The Gotherington embankment collapse Q&A
article by: Ian Crowder & Darren Fairley
posted on: 21 August 2010
updated on: 22 November 2010
You only need to look at the comments on Gotherington slip news
items to see that many people have views about how it should be
tackled as well as questions that the event naturally raises.
Here Darren Fairley, properties director of the GWSR, offers some
frank answers to many of the questions that have been asked over
recent weeks. This is necessarily quite a long document so if
there are particular answers you want to see, click on the link and
it will take you straight there…
Why has it taken so long to
start work - after all the slip happened in April?
Given our railway is prone to slips and it's not that long since
the major Cheltenham event, it's important to have a full
understanding of the causes of this catastrophic collapse, how best
to repair it and most important, how to prevent anything like it
happening anywhere else on our railway in the future.
We have a different priority to the national network. Back
in BR days, a self insuring company, a slip would occur (and they
weren't and aren't uncommon), lots of resources would be thrown at
it and the hole filled with what was readily available to make a
temporary repair so that the public service was up and
running again as soon as possible. A more permanent repair
could then be carried out at an appropriate time when there was
minimum disruption to trains.
We have a different priority. We're not self insuring and
don't have the same kind of resources. We have a
responsibility to ensure that what we do to repair the slip is for
the long term and also meets our insurance company's
requirements. We don't have the funds to do a temporary
repair to get up and running and come back later and do a more
permanent fix.
Today, even on the national network sections of track will stay
closed longer and the actions we are taking is just the same.
A geotechnical survey helps us to understand the root cause of the
problem. A civil engineers' survey and assessment will
suggest the best possible repair solution for the best possible
price for the long term.
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Why not at least have a go at
repairing the embankment ourselves. We have some experienced
civil engineers on the railway who could surely do a good
job?
Safety is our priority, 'having a go' at something so serious
and significant is not an option.
We wouldn't just 'have a go at' at something as serious as a
boiler repair which also has to then be professionally certified,
we would use experts at every stage to ensure a lasting, effective
and safe repair. So why compromise on something that supports
400+ tonnes of rolling loads with the general public on board, when
all of the indicators show we have a bigger problem in wait under
the surface? Patch repairs in BR days have clearly failed now
and adding to it will only store up more problems for the future so
it is right and proper that it is fully investigated and the work
properly planned.
Railway earthworks and geotechnical engineering are not the same
as civil engineering. They go together of course, you need
them all and not just one. Some of our own excellent
engineers have been retired for a while and have even said
themselves that they are not up to date with modern solutions -
which can be cheaper, quicker and last much longer.
We don't have the luxury with something this big to 'just have a
go'. What is visible is just the outward indication of much
more serious problems below the surface - a bit like an
iceberg!. The whole embankment is on the move over a distance
of 250m and in places over 7m high, with a two track railway on
top.
I have personal experience of dealing with slips all through my
20 years on the national network, and I have always found something
unexpected when having gone at something without getting the latest
assessments and research - and that always costs both time and
money.
If we were to have a go ourselves (and there will be occasions
in the future when we will!), who then maintains the rest of the
railway and keeps what we have operating going - we have a lot to
keep us busy and of course, it's growing all the time.
To take a metaphor: If part of your house subsided, after
having paid in all your insurance premiums - even if you had a mate
who was an experienced builder, would you get him to do the repair
or would you use a specialist company recommended by the
insurer? If your house is professionally repaired but the
house still fell over five years later - you wouldn't have to worry
as the repairs are insured as well. Much the same with our
railway.
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Telling the insurers means that
everyone will charge twice as much. If you go to a garage
after an accident, they ask: 'is it an insurance job?'.
Surely if we organised it ourselves we could have done it
cheaper?
Cynical and sometimes true, but I can assure you that in this
case it is most definitely not true. Everyone
involved - including our insurance company - knows that we do not
have cash to splash around and we are ensuring that where possible
local companies are on the tender list so prices are
competitive.
As noted in another answer, having looked after work on the
national network, where insurance is not in the process gives a
good reflection of what others are charged for such work and we are
really getting value for money - everyone that we are taking to is
looking for ways of reducing costs and providing value for
money. They know we are a volunteer organisation.
One other thing to consider is that the insurance premiums we
have historically paid out in the past wouldn't have paid for
Cheltenham, never mind Gotherington. Trying to do it on the 'cheap'
would have exactly the opposite effect!
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Why can't we just dump new
material on top of the embankment to restore it?
Yes we could but…… the result of the geotechnical surveys
clearly shows that large sections of the embankment are slumping
and moving in different ways. So it s a bit like nailing a
jelly to the wall, it can't hold itself up let alone support more
load.
