Owing to software and hardware limitations, sub-modelling approaches are frequently employed to analyse complex problems; a larger donor model will be used to establish boundary conditions for a smaller more detailed model. This approach is a valid technique, but employed poorly can lead to very significant problems. As computer power and software efficiency improve, it is becoming possible to represent a very wide range of length scales with adequate precision in a single model, simplifying the process of multiple length scale simulation. There are now examples of mine models with a precision adequate to represent material behavior from a drive to a mine scale in a single, multiple step simulation. On each length scale, these simulations are not necessarily more complex than historic modelling, but there are fewer assumptions as there are now fewer boundaries between scales at which strain, stress and state data must be simplified. This opens up opportunities for better analysis, and it is possible that certain phenomena that were previously difficult to capture can now be simulated. With better representation of multiple length scales, it also appears that there is a justification for increased geometric and constitutive complexity, and this will impact on approaches to data collection and characterisation. The teachings from multiscale analysis will also aid better sub-modelling. Opportunities arising from multi-scale non-linear modelling and improved sub modelling approaches are discussed and case studies for underground and open pit mines and some tests of sufficiency for multi-scale modelling are proposed.
Advances in computational efficiency and capacity mean that significant improvements in modelling practice for mines are possible. Perhaps the most significant improvement will come from a move towards calibrated, multi-scale non-linear modelling. Multi-scale mine modelling is any modelling where there is defined precision for deformation and distortion of the rock mass at multiple length scales. Generally, the behavior at each length scale is built upon to simulate successively larger length scales. This could be achieved by incorporating geometry and sequencing details at a resolution and complexity suiting the smallest length scale of interest in the problem, but inside a model with similar complexity at longer length scales. Multiscale simulations would also normally involve calibrated homogenization of material properties at one or more of the length scales to reduce complexity and would carefully consider the most appropriate means of specifying boundary conditions, treating the boundary dimensions as one of the length scales where deformation and distortion are simulated accurately. Undertaking true, realistic multi-scale simulation of mining induced deformation demands very high standards.
2. LENGTH-SCALE CONCEPTS
Many mine deformation modelling approaches assume physical phenomena of different length scales cannot, or do not affect each other. This assumption is made to overcome computing limitations, as it allows smaller, detailed sub-models of areas of interest to be analysed using simplified boundary conditions. The central idea is that gross deformation simulated at one scale, relying on a set of simplified material assumptions, can be used to frame the loading system, or boundary conditions for a smaller length scale model incorporating a more advanced material model.