Thameslink: Borough Viaduct

Thameslink Programme: Borough Viaduct

CEEQUAL Excellent (88.9%) – Whole Project Award
Version 4, Dec 2013 | London, England, UK

Winner – CEEQUAL Outstanding Achievement Awards 2016 – Multiple

Client: Network Rail
Design: Atkins and Jestico + Whiles
Construction: Skanska

Assessors: Liz Wood-Griffiths (Network Rail) and Victoria Burnham (Skanska);
Verifier: Catherine Arotsky (Rickaby Thompson Associates Ltd)

Summary

Background

The Thameslink route is one of the busiest routes in the south east. With passenger numbers predicted to continue to increase over the next 20 years Network Rail is investing £6 billion in the Thameslink Programme. This will increase capacity by lengthening trains and increasing the frequency of services.

Part of the programme consists of the construction of a new rail route into London Bridge, including a new twin-track viaduct over the historic Borough Market. The working market is operating almost 24 hours a day with deliveries in the early hours of the morning, market shoppers throughout the day, and visitors to the restaurants and bars in the evening.

The new structure extends for 322 metres and runs alongside the existing viaduct, doubling capacity on this part of the route and removing the current bottle neck at London Bridge Station. The works included removing and replacing the market’s historic roof, temporarily relocating market stall owners, undertaking demolition and construction within the working market, and constructing the 1200 tonne steel truss bridge over Borough High Street.

Achievements

The end result of the project has been widely praised and there has been significant publicity for the re-opening of the market.

By spending time at the start of the project setting up a clear and concise Community Management Plan and getting (and keeping) neighbours on board through regular communication, the project team was able to construct the new viaduct and bridge with minimal disruption. This saved time (not having to stop works due to complaints), money (keeping to the programme, removing the need for compensation due to unplanned disruption), and protected the reputation of all parties involved, including that of Borough Market itself.

Many were unconvinced that the historical features of the market could be retained after such significant construction works but high profile visits – including Prince Charles – and articles in local papers have praised the works and demonstrate the success of the project. Not only have Network Rail and Skanska completed an essential section of the ongoing improvement of the Thameslink network, but the local community has benefited from an upgrade to an important historical landmark.

The result is a market to be proud of: one that encompasses the new functions of the area whilst preserving the historical architecture and one that will continue to increase tourism and business to the area.

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Effects on Neighbours

Engaging stakeholders

The project had a rigorous Community Engagement and Management Plan to ensure the works were sympathetic to the local community and their needs were represented for the entire duration of the works. As a highly residential area and a significant tourist destination it was important to keep disruption to a minimum during the four-year construction period.

Before works commenced, stakeholders were identified and invited to attend focus groups where the plans for the works were shared, and their concerns were listened to and incorporated in the construction plan. These workshops were continued throughout the project, in addition to monthly newsletters and weekly emails. Skanska gave local residents and businesses site tours, which gave them a greater appreciation of the small working area and the complexities of building a major component of London’s infrastructure in a working market.

A market stall with the construction team and archaeologists was set up during school holidays to give children and adults information about the project, including its construction, its future use, and a ‘hands-on’ opportunity to hunt for the historic artefacts found on site and the history behind them. Local firms were actively encouraged to compete for work and the project used local venues (Southwark Cathedral and the Hop Exchange) for meetings and events.

Minimising noise and pollution

The construction team erected full height hoarding around the perimeter of all the working sites in the market. An acoustic barrier, reaching from the ground to the existing viaduct was erected to protect Southwark Cathedral from construction noise. Noise, vibration, and air quality monitors were set up around the site. Alarms triggered a text message to the Environment Manager and Construction Manager if limits were breached, in addition to weekly readings and reporting. The construction team also built a ‘Green Wall’ to minimise visual impact of the construction site and to improve air quality. Water was recovered from the viaduct and reused on site to damp down the works, minimising dust.

Due to the popularity of the market with tourists, the construction team ensured there were no noisy works between 11.00 and 14.00 during market trading hours as not to impact the busy lunchtime period. Construction methods were changed in order to reduce noise and vibration: there was no driven piling, and the project used Brokks to cut sheet piles safely, efficiently and reduce vibration. The project team communicated with the market at all times to ensure they were meeting expectations. During the demolition phase, Skanska regularly reviewed performance with stakeholders. This resulted in a change of practices for a few days following a suggestion from businesses and residents to complete the demolition over a shorter period of a few days (working all day), rather than on and off (adhering to the quite period) for a few weeks. It was this continuous communication with the stakeholders that allowed the project works to be unobtrusive and completed without any serious complaints.

Reducing disruption

Skanska worked with Better Bankside (a Southwark-led initiative focusing on improving the local area), to lessen disruption by setting up a logistics forum with other contractors in the area to reduce road closures and congestion. They also worked with Better Bankside to build community areas: a physic garden and recreation space. A new market was constructed to rehouse the traders displaced by the works.

In order to minimise the disruption in the busy area of London Bridge, the Borough High Street Bridge was constructed on top of the newly built viaduct, fully encased in acoustic hoarding, rather than in-situ. The construction team then ‘slid’ the bridge out along the viaduct and across the High Street in a single weekend. A team from Skanska and Network Rail were on site for the entire bridge launch, answering questions from passers-by, and handing out free tea and coffee from a London double decker bus. The event was an enormous success, and crowds and press gathered to witness this huge engineering achievement. The bridge now acts as a focal point of the High Street – a piece of modern sculpture bridging the gap between the traditional architecture of the market and Cathedral, and the modern design of the Shard.

