Waste Rock Behavior at High Pressures: Dimensioning High Waste Rock Dumps - Multiscale Geomechanics: From Soil to Engineering Projects - page 106

is to implement a particular construction sequence for the advancement of the
deposit, encapsulating the sectors with problematic materials. The option to carry
out a foundation treatment is not always practical [VAL 08].
The presence of permafrost requires special attention. Indeed, in Canada some
waste rock dump failures have been associated with the melting of permafrost due to
stresses imposed by the dump. As mentioned previously, potential sliding triggering
mechanisms must be identified, avoided if possible, or treated because they can
induce major failures or debris flows.
4.7.4. Effects of rain and snow
The main problem with rain is the possibility that the water table can rise well
above the foundation level and induce the migration of finer particles to the bottom
of the deposit or the layer, reducing the permeability of the drainage layer. In these
cases, it is necessary to consider the design of a drainage system.
Snow also deserves particular attention. Indeed, snow tends to remain on the
upper surface of each layer in construction and on the advancing slope, its
accumulation creating potential local instabilities. The modification of the
construction sequence and advancing with a narrow section would allow the snow to
be pushed back and thrown into the interior of the dump. To minimize local and
global instabilities, both due to the accumulation of snow and the presence of finer
waste, the dumping of these materials can be made in the transverse direction to the
advancement of the deposit [ARC 06-07].
Moreover, in very HWRDs, the snow deposited on steep slopes could produce
avalanches along the slope itself. Gentle slopes, as well as intermediate berms, may
help solve this problem.
4.7.5. Effects of in situ leaching on waste rock
Some high waste rock dumps have been subjected to a forced leaching to recover
the remaining copper from these materials. The irrigation process produces an
important increase in the saturation degree of the waste rock, weakens the particles,
and leads to an increase in the concentration of fine particles in the deeper layers.
Consequently, during irrigation, conditions close to saturation can be generated,
creating conditions that favor the start of static liquefaction within one or more leach
cells of the deposit. In Chile, significant deformations have already been identified
in waste rock dumps that were subjected to the forced leaching associated with this
phenomenon.