GWSR General Discussion and Operations

The line is contemporary with the Bicester cut off (the Chiltern line). The latter has suffered with embankment issues. This hasn't been helped by soil moisture deficits over dry summers with bands of clay being most susceptible. There is a band which runs across the Chilterns from east to west and I wouldn't be surprised if it reaches to the Gloucestershire and Warwickshire line. When a railway is renewed it is unusual to replace the earthworks, (rails, ballast, signalling systems, bridges are normally what is replaced). Also the knowledge of what makes up an earthwork is not well known surveys can be taken but I am aware of instances where the material suddenly changes.

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The question that has been in my mind since Chicken Curve has been why this line has been so prone to problems

 

Hey, that's our railway you're talking about there!

I think it's accepted wisdom that the line was built quickly, and on the cheap. Combined with the particular local geology and geography, and lack of understanding at the time of construction, we are where we are. The good news is the impact is much less severe than in the past, in part I think we can put that down to the heroic efforts of our drainage team over the last decade or so.

 

Prompted by this thread, I spent some time trying to find out some details of the local geology. For anyone who has a little knowledge of soil mechanics or geology, these links might be of some interest.

https://www.researchgate.net/public...and_outcrop_patterns_from_temporary_exposures

https://webapps.bgs.ac.uk/Memoirs/docs/B01641.html Ch.2 in particular.

http://www.glosgeotrust.org.uk/downloads/Cotswolds LGAP.pdf

 

As Alex said, it's a combination of factors: local geology and geography, and lack of geotechnical engineering knowledge (i.e. the behavior of structures constructed of piles of earth) at the time of construction. Of these, I would rate the last as the most significant - although the geography, which required lots of embankments, played a significant role. Not so much the geology; there have been a few minor issues with the sides of cuttings, but nowhere near as bad as the embankment issues.

I've been thinking about the geotechnical engineering issues, wondering if I could have done a better job, with the knowledge available at the time; I'm not sure I could/would have. Take the example I gave, where, when they dug down in a slumped embankment, they found a buried grass layer, where the earth of the original embankment had just been dumped straight onto the pre-existing turf (thereby providing a shear plane for the embankment to slide on). If I were given the job of building an embankment today, even without studying geotechnical engineering, I'd cut a trench in the turf, to tie the embankment in - because I now know of that failure mode. But in 1904? There's a good chance I wouldn't have.

Several other lines have also had geotechnical engineering issues on embankments: e.g. the Bluebell (section of embankment South of Kingscote station); the NR N-S line at the Robertsbridge end of the RVR (of which they said "As part of the process of stabilising the bank [the contractor], dug out much of (what they call) peat packing material, being that used in the original construction back in the late 1800's, before replacing this with a more proven rock based packing/fill. Such were the construction methods of the age"). I vaguely recall some others, but can't be bothered to look for them.

I think the GWSR has seen worse than these others only because it has a lot of high embankments.

Noel

 

The GWSR Honeybourne line was a late build, one of the last in the country. It is pretty straight and level, meaning long cuttings and long embankments.
It wasn't built by men with wheelbarrows ( eg Tring cutting) but by mechanical steam excavators and a temporary railway line with tippler wagons. So, lots of soil was moved around.
Slipping soil has been an issue for a long time. There is both anecdotal and physical evidence of previous slip repairs, certainly during BR times, and probably earlier.

 

All fair, yet these embankments are 50-60 years younger than many on the national network seeing much greater use (I’m listening to them go by from my desk!). If what you write is correct (and I’ve no reason to doubt it), the question then is what the earlier builders got right and later builders didn’t.

 

I wonder what the contractual defects liability period was? Is any warranty remaining?

 

Maybe those heavily-used lines on the national network got better maintenance; maybe they had improvements during those long lives. You'd need to study the detailed records for each.

Noel

 

Many mainline embankments have had significant works done over the years to be fair, much larger scale than we can contemplate affording proactively.

 

Interesting is that the section north of Broadway to Honeybourne West Loop (say 4 miles) is perfectly flat, with no cuttings or embankments.