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Rainfall infiltration into and seepage from rock dumps - A review

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... The angle of repose b is highly relevant for assessing waste rock pile stability; its average value is often close to 37°(± 3°; e.g. Baumer et al. 1973;Piteau Associates Engineering 1991;Quine 1993;Aubertin et al. 2002b;Williams and Rohde 2008;Aubertin 2013). ...
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This paper presents the main results from an investigation into the slope stability of unsaturated waste rock piles with various configurations and surface recharge conditions. The analyses first consider waste rock piles with different internal and external configurations, under steady-state conditions to evaluate the effect of the pile geometry on the factor of safety. Transient analyses are then conducted to evaluate the influence of rainfalls of different intensities and durations. For six waste rock pile configurations, the results illustrate how the external geometry of the pile influences the factor of safety. The results presented here show how surface infiltration (water recharge), external geometry, and internal pile features affect unsaturated water flow, pore water pressure (matric suction), and material strength, which in turn influence slope stability. Despite the relatively large imposed recharges, following major precipitation events, the results indicate that the decrease of the factor of safety FS is relatively small when compared with the effect of other influential factors. The results also demonstrate that the external geometry of the waste rock pile has the most significant impact on the factor of safety, indicating that pile stability can be controlled with an appropriate design. Waste rock piles with a uniform slope (single bench) should be avoided as this construction method leads to the lowest factor of safety. The overall results clearly demonstrate that the best way to improve the stability of waste rock piles is to use a design and construction method with benches of limited size.
... The authors stated that fractures played a critical role in the process of rainfall infiltration and water intake into exposed fractures offered a rapid conduit into the subsurface, where complex redistribution processes occurred. Williams and Rohde (2008) monitored rainfall infiltration into a rock dump at a mine in Australia. They found that the majority of rainfall infiltration went into storage within the dump and only a minor amount reached the base of the dump via preferred seepage pathways during a period of 16 months. ...
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Ponded infiltration is very common in silty mudstone and has a great influence on the stability of related slopes, road cuttings, and tunnels. This paper aims to examine the infiltration performance of silty mudstone and predict the distribution of its water content under ponded conditions. By infiltration tests, the infiltration rate (i), cumulative infiltration (I), and their variations with the infiltration time (t) were obtained. Afterward, the variation of water content (w) with t and depth (s) was analyzed. The results show that the i value decreases with the increase in the degree of saturation, and the I value increases first significantly and then slightly during water infiltration. The entire w–t curve at any s is S-shaped, while the w–s curve at any t is full or half inverse-S-shaped. In addition, an equation was developed for the w–s prediction based on the simplified Gompertz curve model, and it was further extended to the spatial–temporal prediction model of water content. The evaluation results demonstrate that the spatial–temporal prediction model has high accuracy and reliability. The prediction model also indicates that the range of the infiltration-affected zone increases and the rate of increase slows down during water infiltration.
... Since the SWRD has yet to wet-up sufficiently from rainfall infiltration to generate "continuum breakthrough", the total base seepage is likely to be of the order of 2% of annual rainfall, since the majority of the rainfall infiltration will go into storage within the dump (Williams and Rohde, 2008). The majority of the base seepage is therefore percolating into the foundation, with little emerging at the toe of the dump. ...
... Waste rocks are generally employed in waste piles dry and they tend to progressively increase in water content with time through infiltration and fluid flow (Williams and Rohde 2008). Potential drainage inputs include the infiltration of snow melt and rainfall through the surface and along the batters, as well as additions of runoff and groundwater along the edge and bottom of the dump (Price 2009). ...
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Waste rock is the large volume of broken rock and low grade ore materials tend to create potential problems, such as acid mine drainage (AMD), leaching of heavy metals, and slope stability problems. These problems are related to the flow of water through the waste rock. In this study, long term numerical simulations of unsaturated flow in a large waste rock pile are conducted to investigate the effect of internal variability in water flow and saturation. The approach first consists of a basic geotechnical properties investigation to define the main features of the pile. This is followed by numerical simulations of the unsaturated flow through the pile based on the results from the field and laboratory characterization. The simulation results showed that pile is unable to fully saturate and drain during the simulated period. It was also found that high evaporation and the high bottom flux rate and also coarse grain nature of waste rock materials results holding few amounts of water in the system.
Article
Waste rock is the large volume of broken rock and low grade ore materials tend to create potential problems, such as acid mine drainage (AMD), leaching of heavy metals, and slope stability problems. These problems are related to the flow of water through the waste rock. In this study, long term numerical simulations of unsaturated flow in a large waste rock pile are conducted to investigate the effect of internal variability in water flow and saturation. The approach first consists of a basic geotechnical properties investigation to define the main features of the pile. This is followed by numerical simulations of the unsaturated flow through the pile based on the results from the field and laboratory characterization. The simulation results showed that pile is unable to fully saturate and drain during the simulated period. It was also found that high evaporation and the high bottom flux rate and also coarse grain nature of waste rock materials results holding few amounts of water in the system.
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Due to the range of climatic regimes in which they are found, mines may be faced with having too much water, or not enough, but rarely do they have just the right amount of water of the required quality. Water is required for dust suppression during open pit mining and, more particularly, for mineral processing. Water is also liberated in the course of mining and may become contaminated. Dust suppression can be carried out with water of relatively poor quality, such as water already affected by mining activity, provided that runoff does not lead to contamination of the receiving environment. Mineral processing generally requires raw water of relatively good quality, although there are enforced exceptions, such as the need to use hypersaline groundwater in the Kalgoorlie mining region of Western Australia. Mineralised mining and processing wastes can be a source of poor quality water, requiring the control of discharge to the receiving environment. The paper highlights a range of different scenarios, illustrating them with typical examples from a range of climatic regimes and mining situations, focusing on open pit mines in dry regions of Australia.
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