Mining_Methods_UnderGround_Mining - Mining and Blasting

BaCkFilling
Backfilling for safety and profit
Permanent support
Empty stopes are frequently backfilled
as a means of providing support
for future mining. Other than
its own body weight, backfill is a
passive support system that has
to be compressed before exerting
a restraining force. Backfill material
is normally generated by the
mine as waste rock underground,
or as tailings from the surface con-
centrator, so backfilling may serve
a secondary purpose as a means
of disposal of otherwise useless
byproducts. The optimum backfill
method is clearly related to the
mi ning method. Costs of backfill
ty pically range between 10-20% of
mine operating cost, of which cement
represents up to 75%. Paste
fill is gaining in popularity because
it uses unclassified tailings and
less water, but the capital cost of
a paste fill plant is approximately
twice the cost of a conventional
hydraulic fill plant of the same
capacity.
Functions of backfill
The original function of backfill in hard
rock mines was to support rock walls
and pillars, and to provide a working sur-
face for continuing mining. This was
initially accomplished by rock fill, and
more often in the present day by hydraulic
fill.
If 3-4% of cement is added to a hydraulic
backfill of concentrator tailings,
and this is topped off in the stope with
a 10% mix, a smooth and hard surface
results. This is useful for mechanized
removal of broken ore from the subsequent
mining operation, and reduces
dilution from the fill.
Backfill also affords the opportunity
for more selective mining and better re-
covery of ore and pillars, thereby increasing
both mine life and total return
on investment.
Other functions of backfill are the
prevention of subsidence, and better
control over ventilation flow through
A.
B.
C.
D.
Drift and fill mining sequence.
Drift 1
Fill
Drift 1
Fill
Fencing
Drift 1
Fill
Drift 1
Cemented
Fill
the mine workings. Cemented hydraulic
fill (CHF) or paste backfill may
also be used to stabilize caved areas in
the mine. Backfill is also considered an
essential tool to help preserve the structural
integrity of the mine workings as
a whole, and to help avoid stressing
ground to the point where rock bursts
take place.
application and design
Drift 2
Fill
Drift 3
Fill preparation and placement systems
should be simple and efficient, with
special attention paid to quality control.
Two systems are used: cyclic filling and
delayed filling. In cyclic systems, the
fill is placed in successive lifts, as in
cut-and-fill mining sequences. The fill
can form a platform for the operation
Drift 3
Drift 3
Drift 3
Fill
Drift 2
Fill
Fencing
Drift 2
Fill
Drift 4
Drift 2
Cemented
Fill
of mining equipment, or mining may
be undertaken below, beside, or through
the backfill.
In delayed backfill, the entire stope is
filled in one operation. In this case, the
fill must be able to stand as an unsupported
wall rigid enough to withstand
the effects of blasting. It should allow
adjacent stopes to be extracted with minimal
dilution from sloughing.
A whole host of factors have to be
taken into consideration when designing
a backfill regime. The geology and
dimensions of the orebody and its dip
and grade are important factors, as are
the physical and mechanical properties
of both the ore and its host rock. Environmental
considerations, fill material
resources, mining method, production
capacity and operations schedules bear
underground mining methods 43