The scheme involves upgrading the sewer underneath Haymarket Terrace, which was built by Victorian water pioneers but is now being improved to meet the city's modern needs.
So far, two tunnellers have helped progress the project by hand digging 90 tonnes of debris.
And while high-tech equipment is being used on the project, a challenging section required a more hands-on approach, with Gerard Boyce and Thomas Peoples using tools to literally dig their way through a 20-metre stretch over a two-week period.
The busy junction outside Haymarket Station was hand tunnelled to avoid damaging a complex web of utility infrastructure such as electricity, gas, telephone lines and broadband.
Scott Fraser, Scottish Water's Corporate Affairs Regional Manager, said: "The original sewer was built by Victorian engineers using old-fashioned methods. Whilst we're using a range of high-tech solutions to help progress this vital work to upgrade the sewer at Haymarket, we've had to use those same basic tunnelling techniques as the Victorians to clear this particular section.
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"The £2.5m work at Haymarket is one of our most high profile projects due to its busy location and the small, challenging work site. This unique environment means we are using traditional techniques combined with modern technology, to efficiently tunnel under a section of road with a large number of vital utilities, which if damaged could impact local residents and businesses.
"The two tunnellers used modern equipment such as gas detectors, laser technology and hydraulic drills to cut the rock face whilst the earth was then shovelled by hand into a traditional cart on rails, which was then lifted by crane back onto the surface."
ASG Tunnelling & Civil Engineering Services was appointed by Scottish Water to precisely hand excavate sections of tunnel where tunnel boring machines are not appropriate for the terrain conditions
John Doherty, Managing Director, said: "We are one of the few remaining family run firms that have the knowledge and experience to take on these hand tunnelling projects.
"I'm extremely proud of hand tunnellers Gerard and Thomas who have completed this work in challenging conditions due to the confined space underground and the sheer number of utilities we encountered and had to work around to get the section completed."
(LM/MH)
