BHP Mitsubishi Alliance (BMA) Broadmeadow Mine is an underground coal mining operation. The project team were faced with a range of geotechnical challenges, including a weathered zone which extended 30 metres below the surface and maintaining a long-term unsupported diameter of at least 3.5 metres. Compounding these issues were additional complicating factors including water hydrology and the presence of methane gas at the shaft site. To support the excavation of the shaft and fan, a robust concrete collar cap was essential. The conditions demanded a sophisticated solution to ensure structural stability and safety.
MDA employed a strategic approach by conducting a thorough geotechnical analysis of the weathered zone and deeper substrata to ensure a comprehensive understanding of the subterranean conditions. To guarantee structural integrity and manage water ingress, a hydrostatic steel liner was designed to span the entire length of the shaft. Piling and an integrated collar cap were also engineered to provide critical support during the excavation stages and life of mine. To mitigate methane risks , the project team utilised existing live trending gas monitoring systems, ensuring continuous surveillance and control of gas levels.
The Engineering, Procurement and Construction (EPC) model was designed through close collaboration with BMA , ensuring all stages of the project aligned with BMA’s vision and standards. The hydrostatic steel liners were manufactured precisely to requirements and installed successfully, providing the necessary reinforcement for the shaft. The construction of the collar cap was accomplished without incident, further validating the design’s integrity. Critically, the management of methane levels during the excavation phase was well executed, showcasing BMA and MDA’s joint commitment to maintaining the highest standards of quality, design, safety, and occupational health.
Construction of guide wall
1.2m diameter secant piles to 35m depth
Cutback & construction of collar cap
Conventional drill pilot hole 314m
Back reaming of shaft to 3.5m dia
Supply & install steel liners 314m
