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BHL - WHN A 400kV Overhead Transmission Line

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CLIENT  Balfour Beatty United Group Ltd JV
PRINCIPAL  Transpower
TIMEFRAME  March 2010 - March 2012


As part of the North Island Grid Upgrade, we were engaged by Transpower to install the driven steel tube tower foundations for over 100 tower sites. The contract duration spanned over two years with site locations scattered from south Auckland to Brownhil, near Taupo.

Initially our Nippon Sharyo DHJ-40 Pile Driving rig was committed to drive the 900mm diameter tubes up to 30m, however continual analysis of ground conditions resulted in a number of sites requiring 1200mm diameter tubes and our PC300 pile driving rig was mobilised to the project to undertake these larger size piles.

Each tower site was finished with either four or eight driven piles (single or twin pile for each tower leg), with sheet piling and concrete coring also being incorporated into our scope of works.

Then approx. 6 months into this contract, we were successful in a design and build tender bid for monopole foundations running adjacent to Lake Karapiro.  Seven towers had been designed as a monopole due to their high visibility, and our single pile design generally involved a 2400mm diameter bored concrete pile up to 17.5m depth, with a 3500mm diameter enlarged head 4.0m long to incorporate the bolt cage for connection to the towers.