Environmental Engineering Reference
In-Depth Information
Figure 13.11.
Issues in dimensioning embankment dams. (a) and (c) are usually poor practice; (b) and
(d) are usually correct practice.
known before construction and is a variable distance from the centreline giving a “mean-
dering” location of the cutoff trench. The cutoff trench width is wrongly defined as
shown, i.e. with width W at the cutoff foundation. In practice it is better to define the
width D E which can be set after general excavation is completed, with an overriding
dimension W min to cover the situation where the depth of excavation to cutoff founda-
tion is deeper than anticipated.
- Dimensioning filter and rip-rap layers as thicknesses normal to the slope (u, v and f)
rather than as widths c, d and e. In most cases construction is in horizontal lifts so the
widths are more appropriate.
- Dimensioning filter zones with varying widths using slopes g, h and i rather than as con-
stant widths. There is no technical need for the filter width to increase with height; setting
out is more complicated and volume of filters is increased by using the varying widths.
- Chimney drains should be vertical rather than inclined, as they are better constructed by
digging back through compacted earthfill (see Figure 9.30) rather than placed concur-
rently with the fill.
13.4.2
Tolerances
Specifications for construction of embankment dams usually include tolerances on the
dimensions of the embankment. These reflect the need to ensure that, for example, the
thickness and the widths of filter zones are maintained even if the position of the filter in
the embankment varies slightly.
The tolerances shown in Table 13.6 would be reasonable for larger earth and rockfill
dams with filters, such as those shown in Figure 1.2.
 
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