The tunnel boring machine broke through in the town’s Saucelhill Park after completing the final section in the middle of the wastewater tunnel for the £17m project.
The project is being delivered for Scottish Water by Amey working with Donegan Civil Engineering.
The scheme is designed to improve water quality and the natural environment in two local rivers.
Tunnelling Tanya, and one other TBM before her, have been constructing the tunnel since autumn 2016 as part of the project, which also includes the installation of combined sewer overflows (CSOs) in the town centre.
Tunnelling Tanya was named by Hope Hunter, a pupil at St Charles Primary School. The TBM has a diameter of 1.5m and weights 23t. The new stretch of sewer was installed at depths of between 4m and 20m.
On the final drive of about 280m, Tunnelling Tanya removed about 5000t of rock and on the entire route an estimated 25,000 tonnes.
During the construction, she installed 109 concrete pipes that form the tunnel.
Project manager Brian Boland said: “This is a great achievement for the team as it is obviously a key moment in the project and follows two and a half years of complex and painstaking work.
“We have experienced significant engineering challenges during the tunnelling and this has meant the work took longer than we had originally anticipated. But we have overcome those challenges and I’m delighted that we have now completed the tunnelling.”
Work will now start on dismantling the TBM and covering the shafts at the breakthrough point.
The new sewer will prevent spills by intercepting the overflows from CSOs currently spilling to the Espedair Burn. It will then transfer these flows downstream to a new CSO.