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ultimately lead to an increase in pore water pressure at the foundation level or in
areas above the contact between two layers.
Such “abnormal” conditions may occur in areas with extremely high rainfall,
with deterioration of the blocks or particles constituting the drainage system because
of natural or forced weathering and/or the increase in the number of thinner particles
due to high stress. The solution in these situations is not simple. Usually it involves
the selection of sound and ideally inert rocks to form the drainage system and to
build it separately, before the deposit begins to be formed. It may even require the
building of artificial drains housed in a trench, always with selected waste rock in
order to avoid the effect of high pressures on the behavior of these materials
[VAL 08].
4.7.2. Water management
A water management strategy must be developed to intercept and divert as much
surface runoff as possible away from the dump, both for reasons of physical stability
of the structure and for environmental considerations. This strategy must consider
solutions designed to avoid excessive watering of the dump. Thus, in periods of high
potential infiltration, it is necessary to provide effective drainage for the dump
platforms; these platforms sloping gently towards collection works, sealing surficial
cracks by scarification and compaction [MOR 01-06]. The traffic of high tonnage
trucks and/or the presence of the finest waste on the rolling surfaces in order to
preserve tires in good conditions, usually leads to highly compacted and relatively
impervious platform surfaces.
Previous situations are propitious to the occurrence of perched groundwater,
creating conditions favorable for the development of static liquefaction. To restore
adequate infiltration conditions, it is therefore necessary to scarify the surface of
these compacted and tightened surficial layers before allowing the following lift to
be dumped. In certain situations, geotechnical low-quality waste should be dumped
in different areas within the dump to reduce or avoid such problems, which
underlines the need to deal with the buttresses constructed with selected waste rock
[BAR 07a].
4.7.3. Foundation conditions
Local deformations induced by the foundation soils of low bearing capacity may
be the mechanism that triggers major landslides. Confronted with this possibility, it
would be advisable to avoid the materials constituting unstable foundations by
removing the weak materials, if the thicknesses involved allows. Another alternative
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