 |
|
London North Western
Railway:
Midland
Railway:
Stratford
Midland Junction Railway
|
|
Cofton Tunnel
Description of Tunnel
Cofton Tunnel, which was situated about seven miles south of
Birmingham on the Derby and Bristol main line, was built in 1838-1841 as part
of the Birmingham and Gloucester Railway. It was 440 yards long, and had a span
of 23 feet, and a height at the centre from rail level of 17 feet 2 inches. The
tunnel, which was not inverted, was built of red brick in lime mortar. In
section it consisted of a segmental arch with curved side walls, springing
level being 8 feet 10 inches above rail level. The side walls were built in Old
English Bond, and are 2 feet thick laid to a radius of 15 feet. The arch was
built in separate 4½ inch rings, with no bonders between the rings, and
varied from 1 foot 6 inches to 2 feet 3 inches in thickness, that is from 4 to
5 and 6 rings. The radius of the inner ring was 11 feet 0 inches. For purposes
of construction eight shafts were sunk, of which three were lined with
brickwork, and kept open for ventilating purposes, the other five being sealed
at the 'eve' and filled in. The first six shafts from the north end of the
tunnel were nine feet in diameter, the other two being seven feet in diameter.
The 'eye' of each shaft in the tunnel arch was formed by a cast iron flanged
curb, consisting of four segments bolted together and weighing approximately 3
tons. The depth of the curbs was 1 foot 9 inches, and they were shaped so as to
conform to the curvature of the arch, the outer edges of the curbs being radial
to the arch at all points.
During the period that elapsed since the time of
construction practically the whole of the original inner ring has been cut out
in patches, and replaced with blue brickwork either in lime or cement mortar,
as a matter of ordinary maintenance. In carrying out this maintenance repair to
the side walls the front half of every header brick in the original facing work
was cut off, and the replacing blue brickwork laid all as stretchers. No
accurate records are available of the dates of such repairs, but the most
recent appear to have been over 20 years ago. Generally speaking the brickwork,
both original and repaired, was in a sound condition, and the regular and
detailed examinations, of which the most recent were in January, 1928. and on
May 6th, indicated no serious deterioration on the visible surfaces. The tunnel
was damp in parts and after the failure some of the brickwork behind the lining
was found to lie in inferior condition, probably largely due to damp. It was
not, however, what would be described as an exceptionally wet tunnel. In 1922 a
scheme was prepared for widening about 2½ miles of this line between
Longbridge and Burnt Green, which included the tunnel, by the addition of two
new lines on the Eastern or down side. The tunnel was too tight in gauge to
permit the use of modern wide carriage stock, and as the height of the ground
above rail level was only about 70 feet it was decided to open out the tunnel
and accommodate both the existing and new lines in an open cutting.
In September 1925, a contract for the construction of this
widening was let to Logan & Hemingway, Contractors, of Doncaster, and in
March, 1926, excavation in the cutting was commenced near the south face of the
tunnel. All work carried out by the Contractors was under the instructions of
the LMS Company's Engineering staff, and the work was supervised by the LMS
Company's Resident Engineer. The Contractors and the LMS Company's Engineering
Staff were in agreement as to the suitability of the methods adopted. Careful
and elaborate arrangements were made lo safeguard traffic on the line, by the
provision of a temporary signal box, special automatic alarm communications.
flagmen, speed restrictions, etc., together with continuous patrolling and
examination of the tunnel. The material above, which consisted of sandstone and
beds of hard marl, was removed in successively lower lifts, and while this
excavation was in progress a slip occurred on the west side of the cutting, and
to deal with this and other slips threatening on that side, it was decided to
construct a heavy concrete retaining wall. This wall was commenced in January,
1927, and was constructed in trench, in alternate lengths 24 feet long by 15
feet wide, and when finished in December, 1927, was 310 yards long, commencing
at approximately the north end of the tunnel, and running south alongside the
tunnel. The foot of this wall was some 4 feet clear of the outer surface of the
tunnel side wall. During this period the cutting over the tunnel was excavated
to a general level of 12 feet above the tunnel arch, and on the east side of
the tunnel to a level approximately the same as the springing level of the
arch, leaving a minimum thickness at the side of the tunnel arch of 12
feet.
Arrangements for Demolition
In November, 1927, the method of excavating the remaining
material round the tunnel and removing the tunnel itself was discussed and a
scheme in six stages was adopted. The first three of these stages included the
removal of the material above and at the sides of the arch down to
approximately springing level, and the fourth stage was the actual dropping and
removal of the arch masonry itself. It was decided that this work should be
carried out by dividing the tunnel into lengths of about 50 feet by cutting
chases through the brickwork across the arch from springing to springing, and
that windows should he cut through the haunches at springing level on both
sides during the week days prior to the Sundays fixed for demolition, the final
dropping being effected by small charges of ammonal in the pillars remaining
between the windows. During all the later stages suitable precautions were
taken to ensure that steam navvies and cranes should only work at a safe
distance from the tunnel and similarly that no blasting should be allowed
within 12 feet of the tunnel.
At the end of April, 1028, it was decided that a length of
400 feet at the northern end of the tunnel should be dropped on Sunday, May
13th, and it was arranged in conference with the traffic officers concerned
that on that date the Engineers should have complete occupation of both lines
for three periods of about four hours each, and occupation of the down line
only throughout the day. On Monday, May 7th, the cutting of the chases and
windows was started on this length. When the chases were marked out it was
found that the southernmost one would come very close to one of the 9 feet
diameter cast iron curbs of the old shafts, and the southernmost length (No. 8)
was therefore extended to 60 feet in order that the chase should be well clear
of this. The windows at springing level in the haunches were each about 4 feet
long by 2 feet 6 inches high, and spaced so as to leave pillars about 3 feet
wide between the windows. A light timber strutting was placed in each window in
order to prevent the brickwork in the top of the window from falling, but this
strutting was not intended to, and in fact could not, give any appreciable
assistance to the pillars in supporting the main body of brickwork of the
tunnel arch.
