| Reasons
for the dam failure
The reason for the foundation failure,
and the failure of the mine management to foresee the problem is still a matter
of discussion, although a number of theories have been proposed. The mine
operators claim that there was no way to foresee the incident and have
subsequently blamed construction contractors for misinterpreting the
geotechnical properties of the site.
A report prepared for the mining company
described the weak point of the dam two years in advance of the failure.
Geotechnical experts suggest that the
foundation failure was caused by chemical attack of the impounded acidic pyritic
slurries on the marl forming the dam foundation material.
Other experts suggest that the dam was
built on expansive clays which deformed with wetting and drying. They claim that
the expansion and contraction of the clays should have been accounted for in the
design of the dam. In addition, reports indicate that the subsoil was unsuitable
to support the mass of tailings that were piled up in the dam.
Acidic seepage, combined with continued
blasting in the nearby open pit mine would have contributed to the dam failure.
Other experts suggest that the dam was
designed with insufficient beach width and that the dam was being filled at a
rate higher that it was designed for.
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