Resistance of a soapstone waste rock to freeze-thaw and wet-dry cycles: implications for use in a reclamation cover in the Canadian Arctic

Abstract

Engineered covers are commonly used to control the potential environmental problems related to acid mine drainage and contaminated seepage from tailings and waste rock storage facilities. Cyclical environmental weathering processes, such as freeze-thaw and wet-dry cycles, can cause rock degradation. However, these processes are usually not explicitly considered when selecting coarse-grained geomaterials for use as cover materials, even though they could be responsible for a decrease in cover performance over time. This study assesses the durability of a non-potentially acid-generating soapstone waste rock unit with respect to freeze-thaw and wet-dry cycles. This waste rock is intended for use as a cover material for the reclamation of mine tailings and waste rock storage facilities at a site in the Canadian Arctic. An experimental approach was developed based on existing standard and non-standard laboratory methods. Degradation tests were conducted on rock cores, rock slabs, and < 50-mm granular materials. These tests examined changes in selected physical and mechanical properties before and after 20 and 80 freeze-thaw and wet-dry cycles. The high density, low water absorption index, and low apparent porosity of the fresh waste rocks suggested excellent rock durability, which was confirmed by the degradation tests that showed acceptable mass losses and negligible evolution of the material’s physical and mechanical properties over time. Considering the results of this study, the studied waste rock unit was identified as an excellent construction material for mine closure purposes. The experimental approach developed for this study could be included in cover design methodologies and applied widely in the selection of rocks for use in mine reclamation schemes in cold regions.