Landslips on SWR network

[YorkshireBear]

As we all knew from childhood :

The irony of this video of course is that there is an actual active landslip on the opposite side of the line there at the KWVR.

 

[kristiang85]

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

Well, the paper I posted above argues to the contrary. Sorry, I should have pasted the abstract:

Trees cover the slopes of many railway earthworks supporting the United Kingdom’s transport network. Root water uptake by trees can cause seasonal shrinkage and swelling of the embankment soil, affecting the line and level of the railway track. This requires continual maintenance to maintain the serviceability of the track and reduce train speed restrictions. However, the removal of trees from railway embankment slopes and the loss of soil suctions generated by root water uptake may negatively impact embankment stability, particularly during periods of wet weather. An improved understanding of the influence of tree removal on embankment hydrology is required so that infrastructure owners can develop a managed system of vegetation clearance.

Hydrological field monitoring data from an instrumented railway embankment are presented and compared with a finite element model of root water uptake incorporating daily weather data. It is shown that trees maintain persistent suctions within their root zone which are unaffected by seasonal wetting and drying at the soil surface. However, the removal of trees from the embankment slope causes wetting of the soil from the soil surface as persistent soil suctions within the root zone are lost.

 

[Deepgreen]

Tree removal may be good for leaf-fall restriction and MAY be OK for stability (open to debate, it seems) but the sheer weight of large trees must also have an effect on earthworks. I don't know what the statistics are for landslips in steam days when earthworks were generally far less tree-lined than today, but I suspect they were not crippling. I would tend to assume that shallow-ish, light-weight surface vegetation (grass, etc.) is very good at binding soil and simply lessening the impact of rain drops on bare soil. Anyone who has ever dug turf will know how strong its binding qualities are.

 

[Bald Rick]

Well, the paper I posted above argues to the contrary. Sorry, I should have pasted the abstract:

All that actually says is more research is required into the implications of removing trees. The Geotechnical engineers I know, including the one responsible for the whole of the SE of England, are unequivocal that trees are not good for earthworks, and need to be removed where possible.

 

[kristiang85]

All that actually says is more research is required into the implications of removing trees. The Geotechnical engineers I know, including the one responsible for the whole of the SE of England, are unequivocal that trees are not good for earthworks, and need to be removed where possible.

I mean I'm only going off my own experience of studying effects of deforestation on erosion patterns (yay for studying geography); yes this is smaller scale and quite different, but the science is broadly the same. Ultimately we are messing about with nature by building the railways through these areas, and to me cutting them down is just too simplified a solution. As has been said, the root systems do lead to instability, and a dead root system is even worse.

Maybe more can be done to look at species with less invasive root systems on the railway structures and re-planting with these. I personally believe full on clearing of vegetation will lead to more land slip issues. And, given how many have happened since the tree cutting programme, which seem to my untrained eye more than normal, this is something that needs to be looked at with urgency.

 

[Bald Rick]

I mean I'm only going off my own experience of studying effects of deforestation on erosion patterns (yay for studying geography); yes this is smaller scale and quite different, but the science is broadly the same. Ultimately we are messing about with nature by building the railways through these areas, and to me cutting them down is just too simplified a solution. As has been said, the root systems do lead to instability, and a dead root system is even worse.

Maybe more can be done to look at species with less invasive root systems on the railway structures and re-planting with these. I personally believe full on clearing of vegetation will lead to more land slip issues. And, given how many have happened since the tree cutting programme, which seem to my untrained eye more than normal, this is something that needs to be looked at with urgency.

The tree cutting programme has been in place for as long as I’ve been on the railway (getting on for 30 years) and no doubt longer than that! It’s just recently been in the news, that’s all.

I can sssure you u that the effects of trees on earthworks has been looked at in some detail by the Geotechnical engineers. And they want them out. Special action is taking to improve slope stability at the same time, if required.

It is of note that the very first thing that was done at Epsom following the slip there earlier this week was to remove all the vegetation in the area.

 

[kristiang85]

The tree cutting programme has been in place for as long as I’ve been on the railway (getting on for 30 years) and no doubt longer than that! It’s just recently been in the news, that’s all.

I can sssure you u that the effects of trees on earthworks has been looked at in some detail by the Geotechnical engineers. And they want them out. Special action is taking to improve slope stability at the same time, if required.

It is of note that the very first thing that was done at Epsom following the slip there earlier this week was to remove all the vegetation in the area.

Fair enough, every day is a school day. The last sentence is interesting for sure; I never would have expected vegetation to be seen as the problem in such things.

 

[Hellzapoppin]

Building an embankment isn't really messing with nature and isn't building a railway through a forest. They are all made up of what ever material was available at the time, often material taken out of cuttings was used to build embankments, the BSW between Stapleton road and Horfield was constructed out of ash and when I first joined the railway was still burning underground, on a wet day spirals of steam could be seen coming out of the ground. I wonder if "virgin" ground is quite happy to have trees growing on it's slopes and the roots do an excellent stabilising job but with made up ground it's the total opposite.

 

[Paul180]

If any one has an interest in reading up on managing railway earthworks this is a good read. https://www.railengineer.co.uk/2012/03/16/managing-earthworks/

 

[robvulpes]

Overhead view of Guildford landslip on BBC1 6pm National News, about 13 mins in. (Should become available for rest of today on iPlayer). Looked like an orange army digging by hand - embankment is all sand there.

