技术报告-尾矿库设计及评估 (英文)

Design and Evaluation of Tailings Dams

and results in less seepage. There are also drawbacks to this design, including the relatively large volumes of

material necessary for construction, and its effect on cost. The increased length of the embankment walls also

may increase the possibility of failure (Robertson 1984, cited in Ritcey 1989). Other disadvantages of the

ring dike system are that the impoundment rises above the surrounding terrain, creating an aesthetic problem

in some locations, and there can be considerable wind erosion of the tailings. In many areas, also, there is no

flat terrain suitable for ring-dike designs.

Although each situation needs to be evaluated on its own merits, the ring dike system has the potential for

better control of seepage than that found in most valley dam locations. If warranted by the characteristics of a

particular tailings, almost total containment and collection of effluent can be achieved using a suitable

combination of low permeability cores, liners, and drainage system. Since seepage control is often a pressing

environmental concern with tailings impoundments, the ring dike system can have an important advantage

over most other layouts.

2.2.3In-Pit Impoundments

This method is much less common than the valley and ring-dike impoundments. It consists of disposing

tailings material into a previously mined pit. The design initially eliminates the need for dike construction.

Since the tailings are protected by pit walls, wind dispersion is minimized. Good drainage can be

incorporated into the design. Many of the failure modes common to tailings embankments (e.g., piping,

liquefaction) do not apply to this design. The lack of dam walls reduces the possibility of slope failure, but

the stability of the pit slopes do have to be checked.

Unless the purpose is to isolate sulfide tailings underneath water, the water table should be below the tailings

disposed in the pit. This may require backfilling with mine rock or overburden. If backfilling underneath the

tailings is necessary, and/or if the surrounding rock is not sufficiently impermeable, a liner may be required.

Ritcey (1989) notes that the hydrogeological parameters affecting the migration of seepage and contaminants

are poorly understood, so tailings with toxic contaminants or reactive tailings may be poor candidates for this

type of impoundment.

When mining in an active pit is proceeding laterally, the mined-out portion of the pit may be suitable for

tailings disposal. In such cases, dikes would be constructed to impound the tailings in the mined-out area.

This embankment could then be raised in a phased approach (Ritcey 1989).

2.2.4Specially Dug Pit Impoundment Design

This design is fairly unusual and involves the excavation of a pit specifically for the purpose of tailings

disposal. The impoundment consists of four or more cells with impermeable liners and surrounded by an

abovegrade dam. Material removed from the pit is used in construction of the dam. This dug pit/dam design

has some of the same advantages as the ring-dike design, including site independence and uniform shape.