Microtunnel Boring Machine (MTBM) Hinehōaka completed the boring for the 1,120-m storage pipeline, which includes a marine outfall, late in 2020, with construction taking place in three separate tunnelling drives using pipe-jacking methods.
Two shafts were constructed in council parkland at the bottom of the cliff face to accommodate each tunnelling drive and a third shaft needed to be constructed in the narrow streets around St Marys Bay.
This shaft was designed to be capable of retrieving the MTBM from a 3.8-m diameter shaft, 25 m below ground.
The new pipeline will reduce wastewater overflows to St Marys Bay and Masefield Beach by 95 per cent.
The high flows after rain events will be stored in the new larger capacity pipeline and pumped back into the sewer network for treatment when there is capacity.
Once complete, the new marine outfall will reduce overflows and discharge to an outfall far away from places where people swim.
McConnell Dowell said one of the major challenges the project team faced was tunnelling very close to, and underneath, restored villas worth millions of dollars in one of Auckland’s oldest suburbs.
To mitigate stakeholder issues and concerns, the project set up a ‘SiteHive’ unit to collect data while the MTBM was operating.
This unit continuously collected noise, dust and vibration monitoring readings from the worksite and this data helped proactively manage consent compliance, as well as record the impact of the operations.
When noise reached predetermined levels a photo and sound recording were taken to capture the activity onsite.
This monitoring meant the team could ensure construction activity operated within the consent conditions and any exceedance was investigated to see what changes could be made to ensure compliance in the immediate future.
The project is scheduled for completion in 2021.
For more information visit the McConnell Dowell website.