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OPTIMIZING MINING METHODS BY ADVANCED NUMERICAL MODELLING OF COMPLEX ROCK MASS BEHAVIOUR

Objective


Advanced rock mechanics modelling techniques were employed in mine design for an optimal, economical and safe recovery of mineral deposits. Using the data generated from a number of example studies, guidelines were formulated for mines where numerical modelling was used as an engineering tool to improve mine design. The example studies were carried out at Tara mines (Ireland) and Moinho mine (Portugal).

The steps which are performed to apply numerical modelling as an engineering tool for mine design, are as follows. First, the setting and the rock mechanics related problem are described. Specific questions are formulated. A suitable location for modelling is chosen. Once the problem is well defined, several parallel lines of action commence, that will result in good analysis, including verification:
the mechanisms of deformation and failure determine the type of modelling calculation, while they also are used as a verification possibility;
the layout of the chosen location is (strongly) simplified to a model geometry;
stress boundary conditions need to be found and applied in the model;
rock (mass) material and joint properties need to be obtained from rock mass ratings in combination with laboratory tests on samples;
a measurement programme needs to be set up with the aim of generating verification data.

Calculations should be started in an early stage with a simple model, which can be improved stepwise based on information generated in the process. It is important to realize that rock mechanics modelling is typically data limited. Therefore, efforts should be focussed on modelling key mechanisms of the problem, rather than trying to model reality. The originally formulated questions should be kept in mind while improving the model.

The modelling exercise themselves generally lead to a better understanding of the rock mechanics processes that play a role in the mine. This may already be applied usefully in the mine design, excavation sequencing and the design of support measures. When, from evaluation of the modelling results, it is concluded that the important rock mechanics processes are properly simulated, options to improve the mining method may be modelled and analysed.
The objective of this research proposal is to develop example studies of optimizing underground mine design, using advanced rock mechanics modelling techniques for an optimal, economic and safe recovery of mineral deposits. The input parameters of the models, such as the existing stress regime, strength properties and rock mass characterization are to come from underground and laboratory measurements and observations.
Underground studies are to be carried out of key problems in mines in Ireland (Tara Mines Ltd), Portugal (Pirites Alentejanas SA) and Greece (Hellenic Ferroalloys S.A.). This research will result in a series of case histories suitable as example studies of the optimization of mine design for use by other small to medium sized mines in the community. The studies will include advises for suitable hardware and software packages for use on small computer systems.
Underground advanced techniques for measuring the in situ stresses will be introduced, such as the borehole slotting stressmeter developed by Interfels. Detailed observation of prevailing fracture and failure mechanisms will be carried out. Techniques to characterise discontinuities will be used. Underground acoustical measurements for fracture and
discontinuity detection will be used. Also data will be collected on the properties of backfill and support elements. The laboratory in Delft is equipped with diversified sophisticated test equipment. With the large true triaxial compression machine fundamental research of rock properties as well as sophisticated model experiments under different stress regimes will be carried out. True triaxial tests on samples (105*105*105 mm) from the mines, including acoustical measurements, will be carried out to determine complex material properties and to support the interpretation of the underground measurements. The properties of discontinuities will be measured using shear box tests.
Using the data from the underground and laboratory measurements, the analysis and numerical modelling of a number typical mining situations will be carried out to determine the applicable design rules for rational mine planning. This analysis will include the behaviour of discontinuities, complex material properties and interaction between jointed rock masses and support elements such as cable bolts, backfill, etc. in order to improve support systems and to understand how to modify the stoping system to meet high ore recovery and safety standards. Detailed example studies will be described in the end report. The software can be used and adapted by other small to medium sized mines in the community to enhance rational mine planning and hence the profitability of the mine exploitation. The project programme will ultimately enhance the economic significance of the small and medium mining industry in the Community. The proposed program will be competently managed and coordinated, by the prime proposer.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Technische Universiteit Delft
Address
120,Mijnbouwstraat 120
2600 GA Delft
Netherlands

Participants (2)

Pirites Alentejanas SA
Portugal
Address
Algares
7600 Aljustrel
Tara Mines Ltd
Ireland
Address
Knockumber Road
37 Navan Co. Meath