On-going benefits

Effects on neighbours do not end with the construction period. During the design and construction of the project, consideration was given to future-proofing the viaduct to ensure minimal disruption during operation. A permanent noise barrier to shield existing buildings from the new train route was erected along the boundary of the market and the Cathedral. The project also gave consideration to a high quality of design, taking into account user enjoyment and additional facilities, and included several notable features:

  • Architectural lighting on the new viaduct and Borough High Street Bridge.
  • Clean-up of Green Dragon Passage and new lighting for increased safety.
  • Additional market access routes.
  • A new market hall on Borough High Street that gives a high profile and striking access to the market for customers exiting from London Bridge Station.
  • A design that is sympathetic to the existing buildings and preserves the view of Southwark Cathedral.

Historic Environment

An important market

The historic Borough market, bounded by Southwark Street and Borough High Street, is on the southern end of London Bridge. The present buildings were designed in 1851, with additions in the 1860s and an iconic entrance designed in the Art Deco style added on Southwark Street in 1932. The market is synonymous with London’s thriving food scene, as well as being the backdrop for films such as Bridget Jones’s Diary and the Harry Potter films. Therefore, it was critical that the works caused minimum impact to the existing historic infrastructure and that the area would be preserved for the flourishing tourist market and the future generations that will live and work there.

Retaining the market roof

Due to the historical importance of Borough Market, it was decided that as much of the old frame as possible should be re-used in the re-construction of the market roof. The new market should provide all the aesthetic qualities that would be expected of a newly built structure, while retaining its historic features.

From the inception stage of the project it was clear that the cast iron roof, which formed the entrance to Three Crowns Square, had to be retained as much as possible. The roof, supported by its 14 columns, had suffered from years of neglect where maintenance had not been carried out and also contained asbestos mainly in the gaskets to the glazed components.

Collaboration between Network Rail, the Borough market trustees, the architect and Skanska resulted in a plan to incorporate the old cast-iron frame and combine it with sections of new-build steel structure to create a modern, new space for the market to move back into following the works. Skanska set up regular meetings with local voluntary organisations, resulting in maximum credit being scored in the Historic Environment section of CEEQUAL.

Surveys and planning

The first step was to undertake a full structural, dimensional and intrusive survey so that previous assumptions, made in the design stage, could be verified and the condition of the various elements assessed. The project also procured specialists from the Museum of London Archaeology team to carry out a complete recorded survey of the roof prior to its dismantling. This has ensured that a standing building record was prepared for the public archive. The deconstruction method was then fully developed and thus the roof was successfully dismantled with extreme care. The original architectural specification called for bolted connections in lieu of the original riveted method. Skanska, in conjunction with a specialist contractor, proposed that the original connection method of riveting could be utilised thus not only preserving the detail, appearance and original intent of the structure, but also ensuring these traditional construction methods are kept alive.

Demolishing the existing roof

The initial phase of the works which involved the demolition of the roof was an especially difficult operation given the condition of the existing roof. Large sections of the frame were corroded and no longer structurally sound, while various additions to the structure over the years made the disassembly more complex. The need to carry out the demolition without causing any damage to the historic members was also a challenging task.

To achieve the successful demolition of the roof, a specialist contractor with experience in cast-iron structures was brought in to carry out the works. Structural assessments were conducted for each section of framework, and the members were sequentially removed and transported off site to be refurbished.

Testing old members for structural integrity

Further testing of the roof members was carried out off site. Corroded or damaged areas were cleaned up and tested for thickness and structural integrity. Members that were too badly damaged were discarded, while others were repaired or strengthened with the addition of new steel members. Finally a picking list was produced of the available historic members to be incorporated into the final design. The members could then be blasted and cleaned up and re-painted, ready to be re-integrated into the new roof structure.

Re-erecting the roof

The roof could not simply be re-erected as it was in the past. The old cast-iron members no longer conform to modern loading conditions, and the requirement for access and maintenance capability required significant strengthening of the structure with new steel members. The challenge involved with this strengthening was to create a structure which conformed to modern standards without taking away from, or overshadowing, the historic features of the roof. The success of the project would depend on how well the new members could be blended in with the old.

Preserving archaeological remains

During the excavation at 11-15 Borough High Street, Railway Approach, and the Wheatsheaf (sites opposite and adjacent to the market), the team uncovered items of high historical significance. At 11-15, a significant Roman building was unearthed (thought to be a bathhouse) and in order to preserve the building in situ, the team redesigned the foundations of the building. The discovery was so significant, it was been put forward for scheduling by the Local Authority. In the vaults of Railway Approach and the foundations of the Wheatsheaf the project uncovered and filled 6 boxes of animal bone, 16 boxes of Roman pottery, 19 boxes of building material (providing a deeper insight to the construction methods of the Romans), as well as various metal trinkets, glass, and painted plaster. The pottery was given to the Museum of London to be put on display – and holds a record of 48 hours from discovery to display! Skanska and Network Rail produced information posters to be displayed on the site hoarding, informing the public of the findings.

Preserving the Wheatsheaf

The route of the new viaduct bisected the historic Wheatsheaf pub. Instead of demolishing the entire building, the upper floors were removed to allow the viaduct to pass through, whist preserving the public house and the listed circular wooden bar.

Network Rail and Skanska have proven to the community that all efforts were made to maintain areas and structures of significant historical importance while improving the rail network in central London, whilst minimising disruption to local business and residents. The project has shown that while upgrades to the rail network are an essential part of improving London’s transport system, it does not need to be at the expense of the local communities.

Information provided by Skanska.