The Tamar Bridge needs to be resurfaced every 20 – 25yrs.
The bridge was last fully resurfaced at the time of the strengthening and widening project in 1999-2001.
However, the Plymouth side span was resurfaced in 2011 as the surfacing material failed prematurely at that location due to the difficult traffic loading conditions – slow moving, heavy goods vehicles, braking as they approached the toll booths.
Routine inspections of the bridge surfacing are carried out every four months and during the last two years these inspections have revealed that the existing surface is nearing the end of its serviceable life and requires replacement.
The project 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.
Delaying the project again could result in further damage to the surfacing material, leading to cracks which then enables water to penetrate onto the steel plates underneath with the potential for corrosion to occur.
The surfacing materials used on large cable supported bridges such as the Tamar Bridge are more costly than standard road construction. The approved budget for the project is £6 million and will be funded from toll income. That project cost also covers replacement of the illuminated lane studs and includes the costs of design and supervision.
Our bridge deck surfacing is very different to standard road construction and is only 40-55mm thick. The purpose of the bridge deck surfacing is to provide a safe durable running surface for vehicles and also to protect the steel deck from wear due to corrosion and fatigue.
Just like standard road construction, bridge deck surfacing has a limited lifespan as the millions of loading cycles from traffic eventually cause deterioration. The deck of the Tamar Bridge needs to be resurfaced every 20 to 25 years to prevent damage occurring to the steel deck. In the last 20 years the Bridge has carried around 300 million vehicles.
TThe 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. In general, taking these factors into account, and when combined with our regular inspection regime, we can predict the expected life of the bridge deck surfacing.
Our inspections and surfacing assessments have determined that the material has worn out and is nearing the end of its useful life. If the surfacing material is not replaced in time, there is a risk that the underlying steel bridge deck could be damaged either by corrosion or through fatigue and that cracking could occur in the deck and deck welds. Additionally, if the surfacing is not replaced in good time then it would start to crack and break up, creating an unsafe running surface for bridge users.
Reliable waterproof patch repairs are difficult to achieve on steel bridge decks, can be intrusive and will not be as durable as full resurfacing. Carrying out this type of patch repair work would cause significant and frequent disruption to our users as well as putting workers at more risk while carrying our repairs adjacent to live traffic.
A specialist, thin asphalt material is used to resurface the bridge deck. At just 45mm thick, this material is much thinner and lighter than the materials used in standard road construction. It is also more expensive due to other factors and processes required during the resurfacing process.
Resurfacing the steel bridge deck involves a series of highly complex processes , the majority of which need to be carried out in dry and mild weather conditions.
These processes are:
- removing the majority of the thickness of the existing surfacing material using a road planer. A thin layer is left bonded to the steel deck so that the steel deck is not damaged by the aggressive teeth on the road planer
- removing the remaining thin layer either by hand using mechanical hand tools or using a large flat blade on a suitable digger/dozer machine
- Blasting the steel deck with grit/shot using an enclosed mobile blasting machine – this process removes any stubborn remains of existing surfacing and deck waterproofing material, and provides a clean deck, enabling engineers to thoroughly inspect the steel deck and welds for cracks or damage
- Carrying out repairs to damage on the deck as required
- Applying paint ‘primer’ to the bare steel deck to protect the steel from corrosion
- Applying a two-layer waterproofing system on to the primer – this provides vital corrosion protection to the steel deck
- Applying a ‘tack-coat’ on to the waterproofing – the ‘tack-coat’ helps the surfacing material bond to the waterproofing material creating a composite surfacing system
- Laying the surfacing material in two thin layers using a special surfacing machine that runs on rails – the rails are set up to ensure that the contractor achieves the correct material thickness while also providing a smooth running surface
- Applying road markings and installing a replacement illuminated road stud system.
In addition to the bridge deck resurfacing works we are also taking the opportunity to resurface the toll plaza area, bridge approaches and will also replace all 6 of the bridge expansion/movement joints.
Reliable waterproof patching repairs are difficult to achieve on steel bridge decks and would not be as durable as full resurfacing. Adopting this approach would also require more frequent repairs to be carried out, leading to closures of lanes over a longer period, and increasing the potential disruption to bridge users.
The work must be carried out when there is the highest chance of prolonged dry or fine weather and the period from April to September provides this opportunity.
Many of the processes outlined above require dry and mild weather conditions. These conditions will give the contractor the best opportunity to achieve the highest quality of workmanship, which in turn will provide the longest service life for the bridge deck surfacing.
