Crossrail is a major new transport project to improve access and reduce congestion in London and the South East of England. Rails carrying mainline-sized trains will cross central London both under and above ground, revolutionising the ease of east/west travel across the capital. Eight new underground stations are to be constructed across central London which will enable interchange with existing rail lines.
The first phase of construction is planned for completion in 2017, with trains beginning to run the following year. The work carried out by Ramboll was used to reduce the Client’s risks on the project by their input to the production of contract documents for all the major tunnelling and station construction works across the central section of the route.
Our geotechnical engineering team supplied specialist geotechnical support as a part of the Arup-Atkins Design Team (AADT), the framework design consultants responsible for bored tunnelling works. The work comprised specialist geological and geotechnical modelling to aid the
design of the bored tunnels, and analysis of impact of Crossrail construction on the thousands of buildings, utilities and rail assets over the central section of the route.
Ground movement assessment
Ramboll undertook detailed analysis of ground movements due to the construction of 42 km of tunnels and the associated stations, portals and shafts. Using this analysis, we then assessed the impact that the ground movements will have on the existing infrastructure including buildings, utilities and rail assets.
Following the assessment of the damage due to Crossrail construction, our engineers then provided advice to the Client and other framework design consultants to minimise the impact of Crossrail on the existing infrastructure.
Following the assessment of ground movements due to Crossrail construction, we were able to design the mitigation measures to prevent unacceptable levels of damage to existing buildings, utilities and rail assets. A number of different mitigation measures were designed, such as compensation grouting arrays, replacement/rerouting of utilities and intrusive structural works.
At station locations, where a number of different construction activities are planned and significant ground movements are anticipated, Ramboll designed a comprehensive instrumentation and monitoring scheme for the duration of the construction programme. This design considered the validation of ground movements due to construction, the movements of existing infrastructure and restrictions surrounding listed buildings and live rail assets.
The majority of the Crossrail tunnels are to be constructed in soft ground; the tunnels between North Woolwich Portal and Plumstead Portal that pass under the River Thames will be excavated through the Chalk.
For the production of the documents for this contract, our engineers also provided specific expertise associated with geological modelling, supporting tunnel design and construction within the Chalk.
The modelling undertaken drew upon numerous phases of site investigation to detail both the groundwater conditions and the geological sequence. Engineering classification of the Chalk was carried out to inform the selection of tunnelling equipment, highlight areas of planned maintenance and potential measures to deal with the ingress of water. The geological model created was critical to identifying commercial risks associated with the ground and establishing relevant baseline conditions within the Geotechnical Baseline Report.
Between Victoria Dock Portal and North Woolwich Portal, Crossrail trains will run along the surface. We were responsible for developing ground models and geotechnical design solutions for a section of the surface line works, where Alluvial Clay and Peat deposits present a host of different challenges to be addressed in the construction of the stations, railway lines and predicting their likely behaviour over the 125 year design life of the structure.
Due to the large geographical extent of Crossrail, and the vast numbers of existing assets, our engineers developed a number of computer programs utilising complex GIS datasets to assess the impact that the construction of Crossrail will have on these assets. This enabled the effects of changes to station and tunnel designs could be assessed both quickly and comprehensively.
A further computer program was developed that enabled over 800 official engineering reports to be produced automatically, resulting in significant time and cost savings in design. This level of computerisation would not have been possible without the programs having access to the Crossrail database which our geotechnical engineers helped develop.