Geoscience Reference
In-Depth Information
For a more accurate understanding of the effects of chemical degradation and its
consequences on the mechanical behavior of waste rock, it is necessary to carry out
more systematic research on waste rock from different lithologies.
4.7.6.
Designing for closure
To construct a HWRD and then ponder what must be done for the closure of this
structure is an unthinkable strategy, given the extraordinary dimensions involved. To
reshape the geometry of a slope with a height of more than 500 m is a situation that
nobody would undertake, not only because of the costs involved but also for the
technical complexities and security issues related to works of this magnitude. The
most reasonable solution for high waste rock is to design a dump that meets the
closure criteria from the outset. The practical implications of this decision means
that the dump must be built with more gentle general slopes, conservative drainage
systems, effective effluent collection systems and treatment of the effluents, if
necessary. The existence of intermediate berms in the design of the dump will also
allow global instabilities to be controlled, and if it is called for, a control of possible
snow avalanches [VAL 08].
4.8. Conclusions
The results from triaxial tests performed on samples of large dimensions for
three types of waste rock with different initial grain sizes have shown that these
materials present adequate shear strength at high pressures. The mechanical behavior
of these materials does not differ substantially from that of other granular materials
used in the construction of dams. It is, therefore, feasible to construct deposits of
great heights with waste rock.
The shear strength envelope of the waste rock curves gradually as the level of
pressure is increased, showing a reduction in the shear strength induced by the
increase in compressibility of the granular matrix, associated with the crushing of
particles. In fact, the compressibility and particle breakage are increased
significantly for effective mean pressures above 1 MPa. It is worth noting that the
final grain size distributions obtained at high pressures for the different waste rocks
tend towards a single grain-size curve, independently of the initial grain size being
tested, for materials conformed by particles of similar lithology. Considering the
mechanical behavior of waste rock at high pressures, subjected to overburden
stresses well beyond any precedent, the front slope of the dump has been designed
with a global angle of the order of 22ยบ (2.5:1=H:V), with the objective of generating
a smaller load zone destined to create a high-strength and high-permeability buttress.
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