Landslips on SWR network

[akm]

I know it's been raining a lot but there do seem to be an unusual number of landslips on the SWR network recently:

- Between Ewell West and Epsom (a week ago)
- Near Liss (last night)
- Between Godalming and Guildford (just now)

Also at Hook not much more than a month ago. Is it just the rain, or is there a deeper issue? The twitter peanut gallery is blaming Network Rail tree clearance.

 

[RichT54]

I know it's been raining a lot but there do seem to be an unusual number of landslips on the SWR network recently:

- Between Ewell West and Epsom (a week ago)
- Near Liss (last night)
- Between Godalming and Guildford (just now)

Also at Hook not much more than a month ago. Is it just the rain, or is there a deeper issue? The twitter peanut gallery is blaming Network Rail tree clearance.

The landslip affecting SWR between Godalming and Guildford is apparently near Guildford and is also impacting GWR services between Guildford and Redhill.

https://www.getsurrey.co.uk/news/surrey-news/live-guildford-swr-delays-cancellations-17451036

 

[hwl]

The original construction quality (wrong material choices) and design often was great on LSWR.
Trees also make the situation worse and the damage they do often long outlives their removal.

 

[Bald Rick]

It’s the rain.

When the soil in an earthwork is saturated, and cannot absorb any more water, any local rainfall starts to run off. This significantly increases the risk of landslips at periods of heavy rain. NR has records of all of its earthworks, and risk assesses each of them for the likelihood of failure- a combination of geotechnical composition (what soil, how dense, etc), method of construction, slope angle, failure history, drainage, vegetation, etc.

NR also monitors the saturation of soil nationwide by a measure known as Soil Moisture Deficit, SMD. This is expressed in millimetres of rain required to get the soil fully saturated. An SMD of 0 means it “cannae take anymore” to quote Scotty. If you have an SMD of 0, or close to it, and more than around 20mm of rain in 24 hours, the chances of a failure at an ‘at risk’ earthwork increase considerably for the following 24-48 hours. It is sometimes necessary to impose precautionary speed restrictions in such conditions - I have done this myself.

Given the amount of rain we have had in the last couple of months, and in the south of England in the last 24 hours, this is not at all surprising and more can be expected.

As an side, conversely an SMD of, say, 300 is very dry, and can lead to shrinkage of clay embankments which causes its own problems.

 

[hwl]

It’s the rain.

When the soil in an earthwork is saturated, and cannot absorb any more water, the water starts to run off. This significantly increases the risk of landslips at periods of heavy rain. NR has records of all of its earthworks, and risk assesses each of them for the likelihood of failure- a combination of geotechnical composition (what soil, how dense, etc), method of construction, slope angle, failure history, drainage, vegetation, etc.

NR also monitors the saturation of soil nationwide by a measure known as Soil Moisture Deficit, SMD. This is expressed in millimetres of rain required to get the soil fully saturated. An SMD of 0 means it “cannae take anymore” to quote Scotty. If you have an SMD of 0, or close to it, and more than around 20mm of rain in 24 hours, the chances of a failure at an ‘at risk’ earthwork increase considerably for the following 24-48 hours. It is sometimes necessary to impose precautionary speed restrictions in such conditions - I have done this myself.

Given the amount of rain we have had in the last couple of months, and in the south of England in the last 24 hours, this is not at all surprising and more can be expected.

As an side, conversely an SMD of, say, 300 is very dry, and can lead to shrinkage of clay embankments which causes its own problems.

Anything built pre Karl Terzaghi* is potential much more likely to be problematic has he laid out the maths of how to calculate stability in the 1920s including how clays behave, effects of drainage (or rather lack of!) and slope angles.
He came up with some simple rules for low intervention man made railway type embankments - well drained, no clay, no vegetation

*Military civil engineer for the Austro-Hungarian Army who started his book writing career by developing the dummies guide to stable trench digging in 1913.

 

[brad465]

It’s the rain.

