Mott MacDonald’s combined approach to geotechnics and underground structures has advanced innovation in the cut-and-cover tunnelling market since it was first used on the Channel Tunnel works.
A radical decision in the 1980s to unite disparate geotechnics and structures teams at the business which is now known as Mott MacDonald has led to several decades of pioneering major cut-and-cover tunnelling projects across the world.
Derek Winsor joined the company’s Croydon-based foundations and geotechnics division when it was launched and has worked his way up to metros and civils divisional director.
He believes the merger of the two teams shaped and enabled a pioneering approach to subterranean schemes over the ensuing years.
Although Mott MacDonald’s predecessor businesses were involved in bored tunnelling schemes in Europe as GE launched in 1968 – as well as on cut-and-cover projects in Asian cities around this time – the story really begins with the Channel Tunnel.
Mott, Hay and Anderson merged with Sir Murdoch MacDonald and Partners towards the end of this megaproject, meaning the consultancy as it is today emerged with a big role to play on subsequent landmark cut-and-cover projects.
“We were the consultants for all the land-based tunnelling for the Chanel Tunnel, which was a massive job at the time,” says Winsor. “There were about 1M hours of work on the project overall; it was unheard of.”
ph0716 delhi metro cut & cover
Just as the UK was shaking off its colonial past and embracing the Continent with the connection to France, so Mott MacDonald was seeking new ways of working.
“I was involved in the under-land elements, which were all cut-and-cover structures, running from the UK portal to the Folkestone terminal,” remembers Winsor. “We did a lot of cutting-edge engineering to overcome the challenges on the project.”
To aid efficiency and productivity, specialists from the formerly very distinct geotechnics and structural engineering teams were brought together allowing a new way of looking at underground challenges.
“Prior to this point, as is common in other organisations, the geotechnics department was seen in the wider company purely as a service provider to delivery teams in other departments,” says Winsor. “Geotechnical engineers were often remote from the project delivery team and this was an obstacle to fully understanding the problems to be solved.”
Following on from work on the Channel Tunnel, the newly formed team (and its untethered way of working) continued to grow and embrace global innovations within the industry such as the Observational Method, pioneered by US soil mechanics engineer, Ralph Peck.
This system allows for more economic and safer design with pared-back requirements made possible by close monitoring and ready-made contingency plans. On the project to link France and England, it reduced cost and saved time.
“Using the method was perceived as a risky move but we argued it was safer as it makes sure you pay a lot of attention to construction sequencing and mitigation methods,” explains Winsor.
“Also, you don’t put in props where you would otherwise have to – and there is a high potential for injuries to occur just from installing and removing 20t props.”
Buoyed by the success of the new division and its use of the Observational Method, Mott MacDonald went on to work on the Limehouse Link in the 1990s.
The engineering consultancy was brought in by the construction joint venture of Balfour Beatty and Fairclough as the east London road tunnel encountered significant challenges. Value engineering using the observational method slashed about £50M from the project, according to Winsor.
Winsor – who has worked in the division since its creation – says having the different functions working side by side created enormous opportunities.
“It was recognised as an unusual idea,” he says. “But there was a US consultancy doing it – Mueser Rutledge, who built the foundations for the World Trade Center.”
Perhaps ironically, one of the next projects Mott MacDonald’s US-inspired team took on was across the Atlantic in Massachusetts. Winsor, now project managing, moved to the US to oversee a package on the Boston Central Artery Tunnel – informally known as the Big Dig.
ph856 msheireb 01 apr2015
This time the team had to spend 18 months persuading the client to look beyond the cut-and-cover technique with a radical solution of using three jacked-in-place boxes on a previously unimaginable scale to create multi-lane highway tunnels under the approach to the busy South Station to form an interstate highway interchange.
“A jack box can go in with as little as a metre of ground above it,” explains Winsor. “It was the only way to achieve the project aims so close to a huge working rail station.
“Our longest was 150m long, 24m wide and 12m tall. Jacking had gone on before but nothing of this scale.”
The divisional structure allowed our people to think outside – or perhaps in this case inside – the box.
“We had the confidence to put forward solutions because we were combining geotechnical understanding with structural techniques. We had the belief to innovate from the experience of previous schemes.”
“By the turn of the last century, our expertise has travelled around the world to make complex underground construction possible.
“Delhi Metro was the next big one I worked on, from 1999 to 2005,” says Winsor. “It was the first major subway in the country and the first serious use of diaphragm walling in the city outside of shallow hotel basements.
“My contract was six stations and we didn’t really know the ground conditions when we started, as nothing this big had been dug in Delhi. The project needed a close relationship between construction team and ground information, which of course we had.”
Back in the UK, Heathrow Airport also needed Mott MacDonald expertise to create the 15m deep, 600,000m3 basement with 2km of diaphragm walls for an expanded Terminal 2B.
“We had been involved in Terminal 5 prior to that, and we took a lot of trouble testing ground conditions,” says Winsor.
“We were able to take data from Terminal 5 and tune up the performance of 20m-long diaphragm wall panels for Terminal 2B. It saved millions of pounds and sped up construction.”
The company is currently completing work on two stations as part of the Doha metro system in Qatar.
“The main hub station at Msheireb is a three-line intersection and accepted 12 tunnel boring machines at one time,” says Winsor. “The scale was challenging.”
Current UK projects for Mott MacDonald include the Northern Line Extension and ames Tideway.
Internationally it is active in several locations, including Singapore and Australia.
Although innovation is playing a major part as always – most recently with the use of sophisticated 3D modelling techniques in Doha – the basics of the division founded back in the 1980s are still serving Mott MacDonald well.
“Geotechnics and foundations are just as cutting edge and fresh thinking as it was in the 1990s,” says Winsor, now leading the team he joined all those years ago.
“Collaboration is still key and there is a definite buzz around it. The close interaction of the two specialisms attracts interest from talented individuals and helps us to recruit graduates and give them a rounded development.”
With this in mind, Winsor predicts a healthy future for the team and Mott MacDonald in this sector. “I see no reason the division won’t still be leading the way on cut-and-cover tunnelling design and construction in another 50 years,” he says.
This article was produced in association with:
mm logo rich black c40 k100