Submitted by Prof. Erling Nordlund on June 7, 2010 - 13:17
Mining of deep seated deposits is associated with stress magnitudes which exceed the strength of the intact rock, geological structures and the rock mass (intact rock and discontinuities acting like a material with complex interactions between discontinuities and volumes of intact rock) resulting in an increased frequency of instability (e.g., fall-outs of blocks, collapse of underground openings) as well as phenomena such as extensive squeezing and seismic events. To ensure mining at great depth (> 1000 m) the behaviour of the rock has to be clarified. Ground control problems at great depth can be grouped into two extremes (i) weak rock (or weak/altered ore contacts in a hard rock mass) and squeezing/large deformations and (ii) hard rock mass and mining-induced seismicity.
Vital for the stability and for successful design of underground openings is the understanding of the interaction between the rock mass and the rock support. The increased stress magnitudes will put new demands on the rock support systems as well as on the process of applying the rock support.
Sublevel caving undermines the ore as well as the surrounding rock, resulting in ground surface deformation and cracking, often called subsidence. If mining takes place close to populated areas the subsidence may affect infrastructure and buildings. In order to be able to forecast the development of the subsidence, the rock mass behaviour has to be investigated and methodologies for prognoses have to be developed. As mining goes deeper an increasing volume of the rock mass will be affected.
Fragmentation is a key component in mining. It spans from geomechanics (in-situ fracturing) over excavation and handling (blasting, haulage and crushing breakage) to the final preparation for beneficiation (milling). Blasting has to create regular breakage geometry and ore and waste pieces that can be treated economically downstream while avoiding waste rock dilution and environmental disturbances. In-situ fracturing governs the blast fragmentation, the internal cracking of fragments the energy efficiency of subsequent comminution. Efficient mining reduces the unit costs and increases the extraction viability of mineral resources. Until now too little interest has focused on the downstream effect of the primary extraction.
The Deep Mining project is divided into four sub-projects
• Ground deformation and subsidence
• Mine-induced seismicity
• Weak ground or non-violent failures
• Blasting and fragmentation