Geotechnical News • June 2012
39
WASTE GEOTECHNICS
A new technical committee to promote and coordinate
activities in mining geotechnique
Michel Aubertin, Murray Grabinsky, Dharma Wijewickreme, and Ward Wilson
The mining industry is an impor-
tant asset for the economy of many
regions, particularly with respect to
exports and employment, but also
through numerous technological
developments. A large proportion
of Canadian geotechnical engineers
and geoscientists have been working
on mining projects, as indicated by
regular presentations at the Cana-
dian National Conference, during the
Cross Canada Lecture Tours, and in
the Canadian Geotechnical Journal.
However, such numerous activities
related to mining geotechnique have
not been systematically coordinated
within the Canadian Geotechnical
Society (CGS).
Technical Committees have been cre-
ated by the CGS to address activities
and issues of permanent importance
or interest to its members, and these
transcend Divisional lines and there-
fore require a different organizational
structure. The field of Mining Geo-
technique constitutes one such wide-
spanning discipline. The CGS Board
recognized this situation and approved
the creation of a new Technical Com-
mittee (TC) during its fall 2011 meet-
ing to promote the development and
visibility of this field. The committee
brings together CGS members with an
interest in the broad field of geotech-
nique applied to mining projects.
Many different areas will be included
in the mandate of the new TC. This
will be the case, for instance, with
issues related to the behavior of under-
ground backfilled openings. Canada
hosts some of the largest and deep-
est underground ore deposits, which,
to extract these deposits safely and
economically, requires the use of local
and regional ground support systems.
In this regard, stope backfilling is
playing an increasingly important role.
Both rock fills and hydraulic sand fills
have historically been used, but recent
advances in thickening and transport
technology make it possible to create
backfill from tailings with a “paste”
consistency, especially for precious
metal mines where the ore is finely
ground to maximize recovery.
The use of paste backfill is an advanta-
geous way of handling tailings pro-
duced by hard rock mines, which have
the general characteristics of low plas-
ticity silts. At water contents around
40%, plug flow transport of these
tailings can be achieved in pipelines
using positive displacement pumps
and gravity. Underground, the depos-
ited paste shows a lava-like flow that
is non-segregating and produces very
little bleed water. Compared to previ-
ous backfill technologies, paste can be
delivered faster, it more completely
fills the mined void space, it dramati-
cally reduces the water to be managed
(as compared to hydraulic fills), and
it more efficiently uses binder added
for the backfill strength needed during
subsequent mining.
Significant achievements have been
made in mine backfill engineering
over the last few years. Backfills in
operating mines have been extensively
instrumented to provide information
about the development of total stresses
and porewater pressures during fill-
ing and curing, as well as to monitor
the response of barricades used to
retain the backfill. Analytical models
based on vertical stress arching within
the backfill have evolved and been
compared with model studies and are
now being calibrated using field data.
Modified Gibson solutions and numer-
ical simulations have been applied to
understand backfill consolidation and
the dependency of pore pressure dissi-
pation on filling rates and the evolving
backfill material properties. Binder
chemistry and its interaction with
process water chemistry and tailings
mineralogy has been investigated. The
role of binder hydration and its con-
tribution to dissipating pore pressures
through self-desiccation (or chemical
shrinkage) is better understood. Fully
three-dimensional numerical models
that incorporate the coupled hydraulic-
mechanical-thermal behaviour of
backfill are becoming feasible. Bar-
ricade design is also becoming more
rational, incorporating advances in
reinforced concrete technology or in
waste rock behavior.
Although recent successes have
resulted in safety and efficiency
improvements in operating mines,
many research challenges lie ahead.
A better understanding is needed of
backfill’s contaminant transport and
fate processes for closed mines that
lie within a regional groundwater flow
system. Significant advances, have
yet to be made on the many concrete
mix design modifiers that are used
routinely in civil engineering. Bet-
ter in situ strength characterization