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The slip is on the run-round
loop. Why don't we just abandon that, make up the running
line shoulder and run single-track?
What is evident is that the sheer fracture of the embankment has
appeared in the centre. Therefore we have to take out
sections of the main line to re-instate its structural
integrity. As soon as we start work the face of the fracture
will crumble and will not support the main line - in any case, the
shear fracture is vertical and is right next to the sleepers of the
running line and it won't support the weight of a train. We
also have to 'step in' the new construction into the main line
support that has not moved (yet) and therefore most of the top
section has to be removed, filled and compacted and treated with
stitching materials (geotextile frabic) to give added
strength. Singling the line will make no difference to the
cost of the repairs.
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Are we going to do the repair
fully with the double track bed restored, or would it be cheaper to
restore just to single track?
What ever we do the same amount of material needs to be taken
out and this is where the majority of the cost is, including
disposing of the ash fill.
The replacement fill and new profile of the embankment in the
grand scheme of things will only save about 10 per cent of the
costs but will stop us from ever double tracking in future.
In the long term, if the money becomes available, should we not
re-instate our railway to is full potential? Take the house
analogy - if it were a three bedroom house and one of the rooms was
seriously damaged, would you settle for a two bedroom house to save
a few pennies short term?
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I know a couple of civil
engineers and discussing the land slip they too are puzzled why it
is taking such a long time to repair. They, like me think it is
more a lot about money not civil engineers' time to repair.
Are you informing us of all the facts.
We have brought in a large number (all with time and effort) of
independent engineers from all manner of backgrounds but familiar
with heritage railway maintenance, construction and
operation.
Any civil engineer will ensure that before making a full
assessment they would want all the facts and information available
- it is very easy to say 'I can do it better' without having all of
the facts in front if us. We have not made all of the
information available to everyone as it is simply not manageable
and not concluded as yet but as some readers have acknowledged, we
have been as open as possible.
One think I think is worth mentioning at this point is that the
insurance company is actually paying for an independent check to
the design and solutions being out forward - that is their money
out of their pocket, but reassures them that we are doing the job
proberly!
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Outside contractors have a
vested interest in putting in high bids once insurance companies
are involved. This is not rocket science, it is a clay embankment.
It is perfectly possible to repair this slip with the railway
working to an engineers brief, just as we did at Cheltenham Race
Course. You could probably knock a zero off the bill by doing
this...
See also previous response about contractors costs.
I think it is fair to say that Cheltenham is a fantastic
job. Everyone saw the state of the damage beforehand (the
damage to Gotherington is just as severe - just that the loop track
is hiding it and there are further problems beneath the
surface). And the Cheltenham repair has held fast and is well
respected in engineering circles.
It was designed and managed in exactly the same way that
Gotherington is being done and by the same engineers. The
actual work was tendered and undertaken by contractors in the same
manner that we are proposing at Gotherington.
Most importantly because of the way Cheltenham was managed and
repaired the insurance company have been much more confident that
we have the ability to repair the railway to a good standard.
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Isn't this a problem that has
been storing up for ages through lack of maintenance of culverts
and drainage - surely someone should have sorted the drainage out
before now? Haven't we brought this on ourselves?
What we have is a railway that is 100 years old. We are
finding that there is a number of things that are affecting the
drainage which, in the main, is ceramic pipework along the boundary
fence line. The ground has moved over the years and the
pipework has settled but not all is accessible or visible. As
vegetation is brought back under control we have a better idea of
what is happening with the drainage that we couldn't see before and
the way the water drains off the nearby ridge and furrow land also
changes with time.
The most proactive way is what we are doing already. Where
we have visible or known problems we are targeting them in the
budgets we have, we continue to survey the line as we clear, and
where we know it will be some time before the vegetation gang get
there we are monitoring as best we can. This is also the case
on the extension up to Broadway, so we are prepared in advance.
The drainage at Gotherington was in this year's budget, but the
cold minus-18 degree freeze caused significant damage that was just
not visible, exactly where the old BR repairs were carried out. In
fact, BR simply loaded the embankment and put a gabion wall at the
bottom to try to stop it slumping. In fact, the embankment
slump has moved around the wall and is also pushing the gabions
over!
With respect to the culverts, they are not a problem at
Gotherington, we will not be inserting any new ones, simply
improving the drainage that leads to them. It should also be
noted that we have significantly more culverts than were on the
drawings we inherited by BR. We have found and repaired a
number of culverts that were not on the BR records and will no
doubt continue to find more as we extend to Broadway - but we do
maintain the culverts.
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What is the first job to be
done?
Drainage.
