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Laying pipes in an underground forest

15 September 2022

Large tree stumps and roots are closer to the ground surface than you would think in urban Christchurch and have been continuously discovered by the Citycare Water Construction Team working to upgrade wastewater pipes recently.

A few scoops by the 13-tonne digger on site exposes the stumps and roots and then clears them to allow access for the installation of more than 4,000 metres of new wastewater pipes and residential connections in Fendalton and Riccarton on behalf of the Christchurch City Council.

“It’s pretty cool to see the tree stumps revealed,” Project Manager Will Rodda says.

“They are quite massive and obviously this area was very heavily forested and the city was just put on top of it as they are not very far down.”

The Wastewater Renewals Fendalton and Riccarton project began in May 2021 and completion is expected in November.

New PVC pipe is replacing mostly earthenware pipe installed 70 years ago and the diameter of the new pipe ranges from 100mm to 225mm diameter depending on what is found underground.

The average trench depth is 1.7 metres, but at times it reaches 3 metres deep in consideration of the water table and the soft ground.

A raft foundation system is used so the team can work in the trench regardless of the water table depth. Trenchshields are required at this depth to ensure the safety of the crew.

As part of this contract, work was required at the intersection of Riccarton Road and Puriri St. This is one of Christchurch’s busiest streets.

This work was tackled on night shift for a week to reduce the traffic interference around the Puriri Street intersection.

Straven Road and Weka Street is another Category A intersection ahead where night shift may be required to manage the traffic situation.

The team has progressively closed off parts of the streets as they move along, sometimes allowing for one-way traffic depending on the pipe location.

Their site is busy with two diggers and trucks in constant motion during working hours.

Every street has dramatically different conditions. For example, at one end of Totara Street there was a high water-table where dewatering spears were required for construction to continue. Thirty metres away it had dried up, allowing construction works productivity to increase.

The construction crew are a mix of experienced workers and some new employees who are learning on the job under the mentorship of their colleagues.

“This project has been great job to educate the young blood coming through the business,” Will Rodda says.

Thank you to the crew for the great mahi on this project. Keep it up.