Weather disruption caused in 2014, and how to prevent it happening again - ongoing discussion

[whole diary]

[paul7575]

A further level of concrete slab was poured last night, at the east end of the main breach (as shown on the lobstervision webcam around 2000 16th March).  That presumably provides additional security for the outer precast sections?

I wonder if that will be the final concrete level and the next thing we'll see along that section is ballast?

Paul

[Chris from Nailsea]

Are there plans to use explosives, as in some mining operations, or to send for the military to bomb or shell the area.

Cue a squadron of Mosquitos ... 

[stuving]

A further level of concrete slab was poured last night, at the east end of the main breach (as shown on the lobstervision webcam around 2000 16th March).  That presumably provides additional security for the outer precast sections?

I wonder if that will be the final concrete level and the next thing we'll see along that section is ballast?

Paul

The screeding has now reached most of the way along, and there's a recent rmweb picture that suggests the level is now high enough. However, these camera angles are notoriously unreliable.

I can't see such a shallow concrete floor doing much to hold anything in place. But then this job doesn't seem to be following the rule book anyway, so who knows? I mean, I thought it was obvious that priority no. 1 was speed, followed by strength combined with not needing further closure for any continued work. But by now the L-sections have taken so long to set in place that it would have been as quick to put up shuttering and produce a reinforced facing wall - surely a better structural solution.

[ellendune]

I can't see such a shallow concrete floor doing much to hold anything in place. But then this job doesn't seem to be following the rule book anyway, so who knows? I mean, I thought it was obvious that priority no. 1 was speed, followed by strength combined with not needing further closure for any continued work. But by now the L-sections have taken so long to set in place that it would have been as quick to put up shuttering and produce a reinforced facing wall - surely a better structural solution.

It may have been as quick to cast. But then they would have had to wait 28 days for the concrete to reach full strength before they could put any load on the wall.  The slab they have laid will not need full strength so ballast can be laid over it quite quickly.

[stuving]

[It may have been as quick to cast. But then they would have had to wait 28 days for the concrete to reach full strength before they could put any load on the wall.  The slab they have laid will not need full strength so ballast can be laid over it quite quickly.

What would load the wall itself, other than a storm of course? It has no weight resting on it.

Coping with the bad weather continuing (which it might have done) could have been a priority. However, the strength of what's there, when partly built, might have been no better.

[ellendune]

What would load the wall itself, other than a storm of course? It has no weight resting on it.

The ballast will apply a asignificant outward force on the wall when it is placed behind the wall.

[stuving]

The ballast will apply a asignificant outward force on the wall when it is placed behind the wall.

Sorry - I can't see that as comparable with the dynamic force needed to decelerate several tons of angry wave. And if what has been built is not meant to be storm-poof, the true sea wall being added in front of it later, then it looks way to strong just to hold the ballast.

But I can see that other factors, not visible to outsiders, may have been important in the design. One is that one about "what if another big storm happens before we are finished?". Obviously the timescale goes out of the window, but being able to easily unbolt and scrap damaged parts could be helpful.

The second point is about design timescales. There would be pressure right from the start to work out what needs to be decided when. So being able to say with confidence, in a couple of days, what can be sourced, delivered, designed, built or whatever may be more important than how long it actually would have taken if there was more time to find out.

How very un-GRIP^▸ (Guide to Railway Investment Projects)-like.

[Red Squirrel]

Is anyone aware of any published analysis of what actually caused the collapse? To my amateur eye, it appears that the principal process may have been a 'bursting' effect caused by the weight of the water that had come over the wall; i.e. the wall was pushed into the sea from behind. If that's the case then the absolute strength of the wall is less important than its ability to shed the load of the returning waves.

[ChrisB]

yep, that's what I read in one of the articles earlier in this thread

[stuving]

Is anyone aware of any published analysis of what actually caused the collapse? To my amateur eye, it appears that the principal process may have been a 'bursting' effect caused by the weight of the water that had come over the wall; i.e. the wall was pushed into the sea from behind. If that's the case then the absolute strength of the wall is less important than its ability to shed the load of the returning waves.

I don't recall seeing anything (even in this thread).

There's a big difference between the free-standing ("parapet" or boundary) wall and the embankment that was washed out. If you look at pictures of other damage along the line, the boundary wall has been nibbled down from the top, which would be by impact from the seaward side. If it also fractured lower down that could be by dynamic force from either side, but followed by being swept out to sea so you'd never know which. I still don't think that really rates as a "seawall". I understand stones get knocked off it most years, and remortaring them is routine maintenance.

The facing and the embankment behind form a proper seawall, with each part protecting the other. The wall always has to be strong enough to retain the dry (or averagely damp) fill, and the question is whether adding water increases the stress enough to break it. I rather doubt if it should, but of course there might have been a weak point. And once a breach is made, that's it - the fill washes out, and no longer buttresses the facing wall. Exit embankment and wall pursued by a wave.

[stuving]

If you really can't get enough of this railway infrastructure stuff, or want to get your hands on some fancy new kit, you might consider going to this:

Infrarail 2014
10th International Railway Infrastructure Exhibition

The UK^▸ (United Kingdom)'s definitive rail infrastructure event takes place at Earls Court 2, London from 20th to 22nd May 2014

They are offering free online registration - they may insist on some industry affiliation, but presumably if you get registered they will let you in.

[Lee]

March 28th is now being widely touted for Dawlish Reopening Day.

[ChrisB]

First train to pass the new Dawlish Cam, Colas Rail Tamper 75406 'Eric Machell'

[Chris from Nailsea]

From the BBC^» (British Broadcasting Corporation - home page):

Dawlish landslip: Army to help clear rail line


More than 300,000 tons of unstable rock and soil has to be removed

The Army has been called in to help reinstate the main rail line to the south west of England after it was destroyed by storms.

More than 300,000 tonnes of unstable rock and soil has to be removed near Dawlish in a controlled landslip.

Network Rail hopes the Royal Engineers will be able to use specialist equipment to remove part of the rock face so the line can be reinstated.

It added it hoped the line would still be reopened on 4 April.

Network Rail said it was unable to work below the area close to Teignmouth Road, Dawlish, because of the risk of rock and soil collapsing.

Rail bosses are considering blasting the rock face and even using a specialist tug based at Falmouth, Cornwall, to fire water at the cliff.

Julian Burnell, of Network Rail, said they were also consulting experts at the Camborne School of Mines. He said: "The Army have been offering us advice since the start of the problem and they have a very small team of one or two officers in place helping us. We are hoping they will be able to use specialised equipment protected by armour, to remove the rock face and soil. Another option we are looking at is dropping water from a helicopter to help control the landslip."

In February, storms washed away the sea wall and left the track, which connects the South West to the rest of the UK^▸ (United Kingdom), suspended in mid air.

Fire crews are continuing to pump sea water on to the cliff to help bring down the rock and soil.

Gaps in the sea wall have since been filled and work to repair the damaged station and platforms at Dawlish have almost been completed.

The first train to use the line, which has been closed since February, managed to travel from Exeter to as far as Dawlish Warren to deliver ballast to the affected area.

[paul7575]

Ballast started being laid from the east end of the main breach just after midnight, and has now progressed about half way along...

Paul