Environmental Engineering Reference
In-Depth Information
There are finite element and finite difference models which can in principle model the
physical processes involved in infiltration through cover. Richards (1992) and Schroeder
et al. (1983) describe such models, which rely on knowledge of the properties of each of the
soil and rock layers in the cover, including saturated and unsaturated hydraulic conductivity
(permeability) and the relationship between suction pressures and water content. These
properties are very difficult to predict and vary by order of magnitude over normal ranges
of compaction density and water content. The Schroeder et al. (1983) HELP model seems
to have fairly wide acceptance. Readers are encouraged to read the latest literature for
available methods.
There are other practical problems associated with the analysis of infiltration through
cover. These include:
- Differential settlement of the tailings or waste rock or drying of the cover can lead to
cracking, with a resultant large increase in effective hydraulic conductivity. This is vir-
tually impossible to predict for cover placed over highly compressible tailings. The use
of geotextiles or geogrids to control cracking would lead to a greater degree of confi-
dence in the predictions, but again these all usually too expensive for use in tailings
storage.
-Vegetation performs a very useful role in promoting transpiration. However the roots
may penetrate the compacted soil layer leading to an increase in infiltration. Use of a silty
sand or sand layer over the compacted soil, or a chemically treated zone to prevent root
penetration may assist.
19.6.6.4
Return of area to productive use
In principle, it is desirable to return the area to productive use. Usually this can only be
for farming or other low intensity usage not affected by long term settlement.