The main contractor for the project is VolkerLaser, an experienced civil engineering contractor with extensive experience working on many types of bridges and complex bridge works. They will be supported by a number of specialist subcontractors.
The project will take approximately 6 months to complete between April and September 2021. However, there is some significant preparation work to be completed off site before the contractor starts work on the bridge deck. Lane restrictions will commence in mid-April 2021
There are a number of construction processes that need to be undertaken in a certain order, similar to a factory production line. The removal of old material has to be undertaken very carefully to avoid damage to the underlying steel deck. Many of the processes require applied materials to become dry or fully cured before the next process can happen and this all adds to the overall time for the works to be completed.
We will ensure that works are carried in a Covid-secure manner and that all contractors adhere to current Government guidelines.
Our project team will be made fully aware of the guidelines in place at the time and they will be briefed regularly at site safety inductions and tool-box talks. Regular reviews will be undertaken at the monthly contract meetings. Additionally, we will ensure that the latest Construction Leadership Council Site Operating Procedures are rigorously enforced. For more information on the last procedures please follow this link:
There are a few reasons why we cannot undertake the works solely at night. The various sequential processes involved mean that the deck surface between processes will either not be safe for vehicles or needs to be left for materials to cure properly. It is also not practicable to undertake the work in small sections as most of the plant and equipment is optimised for larger areas. Once work starts on an area of the bridge deck or cantilever, that area cannot be used by traffic until the resurfacing operation is complete.
In addition there are many residential properties near the bridge and some of the resurfacing processes are noisy. This would cause unacceptable noise to our neighbours and the noise generated by the work would also breach environmental legislation and noise limits designed to protect the public in such circumstances.
Additionally, undertaking construction work at night in generally less efficient and does not generally achieve the same quality end product, while also introducing additional hazards and greater risks for the workforce. Temperature and humidity at night would also be more likely to be outside the acceptable ranges for some of the more sensitive materials.
The bridge normally operates four lanes of traffic with a dedicated pedestrian and cycle lane. However, during this work the bridge will be reduced to three traffic lanes, utilising the south cantilever pedestrian and cycle lane as an additional traffic lane.
Yes, both of the cantilever lanes will be fully resurfaced as part of the project.
Yes, the south cantilever will be closed to pedestrians, cyclists and mobility scooters for the duration of the works.
This will allow the lane to be fully resurfaced as well as acting as an additional traffic lane while other areas of the bridge are being worked on. The contractor will provide a free bus service to enable the affected user groups to cross the bridge safely. More detail will be provided in due course.
Yes – the crossing will remain open throughout the works to the majority of traffic. However the traffic management arrangements and lane restrictions mean that drivers of ‘abnormal loads’ will be required to use an alternative route.
We are working closely with Highways England, Devon and Cornwall Police and local councils to sign the diversion routes which will be shared with hauliers and other organisations as soon as possible.
Yes, due to the traffic management arrangements and lane restrictions required to undertake the work ‘abnormal’ loads in excess of 2.9m (9’ 6”) wide will not be permitted to use the crossing.
There may also be times when abnormally heavy vehicles in excess of 44 tonnes will only be allowed to cross the bridge at certain times of the day. Hauliers will be notified about the restrictions in due course via our website and through the ESDAL2 system. Cyclists are strongly advised to use the free bus service provided.
Regular updates on the project will be posted on the Tamar Crossings website and social media channels, and provided to motoring organisations and the local media.
This will include details any traffic congestion or delays which will also be displayed on electronic messaging signs along the A38 at Manadon Junction and Treulefoot Roundabout
Yes, advanced warning signs will be placed at key locations on the A38 and local traffic network.
It was not possible to carry out the resurfacing works at the same time as the recent kerb works.
It was important for the kerb works to be completed first so that the new surfacing material could be laid right up to the kerbs with minimal construction joints in the new surfacing material. It also means we can create a good seal between the kerb and new surfacing as well as providing the best waterproof protection to the steel bridge deck. Additionally, the contracts require very different expertise, plant, equipment and materials and trying to integrate both contracts together would have been complex, inefficient and more expensive as a result.
This project has been in the planning stage since 2015 and has already be postponed in order to complete other high priority bridge maintenance projects.
Detailed work on this scheme commenced in 2019 and site work was planned to commence in spring 2020. However, due to Covid19 and to allow the kerb contract to be completed the project had to be postponed until Spring 2021. We cannot delay the works any further and work must be completed this year. Traffic levels are still currently below our normal levels for this time of year and we have worked hard with our contractor to develop a scheme that will complete the work as efficiently as possible.