Alternative Foundation Design for Recent Transmission Line Projects in Australia Using Micropiled Precast Concrete Caps-Paper

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The paper presents a micropiled precast foundation system developed for transmission towers on the HumeLink East and Central-West Orana Renewable Energy Zone projects in New South Wales, Australia. These large-scale projects span more than 1,000 km of planned transmission infrastructure and face challenges including remote access, variable geology, and environmental constraints.<br /><br />The alternative replaces conventional large bored piles with a precast concrete cap containing four conical openings. Micropiles are drilled through the openings and socketed into rock, then reinforced with high-strength bars and grouted. The cap’s shape and connection details allow tower erection to begin before micropiles are installed, helping separate foundation drilling from the construction critical path. Factory-produced caps also improve quality control and reduce on-site work.<br /><br />The design uses strut-and-tie principles and was assessed for varied soil and rock conditions, including different rock strengths and overburden depths. Numerical soil–structure interaction analysis predicted maximum vertical settlement below 3 mm. Prototype trials included cap casting, installation rehearsals, and cone, tension, and compression load tests.<br /><br />Compared with bored piles, the system requires smaller equipment, less demanding access infrastructure, and fewer concrete supply operations. The authors report improved safety and productivity, reduced environmental disturbance, and costs comparable to bored piling. For HumeLink East, estimated embodied carbon fell by 13%, fuel-related emissions by 29%, and total emissions by 18%. The paper concludes that the tested system is a robust, adaptable option for transmission tower foundations, particularly in hard-to-access or environmentally sensitive locations.

Keywords

micropiled precast foundation

transmission tower foundations

HumeLink project

renewable energy transmission

precast concrete cap

socketed micropiles

strut-and-tie design

soil-structure interaction

embodied carbon reduction

environmentally sensitive sites