The procedure adopted was that the red brick main outer
thickness of each window was cut away by men working pneumatic hammers; the
light timber strutting was then put in place, and finally the blue brick inner
skin of the tunnel was cut through by pneumatic hammers. During the latter
work, men were employed in the tunnel below to remove any broken brickwork
which fell inside. Throughout the cutting of chases and windows the brickwork
revealed by the. cuts was found to be sound and in good condition, the latest
inspection being made on the Friday morning by the LMS. Resident Engineer who
examined chases and windows from outside and inside, and was satisfied as to
the condition of the brickwork therein.
Colonel AC Trench. 5th July 1928
The remainder of Colonel Trench's report addressing the
conditions immediately prior to the accident which occurred on Friday 11th May
1928, the reasons for the accident and what should have been done instead can
be read in his report given in the PDF document at the bottom of this page.
Courtesy of www.railwaysarchive.co.uk
Minutes of the Proceedings of the Institution of Civil
Engineers
16 December, 1930. President, in the Chair, Sir GEORGE
WILLIAM HUMPHREYS, K.B.E.
The Opening-Out of Cofton Tunnel, London Midland and
Scottish Kailway.
By Robert Towson McCallum, O.B.E., B.Sc., B.Sc. (Eng.),
M. Inst. C.E.
Abridged. (Paper No 4773)
The work described in this Paper comprised the removal of an
old and 'tight' double main-line tunnel and making the open cutting so formed
wide enough to take two additional lines. Two features made it a more than
usually interesting example of tunnel-demolition. Firstly, it became evident
soon after the excavation over the tunnel had been begun that the ground was
folded and much faulted, and as the depth of the cutting was increased serious
troubles were experienced with slips, associated with these faults, in the new
slopes. These, and the threat of further and more serious slips, necessitated
costly remedial and preventive works, including the construction in trench of a
concrete retaining-wall along the outside of the west side wall of the tunnel
throughout its whole length. Secondly, the felling of a length of 265 yards of
arch and clearing the debris had to be carried out in one continuous operation.
The geological structure of the ground played so important a part in the work
that considerable attention was given to it; and an attempt has been made to
analyse the conditions causing the various slips which were such an outstanding
feature of the excavations. Cofton tunnel was situated about 7 miles south of
Birmingham, on a portion of the Derby and Bristol main line of the London
Midland and Scottish Railway known as the Birmingham and Gloucester Railway,
which was authorized in 1836, and constructed in 1838-1841, the Engineer being
Captain WS Moorsom.
Following on Correspondence
Mr HK Beale, of Derby, observed that 25 years ago, or
possibly more, he had been engaged upon an inquiry about a footpath across the
railway near the Cofton tunnel, and had met, by appointment, a very old
ex-ganger who had been employed upon the length in question for many years. He
told Mr. Beale that as a boy he had been employed in driving the Kilsby tunnel
on the London and Birmingham line ; from there he had been transferred to the
Clay Cross tunnel on the North Midland line ; and from there to Cofton. He said
that they had worked at Cofton under great pressure in order to get the tunnel
through ; that at that time the Birmingham and Gloucester Railway was open and
working from Gloucester to near the southern end of the tunnel; and that the
last 8 miles between the north end of the tunnel and Birmingham was ready for
opening, but not working. He added that passengers had come in and out from
Birmingham by coach and had been set down in a field near the south end of the
tunnel at a temporary platform. The old man's recollection was very clear on
the efforts that were being made to get the tunnel through, as only that short
length of the railway had been delaying the completion of the line. His story
entirely fitted in with the Author's theory that the engineers had found
themselves in very difficult ground and at the last moment had had to
substitute a tunnel for an open cutting. It also accounted for there being
eight shafts in ¼ mile of tunnel, the only purpose of which could have
been to get as many working-faces as possible. They could not have been
ventilators in that short length, and as a matter of fact five of them were
found to have been filled when the tunnel was being opened out. The events
recounted by that old man took place nearly 100 years ago ; but his
conversation had left a great impression because he had had such a clear
recollection of his earlier experiences in the railway world. He had also told
Mr. Beale that, while he was working at Cofton, the Lickey incline, which was
about 3 miles south of the tunnel, was worked by engines obtained from America.
Mr. Beale did not remember whether he had said that the American engines were
used on the opening of the railway or whether he was talking of some slightly
later date ; but the old man had evidently actually seen them at work.
Report on the Accident at Cofton Tunnel on 11th May
1928
The report on the collapse of Cofton Tunnel in
1928
A number of men were working in the tunnel under No 8
section, placing sleepers to protect the permanent way in readiness for the
Sunday, and clearing away the brickwork knocked in by the workmen outside who
were finishing the windows, when the whole of No. 8 section of the tunnel
suddenly collapsed on the top of them. One of the men, who was standing at the
north end of No. 8 section, suddenly saw light shine through a crack which
appeared to open at the Barnt Green (South) end, lying towards the west side of
the arch, and which extended to the north end of the section. He had the
impression that the crack was near the west side of the curb, and that the west
side of the roof fell first. Another man standing below saw dust coming from
one of the pillars at the north end on the east side. He shouted a warning and
jumped back in time to get clear. Various other men who were working above
agreed that the arch collapsed suddenly without any warning. The general
impression of those working on the east side was that the arch fell away from
them, whereas two men working on the west side had the impression that the arch
came towards them like a wave, and they were both knocked over by a quantity of
brickwork. Portions of the windows and pillars on the east side were left
standing after the collapse.
|
Donate
Facebook
Search
