234
15 Risk-Informed Decision Making
The SLM methods gives Dams 1A and 1B category 1.4–1.6 based on the selections made in Table 15.5. It is worth noting that the SLM method does not contain
any provision for water balance or freeboard, as it is a general slope methodology, while ORE2_Tailings includes those factors and many other dam-specific ones.
ORE2_Tailings delivers Category 1.45–2.22, mainly because of the short, relatively
widely-spaced boreholes performed during the investigations. The rockfill nature of
the downstream slope of the dams makes it insensitive to erosion, as pointed out by
the engineers, and to a possible crest pipeline breach.
15.5.2 Dam 2
Table 15.6 displays the SLM results from Dam 2.
As shown in Table 15.6, the SLM method yields category 2.2–2.4. In the case of
Dam 2, where there are little tailings-dam-specific features, the correspondence of
SLM with ORE2_Tailings Category (2.17–2.36) is very good.
15.5.3 Dam 3
Table 15.7 displays the SLM results from Dam 3.
The SLM method delivers category 1.6–1.7 (Table 15.7). Because the SLM
method does not consider liquefaction, the divergence here is again significant:
ORE2_Tailings yields category 1.83–2.37.
Dam 3 could be significantly eroded were the crest pipeline to breach and remain
unobserved for more than 12 h.
15.5.4 Dam 4
Table 15.8 displays the SLM results from Dam 4.
The ORE2_Tailings category for such a dam, characterized by the paucity of data
and ignorance on many aspects of its history, is Category 3.3–3.8.
The SLM method delivers Category 3–3.2 again because it does not look at specific
tailings dams deficiencies. Dam 4 is being deactivated, so there are no active pipelines
at its crest.
15 Risk-Informed Decision Making
The SLM methods gives Dams 1A and 1B category 1.4–1.6 based on the selections made in Table 15.5. It is worth noting that the SLM method does not contain
any provision for water balance or freeboard, as it is a general slope methodology, while ORE2_Tailings includes those factors and many other dam-specific ones.
ORE2_Tailings delivers Category 1.45–2.22, mainly because of the short, relatively
widely-spaced boreholes performed during the investigations. The rockfill nature of
the downstream slope of the dams makes it insensitive to erosion, as pointed out by
the engineers, and to a possible crest pipeline breach.
15.5.2 Dam 2
Table 15.6 displays the SLM results from Dam 2.
As shown in Table 15.6, the SLM method yields category 2.2–2.4. In the case of
Dam 2, where there are little tailings-dam-specific features, the correspondence of
SLM with ORE2_Tailings Category (2.17–2.36) is very good.
15.5.3 Dam 3
Table 15.7 displays the SLM results from Dam 3.
The SLM method delivers category 1.6–1.7 (Table 15.7). Because the SLM
method does not consider liquefaction, the divergence here is again significant:
ORE2_Tailings yields category 1.83–2.37.
Dam 3 could be significantly eroded were the crest pipeline to breach and remain
unobserved for more than 12 h.
15.5.4 Dam 4
Table 15.8 displays the SLM results from Dam 4.
The ORE2_Tailings category for such a dam, characterized by the paucity of data
and ignorance on many aspects of its history, is Category 3.3–3.8.
The SLM method delivers Category 3–3.2 again because it does not look at specific
tailings dams deficiencies. Dam 4 is being deactivated, so there are no active pipelines
at its crest.