 

[Deepgreen]

I seem to recall that, following a significant embankment re-build between Worcester Park and Stoneleigh about 12-15 years ago, the ground was seeded with grass and wild flowers. Basically, lawns on sloping surfaces bind the ground but don't disturb anything beneath the surface, and protect the soil from runoff.

 

[Bigfoot]

Overhead view of Guildford landslip on BBC1 6pm National News, about 13 mins in. (Should become available for rest of today on iPlayer). Looked like an orange army digging by hand - embankment is all sand there.

It's not called sand tunnel for nothing.

 

[Peter Mugridge]

I seem to recall that, following a significant embankment re-build between Worcester Park and Stoneleigh about 12-15 years ago, the ground was seeded with grass and wild flowers. Basically, lawns on sloping surfaces bind the ground but don't disturb anything beneath the surface, and protect the soil from runoff.

Was it that long ago? My memory of that landslip is that it was 6 or 7 years ago?

 

[infobleep]

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.

So you know which end of the tunnel it was? The end cloestyto Guildford Station is viable from a private road.

 

[infobleep]

I seem to recall that, following a significant embankment re-build between Worcester Park and Stoneleigh about 12-15 years ago, the ground was seeded with grass and wild flowers. Basically, lawns on sloping surfaces bind the ground but don't disturb anything beneath the surface, and protect the soil from runoff.

Perhaps they should do that everywhere. Would that be possible?

 

[vikingdriver]

Looks like another one, down on the West of England line. Hit by 1L20.

 

[Matt Taylor]

So you know which end of the tunnel it was? The end cloestyto Guildford Station is viable from a private road.

Yes, south end of the sand tunnel. The north tunnel is the chalk tunnel and the south tunnel is called the sand tunnel, we are taught in our route learning that the way to remember it is that the sand tunnel is nearest the beach!

 

[swt_passenger]

Yes, south end of the sand tunnel. The north tunnel is the chalk tunnel and the south tunnel is called the sand tunnel, we are taught in our route learning that the way to remember it is that the sand tunnel is nearest the beach!

I always thought the sand face was just too steep. Seems it’s almost bound to be washed out any time there’s serious rainfall. I bet it wouldn’t be built like that if they were to start again...

 

[RichT54]

I always thought the sand face was just too steep. Seems it’s almost bound to be washed out any time there’s serious rainfall. I bet it wouldn’t be built like that if they were to start again...

I was reading in the Middleton Press "Woking To Portsmouth" book recently and it describes a collapse of the tunnel on 23d March 1895 which swallowed up a coach house and stables that had been located above. It says the brick-lined structure passes through fine sand, the bedding planes of which are almost vertical.

It also says the tunnel was lengthen northwards 1984, by means of concrete segments, to retain the unstable material. What kind of work would be involved to stabilise the area around the south of the tunnel?

 

[Bald Rick]

If any one has an interest in reading up on managing railway earthworks this is a good read. https://www.railengineer.co.uk/2012/03/16/managing-earthworks/

This quote is key to this discussion:

Trees hold up banks – don’t they?

Vegetation has an important influence on earthwork behaviour. Contrary to common belief, trees do not hold up the banks.

Whilst this may applicable to natural slopes or engineered highways earthworks, it is not applicable to the over-steepened cutting and embankment slopes on the railway infrastructure. Field trials on clay cored embankments have demonstrated ground disturbance to be 10 times greater where trees are present compared to grass.

The engineer mentioned in the article retired a couple of years ago. The process he devised for identifying the risk of earthwork failures in prolonged wet spells is the one I summarised upthread.

 

[Matt Taylor]

What kind of work would be involved to stabilise the area around the south of the tunnel?

Not that easy, there's only 500 yds between the tunnel portal and Shalford Junction and this includes two roads going under the railway.

 

[infobleep]

Not that easy, there's only 500 yds between the tunnel portal and Shalford Junction and this includes two roads going under the railway.

This doesn't happen often but of course if its frequency is likely to increase or it occurring recently makes it more likely to occur again then I guess it can't be ignored. Assuming something could be done that is.

I find the geology around Guildford to be quite varied.

 

[infobleep]

If the landslip was to reoccur south of Guildford, would it have any impact on the Christmas engineering works taking place in the area?

 

[Railwaysceptic]

If any one has an interest in reading up on managing railway earthworks this is a good read. https://www.railengineer.co.uk/2012/03/16/managing-earthworks/

I'm astonished to learn that tree roots typically go down only five times as deep as grass roots. I'd have guessed far more than that.

 

[Bald Rick]

I'm astonished to learn that tree roots typically go down only five times as deep as grass roots. I'd have guessed far more than that.

Depends on the tree of course. Some have lots of long shallow roots. But most do go down quite some way, and that part of the article is ‘open to interpretation’.

 

[infobleep]

I see there is engineering works starting tonight in the Guildford area. Is this due to the landslip or recent bridge strengthening works?

I see trains between Farncombe and Guildford are currently picking up delays, which I assume relates to an emergency speed restriction in force.

Great Western Railway are running replacement bus tonight, Friday and Saturday night to 10am Sunday but nothing listed for South Western Railway, beyond trains being diverted and stops cancelled in the journey planner.