Today has seen work continuing on removing the remaining surfacing material on the two cantilevers. Since the start of works at the beginning of June VolkerLaser have removed the surface of both cantilevers to within 5 -10mm of the existing steel deck plate. They have also cleaned 85% of the remaining surface and exposed the steel deck plate on the westbound cantilever, as well as removing all the asphalt from against the kerbs. This same removal work is now continuing on the eastbound cantilever and is expected to be completed by the end of the weekend.
The FIP expansion joints have also been removed, inspected and replaced on both cantilevers.
Engineers will start inspections of the steel deck on Monday to identify any welding repairs that may need to be carried out. These inspections and welding repairs will be co-ordinated to take place alongside the enclosed shot blasting of the steel deck so that paint ‘primer’, the first stage of the waterproofing system, can be applied to the bare steel deck to protect the steel from corrosion.
Subject to appropriate weather conditions, and once the primer has cured, we will begin applying the two layer waterproofing system, providing additional corrosion protection to the steel deck. Once this has been completed, a ‘tack coat’ will be applied on top of the waterproofing. This will help the new surfacing material bond to the waterproofing, creating a composite surfacing system.
Some people have commented that they were unable to see many staff working on the bridge when they drove by. The permitted working hours within the contract are between 7.30 am and 7pm and we are monitoring the works closely to ensure that they remain on schedule.
We have continued to be asked why work cannot begin earlier in the morning and/ or later in the evening, as well as overnight. As we have previously explained we need to consider the impact of the works on the people who live close to the bridge.
We understand why some travellers might prefer longer working hours if that leads to the scheme being completed more quickly, but we need to consider the safety of the workforce as well as the impact on nearby residents.
Removing the existing surfacing material and preparing the steel deck for the laying of the new surfacing material is highly specialised and time consuming work. The layout of the cantilevers, a single lane width, is an additional challenge as it is very difficult to safely have large groups of workers and heavy machinery close together. This restricts the amount of plant, equipment and the number of people working on site at any one time.
The scheme involves a number of construction processes that need to be carried out in a certain order, similar to a factory production line. Many of the processes require applied materials to become dry or fully cured before the next process can happen. This creates natural breaks in the work or processes, and can prevent work on a new process from being started at the end of a day.
Yesterday the surfacing material was removed from a 170 metre length of the westbound cantilever, with 300 metres of edging removed on the eastbound cantilever. The edging work involves using specialist machines called breakers. This is an intensely physical task which requires small teams of workers to rotate the operation to limit the effects of Hand Arm Vibration syndrome. This means that some workers will be stood for short periods of time.
To ensure that the work is carried out as efficiently as possible the teams are taking breaks to coincide with the tipper lorries or sweepers leaving the site rather than stopping at set times.
Another question we have been asked is why the Tamar Bridge has a steel deck rather than a traditional concrete one.
The original concrete main deck was replaced with a new, lighter main deck in 2001 when the bridge was widened and strengthened. At the same time, both of the cantilever lanes were added. All the decks on the bridge are constructed from steel plates that are stiffened longitudinally using steel channels/ribs – this is known as an orthotropic deck.
This lightweight method of construction allows the bridge decks to carry more weight than traditional concrete decks. However, just like standard road construction, bridge deck surfacing has a limited lifespan as the impact from traffic eventually causes deterioration.
The lifespan of our surfacing depends on many factors including the type and thickness of the materials used, quality of workmanship, the number of vehicles using the bridge, the number of heavy goods vehicles, the axle weights of vehicles and environmental factors such as wind or hot and cold temperatures that cause the bridge to move or vibrate.
With 45,000 vehicles a day regularly crossing the bridge, it is vital that the deck, the two giant 76 metre high concrete towers and 1340 metres of main suspension cable, are inspected and maintained to an appropriate standard.
Routine inspections of the bridge are carried out by our team of engineers every four months. These have shown that the surfacing material has worn out and is nearing the end of its useful life. If not replaced, there is a significant risk that the steel bridge deck could be damaged either by corrosion or through fatigue, and start to crack and break up, creating an unsafe surface for bridge users.
As previously explained the resurfacing was originally due to be carried out during 2020, but was postponed until this year because of the coronavirus pandemic and the need to complete the kerb replacement works before resurfacing.
We recognise that this is a difficult period for our customers, and we are doing everything within our control to complete the works as quickly and safely as possible, and minimise the impact of the works on people using the bridge and living and working in near by communities.