Then and now on Chicken Curve – how the Great Western dealt with landslips
article by: Ian Crowder
posted on: 02 July 2011
updated on: 07 February 2011
Here are some photographs that really do bring home the fact
that Chicken Curve - which suffered a catastrophic failure in
January 2011 - has given problems to the Honeybourne Line's
predecessors over the years: infact, as far back as the 1920s.
The line was opened by the Great Western Railway from
Honeybourne Junction as far as Winchcombe in 1904, when a charabanc
service ferried passengers between Winchcombe station and
Cheltenham - a journey that must have been quite an experience for
travellers in the solid-tyred Great Western Railway vehicles of the
day, grinding up and over Cleeve Hill.
But less than 20 years after the line opened, the curved
embankment just north of Winchcombe (Greet) station suffered a slip
and, indeed cuttings and embankments elsewhere on the route were
also giving problems. Another example was a landslip on the
Cotswold side of the deep cutting just north of Toddington (where
there is now a substantial retaining wall).
On 28 February 1924, a lecture was given by A S Quartermaine,
Assistant to the Joint Chief Engineer of the Great Western Railway
to the Great Western Railway (London) Lecture and Debating Society,
entitled 'The Work of an Engineering Division' and was subsequently
published by the Society, along with photographs including two
taken on the Honeybourne Line at what is now Chicken Curve and in
the Toddington cutting.
Following is an extract from the published paper, kindly
provided by Bill Hillier, under the sub-heading 'Slips':
"These are liable to occur either in cuttings or on
embankments, and are almost invariably due to the presence of water
where it is not required. Agricultural land drains are a
source of trouble in this respect and it is essential that water
flowing down these should be intercepted by a ditch on each side of
the line so as to prevent it from percolating into the banks and
cuttings, or forming marshy pools and in fact all water coming on
to the railway should be led into definite channels, and so kept
under control and disposed of quickly in a satisfactory
manner. Clay is a great offender in the matter of slips, but
rock may give serious trouble if it rests on a layer of slippery
material sloping towards the line, or if softer material underneath
it weathers away and leaves it unsupported. The remedy varies
but after the removal of any similar ground to drain the water away
from the seat of the slip by constructing slag drains up the side
of the cutting of embankment about 20 feet apart, 5 or 6 feet wide
and deep enough to reach the bottom of the ground that has slipped,
which may necessitate drains 20 feet or more in depth (see fig 3 -
which shows the cutting north of Toddington station).
"A thick slag wall is generally required to support the
toe of the slope, or if the slip is very deep or troublesome,
piling may have to be resorted to (see fig 4 which shows the
embankment north of Winchcombe station, now known as Chicken
Curve).
"Where rocky ground has to be dealt with it is often
necessary to remove a considerable portion of the rock and
construct slag or concrete walls to keep the remaining material in
place. On districts where slips are of common occurrence, a
slip gang is sometimes kept specially for dealing with these and in
places where steep cuttings of friable rock or other loose material
occur, care is taken to see that these are periodically cleaned
down by the length-men or a special gang."
What this clearly illustrates is that slips on railway
earthworks were (and are) by no means uncommon and that even in the
1920s, serious effort was taken to stabilise problem areas.
On the line between Cheltenham and Broadway, there are three
principal locations where there is a history of embankment slips
that have continued to present problems over the years. The
route, especially south of Toddington, is subject to considerable
water run-off from the Cotswolds and in places such as Chicken
Curve and Gotherington, the land over which the line passes is
extremely wet and where watercourses may have changed direction, or
streams diverted as use of the land has changed.
The three problem areas are:
- Embankment north of Cheltenham Racecourse station, which
slipped in 2007 following the period of heavy rain that led to
extensive flooding in the area. This was successfully
repaired by contractors over the 2007/2008 winter period.
This was a relatively minor slip and caused no disruption to normal
train services
- Embankment to the south of Gotherington station - a serious
collapse of the embankment on the Malvern side of the embankment,
which closed the line south of Gotherington. This occurred in
April 2010 and prompted launch of the Pete Waterman £1 million Emergency Appeal
- Embankment to the north of Winchcombe station (Chicken
Curve). This was where a freight train derailed in 1976 which
led to closure of the route and thus the organised effort to
purchase the route and restore it. In January 2011 this
embankment, which was about to undergo stabilisation work, suffered
a similar failure to that at Gotherington, on the Cotswold side of
the line. This happened before the Gotherington repair had
been completed. Following an exceptionally harsh winter,
which lost the railway several days of its high-income Santa
Special services, the railway was left with a serious financial
position.
There have been minor slips or movement elsewhere on the line
but these have been monitored and remedial work undertaken,
including improving drainage systems. In every case the
embankments have dried satisfactorily and have stabilised.
Currently work is being carried out at Stanley Pontlarge.
Comments Darren Fairley, the railway's volunteer properties
director: "The 1920s pictures are extraordinary and really do
vindicate the work that we are undertaking at Gotherington and,
when funds are available, at Chicken Curve too.
"What the Great Western Railway didn't have at its disposal was
the sophisticated geo-technical knowledge that is used today to
allow a permanent repair to be designed that reflects the local
geological and embankment structures precisely. Although
geo-technical surveying takes time and in the case of Chicken Curve
will cost around £17,000, it is money well spent and could
ultimately save many thousands of pounds.
"The Great Western Railway's engineers had to rely on their best
intelligence of unseen problems deep within the embankment and
beneath it. The techniques at their disposal were the best
available in their day but were inadequate to bring a long-term
solution, as we know only too well. For example, soil nails
had yet to be invented while geo-technical membranes could only
have been dreamed of by the GWR's civil engineers.
"Even a relatively cursory examination of Chicken Curve
embankment shows, on both sides, that there have been many repairs
over the years. And although this latest failure couldn't
have come at a more inconvenient time, it does mean that once it is
repaired we can expect it to remain stable for many decades to
come."
Of the photographs, Darren says: "The interesting feature of the
Chicken Curve work is that relatively flimsy piling appears to be
taking place - by the look of it, rails have been brought to the
site for this purpose. While they may well have served their
purpose for many years, they couldn't be described as a permanent
solution. They have sunk and moved, while the embankment has
'flowed' over the top of the piles so there is no visible trace of
them now and they are clearly no longer doing their job. The
misshapen embankment side in the original picture is recognisable
today in the February 2011 picture.
"There is, however, recogniseable piling on the Malvern
side. In addition, over the years the land on the Malvern
side has been raised by over three metres and this changes the
hydraulic pressures on the embankment, as well as how the land
reacts to water runoff.
"The repair in the cutting at Toddington, however, has proved to
be more permanent. A number of slag drains as described by A
S Quartermaine were dug and have been effective at keeping the
cutting dry; while the substantial slag retaining wall at track
level has prevented the toe of the cutting from encroaching again
on to the track."
Sir Allan S Quartermaine CBE, MC, BSc (Eng)., AMInstCE
(1888-1978) was appointed Chief Engineer, Great Western Railway in
1940 and continued in that role for BR Western Region until
1951. He was president of the Institution of Civil Engineers
1951-1952 and was knighted in 1956.
The Great Western Railway (London) Lecture and Debating Society
existed from 1904 to 1948, then changing its name to British
Railways (Western Region) London Lecture and Debating Society and
continued to 1961. There was a similar Society at Swindon.
The railway urgently needs funds to repair the current
slip. To find out how to contribute to the £1 million appeal
click here