Re-designed with modern materials and with future maintenance in
mind. Why should we carry on digging out ditches every five
years, for the sides to slump into it with all manner of other
detritus, when we can put in a flexible pipe (inspection covers at
20m or so intervals) and a blanketing material that stops the large
amount of silt from blocking it up. This design has proven
extremely effective at Cheltenham and Gotherington South (one side
only) as pilots and we now have a design that we can use elsewhere
and give us more time to not worry about going back to dig out and
get on with something else.
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What can our volunteers do -
for instance, could we save some money by doing the drainage on the
Cotswold side?
To get us ahead of the maintenance game, I would rather we as
volunteers concentrate on the next drainage priorities. We
are going to batch up and make savings with our contractors on a
number of drainage jobs close to Gotherington whilst they are there
so that we can move forward a year or so ahead of our plans and
prevent and stop any other potential problems.
We want to get to a point where we are no longer just tackling
the known places where we can already see a problem developing but
continue to replace the drainage where there are no signs of
problems now, but could be in the future.
(top)
What are the current projected
timescales?
Drainage work is about to start (late August 2010).
We have put out tenders for the main work based on the design
work so far carried out (most of it is now done). We expect
the major work to start by October and provided the funding comes
in over and above the insurance claim payment, it could be ready
for reopening in May.
(top)
Have we considered getting rid
of the embankment and putting in a viaduct? Wouldn't that
solve the problem for good?
The costs of such a structure would be astronomical.
However the consulting engineers have looked at a range of
solutions and we will now be using a combination including soil
nailing and geotextile membrane, as well as excavation and
rebuilding of the most seriously affected sections. Not every
potential solution suits the local underlying geology. But
rest assured, attractive as it might be to look at, a curved
viaduct is not a practical or cost-effective consideration!
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What about other embankments -
the railway has plenty of them, where else could there be landslips
in the future?
The one thing I can be sure of is that there is potential for
further slips. But with the appeal going forward we will have
a much better budget to press on with drainage work, will be better
able to prevent and predict where we might have problems in the
future and get to grips with something that GWR and BR coped with
through the whole life of our stretch of railway.
(top)
Does this mean that the railway
was built 'on the cheap' in the first place and we are beginning to
reap the consequences - after all, they had trouble building the
viaduct by trying to rush the job…
Would we build the railway the same way now? No!! But back then
they were using what was cutting edge technology: in fact ours was
the first to use such a level of automation (so-called 'steam
navvies' - huge rail-mounted excavators). But there was still
a significant amount of human labour - even with the advent of the
mechanical age, human 'navvies' bore the brunt and horses were
still used for musclepower.
But as is evident from Gotherinton, they didn't scrape off the
soil surface or indeed even the existing vegetation to help key the
embankment into the ground. They just dropped the clay
straight on top. As a result there is an 'organic layer' of
soil, grass and vegetation that is preserved under the
embankment. There are even seeds down there - we've retrieved
some and we'll see if they grow…century-old grass! But that
organic layer doesn't help when water permeates through the
structure.
As railways go, we have more than our fair share of
structures. If our line isn't on an embankment, it's in a
cutting. What's more, there are probably over 100 structures
that cross over or under our line, most of them culverts, as well
as two tunnels and a viaduct. It's a century-old challenge
that we accepted when we bought the route - and one we must
maintain to the highest possible standards! These features
are attractive to our customers of course but they also present
challenges in terms of maintenance.
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As the job is going to take a
long time, couldn't we move the run-round loop at Gotherington and
concentrate on getting to Laverton - at least we will then restore
the railway more or less to its pre-landslip length and will at a
stroke cut the cost of all the topping and tailing of
trains.
It is one of a number of ideas that is being looked into.
We have had some great ideas and responses submitted to us
and the Board is looking into a number that would or could present
opportunities for something new for our customers and get more
'bums on seats' whilst we are cut short on the main running
line. Both of these ideas are being seriously considered -
indeed, we have already authorised the Permanent Way department to
press on with the Laverton extension and to get the run-round loop
there in place.
However some ideas will cost more money than they save short
term, so each is having to be looked at separately and as with
everything else, time and effort will be spent as wisely as
possible.
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Can you give a breakdown of
what is going to happen and what each phase will cost?
See the separate
article on this website which shows how the work is being
broken down into seven separate work streams.
(top)
We continued to run over
Cheltenham slip before the work started, why not at
Gotherington?
The slip at Cheltenham was a different scenario. That slip
was not as close to the shoulder of the running track and before
every train we had to inspect the slip for movement. The
Gotherington slip has already taken out the first section of track
and is right against the shoulder of the operating line, but in the
deepest part of the embankment. Even without trains running
we have at times been able to actually watch the embankment
settling down. It would simply not have been safe to run
trains.
