Waste Rock Behavior at High Pressures: Dimensioning High Waste Rock Dumps - Multiscale Geomechanics: From Soil to Engineering Projects - page 82

be disposed of. Wherever these high levels of production concern mines in
mountainous regions, the only available space for stockpiling these materials is in
narrow valleys with steep slopes and, therefore, very HWRDs may be required. In
the past two decades, some dumps reaching heights of 400m to 500m have been
constructedinCanada,Chileandsomeothercountrieswhereminingtakesplace.
In Chile, for example, some dumps in operation will reach final heights of more
than 500m. Moreover, some of these mines are currently considering expanding
their productions, which would mean the building of dumps of 700m or more in
height in the near future. This type of structure would be the highest ever built by
man, requiring a meticulous consideration of all aspects related to long-term
behavior.Thesestructuresshouldbeabsolutelystableinordertobeenvironmentally
sustainableaswellaseconomicallyviable.
Thus,theminingindustry,geotechniciansandresearchersfacea majorchallenge
that calls for a significant joint effort to find appropriate solutions to the many
problems involved in conceiving and building this type of structure. It is, therefore,
of particular interest to analyze the mechanical behavior of waste rock under high
confining pressures induced by the very weight of the stockpiled materials. Indeed,
high pressures may modify the compressibility, permeability, and shear strength of
thesegranularmaterialsinasignificantway.
4.2.Developmentofnewlaboratoryequipmentfortestingcoarsematerials
Mined waste rock has proved to be an extremely heterogeneous granular
material, with particles coming from various lithologies or from the same type of
rock with different mechanical qualities according to the more or less important
weathering degrees. The dimensions of the particles are also very variable, ranging
from finely grained soils to meter-sized blocks. The laboratory equipment and the
test procedures for these materials have often been limited by the size of the
particles and the relatively low levels of the confining pressures applied.
Consequently, the geotechnical characterizations available have corresponded
mainly to those of the finest parts of these materials and for confining pressures that
are generally limited to 1MPa. Having the proper equipment to permit laboratory
tests on samples of greater dimensions and representative in situ tests is a foremost
necessity.
Reasonable doubts can be had on the representativity of the existing constitutive
laws and the failure criteria of very coarse materials, deposited in a loose state and
subjected to high confining stresses [VAL07]. Furthermore, experimental data
related to the behavior of these materials are scarce, as is suitable monitoring in any
stringent way. Follow-up procedures related to the real behavior of these deposits