Replacing elements of the bridge including decayed timber members and the corroded steel brackets.
The Traeth Bach viaduct is located on the DJP line between Llandecwyn and Minffordd Stations, and carries the line and the adjacent toll road over the Afon Dwynyd.
The works required to the structure involved the replacement of a number of elements of the bridge including decayed timber members, which formed the trestle frames supporting the bridge deck and the corroded steel brackets.
As the Afon Dwynyd is tidal at the site location, a combination of traditional, marine civil and sub-sea engineering was required to undertake the works. In addition to this, the elements of the superstructure were changed during railway possessions, while certain elements of the trestle frames were replaced under live load.
Due to the above criteria and the nature of the structure and its environment, it was proposed to divide the work into three phases, with the trestles and superstructure timbers sub-divided into the appropriate frame number.
Floating and land based plant was required to complete the work, with the proposal of the floating plant being used off a 17ft workboat to provide access to the trestles along with 2 x 10.0m x 2.0m floating pontoons. These were mobilised into position by a workboat and securely chained to either side of the trestle to provide a temporary working platform that was easily relocated as the work progresses.
The use of a 5 Tonne mini excavator for moving sections of timber and floating plant from beach into the estuary was proposed for the land based plant for the works.
The stages of the work commenced with the replacement of 12 Diagonal Bracing followed by the replacement of horizontal waling timbers and a small amount of steelwork assemblies. The work was completed with the replacement of the remaining bolt assemblies and the replacement of 197 steelwork assemblies placed throughout the structure. The project was successfully completed within budget and to schedule.