66kV Bromley to Milton

Some of our underground cables in Christchurch City are 40-60 years old. While these older cables are still functioning, they are vulnerable to earthquakes. Replacing these cables to strengthen the network is a major programme of work for Orion. One of the initial projects involved installing a new underground cable from Bromley Substation to Milton Substation.

This award winning project involved installing 7.5km of new cable through some of Christchurch’s busiest roads and intersections. Working through residential and business areas required extensive stakeholder engagement to manage the high impacts of the long-term construction.

Key Facts:

• Construction Works: The project spanned multiple level 2 roads, including a 1.5km stretch down State Highway 76 (Brougham Street) that averages over 20,000 vehicles per day. Using a model to predict traffic delays, the team created a successful programme of night works on Brougham Street, backfilling trenches each night to ensure daytime traffic wasn’t impacted. We created custom-made 32mm thick steel plates that allowed for the safe reopening of intersections to heavy traffic, maintaining traffic flow and safety.
• 7.5km of New Cable: The new underground power cable was delivered to the site on large drums, each 4.5m in diameter and weighing around 27 tonnes. A total of 27 drums of cable were required for the new circuit from Bromley Substation to Milton Substation—three cables per trench. The new cable is supplied by Prysmian Group and takes around 12 months to procure and manufacture. This is the largest physical cable installed by Orion on its network.
• Managing Stakeholder Impacts for Long Durations: This project ran from November 2022 to June 2024. Communications prior to site establishment were vital to ensuring a no-surprises approach to the construction. These conversations needed to occur before the first road cones were set up onsite. We strongly believed stakeholders needed to know we were arriving, what to expect, and how we could help them.
• Specialised Designs: On this project, we had to cross through the Linwood Canal, which was made of multiple pre-cast concrete panels. We also had to cross the cables through the top half of a brick barrel stormwater while maintaining the integrity of the bottom half. Our teams worked with Orion and various specialists to design custom solutions for these challenges.
• Design/Service Crossings: There were approximately 700 service crossings on this project. Isaac potholed and provided a recommended design to Orion for how to navigate these services with the cable. One particularly challenging section was along Hargood Street, which had a very shallow water table. All of the sewer and stormwater laterals on this road were laid too shallow for the cable to go over the top. Instead, the cable had to run beneath, often at depths greater than 1.5m in very wet conditions.
• Deep Trenching: Over 3,580m of trenching at 1.5m deep or greater was required to avoid services.
• Extensive Dewatering and Environmental Management: Controlling the groundwater was a significant challenge. The project spanned many different types of ground, such as sand, clay, and gravel. Isaac had a dedicated dewatering team that worked two weeks ahead of the trenching crew to set up well points and then run the pumps to get the ground dry.

The scale of the 66kV project meant that there were many residents and businesses directly affected by the works. With these vast numbers and range of stakeholders, the team identified that proactive interfacing with the public would be critical throughout all phases of the project: before site establishment, at project commencement, and regularly throughout—right through until the project’s completion.

While navigating this project, our team deployed various community engagement activities to support local businesses and residents:

• Staging Works to Benefit Business Access Time: For example, the industrial area on Maces Road had many heavy haulage units that required the full road width to turn in/out of the entranceways. We had approved TMPs to complete this work during the day, however, we committed to working through areas at night to minimise disruption to the business. Orion also played a key role by approving additional ducted areas so that we could trench and reinstate much quicker and reduce the time spent in these areas.
• Timing Works Outside Te Waka Unua School: The bulk of the trenching could be completed during the school holidays.
• Special Signage: Isaac made special signage to show various generic messages such as “Open for Business”, “Customer Parking Ahead”, “Temporary Parking Here”, “Business Access Here”, and “Shop Access Ahead”.
• Local Functions: The team held functions at local bars and clubs that were impacted by the works. We also purchased lunch directly from affected businesses, including a famously successful curry day in conjunction with a local dairy.
• Crusader Day at Te Waka Unua School: The Crusaders visited and spoke to the children. Afterwards, the children and teachers enjoyed a sausage sizzle put on by both the Isaac and Orion staff.

This project reached a successful completion in June 2024, achieving a high level of satisfaction from both our client and stakeholders.