The Terrace Sewer & Stormwater Renewal

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Customer:

Wellington Water

Consultant:

Aecom

Date:

Nov 2016 – Aug 2017

Type:

Mobile Plant Fleet, Underground Services, Deep Trenches, Traffic Management, Dynamic Pipe Bursting

Customer Type:

Government & Local Government

Scope:

Online replacement of 130m of 250 OD PE sewer & 180m of 525/450mm RCRRJ Stormwater by open trenching in the same trench.
Online replacement of 260m of 250mm OD PE Sewer by dynamic pipe bursting.
Online replacement of 120m of 400 OD PE Stormwater by dynamic pipe bursting.

The Terrace is an iconic street in the heart of the capital’s business precinct, with government departments, head offices and large corporations side by side with each other down each side of this 19th century street. The footpaths are bustling with business professionals and civil servants and the carrigaeway is packed with commuters and delivery vehicles moving about the city. The existing sewer and stormwater pipes under this busy road had insufficient capacity and were in poor condition. Some were over 120 years old. They were buried deep under layers of thick asphalt, reinforced concrete sub-base and overlaid with spaghetti-like networks of important communication, electricity, gas and water services that keep the city moving.

The work to replace these assets was complex and presented a number of significant risks in a high profile environment. Some key risks that were managed include:

  • Traffic management in a busy urban street with heavy traffic and pedestrian movements.
  • Deep trenching around congested services with a variety of sheilding and shoring solutions used to protect the trench.
  • Overpumping of high wastewater flows during an online renewal and protection of the stormwater network (lower and in the same trench throguhout the work).
  • Interface with businessesd and other construction sites adjacent to the work to maintain access and ensure that adjacent activities did not present additional risks to each other.

Part of the scope was to replace an existing 375 dia. RCRRJ stormwater main with a new 400OD PE100 pipe by dynamic pipe bursting. This is a large diameter pipe burst and it is not common in the market place. We completed the burst using out Grundoram Koloss tool with a back bursting fitting (this tool is capable of bursting up to a 600 dia. pipe).

There was significant design change during the work due to a clash of grades between the proposed alignment and existing services. The project team collaborated well with the consultant and customer to keep the project moving and offered value engineering options that addressed budget concerns. The final product is of a high quality and was delivered within the overall programme timeframe.

Relationships with surrounding businesses were positive throughout the construction due to proactive communication and respectful behaviour from the site team. Feedback was excellent and included this from Brandon’s solicitor practice:

“GPFL’s staff have been absolutely fantastic to deal with while this work has been undertaken. They are a cheerful bunch of men who are polite, obliging and patient when we have needed access to and from our driveway.”

 

This type of work is at the core of our business and this project demonstrates some of our key capabilities. The project was recognised with a best project award from CCNZ Wellington & Wairarapa Branch in 2018.

 

 

400 OD PE Pipe Burst of existing Stormwater using a Koloss Grundoram adapted to “back burst”

Deep trenching under tight TM conditions with high vehicle and pedestrian movements. Trench shielding/shoring around congested underground services and to support existing scaffold structures

Deep trenching under tight TM conditions with high vehicle and pedestrian movements. Trench shielding/shoring around congested underground services and to support existing scaffold structures

Installation of sewer main by pipe bursting. Long TM site under heavy traffic flows