技术报告-尾矿库设计及评估 (英文)

Design and Evaluation of Tailings Dams

The valley dam design is particularly sensitive to overtopping by flood waters, erosion near the intersection of

the dam and the valley hillside, and liquefaction due to higher volumes of surface water inflow from drainages

within the natural catchment basin and from high precipitation runon/runoff. As is described in more detail

later, the stability of a valley dam depends largely on the level of hydrostatic pressure within fill material and

the embankment. An unusual, one-time rise in the hydrostatic pressure above design levels may be sufficient

to trigger failure. The control of inflows across, around, or under the impoundment is important to retaining

structural stability and to controlling environmental impacts. Providing adequate internal drainage can help

guard against liquefaction, and improve the permeability and consolidation of the tailings, thereby improving

the stability of the structure.

Because a shorter embankment is required in this configuration, it is more feasible to consider impervious

cores and internal drains as a means of controlling the phreatic surface and promoting stability of the

embankment. Surface water controls may also be necessary. Diversion channels may not always be an

option due to the difficulty of construction along steep valley sides. However, closed conduits may be an

alternative diversion method. Another alternative surface water control in the valley layout is to construct a

smaller water-retaining dam upstream of the tailings dam to collect the water to divert it around the tailings or

use it in the mill. A water-related factor that also must be considered, particularly in valley impoundments, is

the presence of shallow alluvial ground water. Ground water can infiltrate the tailings, thus raising the level

of saturation within the tailings; this can be seasonal, in response to seasonal high surface water flows that

interconnect with the alluvium upgradient of the impoundment (or under the impoundment itself).

It should be noted that any design that calls for diverting or otherwise controlling water flows during the

active life of the impoundment has to consider later periods as well. The water balance may be more

favorable after tailings slurry water is no longer being added to the impoundment/and the dam stability may

be less of a concern. However, if there are toxic contaminants in the tailings, or if the tailings are reactive, the

design must account for environmental performance following surface stabilization and reclamation.

The stability of the tailings impoundment is also dependent on (or at least related to) foundation

characteristics, such as shear strength, compressibility, and permeability. Depending on soil characteristics,

the valley layout can be adapted to account for high permeability materials in the design through the use of

liners and/or adequate internal drainage. Soil characteristics often can be improved through soil compaction.

In addition, the method of tailings deposition and construction have an increased impact on the valley

impoundment layout. The deposition of tailings affects consolidation, permeability, strength and,

subsequently, the stability of the embankment material. All these factors are discussed in later sections.

In some cases, liners or zones of low permeability may be appropriate means of controlling seepage to

enhance stability or environmental performance. The upstream face of tailings dams/embankments (i.e., the

side that contacts the tailings), for example, is frequently designed to provide a layer of low permeability or to

be impermeable. The effect is to lower the phreatic surface through the embankment. This is usually

accomplished with the slimes fraction of tailings and/or with synthetic materials.