Significant space and access restrictions at London’s Borough Market are among many challenges faced by Cementation Skanska on its work for the Thameslink rail upgrade programme, as Paul Wheeler reports.
Google Borough Market, London’s most celebrated and cosmopolitan “foody” destination, and you will find many references from around five years ago alluding to the chaos and inevitable destruction that was certain to result from the Thameslink rail upgrade programme.
However, now the work, which involves constructing a new viaduct across the market’s trading space, is actually under way, the web’s dissenting voices have pretty much disappeared.
Business as usual
Given the initial controversy, the construction activity is decidedly low key. In fact, take a trip to Borough
Market and you’ll see that it’s pretty much business as usual for everyone.
In part this is thanks to the Network Rail-funded construction of the new Jubilee Market, which extends the trading space and provides accommodation for those displaced by the work. But it may also have something to do with the open and collaborative way this logistically challenging and potentially highly sensitive job has been approached.
According to Kevin Hague, project manager with foundation subcontractor Cementation Skanska, the overriding brief throughout the work is to keep the market live. In this respect, winning the co-operation and trust of the market trustees and Southwark Borough Council, along with the client Network Rail, design consultant Atkins and main contractor Skanska, is crucial.
“Given the initial controversy, the construction activity is low key. Take a trip to Borough Market and you’ll see that it’s pretty much business as usual”
The project extends around 350m from London Bridge station to just west of Stoney Street and will effectively double capacity in what is one of the most notorious bottlenecks of the entire UK rail network.
Once complete, there will be dedicated tracks for Charing Cross- and Blackfriars-bound trains for the first time.
This is key to providing Thameslink with the potential to run 24 trains per hour, and opens up scope for routing new direct north-south rail links across London.
The work involves constructing new viaducts and widening the existing Victorian structure.
As the foundation subcontractor, Cementation Skanska’s work broadly breaks down into three sections. At the western end - around Park Street and the Hop Exchange - the existing abutment is being widened on the approach to the new central viaduct.
Foundations comprise 132 550mm to 600mm diameter cased augered minipiles, which extend to a depth of 28.5m, giving a penetration of around 17m into the underlying London clay.
Cementation Skanska used minipiles in this area because of space and access restrictions. Manoeuvring its two Klemm minipiling rigs while co-ordinating the delivery and movement of concrete, casing and reinforcement cages, provided the main challenge, says Hague.
Work in this area also includes 38 segmentally-cased rotary piles for the western abutment of the new Borough Market Viaduct. These are formed by driving short sections of 880mm diameter segmental casing into the London clay using a Kelly bar-mounted Bauer BG22 rig. Once the casing was into the London clay, the Kelly-mounted auger was used to advance the pile bore to the design toe depth.
The new viaduct spanning the Borough Market forms the central section of the job. It will be founded on four pairs of 2.4m diameter, rotary bored piles extending to a depth of 28m, and permanently lined to prevent water ingress, with an 11m-long single section casing through the upper 5m of made ground and around 6m of river terrace gravels.
“The challenge is managing deliveries of materials to the site and movement of the heavy piling plant within the congested market area”
This is the most visible part of the job and the area where the construction activities potentially impact most upon the public and market activities. The piling work itself, carried out using a Bauer BG40 rig, is contained within two hoarded-off areas of the market. Given the area is noisy and bustling - not to mention the near continuous trains trundling overhead - the actual piling activities were planned and executed to minimise the impact on the surrounding environment.
The challenge is managing deliveries of materials to and from the site and the movement of the heavy piling plant within the congested market area. Lorry movements require very carefully managed and visible marshalling, while rig movements requiring full road closures are carried out on Sundays when the market is closed.
The project is unquestionably further complicated by the market’s slightly bohemian and anarchic atmosphere (the area has been used in films including Harry Potter, and Lock, Stock and Two Smoking Barrels). As Hague puts it, people don’t always walk where you would expect them to and “certainly not on the pavements”. It is, he says, an interesting and difficult environment in which to work, and one that is extremely challenging to manage.
Some flexibility in the operations is available thanks to a marshalling yard established by Skanska on an undeveloped site across Borough High Street. This eases the logistics, allowing temporary stockpiling of spoil and equipment.
Cementation Skanska is also using a Soilmec rig to install 22 continuous flight augered piles to support a replacement and upgraded roof structure over the southern section of the market. With relatively light loads, these 750mm diameter piles need to extend only into the top of the London clay at around a depth of 12m.
Green Dragon Court
Work within Borough Market also includes foundations for a bridge abutment at Green Dragon Court.
Comprising six 1.2m diameter, 50m deep piles constructed under bentonite, it will support the western abutment of a new bridge over Borough High Street.
Cementation Skanska carried out the western mini-piling and foundation work within Borough Market between January and the end of July this year.
It has just returned to work on the third section of the job, the Railway approach viaduct leading up from Borough High Street to join the through platforms at London Bridge station, and will be carrying out this work into the new year.
The Thameslink project
The Thameslink Programme is a £5.5bn project to upgrade and expand the Thameslink rail network to provide new, longer and more frequent trains serving more stations between the north and south of London, overcoming the need for passengers to change trains or to use the London Underground.
Work includes the lengthening of platforms, station remodelling, new railway infrastructure and new rolling stock. The project was originally proposed in 1991 and, after various delays, was granted planning permission in 2006.
The work around Borough Market is one of the more controversial elements of the project. Creating space for the viaduct has required the demolition of a number of listed buildings and other buildings within the Borough High Street Conservation Area.
The original Thameslink planning application was rejected at public inquiry following the intervention of then deputy prime minister John Prescott, partly on the grounds that suitable arrangements were not included to replace the buildings which would be demolished within the market. The subsequent proposal, which more fully addressed these concerns, was accepted at a second public inquiry.