Current Status of the Project
We have been progressing the complex access scaffold since summer 2018 – works which involved 75 overnight closures of the railway – and these works will be completed this year. Handing over the access scaffold in phases has allowed the necessary detailed inspections of the structure and cast-iron facade to commence, which allows confirmation of the required scope of works, including any associated design.
The planned works being progressed up to Christmas 2019 consist of access scaffolding, steelwork repairs, concrete deck investigations and testing and removal of redundant utilities.
Access Scaffolding
The complex scaffolding works to provide access to the entire bridge, including access to all 6,300 steel members, is the largest undertaking of access scaffolding on the bridge since the current concrete deck was replaced in 1933.
For those who remember, substantial scaffolding was erected on the bridge for parapet upgrades and façade painting in 1990. However, this did not provide the same wholesale access scaffold that we are currently erecting, which provides full underside of Bridge access.
Due to the location of the works, all the access scaffolding has been brought to site during overnight deliveries. These have been ongoing, up to 6 nights per week, since Summer 2018.
These deliveries involve installing traffic management on the North Bridge, erecting a telescopic crane, and transporting delivery lorries to site.
The materials are then off-loaded from the lorries using the crane and distributed over the protected roof of Waverley Station.
During normal dayshift works the delivered materials are installed into position on the underside of the bridge.
Steelwork Repairs
The steelwork repairs on the bridge fall into two categories: Condition Led & Assessment Led.
The Condition Led repairs, as their name suggests, are repairs to members that are in poor condition. These members have suffered corrosion due to a breakdown of the current protective coatings and an ingress of water. We are currently repairing these members, and in some cases replacing with new members to extend the life span of the structure.
The Assessment led repairs are required to strengthen the bridge to ensure compliance with the latest design codes. As there are 6,300 steel members in the bridge the design associated with this is complex and is currently ongoing.
Concrete Bridge Deck
We have recently completed extensive testing to the underside and topside of the concrete deck on the North Span.
These tests have provided us with detailed information about the current condition of the concrete deck and have allowed us to establish a design for the repairs that are required to extend the lifespan of the deck.
These repairs involve removing large areas of the underside of the concrete deck, as a result these works will be planned to coincide with the traffic management that will be required for the secondary structures as described on the following page. The traffic management will be required to reduce the loads transmitted through the deck whilst sections of the underside are being removed and repaired.
Cast Iron Façade Works
There are only a handful of organisations in the UK capable of undertaking the cast iron works that will be required for a project of this scale.
These specialist contractors have undertaken initial site visits to commence the process of identification of the cast iron that needs to be repaired and that which needs to be replaced.
Overall the process to make a single new casting off-site could take up to 12 weeks using the traditional methods that we will be incorporating on this project.
Secondary Structures
Through the investigations and inspections that have been carried out since access scaffold handover on the North Span (Balmoral end) we have identified hidden ‘secondary structures’ at the bridge abutments and piers. There are 8 of these secondary structures in total. These structures created voids to allow utilities to pass below the bridge deck.
As these structures were uncharted, they have not been able to be maintained and therefore have fallen into disrepair, and the only solution available is for them to be removed and replaced.
We will excavate, remove, and replace all 8 of the secondary structures. Traffic management will be implemented on the North Bridge to facilitate these works, details of which will be issued in the new year.
Traffic Management
We will need to implement traffic management on the road during daytime to undertake these Secondary Structure works.
We are currently progressing the design and plan to undertake the works starting in February 2020.
Removal of Redundant Utilities
We have had Scottish Power Energy Networks on site along with other utility providers. The utility companies have been confirming the status of old utilities which are slung below the bridge.
Following confirmation and proving that each service was in fact redundant the laborious process to remove these commenced. This process will continue over the next few months. As these cables, pipes, and ducts were redundant they have not been maintained. By removing them from the bridge it removes the risk of further deterioration and potential collapse in the future.
Traffic Management
As noted earlier there has been traffic management established on the North Bridge up to six nights per week over the past year. We have also closed Market Street to traffic and managed the pedestrians through the works.
To date the careful planning of the Traffic Management with our colleagues in City of Edinburgh Council has resulted in there being little impact on the general public.
Works coming up over the next few months will follow a similar fashion.
Additionally, we are currently planning the implementation of traffic management on the North Bridge on a 24hrs/7 days per week basis. The replacement of steelwork described earlier is a complex process whereby only single members can be removed and replaced at a time. If traffic management is implemented and the traffic load removed from certain lanes of the bridge it may result in a greater number of members being removed and replaced at any time. This could result in programme period reductions. Other activities, such as the necessary repairs to the underside of the concrete deck also require this traffic management.
When implemented we will maintain one lane for traffic in each direction and maintain both footpaths.
More information will follow in future updates.