Methods for simulating measured field responses for long-term performance of mine waste cover systems

Authors: Shurniak, RE; O'Kane, M Download Paper

DOI https://doi.org/10.36487/ACG_repo/908_36

Cite As:
Shurniak, RE & O'Kane, M 2009, 'Methods for simulating measured field responses for long-term performance of mine waste cover systems', in AB Fourie & M Tibbett (eds), Mine Closure 2009: Proceedings of the Fourth International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 473-484, https://doi.org/10.36487/ACG_repo/908_36



Abstract:
Mine waste cover systems are typically a key component of mine closure plans. For this reason, and because cover systems generally encompass a large component of mine closure costs, it is critical that an acceptable level of risk in determining long-term cover system performance is achieved. Numerical simulations using computers are the most common tool used to evaluate the long-term water balance of mine waste cover systems. However, the accuracy of such simulations is dependent on the quality of data available to determine model inputs. The preferred method for ensuring the most representative model inputs are used is to simulate past performance of the cover using data generated from field performance monitoring, referred to as a field response model. The inputs from a model that provides a representative simulation of measured field responses can then be used as a basis for evaluating long-term mine waste cover system performance. Field response models attempt to recreate complexities of the real world in mathematical terms. Hence, all facets of a cover system’s water balance must be addressed in the model. This includes, but is not limited to, soil-plant-atmosphere interactions, evolution (weathering) of the cover layers, and heterogeneity (as well as layering) of materials. This paper presents the current methodology used by the authors to simulate these processes. In order to illustrate the methodology, results are presented for field response models developed at three sites situated in starkly contrasting climatic regimes: an arid to semi-arid site, a humid subtropical site, and a subarctic site. The examples show that following such a methodology can result in a highly accurate set of model inputs in almost any climatic region. Field response modelling is the most appropriate method of determining and validating a set of model inputs for a mine waste cover system. However, field response modelling requires the accurate prediction of complex soil-plant-atmosphere interaction with time. Hence, the modelling process requires many iterations before accurate estimates of field responses can be realised. The changes to the model made between iterations must be deliberate and documented to limit the number of iterations required to obtain calibration. This paper presents a methodology for cover system field response modelling that can be used to develop a calibrated field response model. The methodology is discussed, and examples of the application of the methodology are provided to illustrate the process. Application of this, or a similar methodology, is fundamental in developing a model that can be used as a basis for evaluating long-term cover system performance under a variety of conditions.

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