Tunnels complete on Scottish water project Mar 2012
Peter Kenyon, TunnelTalk
British tunnelling contractor Byzak has completed the main tunnelling work on Scottish Water's £22 million Airdrie Environmental Project.
Two Herrenknecht machines have completed drives totalling 1.5km, and work is now continuing to complete construction of a new 25m x 11m storm tank at the site of the old Airdrie sewage works.
  • 3.05m diameter Herrenknecht EPBM

    3.05m diameter Herrenknecht EPBM

  • Breakthrough on the main 1.2km storm tunnel

    Breakthrough on the main 1.2km storm tunnel

A 3.05m diameter TBM was used to excavate the main 1.25km x 2.6m i.d. storm water collector tunnel that will transfer water from town centre interceptors to the new storm tank.
Project manager Brian Dalton said the TBM has encountered a mix of boulder clay, mudstone, sandstone and mine workings along the route, with heavy water ingress experienced in some sections.
The main tunnel structure is lined with 2.4m diameter precast concrete segments. Peak progress rates were recorded at 60-70m per week, said Dalton.
A further 580m of 1.5m diameter interconnecting pipejacking is also being carried out as part of the project, with a second Herrenknecht AVN 1600D slurry machine being used to carry out a 120m length of this where it passes under the railway station and railway line. Work on these excavations is ongoing, but is expected to be completed later this month.
  • The exit shaft

    The exit shaft

  • 25m x 11m storm tank

    25m x 11m storm tank

Elsewhere there is directional drilling and large diameter open cut sewers at depths up to 6m. Other underground works include segmental shafts and major reinforced concrete structures for combined sewer overflows in addition to the main storm water storage tank.
Work is also continuing to construct a relief outfall pipeline that will allow discharge of screened and settled water from the new storm tank into the River Calder in cases where heavy rainfall causes it to fill over its capacity.
Under normal circumstances settled water from the storm overflow tank will be allowed to return to the existing sewerage in a controlled way, from where it will make its way to the Daldowie Wastewater Treatment Works.
  • Precast concrete segmental lining

    Precast concrete segmental lining

  • The launch pit

    The launch pit

The 90-week project, which went into its site investigation and ground assessment phase in January last year, broke ground from an 8m diameter launch pit in May, and is scheduled for completion by the end of this year (2012).
Once complete the works will alleviate persistent flooding in the Scottish town of Airdrie, relieve the overloaded existing sewerage system and enable Scottish Water to meet new EU regulations.
Contractor Byzak has worked on a number of tunnelling projects for Scottish Water in Scotland, and claims to operate the largest fleet of TBMs in the UK.
Geoff Aitkenhead of Scottish Water, said: "The Airdrie Environmental Project is one of the largest projects that Scottish Water is doing in Scotland in the 2010-2015 investment period."

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