Safety is one of the main concerns in underground mining. Blasting within the mines for ore removal is one of the main causes of instability within the mine backfill that leads to accidents. A project led by Dr Riyu Wei of the University of Queensland is using finite element (FE) modelling techniques to better predict failure risks due to blasting effects in underground mines.
Cut-and-fill mining is applied for mining of steeply dipping ore bodies, in strata with good to moderate stability, and a comparatively high grade mineralisation. Cut-and-fill allows selective mining, to recover high grade sections separately, and leave low grade rock behind in stopes. The method involves excavating the ore in horizontal slices, starting from a bottom undercut, advancing upward. The ore is drilled, blasted, the muck loaded and removed from the stope. When the full stope area has been mined out, voids are backfilled with sand tailings or waste rock. The fill serves both to support stope walls and working platform for equipment, when mining the next slice. Figure 1 shows a schematic diagram of an underground mine to which cut-and-fill is being applied. Figure 2 shows a 2D model used for blast modelling.
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Figure 1: Schematic diagram of underground mine |
Figure 2: 2D cross-section used for blast modelling. |
The project has focused on achieving two major outcomes: developing numerical models with which to study the blasting, and building a virtual environment in which the numerical models may be studied.
In order to develop numerical models for the blasting, the group was first required to develop a representative blast loading function of the test blast shots (single cartridges of explosives), as well as full scale models (columns of explosives). Using this blast loading function, they then numerically determined the peak particle velocities for paste fill stopes (for cement content ranging from 2-6%) using finite element (FE) methods. For verification of results, a comparison was made with in-situ measurements of peak particle velocities.
They have also been able to model the stress distribution in the rock surrounding the blast. The stress distribution for a single column blast is shown in figure 3. This is similar to the analysis performed on MRI magnets.
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Figure 3: Stress distribution in
rock surrounding a single column blast. |
A rock blasting simulation, modelled using the finite/discrete element package ELFEN, is shown in Figure 4. The blast was simulated by applying a time-varying pressure to the walls of the blast hole (seen in the first image).
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| Figure 4a: Blast initiation.
A time-varying pressure was applied to the blast hole to simulate the explosion. |
Figure 4b: Complete blast |
The second major accomplishment has been the development of a virtual environment in which to study the models. This has been developed alongside the numerical models, and is able to import 3D finite element data, display and manipulate FE models, and display and animate analysis results (deformation, stress, velocity, etc.). Figure 5 shows the graphical user interface of this environment with a test finite element model.
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Figure 5: Graphical interface of the environment with a test model. |
This project is also supported by DEST under the International Science Linkage Program. It is in collaboration with Dr. Warna Karunasena and Dr. Nagaratnam Sivakugan at the School of Engineering, James Cook University. Several papers on this research have been submitted to computational modelling conferences in Australia and internationally in 2006.
Contacts
Dr Riyu Wei, ACMC, University
of Queensland
Dr. Warna Karunasena,
Dr. Nagaratnam Sivakugan, School of Engineering, James
Cook University
Department of Education, Science and Training
Reports:
Project Proposal (62 KB PDF)
Progress Report (August
2006) (509
KB PDF)