How AstraZeneca's tunnel beneath Cambridge Biomedical Campus was built

The team building AstraZeneca's tunnel on the Cambridge Biomedical Campus worked 24-hour shifts five days a week to get the job done.

They excavated 2,700 cubic metres of ground, took out enough water to fill 60 Olympic swimming pools and used a robot to spray the primary lining.

Richard Foster, project management lead for AstraZeneca, said: “It’s still very much a mining activity. You can almost imagine them with picks and shovels in there.

“You often see tunnel boring machines but this was hard graft by the guys. It was a traditional skill fortified by the technology.

“They went through 24-hour shifts and made themselves Irish stews in the night.

“The tunnel is a link from our south plot to our north. We are concentrating all of our science work on the north plot on our R&D centre, so we’ve located all the mechanical and electrical plant we can on the south plot.

“To get the power, water, cooling and heating from south to north, we did look at bridges but they are unsightly. We looked at open-cut burying of services but that’s not great because you can’t get back to them and maintain them.

“So we put a tunnel 128 metres long 14 metres below ground level directly under Francis Crick Avenue and it’s about 4.5 metres in internal diameter.”

Bryn Sturman, operations manager for construction firm Skanska, said ground modelling was carried out, before access shafts were dropped down. A 360-degree excavator that digs at the head of the tunnel first was used and a 250mm primary lining was sprayed robotically, before the final concrete lining was pumped in.

“You carve away at the tunnel first, spray it with a concrete lining then put a secondary lining to put the smooth face on,” he said.

“It’s an open excavation face. We dig two metres at the head of the tunnel then spray that to stabilise the ground. It goes off in 20 minutes and we do tests to make sure it’s hard and then dig out the bottom of the tunnel. So if there was a collapse no-one is put at risk.

“As the machine excavates it’s got a conveyor belt that pulls the spoil through the middle of the machine. Then there’s a machine behind that brings it to the shaft, then at that point a crane lifts it out to go off site. An intermediate shaft meant we always had a means of escape.”

The clay proved to be wet.

“We had a drain underneath the finished tunnel and we pumped that water out and treated it for C02, ph value and silt before discharging it.”

Could a metro system be dug beneath Cambridge?

“You wouldn’t use the same system but with the technology that’s available now, yes it’s feasible. The technology is quite overwhelming,” said Bryn.