Waste landform cover system and geometrical design - integration with waste placement and landform optimisation approach

摘要

One of the foremost challenges in mine landform design is the design of stable waste landforms that provide geochemical and geotechnical stability that resist long-term erosion and degradation of cover systems. Surface instability can expose reactive waste and lead to acid and metalliferous drainage, increased sedimentation of downstream waters, cause poor revegetation or related environmental impacts.The landform surfaces are the interface between the mine landform and the surrounding environment and therefore affect long-term environmental impact. This paper focuses on practical design guidance from early concept development through to the quantitative assessments required for detailed design. This extends to discussion on overall geometry of landforms, veneer stability, cover system design and the selection of cover system materials. These factors should be considered together and integrated with internal waste landform design to provide confidence in design, and improve closure outcomes. Surface water is intrinsically linked with surface (in)stability and the landform features, such as cover system selection, plateau grading, selection of embankment profiles and drainage structures, require an integrated approach to ensure that the design meets the stability objectives. Landform cover systems are commonly adopted for closure to manage water and oxygen ingress. In many instances the cover system forms a critical component of the closure solution to limit/mitigate the impacts of acid metalliferous drainage, and to enable rehabilitation success. Cover systems are most effective when developed in unison with the landform construction and geometry to improve the stability of the cover system, to accommodate surface water management features, and to realise efficiency in materials scheduling. Embankment stability is affected by geometry, including slope lengths, gradients and catchments. Longer, shallower slopes have larger catchments and potentially more runoff, whilst shorter steeper slopes have less catchment but (owing to the steep grade) require less energy to mobilise waste. A balance needs to be reached for best performance which is unique for the specific material types and hydrological setting.