At a BMA site in the Bowen Basin, historic spoil believed to be over 20 years old is required to be re-dug and re-dumped from an historic offset pit to permit mining progression. The spoil had been initially dug and rehandled by dragline in a predominantly tertiary and weathered horizons. Therefore, the spoil is highly variable. Poor tip head performance has been experienced with this spoil and was hypothesised to be due to degradation from long-term exposure to the environment, as well as disturbance caused by re-handling. Bulk samples of the spoil were collected from freshly paddock dumped loads to represent the in situ condition at tip heads. A suite of laboratory testing has been undertaken to understand the index characteristics as well as the geotechnical behaviour of this spoil such as Atterberg limits, particle size distribution, triaxial and large-scale direct shear. Shear strength testing was undertaken in both unsaturated and saturated conditions to respectively investigate the spoil’s short-term performance at the tip head and long-term performance under prolonged exposure to surface and groundwater. This paper presents the interpretation of the test results, as well as presenting a case study on the operational controls for dumping that have been implemented at the site. It is expected that this study will also inform the long-term stability analyses of weak spoils as part of mine closure studies.

Legacy mine sites are becoming attractive locations to install Variable Renewable Energy (VRE), as developers are losing social licence to build solar PV power stations on agricultural and farming land.
Mining operations typically include high voltage electrical infrastructure for powering the site which with some engineering and augmentation to the network can be repurposed as a generator and/or energy hub.
There are several mining sites across Australia that have been repurposed after mine closure for the purpose of solar PV generation, most notably the Kidston gold mine tailings dam (Figure 1), which now supports a 50 megawatt (MW) solar farm. There are several other solar PV projects that have been announced on mining sites and a few more which are adjacent to power stations on either the ash dams or former mining sites.
The challenge with most mine tailings and mine closure sites for the repurposing of their site for other infrastructure is the cost of engineering the fill to provide a stable hard stand that will support the new infrastructure, which is especially difficult on mine tailings, mine spoil or just land that has been mined or may be contaminated.
The purpose of this paper is to explore the technical capability of a novel concrete ballasted solar PV tracking structure to be installed totally above ground on mine sites, tailings dams, ash dams and other contaminated sites.
The technology uses a concrete rail similar to what is installed for residential street kerb and guttering. The structure is built on four legged tables which are connected by a coupling which allows for some construction and operational movement.
The technology is patented by Alion Energy Pty Ltd which has fundamentally redesigned the way solar power stations are built, how bifacial energy gains are generated, and how these solar facilities are maintained.

The Main Creek Tailings Dam (MCTD), located at Grange Resources Pty Ltd’s (Grange) Savage River Mine in north-west Tasmania has been in operation since 1985 and is transitioning from an operational TSF to closure. The MCTD is an upstream constructed facility with a maximum height of approximately 83 m. Tailings stored in the MCTD are potentially acid forming (PAF) and require careful management through operation and closure to minimise the risk of Acid and Metalliferous Drainage (AMD) forming in the TSF.
The site is situated on the west coast of Tasmania with rainfall significantly exceeding evaporation. Therefore, a water cover would typically be most suitable, however, due to the upstream constructed embankments a soil cover is required adjacent to embankments to meet long-term stability requirements.
During operations, three trial covers were constructed and instrumented to monitor the performance over several years. The information obtained was used to evaluate cover performance and calibrate numerical transient seepage models. The preferred cover based on the trial cover performance was a combination of clay and rock fill cover which maintained a high degree of saturation in the clay, minimising oxygen ingress to the underlying tailings, and reducing the likelihood of AMD formation.
The preferred clay and rock combination cover was assessed and optimised during the detailed design phase by undertaking 2-dimensional transient unsaturated seepage modelling in SVFlux, considering a conservative climate scenario.
Construction of the clay component of the combination cover has recently been completed. The construction process, challenges, and QA/QC is discussed in this paper.

