Terrain assessment, drainage and erosion - Geotechnical Investigation and Design Tables - page 200

•

Refer to Chapter 16 for use of geotextiles as a filter.

•

Thickness of filter typically > 20 D max.

Figure 15.4 Seepage control.

15.26 Seepage loss through earth dams
•

All dams leak to some extent. Often this is not observable. Design seeks to control
that leakage to an acceptable level.

•

Guidance on the acceptable seepage level is vague in the literature.

•

The following is compiled from the references, but interpolating and extrapolating
for other values. This is likely to be a very site and dam specific parameter.

Table 15.26 Guidance on typical seepage losses from earth dams (Quies, 2002).

Dam height (m) Seepage, litres/day/metre, (Litres/minute/metre)

O.K. Not O.K.

<

5

<

25 (0.02)

>

50 (0.03)

5-10 50 (0.03) 100 (0.07) < >

10-20 100 (0.07) 200 (0.14) < >

20-40 200 (0.14) 400 (0.28)

< >

40 400 (0.28) 800 (0.56)

> < >

15.27 Clay blanket thicknesses
•

A clay blanket can be used at the base of a canal or immediately inside of a dam
wall to increase the seepage path (L), thus reducing the hydraulic gradient (i

=

h/l).