Fully coupled deformation and hydrology (hydromechanical ) simulation for open pit mines

3d Simulation of Pore water pressure and slope stability

Water pressure impacts on stability and rock damage affects flow, but in the past, coupled hydromechanical simulation was uncommon. Now, 3-dimensional, fully or partially coupled hydromechanical simulation for entire mines is possible. The models include large numbers of explicit discontinuities and mapping of hydrological domains.

How does it work?

The standard, conventional equations governing fluid flow and pore water pressure can be solved simultaneously with the equations for deformation and damage inside 3D mine scale FE (non-linear) models. A relationship between permeability and rock damage is also defined and acts as a constraint on the solution. In a fully coupled simulation the deformation part and the hydrology part are not changed from normal best practice; they are just coupled so that the interactions are accounted for at every time step.

Discontinuities can be handled in a number of ways consistent with normal hydrological modelling—they can be included explicitly or implicitly and the different hydrogeological domains can be mapped with the geological domains, or as separate volumes. All else being equal, the results for 3d fully coupled modelling are more realistic and the models require fewer assumptions, resulting in lower uncertainty.

Fig.1: Examples of pore pressure distribution for 3-dimensional very large open pit FE models

How is it used?

The fully or partially coupled hydromechanical simulation can be undertaken for any existing or future BAE Finite Element model. The main issue is the availability hydrological data. Over time, more data will need to be collected to take full advantage of the new technology and BAE is certain that the costs will be justified. Even with existing levels of data, the coupled models are showing their value, giving more realistic answers and better matches with field measurements.

Is your mine ready?

Fully and partially coupled 3-dimensional hydromechanical modelling should become standard practice for pit slope simulations – there are no technical hurdles to using the technology to improve model reliability today. The methods capture an important aspect of pit slope behaviour that isn’t often handled well. Any large slope where pore water pressure is a factor in stability should undertake fully coupled analysis.

Contact: dbeck@beckarndt.com.au for more details