In-pit tailings storage facility (TSF) design should consider the development of a sustainable post- closure landform. Furthermore, the facility should endeavour to achieve the closure design intent. Often, an encapsulating alternative is preferred. This paper describes some technical considerations encountered during the geotechnical stability assessment for a capping concept design. The concept design involved the use of geosynthetic reinforcement to improve constructability. This is due to the very low strengths, less than 10 kPa, of the tailings under the crust. The data presented in the paper comprises the geotechnical interpretation of a site investigation at a TSF below the existing ground surface in Australia. Polypropylene (PP) and Polyester (PET) are two common types of geotextiles used in engineering applications that require high tensile strength. However, their durability under long-term strain can vary depending on the pH of the service environment, exposure to ultraviolet radiation (UVR), and other factors. The paper aims to describe the technical considerations and methodology recommended for undertaking similar assessments in the future and provides some high-level discussion regarding geosynthetic reinforcement material selection in contrasting pH environments.

The Cobar region (the region) is located approximately ~700 km west of Sydney in central western New South Wales (NSW). The region has a semi-arid climate with low humidity, low rainfall and high evaporation. Annual rainfall is ~400 mm while evaporation averages 2000 mm. The Cobar basin is a significant metalliferous region in Australia, containing extensive base and precious metal deposits. During ore processing, potentially acid forming (PAF) tailings are generated and discharged to tailings storage facilities (TSF). PAF tailings require careful rehabilitation to minimise the risk of harm to the receiving environment.
Rehabilitation of a TSF usually requires the design of a cover to limit/prevent tailings interacting with oxygen and/or water to reduce the potential of acid mine drainage (AMD) that can be transported to the receiving environment. In semi-arid environments a store and release cover is typically used, in combination with other safe guards (ie a capillary break (CB) or reduced permeability layer (RPL)).
Due to material availability, cover designs regionally vary in thickness but are still considered suitable in regards to performance, often expressed as seepage. Notwithstanding, there are additional cover performance issues that need to be acknowledged.
Erosion plays an important part in Australian landscapes. Erosion (usually driven by water velocity) causes the cover surface to change with time. Long-term erosion stability is more complex than a simple laboratory analysis as material characteristics are a small part of understanding erosion stability. There are additional factors that need to be considered including; climate, slope and groundcover.
Typically, cover design does not consider erosion driven changes as a performance criterion. LAPSUS evolution modelling has been applied to three published cover designs for the Cobar region to examine performance changes over time in response to erosion driven change.
The LAPSUS modelling predicted that the cover design performances were affected by erosion after 100 years. All cover designs experienced localised erosion in the form of rills and gullies that penetrated the full thickness of the cover. In regards to overall soil loss, it was found that cover thickness is not a determining factor.

In arid and semi-arid regions, evaporation dominates the evolution of water balance in store-release (SR) cover systems. It can facilitate diffusion-driven salt uptake from the hypersaline tailings into the covered soil by inducing upward advection. The performance of SR covers in limiting evaporation- driven salt migration fewerinvestigated needs to be investigated more. A one-dimensional numerical model that couples the transport of liquid water, water vapour, heat and solute was developed. The model was calibrated with the monitored data obtained from an instrumented column, which consisted of 0.6 m thick monolithic silt cover overlying 0.6 m thick compacted bauxite exploredons were conducted to explore the evaporation behaviour and salt distribution in monolithic covers using three representative cover materials over compacted and loose tailings. Under given atmospheric conditions, the maximum salinised depth in the cover was determined by the location where the upper boundary of the freshwater-saltwater mixing zone overlapped with the vapourisation plane. In one-year drying simulations, the fine sand cover was most vulnerable to salinisation as over two- thirds of the depths were affected by the uptaken salt when covering both types of tailings due to intense capillary effects. Although the clay cover could keep two types of tailings saturated in the one-year drying process, the silt cover was more recommended as the main component of SR covers due to its similar robust ability to limit salt uptake and moderate water-release capacity.