Investigation of Shear Strength and Breakdown of Mine Waste Rock

To investigate the shear strength of mine waste rock, large-scale laboratory direct shear tests were carried out on Breccia, Weathered Shale, Breccia on Weathered Shale, and Weathered Shale on compacted clay, under applied normal stresses of 250 kPa, 500 kPa or 1000 kPa. The Breccia, Weathered Shale and Breccia on Weathered Shale samples were loosely-placed and tested dry, representing the bulk of the waste rock dump volume in the field. The Weathered Shale on compacted clay was tested under both dry and wet (the worst case) conditions to represent the interface between Weathered Shale and compacted clay liners within waste rock dumps. The peak shear and normal stresses were corrected for area reduction and plotted to provide the shear strength envelopes, from which shear strength parameters were recommended. To assess the potential for breakdown of the waste rock on wetting, particle size distribution curves were obtained by dry and wet sieving. Also, slake durability indices were obtained for Breccia and Weathered Shale by carrying out slake durability tests. Overall, the results indicated negligible potential for breakdown of the Breccia and Weathered Shale on wetting.