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

The “HumeLink East” and the “Central-West Orana Renewable Energy Zone (CWOREZ)” transmission line projects are amongst the largest energy infrastructure projects in the state of New South Wales, Australia, encompassing a combination of over 1000 km of new transmission lines and upgraded infrastructure. These projects are crucial for Australia’s transition to low-emission renewable energy sources, enhancing grid reliability and sustainability by increasing the delivery of renewable energy across the national electricity grid. This paper describes an innovative approach to foundation design and construction for transmission towers, which has been co-developed and successfully implemented at Humelink East and is currently being assessed for implementation at CWOREZ. The paper specifically focuses on the use of micropiles connected to tower legs with precast concrete caps. Traditional transmission tower foundations often rely on single cast-in-situ concrete bored piles at each leg. However, these can present challenges that are hardly overcome when the geological conditions are not favourable as well as in difficult access areas and environmentally sensitive locations. The alternative design using micropiles offers a flexible, adaptable, and environmentally friendly solution. Micropiles are drilled to competent geological layers, allowing for precise adjustment on-site. They are less invasive and require smaller equipment, making them ideal for sites with access restrictions and difficulties. Key benefits identified from this foundation option include: enhanced suitability for a wider range of geological scenarios; reducing the risks associated with uncertain ground conditions; reduced environmental impact with less disruptive installation processes minimizing disruption to sensitive areas, such as wetlands, and reduction of noise and disturbance in populated regions; transportation and access ease with smaller equipment and prefabricated components; reduced carbon footprint thanks to significant reduction in required earth works and in-situ concrete volume. Humelink East has demonstrated and CWOREZ supports the practical benefits of this innovative foundation design. By replacing traditional bored piles with micropiles and precast caps, these projects aim to achieve significant environmental and logistical advantages. This paper presents details of some of the unique innovations (such as using precast pads only to enable partial tower erection thereby removal of piling operation from the critical path of the delivery) and the key design and performance data from these projects. The micropiled precast foundation design not only meets the structural requirements of transmission towers but also aligns with contemporary environmental and sustainability goals. By broadening the scope of well-known and trusted ground and structural engineering techniques, this solution offers a robust, adaptable, and eco-friendly alternative for transmission tower foundations, paving the way for future developments in the industry.