The International Conference on Discrete Fracture Network
Engineering, October 19 - 22, 2014, Vancouver, Canada
Stability Analysis of an Ore Pass Using a DFN-DEM
model
K. Esmaieli, J. Hadjigeorgiou
Lassonde Institute of Mining, University of Toronto, Canada
Abstract
This paper reports the results of an investigation into the stability of an ore pass, at a mine
in Canada and the successful implementation of the recommendations. The ore pass
serves as a transfer point with ore dumped from the surface to an underground silo and
used to feed an underground crusher. The investigation was undertaken given a
significant degradation in the area where the ore pass intercepts a fault zone.
A site investigation collected core logging information obtained from a geotechnical
borehole, drilled closed to the ore pass and underground mapping data. This database was
used to generate and validate a 3D Discrete Fracture Network (DFN) model for the four
rock mass zones intercepted along the ore pass. The ore pass geometry was introduced
into the DFN model to identify the size and location of potential wedges along the ore
pass walls. The kinematic analysis underestimated the extent of the failure zone in the ore
pass walls. Site observations indicated that the actual ore pass degradation zone extended
deeper into the rock mass, beyond the predictions of the DFN model. This implied that
gravity driven wedge failure was not the only failure mechanism controlling the integrity
of the ore pass. In effect material flow in the ore pass contributed to ore pass wall
degradation.
In order to investigate the impact of material flow on the ore pass wall degradation, 2D
traces of fractures along the ore pass wall were derived from the 3D DFN model. These
fracture traces were linked to four intact rock models simulated by 2D Particle Flow
Code (PFC2D). This allowed generation of four synthetic rock mass (2D SRM) models
that represented the rock mass domains along the ore pass. The ore pass geometry was
excavated within the SRM models. Five projectile rock fragments of various sizes were
thrown against the ore pass walls using an impact velocity of 12 m/sec. This was
determined based on simulation of a material flow analysis. The projected rock fragments
were 2.1 m (representing the big rock boulders dumped occasionally into the ore pass),
0.9 m, 0.7 m, 0.4 m and 0.2 m in diameter. The projected rock fragments caused damage
to the ore pass walls, which was recorded in the form of micro cracks. The extent of
damage varied along the four rock mass domains, with higher damage observed along the
domain where a fault zone intersecting the ore pass. Following this investigation the mine
implemented a series of recommendations that have been shown very effective in
mitigating the problems associated with the ore pass. These included the enforcement of a
strict management plan to ensure that no large rock boulders were introduced in the ore
The International Conference on Discrete Fracture Network
Engineering, October 19 - 22, 2014, Vancouver, Canada
pass. Further interventions included the installation of long cables that reinforced the
surrounding rock mass of the ore pass. This contributed to the structural integrity of the
ore pass and limited the introduction of large rock sections falling into the ore pass.