Environmental Engineering Reference
In-Depth Information
10
Control of seepage, internal erosion and piping for
embankment dams
10.1
GENERAL REQUIREMENTS AND METHODS OF CONTROL
The objective in designing a new dam, or when assessing an existing dam, is to be satis-
fied that the dam has adequate measures to control seepage and potential internal erosion
so that:
(a) Pore pressures in the dam and the foundation are such that there is an adequate mar-
gin of safety against slope instability;
(b) Internal erosion, which might progress to form a pipe and breach the dam, will not
occur. This applies to piping in the embankment, in the soil or rock foundation, from
the embankment to the foundation and the foundation into the downstream zones of
the embankment.
These objects are achieved by zoning of the dam, provision of filters and high seepage
discharge capacity zones and other embankment design and foundation treatment meas-
ures. Figure 10.1 shows some of the measures which are used.
The design features are:
A: Low permeability “core” of the dam, to limit seepage through the dam;
B: Chimney filter drain, which intercepts seepage through the dam and controls internal
erosion of the core and pore pressures in the dam, if the downstream zone C is low
permeability;
FSL
B
I
A
C
E
D
F
G
H
High permeability
soil or rock
Low permeability
soil or rock
Figure 10.1.
Design features for controlling seepage and erosion through and beneath earth dams on
highly permeable foundations A, low permeability core; B, chimney filter drain; C, down-
stream zones; D, horizontal filter drain; E, upstream low permeability blanket; F, slurry
trench; G, grouted zone; H, relief wells;I, weighting berm.