NR also monitors the saturation of soil nationwide by a measure known as Soil Moisture Deficit, SMD. This is expressed in millimetres of rain required to get the soil fully saturated. An SMD of 0 means it “cannae take anymore” to quote Scotty. If you have an SMD of 0, or close to it, and more than around 20mm of rain in 24 hours, the chances of a failure at an ‘at risk’ earthwork increase considerably for the following 24-48 hours. It is sometimes necessary to impose precautionary speed restrictions in such conditions - I have done this myself.

Given the amount of rain we have had in the last couple of months, and in the south of England in the last 24 hours, this is not at all surprising and more can be expected.

As an side, conversely an SMD of, say, 300 is very dry, and can lead to shrinkage of clay embankments which causes its own problems.

According to the Environment Agency's South-East Water situation report, SMDs are 0 everywhere, so yes the South East is completely saturated.

Also while it's not SWR network, the Medway valley has a tree blocking the line and accompaning landslip at Halling currently causing disruption.

 

[theironroad]

It’s the rain.

When the soil in an earthwork is saturated, and cannot absorb any more water, any local rainfall starts to run off. This significantly increases the risk of landslips at periods of heavy rain. NR has records of all of its earthworks, and risk assesses each of them for the likelihood of failure- a combination of geotechnical composition (what soil, how dense, etc), method of construction, slope angle, failure history, drainage, vegetation, etc.

NR also monitors the saturation of soil nationwide by a measure known as Soil Moisture Deficit, SMD. This is expressed in millimetres of rain required to get the soil fully saturated. An SMD of 0 means it “cannae take anymore” to quote Scotty. If you have an SMD of 0, or close to it, and more than around 20mm of rain in 24 hours, the chances of a failure at an ‘at risk’ earthwork increase considerably for the following 24-48 hours. It is sometimes necessary to impose precautionary speed restrictions in such conditions - I have done this myself.

Given the amount of rain we have had in the last couple of months, and in the south of England in the last 24 hours, this is not at all surprising and more can be expected.

As an side, conversely an SMD of, say, 300 is very dry, and can lead to shrinkage of clay embankments which causes its own problems.

Very informative. Thanks.

 

[Bald Rick]

According to the Environment Agency's South-East Water situation report, SMDs are 0 everywhere, so yes the South East is completely saturated.

Also while it's not SWR network, the Medway valley has a tree blocking the line and accompaning landslip at Halling currently causing disruption.

That’s a fascinating report, thanks for posting it. Given the last three weeks, the December report will make interesting reading.

 

[kristiang85]

The original construction quality (wrong material choices) and design often was great on LSWR.
Trees also make the situation worse and the damage they do often long outlives their removal.

But generally tree roots hold together soil and helps alleviate landslips and runoff - so once the trees are removed the risk of erosion goes up. I think this is the law of unintended consequences at work with the vegetation removal.

 

[Edders23]

water is probably civil engineerings' worst enemy no matter how good the quality of the work rain can undo it

I suspect we will be reading of multiple landslip problems up and down the uk over the next month or two not just SWR

 

[Bald Rick]

But generally tree roots hold together soil and helps alleviate landslips and runoff - so once the trees are removed the risk of erosion goes up. I think this is the law of unintended consequences at work with the vegetation removal.

A common misconception. Tree roots weaken the earthwork structure, and cause uneven absorption of water. This causes variances in stress levels within the geotechnical make up of the earthwork, and leads to a higher likelihood of failure.

 

[Edders23]

A common misconception. Tree roots weaken the earthwork structure, and cause uneven absorption of water. This causes variances in stress levels within the geotechnical make up of the earthwork, and leads to a higher likelihood of failure.

Does grass stabilise as that's something I was always told

 

[B&W]

A common misconception. Tree roots weaken the earthwork structure, and cause uneven absorption of water. This causes variances in stress levels within the geotechnical make up of the earthwork, and leads to a higher likelihood of failure.

