36 | “The excavation of the shaft was done in 1.5m stages and each 1.5m stage took a week. It sounds like a slow process but using shotcrete and soil nails instead of building permanent walls as we excavated down actually saved a lot of time.” New intake gate brings extra level of protection from page 34 Downer - Tekapo REGIONAL DEVELOPMENT Downer NZ’s role in leading this challenging project was recognised at the 2021 Construction Excellence Awards when the company was named as overall winner for projects valued between $5 million and $20 million. “We were one of 15 major projects in that category – we’re very proud to have been picked as the best overall.” A 14-metre diameter vertical shaft had to be constructed to enable the gate’s installation some 22m below ground, breaking into the existing intake tunnel to install a permanent steel stent. Access to the intake tunnel to Tekapo A was restricted by Genesis in order to maximise renewable generation from the scheme during the peak demand season with works having to meet just two shutdowns of 17 and eight weeks respectively. The first shutdown by Genesis started in January 2020, allowing excavation work to proceed above the intake tunnel and for the stent to be installed to sustain power generation. Works continued during the 2020 COVID-19 lockdown as an essential service. The second 8-week outage was split over late 2020/early 2021, enabling delivery of the gate and its hydraulic operating ram. “We had five or six different trades on site at the same time during that second outage to do electrical and mechanical works, air conditioning, pumps and so on and make sure everything was ready for commissioning. Genesis was very satisfied to have the project completed on time and under budget.” Downer worked collaboratively with Genesis designers AECOM and subcontractor Parfitt Construction throughout the project. “Parfitt Construction took on the bulk of the excavation and concrete work and we had workshops with AECOM to look at construction options. That is how we came to develop and install a permanent stent, rather than a temporary solution. “It was a smart piece of engineering that saved Genesis time and money.” Before the main works started, preliminary earthworks and construction of a retaining wall were carried out to clear a footprint for the shaft. “The embankment was practically at a vertical angle. We took it back in layered stages and shored up the ground using drilled and grouted soil nails and spraying shotcrete over it. We used the same method to dig the shaft and shore up the sides prior to installation of the permanent shaft wall. “The excavation of the shaft was done in 1.5m stages and each 1.5m stage took a week. It sounds like a slow process but using shotcrete and soil nails instead of building permanent walls as we excavated down actually saved a lot of time.” The depth involved meant working under revised and stringent mining regulations that many on the team were not familiar with. “The WorkSafe High Hazard Unit guided us through it. The regulations are strict for good reasons as there are a lot of risks when working underground.” A 120 tonne crane serviced the shaft from the top with only one piece of machinery – for excavating or drilling – deployed at a time, carefully lowered into place. Access for machine operators was by a staircase at the side of the shaft. No workplace injuries occurred on the project. When it came to fitting the gate, made by Dunedin’s Farra Engineering Ltd, tolerances were very tight and the gate itself was lifted into place in two halves. “It had to fit between pre-installed stainless steel runner plates and the gate had to seal. In some places there was less than a millimetre tolerance for getting the gate seals to fit between the runner plates.” Plant commissioning tested the gate under various conditions performing as expected, achieving an excellent seal/isolation of the lake. When it came to fitting the gate, made by Dunedin’s Farra Engineering Ltd, tolerances were very tight and the gate itself was lifted into place in two halves. 03 684 8034 Mobile 027 4399 408 info@coolair.nz www.coolair.nz 3 Cliff Street, Timaru Cool Air are proud to have completed the ventilation & air conditioning for the Tekapo A Intake Gate supporting DOWNER on this Project. • Refrigeration • Air Conditioning • Heat Pumps • Ventilation • Ducted Systems • Freezer Rooms • Cool Rooms www.jle.co.nz Supply, Installation and Commissioning of MCC Switchboards, Industrial UPS systems, Field Distribution Boards, Back-up site generation, PLC Control Systems, Lightning Protection and more. JLE - The trusted choice in the industrial and infrastructure sector, delivering electrical and mechanical solutions through collaboration with our Aotearoa and international partners. We would like to thank our business partners; Genesis Energy, Downer NZ, ABB, Aorangi Electric, G&H Comms. JLE are proud to be associated with the Tekapo Intake Gate Project Electrical power & control systems installed. CONGRATULATIONS DOWNER! JLE Team members outside the intake equipment room. 0800 ASK JLE 0800 275 553
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