MINING INDUCED SEISMICITY RESEARCH
BAE are continuing to develop our advanced inelastic modelling applications for evaluating seismic risk.
The current state of development is as follows:
- Strain softening, dilatant LR2 Finite Element models have been proven to provide excellent efficacy in forecasting seismogenic potential at a large number of operations, using correlations between Dissipated Plastic Energy (DPE) and the likelihood of event occurrence (event rate/volume/time). The prediction efficacy is best practice. An example is shown in Figure 1. This figure shows the computed correlation between event probability and DPE rate at an example mine. Each dot represents many hundreds of seismic measurements.
- Decompositions of DPE, or increments of plastic strain in the LR2 models show a good match between modelled mechanisms and measured seismic moment tensors. This allows more detailed interpretation of the models, as well as improved utilisation of seismic system data for calibration. From mining to oil and gas, the combination of the LR2 modelling and moment tensor analysis provides unprecedented understanding of rock mass failure mechanisms.
- The correlation between DPE, increments of plastic strain and measured seismicity can be computed for faults as well as for the rock mass. An example of the correlation between fault slip seismicity and fault slip DPE is shown in Figure 2.
- A materials basis for DPE/plastic strain/seismicity correlation has been demonstrated using simulated rock mass specimens. Genuine dynamic modelling of discontinuous rock mass specimens confirms the DPE correlation can be explained in terms of simple, well understood rock degradation mechanisms. See for example Beck et al 2009. An example Figure from that paper is shown in Figure 3.
- In caving mines around the world, the correlations between LR2 predicted seismogenic potential and measured seismogenic zones are being used to interpret and understand caving processes with better precision. An example is shown in Figure 4: model predicted and measured seismic event densities (inter event distances) and actual seismic events are shown. The close match provides best in industry confidence in the model and allows the forecasting quality to be quantified.
- Passive tomography has been integrated with LR2 FE modelling at several mines to better understand the effects of pre-conditioning, to improve model calibration or to track the development of induced rock mass damage. Combined with systematic, high similitude modelling, the passive tomography provided a remote, 3d, quantitative measure of changes in the rock mass.
These developments provide real, quantitative tools for engineering seismicity. At a growing number of mines, engineers have been able to adapt their designs in early planning stages to reduce overall risk.
To enquire about this topic, please contact David Beck.
Figure 1: Computed correlation between rock mass seismic event probability and DPE rate at an example mine
Figure 2: Computed correlation between fault slip seismic event probability and DPE rate at an example mine
Figure 3: Simulated Seismogram of event occurring at transition from stable to unstable specimen behavior. “Measured” at a corner node of a discontinuous LR2 model, loaded using stress path at the point shown in a global scale model of a block cave
Figure 4: Correlation between modelled DPE and measured seismicity, expressed in both cases as the inter-event distance for a single month
Estimating rock mass properties and seismic response using higher order, discontinuous, Finite Element models
D.A. Beck, M. J. Pfitzner, S.M. Arndt and B. Fillery
Beck Arndt Engineering Pty Ltd, Sydney, Australia.