Tailings Disposal - Mining and the Environment: From Ore to Metal - page 726

TABLE 18.2
Target Design Criteria for Tailings Impoundments - After mining the TSF must remain as safe as during mine
operations

Engineering and Construction
Cofferdams and diversions
Factor of safety against slope failure
No specifi c earthquake allowance (included in slope safety factor)

1:10 year Design 1:100 year
1.3

Operation
Spillways
Earthquake
Static safety factor for slopes
Erosion protection on slopes

1 in 1000 year fl ood
1 in 100 year event to 1 in 475 year event
1.3 to 1.5
1 in 1000 year rainfall

Closure
Spillways
Earthquake (some damage, minimal release)
Static safety factor for slopes

Probable maximum fl ood
Maximum credible earthquake

Trap Effi ciency
Average trap effi ciency for solids
Range of trap effi ciencies
Minimum size 100% trapped
% trapped for fractions 0.004-0.01 mm
Effl uent D50

95%
90-96%
0.004-0.1 mm
40% to 50%
0.004

Source:
Environmental Workshop 14-18 October 1996 Newcastle, New South Wales Australia, Proceedings Volume 2, Mineral Council of Australia p.189

Basic engineering methods such as dam stability or foundation and seepage analysis are
essentially the same. Nonetheless, some aspects of tailings storage are specii c such as the
need to control potential environmental contamination and to design for a long closure
phase. Some of the basic design criteria for TSF follow. Target design criteria commonly
used for tailings impoundments are summarized in Table 18.2 :
●

Tailings Storage Facilities are designed to facilitate closure objectives.

●

Embankments are engineered and constructed from local soil, waste mined rock,
coarse tailings or a mixture of these materials.

●

Embankments are designed to accommodate all tailings generated over the mine life,
possibly allowing some contingency.

●

Tailings impoundments are usually developed in stages to minimize initial capital
expenditures. Embankments may be raised many times during the mine life; com-
monly at the rate of one raise each year.

●

Allowances in the design are made for possible future expansion of the TSF to accom-
modate future potential increases in proven reserves.

●

Diversion channels are often provided to intercept and divert clean surface water,
which would otherwise l ow into the TSF. This helps in overall water management
and reduces the freeboard required to avoid overtopping.

●

Decant water systems are designed to accommodate extreme rainfall events.

●

Tailings slurry is commonly discharged from the perimeter of the impoundment above
the level of previously placed tailings. This is known as aerial disposal, as distinct from
sub-aqueous disposal. Near the discharge point(s), deposited tailings contain a higher
proportion of coarser particles, because these settle more quickly, forming a tailings
beach. Further from the discharge point(s), tailings deposits contain a higher proportion