Is it not perhaps worth questioning whether the wet bed issue is maybe more a question of geography, rather than lacking maintenance (Although I'm sure this contributes). The GWML is one of a few rail lines in the country which follows a river valley for a long time period, and the valley of a large river at that. It's also a line which has seen relatively little alteration in alignment since opening, which was chosen far before drainage was understood. This Autumn is rivalling the wettest on record, but unusually the rain has been very spread out, and rather than short term flooding we've seen a very high water table for the entire period, which won't have helped the drainage from the ballast, on a route which in some places is very, very renowned for its terrible drainage, and is currently seeing more traffic in many places than it has at any other point. Combined with a warmer period turning into a very sudden freeze overnight, which will have worsened the state of the rails and ground in terms of harness and brittleness. I wouldn't say it is hugely surprising that we're seeing such a huge amount of wet beds, and would say that it is something which will be rather hard to fix if we continue to see rapidly changing, wet conditions in future.
A permanent way person can explain it better than me. But I will have a go. The whole track formation is designed to put less pressure on the natural ground surface than the equivalent of the heel of a shoe of a person wearing high heels.
Under the ballast, there is supposed to be a membrane to prevent the surface soils from getting into the ballast. The ballast (if in good condition and with the required depth) is designed to spread the weight of the load from each sleeper. The sleepers in turn support the rails and even out the weight across the ballast. The rails also help to partially distribute the weight of each wheel between the sleepers.
The size of the ballast means if it’s in good condition, it’s self draining. But of course, this relies on the lineside drains being in good condition.
If the ballast is not kept compacted under each and every sleeper, the passage of trains will result in some sleepers rising and then slamming into the ballast as each wheel moves along the rails. It’s the passage of trains that causes this effect. Hence the importance of either machine tampering or manual packing (preferably with portable tools similar to kango hammers rather than just shovels and jacks).
If this is not sorted out relatively quickly on busy high speed, mixed traffic or heavy freight lines, the situation can escalate rather quickly.
As the ballast gets hammered, it breaks up. If the weather is dry, you get dust and gravel. But if it rains, you get mud. It’s the mud that results in the ballast retaining water, as it clogs up both the ballast and the lineside drains.
Once you have mud, the ballast is no longer able to properly support the weight and is no longer as effective in distributing the weight. Plus, with the passage of trains, some of the mud ends up on the top of the sleepers where it just makes a mess.
The type of stone that was used for the ballast also makes a difference, as some stone is more hardwearing than other types.
As more of the ballast is damaged, the track will visibly start to dip. The vertical distance that the rail and the sleeper can move (as a train passes over) can quickly get to between 3 to 5cm.
Eventually the forces experienced by the sleeper may result in rail fasteners working loose. Bolts/nuts/screws working loose. Concrete sleepers may crack or break. And the increased stress on the rail may result in defects in the steel. Or the rail may crack or break.
Since a reorganisation in 2011, the function that looks after the lineside infrastructure including, drainage (track and lineside), fencing and ventilation has been under pressure. The reduction in staff back then has only been partially addressed since then by limited increases to staff levels.
Would the sleeper have failed some time before the rail in this case?
Looking at the photo, yes, it’s likely the sleeper failed before the rail.
How many trains per hour compared to now? how much work done whilst trains were running?
You also have to take account of the type of trains. HST (class 43) power cars hammered the track more than EMUs or DMUs do. But I don’t know how 80X compare.
Forgive my ignorance - but should there be separate rails with a fishplate to join them that's failed? Or is it a fracture? From the rounding of the end of the left hand running rail it looks like it's been springing up and being hammered by wheels hitting it - was that at line speed?
That photo is part of the rail near point work. Modern high speed point work rails are welded. So no fishplates. If you mean temporary clamping, that looks a bit beyond that. Especially with the damage to the sleeper and the poor condition of the ballast.
The current groundwater conditions are not ‘normal’ for this time of year. I’m quoting an environment agency report here for a similar area of London which is public, but I’m not sure where as I’m accessing from a closed system. The levels of rainfall this autumn have not been normal. In November the rainfall was 138% of the long term average, and 343% of the long term effective rainfall average. The groundwater in the area has been assessed as ‘exceptionally high’ by the environment agency.
As I mention it’s also not all about groundwater, the ground under the railway is in effect a foundation. Far more trains passing over it than the period you mention, which are a different weight. Added to increased weight of equipment like the OHLE etc will have have an impact. Previous winters have been cold, but the sudden change was unusual, normally it gets colder over a period of weeks, and this will have meant the ground conditions were significantly different between the last and fairly trains of the days passing over, meaning the track may not have settled with the changing conditions.
See my comments above. Unless you can see lots of water, such as the track being flooded or the cess being flooded, as long as the ground under the formation cannot flow, it’s not generally a problem. Problem areas will be near rivers.
There are areas elsewhere where the water table is not very far below ‘natural’ ground level and this normally does not cause problems.
The modern railway operates in a very different environment than the Victorian one, or even the 1960s one. Train weights, speeds and frequencies are higher, other equipment adds weight and the basic infrastructure is just plain older. Maintenance of gulleys, drains, etc., may (only may) have fallen, leading to less ability to deal with extremes of weather. Last year the intense dry heat of the summer will have caused the ground to dry out abnormally, while this year it has been the opposite - a cool, wetter summer followed by a very wet autumn. Ground stability problems could only increase. Then there is the railway operating system - it is massively more complex now and, and a result, much more delicate and subject to failures. This includes signalling, power supplies and rolling stock. In summary, the railway today is a hugely more fragile beast than in times past. It will therefore fall over much more often (and can be brought back to life much less easily in many cases owing to changes in working regimes).
For main lines, the rails, sleepers, ballast, membrane, signalling system, OLE etc. are all younger than the Victorian era. Indeed, for main lines, the rails and sleepers and al least the top layer of ballast will be more recent than the 1960s. The signalling on the area under discussion is far more recent. As is the OLE.
Yes, the line of route is the same. Most of the cuttings, embankments, tunnels, stone and brick bridges and other structures may be original Victorian in age. But over the years, the railway would have maintained these. BR for example spent a lot of money on improving Box Tunnel.
80X I would think are lighter than steam locomotives, and don’t hammer the track like steam locomotives. Heavy freight trains can and do affect the track more than normal passenger trains.
The biggest issues are:
- Modern computer based signalling and axle counter systems tend to fail in a different manner, hence typically causing bigger problems when it does fail. Conventional relay based interlocking was very reliable, the big failures were normally only caused if a lineside cable was damaged or degraded.
- Less resources are being put into routine maintenance and renewal, this will eventually cause problems. This will have more of an impact on busy high speed lines.
- The change from working with lookout warning to having to have the line blocked means it’s significantly harder to try to fix problems during the day.
- And yes, vegetation and drainage work being under resourced is causing problems, Network Rail know this.
