Caving Initiation, Propagation and Subsidence

Artists rendition of material movements into a fictional inclined cave, following slope failure. In this case the failure is a similar scale to the cave.

To better estimate the likely performance of caves, a tool that properly accounted for the physical coupling of the caved material to the un-caved rock mass and the draw schedule, driven by the known physics of both parts of the problem was needed. No such tool was available.

After analysing a number of alternatives, a coupled Discontinuum Finite Element (DFE) – Cellular Automata (LGCA, or Newtonian CA) scheme was developed, making use of our existing DFE capability and our partners’ cave simulation tools.

In this scheme, the CA part computes the particle movements within the cave and changes in airgap geometry, while the DFE part computes a new solution for stress, deformation, damage and fault movement – hundreds, or even thousands of explicit faults can be incorporated in the DFE models.

As a consequence of the draw and the solution for stress and strain in the rock mass, an unstable zone in the cave back develops at each coupling step and sloughs into the cave, at which point these elements become available to be drawn in the CA step. The process is repeated, following the draw schedule, and is able to simulate most cave propagation phenomena including stalling and chimneying.

Example of 3D non-linear mine-scale block cave modelling results

The coupled DFE-LGCA simulation procedure enables rapid simulation of cave propagation, flow and induced deformation driven by the cave draw schedule with a level of reliability shown to exceed any other available tool in all comparative studies undertaken so far. The method can be calibrated directly using observations of cave back location, grade and recovery, seismicity, tunnel damage, tomography or ground movement.

BE believes that this technique represents best practice for cave simulation in the world today. The key ingredients are the coupling, the improved represantation of structures to a smaller scale, capturing of the changing swell and flows and realistic discontinuous deformation.

For more details contact Dr David Beck at dbeck@beckengineering.com.au or +61 412 135 782.

You can download a paper on the technique at: A coupled DFE-Newtonian Cellular Automata scheme for simulation of cave initiation, propagation and induced seismicity