Rock mechanical analyses for the Boliden deep repository at Rönnskär
Project Background
The Boliden AB mining company owns and operates six mines and five smelters, one of which is the Rönnskär copper smelter facility outside of Skellefteå, Sweden. The smelter facility separates commercial metals from waste material such as heavy metals (mercury, cadmium). To safely dispose of the process waste, Boliden is constructing a deep underground repository underneath the Rönnskär smelter at a depth of 330 m.
To satisfy geomechanical and hydrogeological regulatory and internal requirements, a number of rock mechanical analyses have been conducted by Itasca. The work has included stability analyses of the repository rooms, optimization of geometries, and long-term effect on flow paths. The latter is critical to the long-term function of the repository. The influence on flow pathways was judged with 3000 years as a reference time frame.
Global and local stability was evaluated using elasto-plastic analyses in FLAC3D while the long-term effects on flow-paths were considered via reducing strength parameters for joints simulated in 3DEC.
Results Summary
For this project Itasca used a combination of continuum and discontinuum models to evaluate global and local stability as well as long- term effects on flow paths for a one-of-a-kind facility. The models were able to demonstrate that the potential for increased flow in the rock mass due to the excavation of the repository over a time period of 3000 years is negligible. The models also demonstrated that there would be no measurable surface influence. An optimized production layout was also delivered from the project work.
Excavation of the facility began in 2019 (ramp was excavated in 2017) and by mid-2020 six of the planned storage rooms are under excavation. The in-place measurement program show (thus far) expected deformation behavior during excavation, thus validating both the geomechanical model and the numerical modeling results.
