To support our civilisation’s requirement for carbon steel, longwall mining of the Bulli Seam at Appin and Tahmoor Collieries has occurred to recover high quality coking/metallurgical coal, being for steelmaking. The Main Southern Railway crosses the footprint of both mines, and it was therefore important to manage the risk to infrastructure and public safety during longwall retreat in this strain-driven environment. One technical issue is the response to subsidence-induced ‘valley closure’. This has occurred in both gently undulating Wianamatta Group Ashfield Shale and the steeper upper Hawkesbury Sandstone valleys.
This paper covers the observed responses of embankments on the Main Southern Railway and the heritage railway Picton to Mittagong Loop Line, and illustrates the responses of the embankments to valley closure that produced up to 11% strain, as well as illustrating displacement field development and derived principal strain vectors. The responses of four embankments are presented beneath which longwalls have been successfully extracted, and done so without adverse impact upon public safety. An understanding of the strain-driven responses of the embankments is presented.
This paper is adapted from and builds upon a submission to 11th Triennial Conference on Mine Subsidence – refer to Leventhal et al (2022).