Then and now on Chicken Curve – how the Great Western dealt with landslips

By: Ian Crowder, 2012

 

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.

 

(Note: SInce this article was written, the Pete Waterman £1 million Emergency Appeal successfully reached its appeal target and all the embankment repair works referred to have been completed and paid for.)