Whilst it was a hard decision to stop running services when we
did, I'm glad that someone didn't have to be in the position of
watching the trains running over the affected area and make the
decision at the end of each day on whether to repeat the process
again tomorrow. The risks were just too great. Having a
train coming of the rails and possibly falling down the embankment
is just unthinkable - it would close us down and have a serious
effect on the rest of the railway movement.
Safety comes first. Full stop. I am totally certain
that we have taken the right decision for the right reasons and
that we have not taken any unnecessary risks in the process.
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Is everyone on the railway
being properly briefed?
I wish I could have gone round a few more departments and
briefed out what we are doing and why but of course we are all
volunteers, most of us have 'day jobs' too.
It would be great if we could share all the information that we
have gathered with all the shareholders, members and departments as
it comes in. But the nature of such information is that as it
comes in, decisions have to be made and second opinions sought to
arrive at the best solutions - passing on everything would simply
put out conflicting and confusing messages.
We have tried to keep everyone informed on this website and this
Q & A is an example of how open we are trying to be. We
welcome questions still, of course, you can use the feedback form
at the bottom.
Suffice to say we do have some of the best brains in the
business at work on the solution and we will undertake the repair
to the highest possible standards so that the Gotherington
embankment is never a problem for our successors over the next 100
years. The board's interest is to take decisions that will
keep our railway operating for the long term and secure all work at
the best price whilst at the same time, continuing to maintain the
operational railway. I have no doubt that the rest of the
railway industry is watching us closely and already, we have earned
respect nationally for the professional approach we have
taken.
All that will stand us in very good stead for the future and
underlines that on the GWR, we do things properly, safely and with
the interests of our volunteers and customers very much in
mind.
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Glossary of terms
We've used a few terms in our descriptions of what's happened at
Gotherington in our various articles so hopefully the following
might help to clarify what we mean!
Geotextiles - Robust permeable fabrics that can
come in a range of forms to suit different terrains. They
filter, reinforce and protect soil surfaces and are today widely
used in earthwork construction, repair and stabilisation projects -
for example railways, airport runways, road projects, dams,
reservoirs, protecting erosion along canals, rivers and
estuaries. Once installed, they still enable grass and other
light vegetation to establish itself and thus blend the material
into the environment.
Soil nailing - a technique developed in France
in the 1970s and now widely used throughout the world for civil
engineering projects. It has proven to be an extremely
effective way of stabilising and increasing the shear strength of
soil slopes such as cuttings, embankments and retaining
walls. Holes are drilled and slender threaded bars inserted,
usually with expanding 'plugs' (a bit like DIY wall plugs that
firmly secure screws in a wall) that lock the bar into the
surrounding soil. The bore surrounding the rod is then grouted
which prevents corrosion and large nuts are used to secure the bars
against large plates (or 'nail heads') on the slope surface which
tie in to geotechnical reinforcing grids where appropriate to
complete the repair. These are easily confused with, but not
the same as, ground anchors which are grouted up hard and tight and
tie sections of rock etc. together where they have become
unstable.
Shear face - the line of fracture within the
soil of an embankment failure. Usually follows a vertical
line, curving out as the face descends, leading to complete failure
of the embankment.
Geotechnical research or surveys - carried out
by geotechnical surveyors, the objective is to obtained detailed
information about the makeup and properties of soils and rock
beneath the surface, in order to enable foundations or earthwork
failure repairs to be designed that provide the best solutions for
the local conditions. The work involves both surface and
sub-surface exploration. Subsurface exploration involves
drilling boreholes, extracting materials for laboratory analysis
and inserting instruments to measure earth movement, moisture
content etc.
Culvert - a channel built beneath an embankment
or other structure to drain water or carry a stream. The
railway has a large number of them particularly where the line runs
close to the limestone Cotswold escarpment to carry water run-off
through the embankments which would otherwise act like a dam.
Ridge and furrow - a method of farming dating
from the Middle Ages in which the ridges were formed by the method
of ploughing then used. The typically corrugated land surface
results from the type of oxen-drawn non-reversible ploughs which
worked in the same way year after year, which tended to pile the
soil up into fertile ridges, while the furrows aided
drainage. Earliest known examples date from immediate
post-Roman times and it was most recently employed in the
17th century. It is visible where there has been
no ploughing since - for example where the land has been used for
livestock - and can be seen on a number of fields adjoining the
railway. It is relevant to the Gotherington slip because
water tends to follow the furrows. The embankment is built
over corrugated land which can still be seen on the Cotswold side
and these corrugations still pass at an oblique angle beneath the
railway. The furrows have allowed water to permeate the
embankment soil.
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