Working on the 1.3km, eighteen-span concrete box girder viaduct brought considerable challenges around working from height and minimising disruption to traffic.
The Bearing Replacement Programme was carried out over a number of phases. One of these phases involved the replacement of a pair of bearings on top of North Pier 5 – some 35 metres above the River Orwell.
Prior to the possession, innovative temporary works were put in place to enable a controlled lift of the deck. Three jacking systems coupled with a computerised monitoring system were installed and commissioned. The main lifting jacks were positioned on the pier top acting to the underside of the deck with a maximum uplift capacity of 3,500 tonnes.
Due to the design of the temporary works, the eastbound carriageways had to be closed while work was going on, which meant that the team had a short 52-hour window to complete the job.
In order for the concrete grout to cure in time for the carriageway to re-open, the area at the top of the pier head had to be heated to 20°C. This was no mean feat considering the job was carried out over a cold weekend in February.
The team overcame this by shrink-wrapping and double boarding the scaffolding at the top of the pier head, and installing infra-red heaters and hot air blowers. The solution worked a treat and the concrete grout cured in time for the carriageway to re-open for the Monday morning rush hour.
