Hangingwall Subsidence

LKAB Contact Christina Dahnér-Lindqvist    LTU Contact Sten-Åke Elming
Posted in Sustainable mining

Underground mining often results in deformation of the overlying strata (subsidence). If the conditions are suitable the subsidence is concentrated to the surface over the mined area and occurs because removal of the orebody changes the conditions of static equilibrium within the rock mass. In cases where, for instance, the orebody is flat-lying, the surface deformations form a trough centered over the mined area. This type of subsidence is termed continuous because the deformation is gradual and surface cracking is often not present or very limited. Under other conditions the subsidence may result in formation of large cracks, scarps, and sinkholes. This type of subsidence is termed discontinuous, because the deformation is not gradual but occurs in steps. The type of deformation taking place depends on the mining method, geometry of the orebody, stress state, structural geology, and strength of the rock.

Underground mining often results in deformation of the overlying strata (subsidence). If the conditions are suitable the subsidence is concentrated to the surface over the mined area and occurs because removal of the orebody changes the conditions of static equilibrium within the rock mass. In cases where, for instance, the orebody is flat-lying, the surface deformations form a trough centered over the mined area. This type of subsidence is termed continuous because the deformation is gradual and surface cracking is often not present or very limited. Under other conditions the subsidence may result in formation of large cracks, scarps, and sinkholes. This type of subsidence is termed discontinuous, because the deformation is not gradual but occurs in steps. The type of deformation taking place depends on the mining method, geometry of the orebody, stress state, structural geology, and strength of the rock.

As mining proceeds to greater depth an increasing volume of the rock mass on the east (hangingwall) side of the orebody will be influenced. The surface deformations and the cracking of the ground surface will therefore move toward the railway and the city of Kiruna. Prognoses of future subsidence (surface deformations) will thus require a good understanding of the rock mass properties and behaviour, the failure mechanisms causing the subsidence and details about the distribution of surface deformation (smooth, stepped, etc.).

 

The objective of the project is
- To develop a structural geological model of the Kirunavaara hangingwall.
- Identify different structural-geological regions in the Kirunavaara hangingwall on basis of their physical properties.
- Increase the understanding of how plastic and brittle deformation zones are interrelated, e.g. to what extent are brittle deformation zones guided by former plastic deformation zones.
- Increase the knowledge about the relation between magnetic, mechanical and seismic anisotropy.
- Input in the numerical rock mechanic modelling by providing information about the local geology, the structural geology and anisotropy of elastical/mechanical properties.

 

The objective of the project is

- To develop a structural geological model of the Kirunavaara hangingwall.

- Identify different structural-geological regions in the Kirunavaara hangingwall on basis of their physical properties.

- Increase the understanding of how plastic and brittle deformation zones are interrelated, e.g. to what extent are brittle deformation zones guided by former plastic deformation zones.

- Increase the knowledge about the relation between magnetic, mechanical and seismic anisotropy.

- Input in the numerical rock mechanic modelling by providing information about the local geology, the structural geology and anisotropy of elastical/mechanical properties.