Kaymac Marine & Civil Engineering Ltd were commissioned by Balfour Beatty Rail to provide a working platform for the preparatory works and repairs to be carried out on the structure during all states of the tide. St Julian’s Viaduct lies within the navigable River Usk, which has a tidal range in excess of 12 metres during Spring Tides.
Kaymac Marine & Civil Engineering Ltd were commissioned by Balfour Beatty Rail to provide a working platform for the preparatory works and repairs to be carried out on the structure during all states of the tide. St Julian’s Viaduct lies within a navigable river which has a tidal range in excess of 12 metres during Spring Tides. Kaymac used their experience in the marine environment to provide a solution that would allow access for the workforce of various contractors to carry out the contract works.
The design was developed so that the original scope of carrying out the works from vessels, which could only be carried out at certain states of the tide, could be replaced with a floating pontoon system that would be large enough for the material requirements and that could rise and fall with the tides throughout the day.
The designed solution consisted of a temporary steel bracket system that was installed to each steel pile, connected via vertical cylindrical hollow steel sections. The brackets support these cylindrical sections which extended from the bed level to the top of the piles (a greater distance than the tidal range of the highest predicted Spring Tide) and act as guiderails. Kaymac’s own steel pontoon system was then modified to fit these guiderails with additional steelwork and bracings, which allow the unit as a whole to rise and fall through all states of the tide.
Kaymac’s planned works were carried out in 3 phases, with the pontoon being moved between the 3 piers within the watercourse. The brackets to the central pier (Phase 1) were installed though utilizing Kaymac’s own multi-purpose working vessel the ‘Gundog’, which is fitted with an onboard hi-ab crane and also a MEWP. Through a combination of diving and dry working operations, the brackets were fitted to the piles by Kaymac’s own workforce. Winch and anchor systems were used to ensure that the ‘Gundog’ was able to hold station during the lifting operations countering the strong river flows and tidal nature of the River Usk.