Over the last 10 years, Landloch Pty Ltd has developed and applied a distinctive approach to the design of final waste dump shapes and the management of their rehabilitation. Various elements of that approach have been recommended and/or adopted by both industry and regulators to greater or lesser degrees, and with varying levels of both commitment and success. This paper briefly outlines the approach applied, and discusses its limitations and successes, using examples from a number of mine sites. It then considers alternative approaches to landform design that have been advanced, including use of generic guidelines, attempts to mimic natural landscapes, and attempts to simply mimic advanced design methodologies. Conceptual weaknesses of those alternative approaches are reviewed, and potential for further refinement is discussed, again, using data from various sites.
Over the last 10 years, Landloch Pty Ltd has developed and applied a distinctive approach to the design of final waste dump shapes and the management of their rehabilitation. Various elements of that approach have been recommended and/or adopted by both industry and regulators to greater or lesser degrees, and with varying levels of both commitment and success. This paper briefly outlines the approach applied, and discusses its limitations and successes, using examples from a number of mine sites. It then considers alternative approaches to landform design that have been advanced, including use of generic guidelines, attempts to mimic natural landscapes, and attempts to simply mimic advanced design methodologies. Conceptual weaknesses of those alternative approaches are reviewed, and potential for further refinement is discussed, again, using data from various sites.
Computer simulations of runoff and erosion are a key element in the design of stable waste dump outer batter profiles. The Water Erosion Prediction Project (WEPP) model is used to develop erosionally stable landform batter surfaces. Although the WEPP model has been widely validated elsewhere, there is a perceived need to similarly validate the model for mine site conditions. Erosion monitoring data collected on landforms for which model parameters are known can be used for two primary purposes: a) to demonstrate that erosion rates are consistent with site targets; and b) to validate and more precisely calibrate the erosion model used in landform design, enabling continuous improvement in the design process. Model validation techniques are discussed and validation data for several landforms are presented. In general, cumulative erosion rates measured since completion of construction show good agreement with predicted erosion rates. The data have provided validation of the landform design process used; confidence in the surface stability of existing landforms that have been constructed; refinement and improvement in the design process; and a means for continual improvement in landform rehabilitation methods.
A major concern for rehabilitation and closure of waste landforms on mine sites is their long-term erosion stability. In Western Australia, regulators are requesting landforms remain 'stable' for hundreds of years or the 'long-term'. Therefore, assessing a landform's potential long-term erosion stability requires the use of erosion and/or landform evolution models and defensible erosion thresholds below which rehabilitation landform designs are considered acceptably erosion resistant or 'stable'. The Pilbara Rehabilitation Group, through four member companies-BHP, Fortescue Metals Group, Rio Tinto, and Roy Hill-initiated a project aimed at defining acceptable rates of erosion for rehabilitation landform design for the Pilbara region of Western Australia. As part of the project, a review of information relating to erosion rates on natural and man-made landforms was conducted. This review showed that a wide range of approaches have been used to define acceptable erosion rates, including linking them to rates of soil formation; maintenance of soil quality, which may include considerations of plant/crop productivity, effective soil depth, and soil organic matter and nutrient stores; rates of natural erosion in adjoining areas; potential for gully formation; and water quality impacts. Based on this review, a guideline was developed to define acceptable erosion rates for use in the design of stable mine waste landforms in the Pilbara region. The guideline uses a risk-based approach, with erosion thresholds being linked to the waste material's physical properties and the adverse environmental impacts that may result from landform failure.
Berms remain a persistent feature in waste dump landform designs as they are perceived to provide the benefits of reduced slope length, protection against future batter erosion by partitioning the slope with level or backsloping berms, and reduced flow velocity. Underpinning this rationale is the belief that the berms will be a permanent and unchanging feature that controls erosion over the long term. These assumptions are not true. Berms begin to evolve immediately after their construction by trapping sediment and having a beneficial effect over the short to medium term. Longer term, berms fill with sediment and overtop. The time it takes to overtop depends on the material, the size of the berm, and the climate. Once a berm is breached, previously hydraulically disconnected batter sections become a connected flow network that delivers large volumes of runoff from upper slopes to lower slopes that were never designed to withstand them. This process can be caused, or contributed to, by poor quality construction techniques.
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