The aim of work package 4 is to investigate how satellite and airborne remote sensing in addition to modelling can be used in management and monitoring of mine structures and processes.
Work package 4 involved remote sensing and field measurements in two sub-arctic mine sites in Northern Sweden (Aitik mine) and Northern Finland (Laiva mine). In the case of Laiva mine, unmanned aerial vehicles (UAV) were utilized to monitor subsidence of paste tailings. At the same site, yearly thermal regime of the tailings was monitored with temperature loggers and frost depth indicators. Gathered thermal data and measured geotechnical properties were utilized in modelling of frost depth and tailings paste mechanical behaviour. In the case of Aitik, satellite remote sensing was used in monitoring surface movements of tailings dams by utilizing SAR Interferometry (InSAR) with freely available medium-resolution (Sentinel-1) and commercial high-resolution (TerraSAR-X) data.
Brief descriptions of each study are provided below with links to publised articles or detailed report.
UAV Remote Sensing Surveillance of a Mine Tailings Impoundment in Sub-Arctic Conditions:
Mining typically involves extensive areas where environmental monitoring is spatially sporadic. New remote sensing techniques and platforms such as Structure from Motion (SfM) and unmanned aerial vehicles (UAVs) may offer one solution for more comprehensive and spatially continuous measurements. We conducted UAV campaigns in three consecutive summers (2015–2017) at the Laiva mine site. The aim was to monitor the 0.5 km2 tailings impoundment and measure potential subsidence of tailings. SfM photogrammetry was used to produce yearly topographical models of the tailings surface, which allowed the amount of surface displacement between years to be tracked. Ground checkpoints surveyed in stable areas of the impoundment were utilized in assessing the vertical accuracy of the models. Observed surface displacements were linked to a combination of erosion, tailings settlement, and possible compaction of the peat layer underlying the tailings. The accuracy obtained indicated that UAV-assisted monitoring of tailings impoundments is sufficiently accurate for supporting impoundment management operations and for tracking surface displacements in the decimeter range.
Geothermal study of a tailings deposit - Frost line modelling and comparison to field data:
Seasonal freezing and thawing can have significant effects on tailings management. Tailings delivery, depositional schemes and water treatment are examples of activities that must be dealt with extra concern in sub-zero temperatures. Changes in mechanical properties, drainage possibilities or embedded frozen tailings layers are effects that can arise. To avoid such consequences, a good understanding of the seasonal effects on the tailings deposit is needed. To get a better understanding of the geothermal regime in tailings, this task presents a study with geothermal modelling performed for the Laiva tailings facility in Finland, where major seasonal freezing and thawing periods are present. Ground temperatures and frost lines were predicted via one-dimensional modelling using air temperatures and snow cover depths from adjacent weather stations, and basic soil properties from the facility. Simulated results were compared to data obtained from thermal instruments in the field. The snow cover and its estimated thermal properties were shown to have large influence on the results. The model was able to accurately predict the thermal regime measured in the field. Strong agreement was shown, both in terms of ground temperatures and frost front positions. The methodology presented, is useful for tailings management schemes in cold regions.
(Manuscript under review, for more information contact: roger.knutsson(at)tailings.se)
Tailings paste behavior with computational fluid dynamics modelling
Computational fluid dynamics (CFD) was used to model the behaviour and spreading of thickened tailings in tailings pond. Special interest in modelling was to study the paste accumulation and spreading right after the paste discharge. Modelling was done in 2D, and the modelling (ANSYS Fluent) geometry was a cross-sectional surface of a tailings pond at the location of a paste discharge pipe. Volume of Fluid (VOF) multiphase model was used to model the height and location of paste layer, and the non-Newtonian behaviour of the fluid was taken into account with the viscosity model. CFD is an interesting method to study the effect of characteristic parameters on paste behavior and CFD modelling is a promising tool also in tailings dam modelling, but the models can be computationally expensive.
Remote sensing with satellites: Using satellite data (InSAR) to monitor tailings dam movement
Dam failure and the release of mine tailings into the environment can have major environmental and social consequences. Monitoring of the stability of the tailings dams is therefore important to identify potential problems at an early stage such that measures can be taken and accidents prevented. This is traditionally done through regular in situ measurements. Ground movement can also be mapped accurately through the analysis of radar satellite data using a technique called interferometry (InSAR). In this project we investigated how InSAR can be used to monitor the stability of tailing dams. We processed data from the European Copernicus Sentinel-1 satellite, which provides open data access. In addition, we used data from the commercial TerraSAR-X satellite. Both satellites are able to detect ground movement at the tailings dam, however with different spatial and temporal resolutions.
(Report available soon)
Last updated: 29.11.2018