Tauranga Southern Pipeline Harbour Crossing

Project involving the installation of 1600m of 915mm OD pipe via Horizontal Directional Drilling as part of the Southern Pipeline Sewer. Installation depths up to 35m below the Tauranga Harbour and included a 915mm OD steel outer casing installed via HDD, with 800mm OD PE pipe slip lined into the steel casing. HDPE pipe was butt welded into a number of strings then intermediate butt welded together during slip lining into the steel casing. 

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ARAL’s Nigel Parkinson was involved in the pipeline project from May 2016 during the tender documentation and feasibility design stages. The project had identified significant challenges and risks with Geotechnical conditions and alignment selection, yet were preparing to go to market with a single PE pipe trenchless or trenched solution under NZS3916 Design and Build. During the tender evaluations a number of concerns were identified regarding installation loads on the PE pipe and potential for hoop stress failure and pipe collapse. It was also noted that in terms of international complexity and risk, the proposed trenchless installation was considered a high-risk operation as currently proposed. Nigel worked alongside a design review team from around NZ, Australia and the United States to provide a comprehensive and robust review of all aspects of the HDD and alternative trenchless installation techniques. Based on the design teams' recommendations, the tenders were put on hold and additional geotechnical investigations and design work completed. Based on this work, a number of design changes and specifications were made and the tender docs reissued for pricing by the previous tenderers.  

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The solutions included specifying a steel carrier pipe for HDD installation which was able to withstand the anticipated installation loads, then sliplining the PE product pipe in place. This design change and the supply of an additional suite of geotechnical information in proximity to the proposed tenderers alignments was considered to reduce the risk rating from very high to medium. 

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Since tender award Nigel has provided expert trenchless construction advice and Engineers Representative Assistance through the construction stages with the project currently approaching commissioning. He travelled to Australia to conduct pre-shipment inspections of the drilling and support plant, assessing the condition and capacity of the plant to undertake the proposed work. He then supported the TCC team remotely from Auckland and then at TCC request made himself available to regularly visit site and observe the trenchless operations culminating in the 5-day long 24hr pipeline installation operations. He has fulfilled numerous roles for TCC and become an invaluable resource for the Council.  

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All project work had to be integrated into TCC’s document management system – ‘Objective’. Nigel and the project team adopted this tool, working within the system both in the TCC office and via remote access from Auckland. Working alongside Chris Thomas and the rest of the project team, the document records for this project are extensive and have been invaluable in assessing contractor claims, managing programme, risk and administering the contract. 

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The Engineering team had to provide regular updates to the TCC Project Manager, for reporting to the project advisory board (PAB) and TCC CEO. Given the high risk and high-profile nature of the project, TCC appointed a PAB comprising a number of former construction and consultant directors to advise on the project risks and direction at regular intervals and in significant events.