Mining in focus
With the growth of computer power available
to practitioners and researchers, the development
of finite element theories became practically
possible.
the actual failure, as some form of plasticity
behaviour (that is, limiting stresses) is required
to model failure conditions.
Critical state soil mechanics
Hard data from the field have also contributed
to our understanding of TSFs — by informing
our technology-driven modelling. In the 1960s,
the inventory of field and laboratory test
results were used in developing the theory of
critical state soil mechanics. Over the next 20
years, the theory of critical state soil mechanics
gained general acceptance, forming the basis of
our understanding of clay soil behaviour. This
theory was in turn applied to the behaviour
of sandy soil. These theories were extended in
the past 20 or so years to develop even more
sophisticated elastoplastic models that include
strain hardening and softening models.
As computing power and models
developed in the 1970s, they were put to
good use addressing practical problems in
soil mechanics such as seismic behaviour,
static liquefaction, and progressive failure. The
results improved in each decade as the models
improved. Almost realistic seismic behaviour
modelling of dams using elastoplastic
models began in the 1970s, and the software
gradually evolved to be able to model tailings
dams as well.
The first methods developed for slope
stability assessment were limit equilibrium
slope stability methods; for some of these,
closed-form mathematical solutions could
be developed, and many problems could be
solved without significant computing power.
However, they assume that the failure surface
will develop at the same time in all materials
through which the failure surface passes.
For geotechnical materials with different
stiffnesses and failure paths, this assumption
would not apply.
With the growth of computer power
available to practitioners and researchers,
the development of finite element theories
became practically possible. These evolved
from linear elasticity and non-linear elasticity,
to simple elastoplastic models and later to
more sophisticated elastoplastic models
which included critical state theory models.
More recently, even more sophisticated
models emerged, considering strain
hardening and softening.
Each of these have made a contribution to
the way we have approached TSFs, although
there are weaknesses. With linear elasticity, for
example, there are two reasons that constrain
its application. In the first place, most natural
geotechnical materials do not have a linear
elastic stress strain curve, so a linear elastic
model can only approximate the behaviour
of natural materials at certain parts of the
stress strain curve. Secondly, it cannot model
Advances in technology promise to pave the way to
safer and more environmentally sound tailings storage
practices.
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APRIL 2019 MINING MIRROR [21]