IT is Glasgow's Queensferry Crossing - but the Shieldhall Tunnel is an impressive feat of engineering few will ever see.

Deep under Glasgow's streets, a team of engineers and miners has been tunnelling across the city to create a new sewage system.

Earlier this month the tunnel met a milestone when a giant state-of-the-art tunnel boring machine (TBM) reached the end of its 3.1mile route and broke through in Queen's Park.

Once completed, the tunnel will be able to store the equivalent in waste water of 36 Olympic-sized swimming pools.

It will help to improve the water quality of the River Clyde, reduce flooding in under threat parts of the city and help make the city's sewage system more environmentally friendly

But the project has had other additional benefits for Glasgow's residents.

Dominic Flanagan, project manager, said: "There have been side benefits that have developed as the tunnel work has gone on.

"There are the obvious things, such as the work we have done in Queen's Park to improve the path surfaces and the additional cricket pitch we are installing, as well as a pétanque area in a nod to our French colleagues.

"There are benefits to the households that are affected by flooding and will now have this reduced.

"But there are others that people may not realise."

One of these is the filling in of old coal seams in the Queens Park area.

Some of the coal seams are between half a metre and one metre and a half and more than 15000 tonnes of grout was used to fill these in.

During investigations of the ground, around 4000 boreholes were made.

Records of seam locations from the Coal Authority go back only so far, meaning there are undocumented mines.

The Scottish Water team had help from JWH Ross, a 160-year-old Glasgow minerals consulting firm that advised on the extent of minerals below Glasgow's surface and of the problems they can create.

One of the surprise finds during preparatory works for the Shieldhall Tunnel was a 60 metre deep mine shaft under Titwood Road.

Dominic said: "There were indications that something was there but we didn't know what it would be and there were no records of this mine shaft.

"We've filled it in now and so that makes the area that bit safer."

Coal seams under the paths at the Victoria Road entrance to Queen's Park now mean that area is safer too.

Previously, Dominic said, Queen's Park Arena had applied to hold a market at the paths and were turned down due to safety issues caused by the coal seams.

Now the ground is secured, the market could go ahead.

When designing the Shieldhall Tunnel, engineers are thinking ahead to the next 120 years, making sure the tunnel will last that length of time.

During the peak of its construction almost 150 people were involved from countries such as Canada, Zimbabwe, Iran, Turkey, France and Greece.

Bosses had to safely negotiate three railway lines and the motorway in taking the tunnel underneath the city.

Dominic said: "There was a lot of preparatory work before anything could get underway.

"We had to look at how can we provide a level of assurance to Network Rail and Transport Scotland, to make our other stakeholders happy and comfortable.

"We chose to use Glasgow's parks in order to minimise disruption to residents, going under Queen's, Bellahouston and Pollok parks, but we had the challenge of ensuring we caused no disruption to railways and roads."

In Glasgow there have been no major tunnels built in the past 50 years and so that caused its own unique challenge.

Dominic added: "If you take a tunnel job in London, they're working underground all the time in London so you know the ground is going to be London clay or London chalk.

"How many tunnels have been built in Glasgow in the last 50 years - none really, it's not something that happens every day.

"We made 180 bore holes along the route at different depths down to 60 metres into the ground.

"There's enough information to tell you what you should find but what you do find can be a different matter.

"In terms of engineering and endeavour, we are more complex than a bridge. This is the Queensferry Crossing for Scottish Water.

"But most people will never see what we've created or know that we are here. In fact, if people notice us then it means we've done something wrong."