so would have fewer subscribers to reach per block unless they build new chambers and use those in lieu of aggregation cabinets.

At some point I must have a look at one of the hybrid builds around here. There are a few areas where Openreach haven't been able to use new overhead plant so have instead build some underground.

Are they perhaps just using microduct to take fibre to poles for distribution or are they doing small access network overbuilds of microduct in lieu of overground plant entirely? How's that working if that is what they are doing as they'll have to stop at property boundaries and install a TOBY or obtain wayleave from everyone in the street to install the new plant.

Sorry for the mass of questions.

In reply to a post by gary333:

The diagram I placed is for full HFC rather than fibre.

On a FTTH (as Virgin Media call it) to HFC the 96mm pipe could be substitated for multi-duct or micro-duct bundles, however this would still need to be at a minimum of 250mm (260mm Scotland).

Yeah that document is usually found at this webpage: https://www.virginmedia.com/lightning/network-expans...

Current version as of 2019/5/25 is https://keepup.virginmedia.com/content/networkExpans...

Not sure. I only saw it in the internal magazine and it didn�t go into great detail.

It�s something for the future anyway. Most of the existing FTTP rollouts will be very heavy on the overhead as they are already planned and going ahead (even though a lot of the public are furious at the new overhead line plant), it�ll be future Fibre First builds where you start to see microducts. Especially in areas where armoured cables were used, or where the ducts were too small/old to take any more cabling. They are essentially building a new network there, on a local level anyway.

In reply to a post by Icaras:

They are essentially building a new network there, on a local level anyway.

New network = microducts - whomever is building them. Good to know, thanks.

I had problems with the internet due to these repairs.

Nah. The error was by the contractor who hit VM's plant. Had they done their job properly they'd have had the VM plant marked up and, if hitting it unavoidable, have informed VM and paid for VM to lower the plant to ensure safety and compliance.

Nah. You miss the point of my OP -- the microduct was well above the specified depth of 300mm which in my view is insufficient anyway. I predict lots of fun in the future ... but I hope our driveway does not have to be cut up yet again.

But? You said in three places that they were 300mm deep. The first two below are in this thread, and the third is the earlier post you refer to in the first.

In reply to a post by Malwaremike:

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.

In reply to a post by Malwaremike:

Installation around here is 8mm microducts laid in a 300mm deep trench cut along the footways and crucially under my driveway and that of my neighbour.

In reply to a post by Malwaremike:

The trenching is only 300mm deep.

Please view my post of May 23:

Two ducts across our driveway have been severed at a point only 200mm below the blacktop surface.

That did confuse me when I first read it. For me to work out which of your posts is incorrect is difficult, but a 3-1 ratio suggests 300mm.

In reply to a post by CarlTSpeak:

In reply to a post by Icaras:

They are essentially building a new network there, on a local level anyway.

New network = microducts - whomever is building them. Good to know, thanks.

I know. That�s what I�ve put.