技术报告-尾矿库设计及评估 (英文)

Design and Evaluation of Tailings Dams

to the phreatic surface can be caused by: malfunction of drainage systems, freezing of surface layers on the

downstream slope of the dam, changes in construction method (including the characteristics of the placed

material), and changes in the elevation of the pond. The level of the water table also may be altered by

changes in the permeability of the underlying foundation material; sometimes these are caused by strains

induced by mining subsidence (Vick 1990).

In addition to maintaining the phreatic surface for stability purposes, dam design now includes factors related

to environmental impacts associated with tailings seepage. By the use of liners, drains, and pumpback

systems, tailings seepage may be controlled. These techniques are discussed in more detail in a later section

of this report. The design should also address the future reclamation of the site.

3.2

3.2.1Design VariablesTailings-Specific Factors

Tailings composition, pulp density, grading, and other characteristics are used in the design of tailings

impoundments in three basic ways: tailings analysis to assess the potential use of tailings sands in

constructing the embankment, analysis of tailings to be placed in the impoundment to determine their

potential impact on structural stability and seepage characteristics, and mineralogical analysis to determine

the potential chemical aspects of seepage or other discharges from the impoundment. In addition to the

physical characteristics, the method of deposition of tailings into the impoundment plays a role in the

"engineering characteristics." (Vick 1990)

Tailings sands are often used as an inexpensive source of material for embankment construction; by removing

the sands for embankment construction the volume of tailings to be disposed of is reduced. Depending on the

gradation (grain size distribution) of the tailings, a cyclone may be used to separate sufficient amounts of

coarse sand from the whole tailings to construct the embankment, leaving a higher percentage of slimes to be

deposited behind the embankment. Cycloned sands can have both high effective strength and high

permeability, the two major characteristics necessary for downstream embankment material. In addition,

cycloning results in the deposit of the less permeable slimes behind the embankment, possibly reducing

impoundment seepage.

With regard to their general physical properties, tailings are considered to be soils, subject to traditional soil

mechanics patterns of behavior. Index properties (gradation, specific gravity, and plasticity) are determined

by relatively simple tests that can be performed on tailings produced in bench testing of the mill process.

These index tests are a guide to the engineering properties of the tailings. Caution is required, however, since

tailings differ in subtle ways from soils having similar index properties (Vick 1990).

Tailings properties that impact design, stability and drainage of the impoundment include in-place and

relative density, permeability, plasticity, compressibility, consolidation, shear strengths, and stress parameters

(Vick 1990). In-place density is an important factor in determining the size of impoundment required for a