Irish Railway Record Society
CAHIR VIADUCT DERAILMENT REPORT
by Denis McCabe
The Railway Safety Commission (RSC) report
on the derailment of a cement train at Cahir Viaduct on 7 October 2003 was
published in August. The train consisted of locomotives 134+185 + 22 four-wheel
laden cement wagons and was working the 03:35 Limerick-Waterford. The bridge
structure was severely damaged in the derailment and the rear 12 wagons fell
through its floor into the River Suir below. The driver was not hurt in the
accident, but the line remained out of service until September 2004. Damage to
rolling stock and the bridge was over €3m and therefore was classified as a
‘serious incident’ under EU Railway Safety Directive 2004/49/EC. The
Directive requires that all serious railway accidents be investigated.
A Statutory inquiry into the circumstances
of the accident was conducted by the Interim Railway Safety Commission (IRSC).
The IRSC’s Inquiry utilised documentary evidence provided by IÉ and by
consultants that IÉ engaged to assist in its own internal inquiry into the
accident, verbal evidence given in interview by various parties involved either
directly or indirectly in the accident, and data obtained directly by the IRSC
in its various site inspections.
The report extends to 72 pages and extracts
are noted below.
EXECUTIVE
SUMMARY
The report said ‘Examination of the site
and recovered debris, and interviews with individuals directly involved in the
accident, did not confirm the cause of the derailment. Similarly, the modelling
of the viaduct and train dynamics conducted by IÉ’s consultants failed to
predict conclusively any derailment mode. The analysis therefore seeks to
eliminate the factors that it could be said with a reasonable degree of
certainty had not materially contributed to the accident, and to consider the
factors that remain’.
‘While it is not possible to state
definitively what caused the accident, it appears that shortcomings in the
timber deck structure of the viaduct and shortcomings in the associated
inspection and maintenance regime were the most significant causal factors. If
these had been fit for purpose it is unlikely that the accident would have
occurred’.
‘IÉ was addressing some of these
shortcomings at the time of the accident, and has since introduced or proposes
to introduce remedial measures’. ‘A copy of this report in draft form,
excluding the conclusions and recommendations, was forwarded to all interviewees
for comment. Two responses were received, the content of which was taken into
account in finalising the report’.
BACKGROUND
The report gave details of the train, track,
Viaduct and weather. These are not reproduced here, but details of the Viaduct
were provided in JOURNAL 153. The down direction is from Limerick to Waterford.
It noted ‘50kg/m flat-bottomed rail was
laid up to and over the Viaduct, and terminating about 53m beyond the Waterford
abutment. This was manufactured in 1977 and initially laid on the more heavily
trafficked Limerick to Limerick Junction section of the railway before being
cascaded to the Tipperary to Clonmel section in 1996. 87lb/yard (43kg/m)
bullhead rail was laid from that point and continued through Cahir Station. On
the approaches to the Viaduct, the track is of traditional ballasted type with
timber sleepers. On the ballasted track and the Viaduct, the rails were seated
on cast iron sole plates. These support the rail and give it an inward
inclination from the vertical of 1 in 20. On the Viaduct itself, the rails and
sole plates were connected to the way-beams with wood-screws. The track was laid
in panels with rails joined by fishplates. For the 50kg/m rail the panel length
was 36.6m. There were joints approximately 17m before the viaduct on each
approach and on the Viaduct itself approximately 20m from each abutment’.
‘Two element types comprised the primary
deck, the main longitudinal support girders and the transverse girders. All were
originally fabricated from plate and angle sections riveted together but a
number of the transverse girders at the Waterford end of the Viaduct had been
replaced with rolled mild steel beams after an accident in 1955’.
‘The approximate dimensions of the main
girders are 3500mm from top to bottom flange and 750mm between webs. At regular
intervals along the girders, there are internal diaphragms between the webs. The
transverse girders and beams, of which there were 95, spanned between the main
box girders spaced at 915mm centres. They were approximately 8075mm long, with
the exception of those at the abutments at each end of the deck that were of
various lengths to accommodate the oblique angle of the Viaduct. The wrought
iron transverse girders had a flange width of 230mm and a depth of 483mm, and
the steel beams a flange width of 190mm and depth of 610mm. The wrought-iron
girders were riveted to the inner webs of the main beams with their bottom
flanges immediately above those of the main girders, the whole assembly forming
a trough through which the railway passes. The deeper mild steel beams were
fitted to the main girders with their bottom flanges set slightly below those of
the main girders’.
‘The secondary timber deck structure was
of way-beam type where the rails are carried on longitudinal timber beams
instead of transverse sleepers. These way-beams were nominally 305mm wide and
305mm deep (12" x 12") and ran continuously under each rail across the
Viaduct. They were attached to the transverse girders/beams by bolts, which in
the case of the wrought iron girders passed through the top flange, and in the
case of the steel beams had clips that gripped the outer edge of the top
flange’.
‘Outside each way-beam there was a timber
guard-beam, nominally 152mm wide and 406mm deep (6" x 16"). The
guard-beams were staggered longitudinally relative to the way-beams. Their
apparent purpose was to provide derailment protection. At approximately 3000mm
intervals, timber transoms kept the way-beams apart. Long steel tie-rods
prevented the way-beams from spreading and, together with shorter tie-rods, were
used to hold the guard-beams and way-beams together’.
‘At every second way-beam joint there were pairs of steel flitch plates that were the same depth as the way-beams to which they were bolted on either side [Steel plates typically applied to the side of a timber structural member to provide added strength. In the case of the Viaduct, these plates also located and secured the way-beams]. The plates were approximately 2060mm long and spanned three transverse girders to which they were riveted. They were mounted at longitudinal intervals of 11.7m in staggered fashion, reflecting the probable original length and layout of the way-beams. The flitch plates helped to provide lateral, longitudinal and rotational fixity to the way-beams and, along with the staggered guard-beams they provided longitudinal continuity’. ‘The Viaduct was designed to accommodate two sets of railway tracks but carried only one set which was offset to the Up side of the deck centreline’.
The report gives details of the journey until the time of derailment, response to the derailment, pollution containment measures, recovery of the derailed vehicles, examination, testing and investigation. It also provided details of maintenance and inspection regimes of the train and viaduct. For space reasons, these are not included in this summary.
Copyright © 2007 by Irish
Railway Record Society Limited
Revised: January 09, 2007
.
