As the ground engineering construction work on Crossrail reaches the halfway stage, head of geotechnics Mike Black reflects on his two decades working on the scheme
Linking London’s Paddington and Liverpool Street stations with a large diameter, high capacity rail link was first mooted in the 1940s and the name Crossrail was first coined in the 1970s. There are no two ways about it: construction of the new rail link has been a long time coming, but now, after two years on site, the ground engineering works are nearing 50% completion.
While London’s commuters have waited a long time for the scheme, one member of the delivery team has devoted much of his career to the project having worked on it for more than 20 years. Mike Black first started working on the scheme as a contractor in 1992 and worked his way up through Crossrail to become head of geotechnics.
“It has been a great experience to spend so much time on the project and seeing it through every phase from a line on a map through to delivery,” he says.
Although he may not have known it at the time, most of his jobs after graduating from Portsmouth University with a degree in geology were setting him up for his career at Crossrail.
Black started out as a mud logger working in the North Sea for a year before moving onto the Channel Tunnel where his career in tunnelling was sealed.
During his four years working on the Channel Tunnel he worked with the NATM instrumentation and monitoring division. “I learnt a huge amount in that time,” he says.
On completion of the Channel Tunnel, Black joined Mouchel to work on the A27 Southwick Tunnel and spent a year working on the design before moving into the designer’s office on site.
“My role on the scheme was more geological assessment related than on the Channel Tunnel,” he explains. “I was involved with the required excavation support (RES) assessments, although we didn’t call them that back then.”
Black describes the approach to RES as the key difference between NATM and the sprayed concrete lining (SCL) being used on Crossrail.
“On NATM projects, the support design is based on the observational method but with SCL the design criteria used is based on observation, although the design criteria is pre-determined,” he says. “NATM works well in hard ground but SCL presents less risk for tunnelling through soft ground.”
Black’s job with Mouchel then took him to Plymouth to work on the ground investigation for a sewage intercept project. The work was to stand him in good stead for his move to the Crossrail team a year later where the main focus at that time was on the ground investigation stage.
Although he has notched up two decades on the scheme, Black was also able to undertake an MSc at City University and work on the CIRIA link project on ground movement on the Jubilee Line during the periods when Crossrail did not have the support to drive it forward.
Less risky project
Black believes that the project could have been built in 1992 but the work that is being delivered now presents far less risk.
“Tunnelling technology has come on significantly since then, but there was some good technology available then too,” he says. “Although the Jubilee Line was constructed using earth pressure balance tunnel boring machines to minimise ground movements, the original Crossrail scheme planned to use open face techniques which would have presented a greater risk than the scheme that is now under construction.”
In the 1990s the tail end of the site investigation phase wound down and the project entered a hiatus. Black’s work became much more about safeguarding the route than actual geotechnical design.
“When the project was resurrected in the early 2000s the route was changed and called for more site investigation,” he says. “The 1990s plan was to bring people from the suburbs into London but the revised scheme was more of a commuter service with more stops that meant it became more of a high-capacity Tube service but extended further out into Greater London.”
He says the ground investigation for the expanded tunnelling work called for under the revised scheme took another five years to cover the new sections and fill in gaps within the existing ground model elsewhere on the route.
Black also played a key role in taking the project through its hybrid bill and his in-depth knowledge was essential during the select committee hearings. He believes that this knowledge of the scheme has also helped now the work has reached the construction phase.
Construction work started at Canary Wharf and Black says it was a real milestone for the scheme and for him personally.
He is part of a team of three working on the geotechnical issues. His remit calls for a general overview of the whole scheme but he has a more detailed responsibility for the western tunnels from Paddington to Farringdon, while his colleague John Davis is overseeing the eastern end of the tunnelling. Both are supported by Christian Dodge who covers the whole scheme.
“Most of the design work is now done so our work is mostly focused on supporting the site teams as and when issues arise,” he says.
“It has been a great experience to spend so much time on the project and seeing it through every phase from a line on a map through to delivery”
Now the tunnel boring machines (TBMs) have started to break through into the station boxes, Black says there are a number of milestones expected over the next six months.
When GE caught up with him, he said that the first TBM on the western tunnels was just “tens of metres” from breaking through there (see news for details of the breakthrough). “We have made good progress,” he says. “The second TBM on the western tunnels – Ada – achieved 50m of construction in one day recently.”
At Stepney Green, the first TBM is expected by the end of the year and the machine launched from Canary Wharf is expected to reach Stepney Green early next year.
“The first TBM to be launched at Pudding Mill Lane has passed below the River Lee with no ground movements,” he adds.
Staying on track
He admits that there have been a few delays but is confident that the lost time will be recovered.
According to Black, the ground conditions have been better than expected so far and this has helped keep the work on track. “We expected to encounter more groundwater, particularly in the faulted areas of the Lambeth Group,” he says. “The groundwater that we have found has been under lower pressure than expected too.
“However, we are only half way so we must not get complacent.”
Black describes one success on the scheme so far as the pile removal work undertaken by Bauer to enable construction of the Moorgate station box to keep on schedule.
Some have criticised Crossrail for playing it very safe when it comes to the engineering design and Black concedes that the shafts and boxes are very robust.
“Given the location of the work and the profile the scheme has, this is not a project to experiment on,” he explains.
“Innovation is happening and we are working to ensure best practice is captured so it can be applied to Crossrail 2 and High Speed 2.”
Some of the innovation comes in the form of use of Cambridge University’s fibre optic strain monitoring.
“Monitoring the strains during construction and operation of the diaphragm walls and SCL will provide useful design information for future projects that may allow for less conservatism in the design,” says Black.
Black hopes that he and his team will be able to move onto working on Crossrail 2 once his work on Crossrail finishes in order to maximise the use of knowledge gained over the last two decades.
While Crossrail 2 may provide Black with his next job, it is clear that the current scheme has been an enjoyable experience for him.
“The scale of the work has been great and we are never sure what each day will bring,” he says.