Another problem I understand is that is after tree removal roots die and leave cavities in the structure. ( Ironically very similar to what Fracking tries to do!) This leads to uneven flows of liquids through a structure etc. Fascinating subject, the name of the guy whose lengthy formula we used to use in Fluid Mechanics for flows of liquid through soils escapes me this morning.
The EA reports are very good, I see the groundwater recharges across the South East have started up to a month earlier than in average years and the Bournes are expected to flow widely this winter.

 

[Taunton]

A common misconception. Tree roots weaken the earthwork structure, and cause uneven absorption of water. This causes variances in stress levels within the geotechnical make up of the earthwork, and leads to a higher likelihood of failure.

As we all knew from childhood :

 

[hwl]

Does grass stabilise as that's something I was always told

Yes - shallow roots, stops surface erosion of material and discourage other bigger stuff from growing.

 

[hwl]

But generally tree roots hold together soil and helps alleviate landslips and runoff - so once the trees are removed the risk of erosion goes up. I think this is the law of unintended consequences at work with the vegetation removal.

Completely and utterly wrong as regards man-made earth works such as cutting and embankments.
Removing vegetation bigger than a bush is beneficial to stability.

 

[Bald Rick]

Does grass stabilise as that's something I was always told

Yes it does. Anything with shortish narrowish roots, and lots of them.

 

[Bald Rick]

The EA reports are very good, I see the groundwater recharges across the South East have started up to a month earlier than in average years and the Bournes are expected to flow widely this winter.

The recharges needed to. We had a letter through the door a couple of months ago warning that without prolonged rain we would be having water restrictions next spring summer. It’s barely stopped raining since! Having said that, we are not far from the ‘Lilley Bottom’ site which is still showing below normal ground water levels. Although that was at the end of last month, since when plenty of water has fallen out of the sky.

 

[brad465]

That’s a fascinating report, thanks for posting it. Given the last three weeks, the December report will make interesting reading.

The EA reports are very good, I see the groundwater recharges across the South East have started up to a month earlier than in average years and the Bournes are expected to flow widely this winter.

I happen to work for the EA in Water Resources, and while I wasn't involved in the writing of that report, I know the people who do well. Reports are usually released between the 10-15th of a given month outlining the Water situation of the previous month, so January 10th will be when to start looking for this month's report.

 

[Taunton]

The recharges needed to. We had a letter through the door a couple of months ago warning that without prolonged rain we would be having water restrictions next spring summer. It’s barely stopped raining since.

Actually, I don't think it has stopped raining! The UK rainfall this century (since 2000) has been nearly twice the historic average, at close to 1500mm where the accepted average has been 900mm. 2019 is going to be a wet year as well.

https://www.statista.com/statistics/322810/average-rainfall-in-the-united-kingdom-uk/

The water authorities need to do significantly more about managing their supply arrangements. They are very happy to increase charges, install meters, etc, without commensurately spending the increased revenue on the supply. Not for nothing has Thames Water fallen into the hands of overseas high-return investors.

 

[GarethW]

May I just add my thanks too for posting that report - fascinating.

 

[randyrippley]

Actually, I don't think it has stopped raining! The UK rainfall this century (since 2000) has been nearly twice the historic average, at close to 1500mm where the accepted average has been 900mm. 2019 is going to be a wet year as well.

All that melting ice has to go somewhere

 

[Matt Taylor]

The landslip is outside St Catherines Tunnel which is the southern tunnel outside Guildford.

In other news a 458 hit a car on a level crossing at Wokingham last night, car driver arrested on suspicion of drink driving.

 

[Bessie]

But generally tree roots hold together soil and helps alleviate landslips and runoff - so once the trees are removed the risk of erosion goes up. I think this is the law of unintended consequences at work with the vegetation removal.

100% agree. I do think vegetation removal has gone too far in some places.

 

[kristiang85]

Completely and utterly wrong as regards man-made earth works such as cutting and embankments.
Removing vegetation bigger than a bush is beneficial to stability.

