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London's Underground's (LU) Victoria Station is one of the busiest in the capital, used by almost 80 million passengers each year. Building Information Modelling has been a vital component in the £700m project to increase the station's capacity.
From ground level downwards, the Victoria Station Upgrade (VSU)is incredibly challenging. It aims to:
The station serves the Victoria and District & Circle lines with two existing ticket halls. The upgrade will double the size of the existing Victoria line ticket hall – referred to as the South ticket hall. A new entrance and third ticket hall will be created on Bressenden Place, on the north side of Victoria Street. This will link to the platform tunnels, the South ticket hall and the District & Circle line ticket hall by new passenger tunnels. Eight new lifts will provide step free access from street to platform levels.
New tunnels will range from 4.5m-9m in diameter. Ticket hall boxes will be up to 15m deep. Both ticket halls will be under busy thoroughfares – the North ticket hall under Bressenden Place and South ticket hall under Wilton Road. To minimise traffic disruption, contractors will use top-down construction.
All construction is taking place alongside existing infrastructure – the site is crisscrossed by existing pipelines, sewers and power and communications cables.
Construction will take place next or beneath the foundations of buildings. Secant piles forming the walls of the North ticket hall will be within 3m of the Victorian culvert carrying the River Tyburn. The passenger tunnel linking the North ticket hall to the Victoria line ducks under the culvert and scrapes over the southbound Victoria line platform tunnel with limited clearance. An escalator squeezes between the twin bores of the Victoria line north and southbound platform tunnels with a mere 300mm clearance.
Existing tunnels are shallow – the crowns of the District & Circle line tunnels are just 2.5m below street level in some areas. The crown of the Victoria line is about 14m below ground. Threaded between them, the new tunnels will be constructed at the interface between London Clay and overlying, water bearing river terrace gravels. To prevent disturbance, workers will use jet grouting to stabilise the gravels and prevent disturbance to existing tunnels when excavation begins. The grout block will also create an impermeable barrier to keep the new works dry.
Jet grouting involves inserting a hollow drill bit into the ground and injecting cement grout at pressure so that it mixes with surrounding material. Jet grout columns will around 1.6m in diameter, each overlapping with its neighbours by a minimum of 150mm. To ensure required coverage is achieved, diameters of 1.4m and 1.8m will also be used. In all, 2500 jet grout columns will be created. The process will effectively create a solid block of weak concrete, designed to achieve a minimum strength of 1MPa but expected to be stronger, providing a safe environment for tunnelling.
For added complexity, this surgical construction is taking place in the middle of one of the UK capital's busiest transport interchanges, with underground and mainline rail stations and a bus terminus used by hundreds of millions of passengers a year. The site is surrounded by government departments, offices and shops. Space is restricted and it is imperative that construction activities do not cause undue disruption.
To manage the daunting challenges and risks of VSU, the project team is using Building Information Modelling (BIM) on a scale, unprecedented in the UK when work got under way in 2006 and remains exceptional. BIM is a process that incorporates 3D design, simulation and analysis, quantity surveying and a host of other tools, and provides a platform for collaboration. LU initiated this approach because without a spatially accurate, fully co-ordinated 3D model it would be near impossible to visualise and co-ordinate the project. The model was an engineering requirement.
Taylor Woodrow and BAM Nuttall (TWBN) are delivering the project under an NEC Option C design and construct contract, with shared gain/pain. Mott MacDonald developed LU's concept design, helped steer the project through the statutory Transport & Works Act processes and is now working as the designer for TWBN.
LU completed site acquisition in March 2011, with site preparation beginning in summer 2011. SCL tunnel excavation started in summer 2012 adjacent to the North ticket hall and advance southward. The North ticket hall is scheduled for completion at the end of 2016. Work on the South ticket hall began in October 2012. Victoria Station Upgrade is on schedule to be delivered into service in 2018.
When design got under way in 2006, VSU pushed the use of BIM far beyond anything previously attempted in the UK and set standards internationally. Use of BIM on the project predated the government strategy. Indeed, VSU was a reference point during development of the strategy and remains an exemplar in terms of information model maturity.
The VSU model encompasses the entire project and incorporates 18 discrete design disciplines, showing how the entire project fits together. The BIM working process was built around:
To maximise interoperability between disciplines LU used ProjectWise, its preferred collaboration software, wherever possible. When not, the transition of electronic information between the different platforms being used was assisted by tailoring software configurations and using 'platform agnostic' models. Bentley Systems' ProjectWise enabled collaboration.
The experience built up by the VSU project team has resulted in invitations to advise and assist clients. These include Crossrail and Transport for London, with development of content management systems for their own projects.
To co-ordinate the new infrastructure with the old and minimise the risk of clashes, Mott MacDonald created a 3D record of existing LU and third party assets. This drew on 'as built' records, supplemented with data generated by millimetre-accurate laser surveys. When site preparation and service exposure got under way in spring 2011, TWBN supplemented this information by logging the exact location of cables, pipelines and other structures encountered.
BIM has been used to co-ordinate the design of 2500 jet grout columns. To get in around the existing infrastructure, they will be raked in every direction. The position and orientation of every drill string is uniquely identified in the BIM model. The model was used to perform a reverse 'clash detection' process, ensuring that there were no voids within the consolidated ground.
Ground improvement contractor Keller is able to use the unique identification and co-ordinates for each jet grout column to position its rigs. This process is unique to VSU and Keller has indicated that the improvement in accuracy, efficiency and the mitigation of risk will lead them to apply it to other projects. There is the potential to use data extracted from the BIM model to automatically control rig set-up and the depth of drilling. Keller embraced BIM, demonstrating that it is practical for subcontractors to rapidly develop the advanced level of BIM maturity needed to achieve government efficiency targets – Keller achieved BIM maturity level two in only two years.
The BIM model helps deliver time and cost savings by allowing checks for structural, architectural and building services clashes within the station. On design of the ticket halls, automation within the model has yielded time savings on structural recalculations required following architectural changes. For example, when changes were made to the position of openings in structural slabs, the model calculated the new load paths and regenerated the reinforcement design with minimal rework.
Quantities of materials are automatically calculated by the model, giving visibility to the cost impacts of design changes. LU is looking to take the benefits further and feed reinforcement data from the model into the fabricator's steel bending machine.
3D printing technology – stereolithography – heped to generate physical scale models of the virtual BIM model. In combination with viewing tools such as interactive PDFs, this improved the project team's ability to communicate their design and construction intentions to stakeholders and the public. This contributed to timely feedback and modification, avoiding the potential cost and delay associated with later stage changes.
As the project moves into the build phase, the richness of information contained within the 3D model will improve. This helps the contractor's ability to understand and resolve details. It will also enable TWBN to check work against specifications and validate any anomalies. The integrated single model enables continuous review and testing of the design for constructability, and potentially for maintenance and operation of the asset.
Post-completion, the detailed model will provide LU with an accurate record of assets – those belonging to third parties as well as its own. Containing spatial and technical information, the model has the potential to assist LU in managing the station throughout its life.
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