Central City Wastewater Pipeline Replacement

Scope 

• 650 m of PVC gravity wastewater pipeline, 225mm – 375mm NB
• 12 No. new concrete manholes
• Break in and connect to existing manholes
• Cross under existing tram track
• Support 180m of tram track along the side of the trench

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Project Description

The overall project primarily comprised open-cut sewer replacement on existing alignments, but at a greater depth. A 65m section of existing pipe was also slip-lined with 280mm OD PE.

The pipeline installed ranged from 1.4m to 3.5m deep, with pipes installed predominantly in 4m lengths in sandy gravels. Localised well sand surface pumping were used to control the ground water.

Our team faced a number of challenges. In particular, it was necessary to protect the existing tram track network which crossed the main trench and continued alongside the trench for 120m. The depth of the new wastewater pipe in this area was up to 3.2m deep and required significant sheet piling and propping so pipe could be installed underneath and alongside the tracks.

Sheet piling was also installed in close proximity to badly damaged buildings which were at risk of further collapse. We managed this significant hazard by using a high frequency ‘city’ vibro hammer and closely monitoring vibration. To our team’s credit, these works were completed safely and without any further damage to nearby buildings.

With our specific expertise in piling and temporary works, and our organisational capability and capacity (we were able to commit a team of highly skilled personnel to the project) we achieved delivery to an extremely tight programme and within budget.