There's been studies on this: https://researchportal.bath.ac.uk/e...nce-of-tree-removal-on-embankment-slope-hydro

 

[nw1]

Actually, I don't think it has stopped raining! The UK rainfall this century (since 2000) has been nearly twice the historic average, at close to 1500mm where the accepted average has been 900mm. 2019 is going to be a wet year as well.

https://www.statista.com/statistics/322810/average-rainfall-in-the-united-kingdom-uk/

The water authorities need to do significantly more about managing their supply arrangements. They are very happy to increase charges, install meters, etc, without commensurately spending the increased revenue on the supply. Not for nothing has Thames Water fallen into the hands of overseas high-return investors.

It does seem like it has been very wet in the past 20 years or so - main root cause seems to be high pressure over the Greenland area forcing the low track much further south than its historical mean. Seems to be common for the southern UK to bear the brunt of the rain nowadays. I do recall the 80s and 90s having perhaps as frequent rain, but much lighter, particularly in the winter months - the Azores high seemed to have more impact in those decades.

I'm not sure how accurate those statistics are though, I don't recall 2011 being an especially wet year, the summer was wet here (Hampshire), February also fairly wet but the spring and autumn pretty dry. Further north ISTR the summer also being dry and talk of drought. On the other hand 2012, which was very wet here from April onwards, doesn't come out especially so. The horrendous flooding of early 2014, in a year which had further wet episodes later on, also doesn't seem to make much impact on these stats. I'm fairly sure the wet weather in 2012 and 2014 was pretty general south of Scotland.

 

[fgwrich]

The landslip is outside St Catherines Tunnel which is the southern tunnel outside Guildford.

In other news a 458 hit a car on a level crossing at Wokingham last night, car driver arrested on suspicion of drink driving.

Indeed, nice job by some of our colleagues over at BTP Reading.

https://www.bbc.co.uk/news/uk-engla...9L0b88ZmpnyeZrXyY80lOPgthvNJxg4tZQiXQs6Zi7v6E

Wokingham train crash: Car driver arrested

Image copyrightDANNY COOKE VIDS
Image captionAll trains from London to Reading are currently terminating at Ascot
A driver has been arrested on suspicion of drinking and driving after a crash with a train at a level crossing.

Video footage shows the South Western Railway train on top of the car at the Waterloo level crossing in Wokingham, Berkshire, at 23:30 GMT on Thursday.

There were no injuries but passengers had to continue their journey by coach.

Train services between Wokingham and Ascot are currently suspended and trains from London to Reading will now terminate at Ascot.

British Transport Police said the driver was also being questioned over endangering safety on the railway.

A South Western Railway (SWR) spokesman said: "We are doing everything we can to keep customers moving and are arranging alternative transport."

Replacement buses are in place between Wokingham and Ascot, serving stations in between, and train tickets are being accepted on alternative rail and bus routes.

Travellers are advised to check the SWR website for more information.

 

[fgwrich]

I note Hook as being mentioned above - Is that another Landslip on the Down Slow again in a similar area to before?

 

[Llanigraham]

100% agree. I do think vegetation removal has gone too far in some places.

But as has been shown by several posters since, the posting by kristiangl85 was incorrect.

 

[Deepgreen]

I think there are a few weather/climate factors at work here:
1. A succession of hot, dry summers which have caused clay and other soils' contraction, which loosens earthworks and increases erosion during storms,
2. Some quite long wet spells in autumn and winter with more intense bursts of rain than had been the case for a long time, also causing greater erosion,
3. Some quite intense windy spells in summer/autumn which have swayed large trees around before they have lost their leaves, causing more root and soil movement/cracking.

There is also the continuing background ageing of the infrastructure, which will tend to lead to an increased rate of failure. On top of this, the increasing complication and delicacy of line-side control systems means that they are more easily damaged and less quickly repaired than older, mechanical systems.