3rd rail for some electrification projects

[Taunton]

The Severn Tunnel water penetration is something which, in the old story, was long addressed by the old GWR but later allowed to let go, as described above "allowed to degrade over decades". The GWR actually installed IBS in the tunnel (known as "the traffic lights"), two of them each way, in WW2, which with track circuits and electric controls would never have worked if it was, as envisaged above, endemically wet. They needed to be notably reliable on the steep gradients with unfitted freight trains and pilot locos on the front, not back, to allow multiple trains in the tunnel at IBS spacing. They were taken out by BR, and then in the 1990s replaced by axle counters. Which latter led directly to the Severn Tunnel collision.

In addition to pumping the Big Spring, the Sudbrook pumping station also pumps from the sump at the bottom of the tunnel and from various intermediate points. It's the collection arrangements for the pipe inlets that are an issue. yes water streams down the sidewalls but it is the collection arrangements that have needed attention. One hopes the OHLE job has addressed this back to the old standard as well as the wiring installation.

If I'm not mistaken Balcombe Tunnel on the Brighton line is another "very wet" one. 3rd rail electrified for the last 90 years of course.

 

[MarkyT]

The Severn Tunnel water penetration is something which, in the old story, was long addressed by the old GWR but later allowed to let go, as described above "allowed to degrade over decades". The GWR actually installed IBS in the tunnel (known as "the traffic lights"), two of them each way, in WW2, which with track circuits and electric controls would never have worked if it was, as envisaged above, endemically wet. They needed to be notably reliable on the steep gradients with unfitted freight trains and pilot locos on the front, not back, to allow multiple trains in the tunnel at IBS spacing. They were taken out by BR, and then in the 1990s replaced by axle counters. Which latter led directly to the Severn Tunnel collision.

In addition to pumping the Big Spring, the Sudbrook pumping station also pumps from the sump at the bottom of the tunnel and from various intermediate points. It's the collection arrangements for the pipe inlets that are an issue. yes water streams down the sidewalls but it is the collection arrangements that have needed attention. One hopes the OHLE job has addressed this back to the old standard as well as the wiring installation.

If I'm not mistaken Balcombe Tunnel on the Brighton line is another "very wet" one. 3rd rail electrified for the last 90 years of course.

There were still track circuits right through the tunnel until they were replaced by some of BRs earliest axle counters, even though the intermediate signals were discontinued when Newport panel took over signalling of the tunnel. They may have been decommissioned before that of course after wartime traffic peaks had subsided. There remained some tunnel emergency signals however, presumably in the same locations as the IBS homes, and possibly even using the same heads initially. These were normally extinguished and were lit red by a special switch on the panel. They were unusual in having their lamps continuously 'cold proved' by a small current passing through their filaments, insufficient to produce a visible illumination. When intact, the current would hold up a series relay that would activate a signal box alarm if de-energised. There were also approach lights for trackworker safety partway through the tunnel and various emergency wires and button systems installed or proposed over the years as well as telephone circuits and patrolman's lockouts etc. Axle counters, with their sensors outside the portals, removed the most troublesome track circuit equipment from the tunnel but could not eliminate everything electrical.

 

[Taunton]

Interesting, thank you. I believe the tunnel emergency signals were also operated by the emergency wire, long installed along the tunnel walls (Tuplin writes about the wire being used in GWR days for a runaway, it put the IBS to red then and presumably the tunnel entrance signal as well). Did it put the signals to red in both directions?

Don't believe the track circuit equipment was troublesome in earlier times, but progressively became so.

 

[S&CLER]

Just as a matter of interest, how does the water ingress in the Severn Tunnel compare in terms of volume with its near-contemporary the Mersey rail tunnel? Rising water table problems on Merseyrail were much in the news a few years ago but they don't seem to have been lately. The Wirral Line seems to operate pretty reliably, which suggests that the problem has been brought under control.

 

[MarkyT]

Interesting, thank you. I believe the tunnel emergency signals were also operated by the emergency wire, long installed along the tunnel walls (Tuplin writes about the wire being used in GWR days for a runaway, it put the IBS to red then and presumably the tunnel entrance signal as well). Did it put the signals to red in both directions?

Don't believe the track circuit equipment was troublesome in earlier times, but progressively became so.

I'm sure the emergency wire replaced all signals protecting the tunnel on both lines as well as illuminating the midway emergency signals and activating a signal box alarm. When I was in the drawing office, there was a project to replace the continuous wire with emergency stop plungers and telephones located in each of the refuges along the tunnel length. It wasn't my design job, but I volunteered to help out on a (lucrative) weekend night site visit with a colleague to do a walk through survey with a measuring wheel of precise distances between the refuges, so cable lengths could be pre-cut accurately for quick installation. We had to use the local PW ganger and his specialist lookouts for protection. Those guys were amazing, capable of detecting approaching trains long before they arrived by subtle changes in sound and air pressure, their extra-sensory perception no doubt assisted by the pre-shift Brains consumed in the Staff Association (this was the 1980s!). I don't think the plungers were ever installed, with other events overtaking it. It seemed there was always some minor or sometimes major S&T design job going on for the tunnel to address some issue. I've read that BR tried to reintroduce intermediate block signals in 1969 but these were very short lived due to reliability issues. I expect the emergency signal heads I saw were these ones repurposed. For completeness, in the Newport panel days there were also some active distant signals inside the tunnel at either end reading out and applying to stop signals situated beyond the portals. These were cabled direct from equipment cabinets outside the tunnel though, so there was no other associated signalling equipment within it.

 

[Gloster]

Just as a matter of interest, how does the water ingress in the Severn Tunnel compare in terms of volume with its near-contemporary the Mersey rail tunnel? Rising water table problems on Merseyrail were much in the news a few years ago but they don't seem to have been lately. The Wirral Line seems to operate pretty reliably, which suggests that the problem has been brought under control.

I read somewhere that changing land use, presumably less heavy industry, in Liverpool had lowered the level of the water table in the city itself. It is not my area of competence, but could this have had a knock-on effect on ingress in the tunnels?

 

[Bald Rick]

Just as a matter of interest, how does the water ingress in the Severn Tunnel compare in terms of volume with its near-contemporary the Mersey rail tunnel? Rising water table problems on Merseyrail were much in the news a few years ago but they don't seem to have been lately. The Wirral Line seems to operate pretty reliably, which suggests that the problem has been brought under control.

Sudbrook pumping station pumps out about 65 million litres of water from the Severn Tunnel every day.

As we know, the SI unit for relatively large liquid volume is an Olympic swimming pool - it’s 26 of those.

We also know that the SI unit for large areas is Wales. In this case, if my arithmetic is right, Sudbrook pumps out enough each year to cover Wales in just over 1.1mm of water. That’s about 0.1% of Wales annual rainfall, just in the Severn Tunnel.

 

[Elecman]

I read somewhere that changing land use, presumably less heavy industry, in Liverpool had lowered the level of the water table in the city itself. It is not my area of competence, but could this have had a knock-on effect on ingress in the tunnels?

Actually the opposite less heavy industry using pumped groundwater has caused th3 water table to rise considerably

 

[Gloster]

Actually the opposite less heavy industry using pumped groundwater has caused th3 water table to rise considerably

That was probably it. Just a case of me getting things ark about face due to technical incompetence.

 

[Elecman]

The Mersey tunnels and Loop line have major pumping facilities at Shore Road and St Georges Dock as well as not insignificant pumping facilities at Liverpool Central and elsewhere