Train hits masonry in Polhill Tunnel

[Antman]

The northbound line is closed between Sevenoaks and Orpington with trains presumably diverting via Swanley although the southbound line remains open

 

[contrex]

Polhill?

 

[ComUtoR]

Polhill?

Yep. It's got a garden centre and everything. (TN14 7AD)

 

[HarleyDavidson]

Wow a garden centre in a tunnel. Bet it does a roaring trade in mushrooms.

 

[theageofthetra]

Thats going to have hit at 75 or 80 are the crew ok?

 

[Antman]

Thats going to have hit at 75 or 80 are the crew ok?

Nobody injured as far as I'm aware

 

[BestWestern]

It is slightly concerning when chunks of tunnel just fall in, seemingly of their own accord (obviously with help from the rail traffic passing beneath them).

What does the structural maintenance/inspection regeime consist of?

 

[ian959]

Would this sort of thing start to become more regular across the network given the age of the tunnels? Polhill Tunnel is nearly 150 years old and according to Engineering Timelines is subject to water seepage.

In February and March 1948, tunnel maintenance work was carried out, including renewal of ballast and tracks as necessary.
Over the years, in various places water seepage has caused the tunnel’s chalk arch supports to disintegrate. The affected areas of chalk have been cut out and repaired with brickwork.

 

[yorksrob]

Would this sort of thing start to become more regular across the network given the age of the tunnels? Polhill Tunnel is nearly 150 years old and according to Engineering Timelines is subject to water seepage.

My sister commuted on that line regularly for some time and according to her, delays due to bricks falling off the roof of Sevenoaks tunnel were quite common. Always on the way home, rather than to work, much to her chagrin

 

[notadriver]

Thats going to have hit at 75 or 80 are the crew ok?

80 mph line speed attainable in both directions. Quite loud at the speed never mind hitting something.

 

[theageofthetra]

Lucky to get 70 on the up in a 465! Access to this tunnel on the London side is horible there is a deep and sheer cutting almost 2/3 of the way to Knockholt. Bit off topic but this tunnel was constructed by Welsh miners hence why in Dunton Green you have a Miners Arms pub & there are some Welsh street names e.g Glyn Davies Close.

 

[MotCO]

Another random useless fact is that there is another tunnel further up the line towards Chelsfield which was the inspiration behind E E Nesbit's Railway Children, where a runner entered a tunnel and lay injured.

 

[hulabaloo]

Lucky to get 70 on the up in a 465! Access to this tunnel on the London side is horible there is a deep and sheer cutting almost 2/3 of the way to Knockholt. Bit off topic but this tunnel was constructed by Welsh miners hence why in Dunton Green you have a Miners Arms pub & there are some Welsh street names e.g Glyn Davies Close.

Ha, I used to work in Dunton Green and never knew that - thanks!

 

[SemaphoreSam]

Is this potentially another Black Harry? Sam

 

[bramling]

Is this potentially another Black Harry? Sam

Unlikely. The collapse in that tunnel was a method of collapse which is nowadays well understood - namely a backfilled construction shaft where the backfill was supported by timber, which over time had rotted, placing the entire load of the backfill onto the brick linking beneath the timber, the brick lining not being sufficient to withstand the load. Since that incident, a lot of work took place identifying disused construction shafts and ensuring this risk is included in inspection regimes. (Never say never, though).

Localised brick falls are not uncommon in tunnels, or chalk/rock falls in unlined tunnels. The Higham-Strood tunnels used to be particularly known for this until a few years ago when they were lined. Underlying factors can include local ground conditions, bad quality of materials or workmanship during construction, or water ingress.