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Four river bridges on the Thiruvarur–Pattukkottai gauge conversion, rebuilt from the foundations up with 18.70 metre PSC ‘U’ girder spans.
The work
When a metre gauge line is converted to broad gauge, the track is only part of the job. Broad gauge stock is heavier and faster, and structures designed for the old loading cannot simply be re-decked and reused.
On the Thiruvarur–Pattukkottai conversion, four major bridges carrying the line over watercourses in the Cauvery delta needed replacing outright — new foundations, new substructure, new superstructure, and full river protective works either side.
Delta rivers do not wait. Substructure in a watercourse means working the season, not the programme.
We took both packages for Southern Railway's Construction Organisation at Chennai, accepted on the same day in June 2016, and replaced twelve short steel girder spans with ten long prestressed concrete spans.
Span arrangement
Each bridge went from three short steel girder spans to two or three long PSC spans. Select a bridge to compare what stood before against what stands now — both drawn to the same scale.
Drawn to a common scale from the span arrangements recorded in letters of acceptance MTK/101 and MTK/102, both dated 16.06.2016.
Span lengths and counts are as specified. Pier proportions and bed levels are indicative only.
Across all four
Fewer piers in a river is not a cosmetic gain. Every pier is an obstruction that raises the water level upstream, accelerates flow between the openings and scours the bed around its own foundation. Taking two out of the water and widening the opening by half makes these crossings materially safer in flood.
The superstructure
A PSC ‘U’ girder is a prestressed concrete trough — a flat soffit with two walls rising either side, carrying the ballast and track between them rather than on top of a flat deck.
The shape does three useful things at once. The walls act as deep beams, so the section is stiff without needing extra structural depth below rail level, which matters when the formation height is fixed. The trough contains the ballast, so the track sits in a channel instead of on an open deck. And the walls double as a parapet, removing a separate item from the deck.
Cast in a yard beside the site and lifted into place as complete units, they also cut the time spent working over water to the erection itself.
The four bridges
Chainage: 42875
Existing: 3 × 12.20 m steel girder
Constructed: 3 × 18.70 m PSC ‘U’ girder, with river protective works
Package: MTK/102 · accepted 16.06.2016 · completed 13.12.2019
Chainage: 46784.60
Existing: 3 × 12.20 m steel girder
Constructed: 3 × 18.70 m PSC ‘U’ girder, with river protective works
Package: MTK/102 · accepted 16.06.2016 · completed 13.12.2019
Chainage: 40000
Existing: 3 × 7.60 m steel girder
Constructed: 2 × 18.70 m PSC ‘U’ girder, with river protective works
Package: MTK/101 · accepted 16.06.2016 · completed 10.06.2018
Chainage: 41614.20
Existing: 3 × 9.20 m steel girder
Constructed: 2 × 18.70 m PSC ‘U’ girder, with river protective works
Package: MTK/101 · accepted 16.06.2016 · completed 10.06.2018
Scope of works
Both contracts ran to a twelve-month period against a milestone statement, priced on USSOR 2011 Zone I rates with separate annexures for non-schedule items.
Removal of the existing steel girder superstructure and redundant substructure from the watercourse.
New foundations in river bed conditions, with dewatering and temporary works to keep the excavation dry.
Abutments, piers and pier caps set out to the new, longer span arrangement.
Casting, prestressing and erection of 18.70 m girder units, ten in total across the four bridges.
River training, bed and bank protection, aprons and guide work either side of each crossing.
Ballasting and track laying over the completed decks, with approach formation either side.
On site
Click any photograph to enlarge. Captions describe the stage of work shown and should be checked against site records.
Get in touch
Send the bridge numbers, the existing arrangement and the waterway required, and we will come back with the span arrangement we would propose and our record on similar crossings.