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Malaysia Water Research Journal
earth fill and rock fill dams is seepage and piping as shown in Table 1.
Table 1. Causes for dam (over 15m height) failure (ICOLD)
Causes Failure Percentage (%)
Piping and Seepage 38
Overtopping 35
Foundation 21
Others 6
This survey was carried out in 1973. Hydraulic failure accounts for over 40% of
earth dam failure and may be due to one or more of the following:
i. By overtopping: When free board of dam or capacity of spillway is insufficient,
the flood water will pass over the dam and wash it downstream.
ii. Erosion of downstream toe: The toe of the dam at the downstream side
may be eroded due to heavy cross-current from spillway buckets, or tail
water. When the toe of downstream is eroded, it will lead to failure of dam.
iii. Erosion of upstream surface: During winds, the waves developed near the
top water surface may cut into the soil of upstream dam face which may
cause slip of the upstream surface leading to failure.
iv. Erosion of downstream face by gully formation: During heavy rains, the
flowing rain water over the downstream face can erode the surface,
creating gullies, which could lead to failure.
Seepage always occurs in the dams. If the magnitude is within design limits,
it may not harm the stability of the dam. However, if seepage is concentrated or
uncontrolled beyond limits, it will lead to failure of the dam. Following are some
of the various types of seepage failure:
i. Piping through dam body. When seepage starts through poor soils in the
body of the dam, small channels are formed which transport material
downstream. As more materials are transported downstream, the channels
glow bigger and bigger which could lead to wash out of dam as shown in
Figure 1.
Figure 1. Failure of dam due to piping through dam body
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Institut Penyelidikan Hidraulik Kebangsaan Malaysia (NAHRIM)
National Hydraulic Institute of Malaysia (NAHRIM)