Environmental Engineering Reference
In-Depth Information
Table 8.5.
ANCOLD (1999) consequences of failure classification.
Severity of damage and loss
Population at risk
Negligible
Minor
Medium
Major
0
Very low
Very low
Low
Significant
1 to 10
Low
Significant
Significant
High
Note 4
Note 5
Note 5
11 to 100
Note 1
Note 2
High
High
101 to 1000
High
High
Note 3
More than 1000
Note 3
Extreme
Note 1: With a PAR exceeding 5 people, it is unlikely that the severity of damage and loss will
be “Negligible”.
Note 2: “Minor” damage and loss would be unlikely when the PAR exceeds 10.
Note 3: “Medium” damage and loss is unlikely (but could be possible) when PAR exceeds 100.
Note 4: Change to
Significant
where it is possible that one life could be lost.
Note 5: Change to
High
where it is possible for more than one life could be lost.
Note 6: ANCOLD (1999) use the term “Hazard” rather than “consequences of failure”.
Also, logically, the consequences of failure should also be considered, with more reliable
types used where the consequences of failure are high. This can be done within a formal
risk framework or, in a less formal way, using the population at risk and severity of damage
and losses. Organisations such as ICOLD and ANCOLD have classification schemes for
consequences of failure, usually called “Hazard” classification. For the purposes of this
book we will use the ANCOLD (1999) classification. This is shown in Table 8.5.
The severity of damage and loss is assessed from estimated costs, loss of services and
business, social and economic and natural environmental. These are shown in
Table 8.6
.
The highest classification of damage and loss assessed from Table 8.6 is used when assess-
ing the consequence of failure classification in Table 8.5.
8.2.4
Types of embankment dams, their advantages, limitations and applicability
Table 8.7
summarises the types of embankment dams, their degree of control of internal
erosion and piping and pore pressures for slope instability, and suitability in relation to
the consequences of failure classification.
This table is for new dams and assumes the dams are well designed and constructed so fil-
ters meet no-erosion filter criteria and drainage zones have sufficient capacity to discharge
seepage through the dam and the foundation.
There are many existing homogeneous, earthfill with toe drains, zoned earthfill and
earthfill with horizontal drain dams which are in significant and high consequences of
failure locations. Whether these dams are suitably safe depends on their performance,
monitoring and surveillance, and other detailed factors. These can be assessed as detailed
in Chapters 9, 10 and 11.
8.3
ZONING OF EMBANKMENT DAMS AND TYPICAL CONSTRUCTION
MATERIALS
8.3.1
General principles
The following discussion describes “typical” zoning and construction materials for the most
common types of embankment dams. Each dam should be designed to satisfy the particular
