Foundation preparation and cleanup for embankment and concrete dams - Geotechnical Engineering of Dams - page 701

17

Foundation preparation and cleanup for embankment
and concrete dams

17.1 GENERAL REQUIREMENTS

17.1.1 Embankment dams

The degree of foundation preparation which is necessary for a dam embankment depends
on the:

-Type of dam;
- Height of dam and the consequences of failure;
-Topography of the dam site;
-Erodibility, strength, permeability, compressibility of the soil or rock in the dam foun-
dation;
-Groundwater inflows to excavations;
- Climate, and river flows.

Foundation preparation for the “ general foundation ”, i.e. the foundation beneath the
bulk of the embankment, is quite different from that for the “ cutoff foundation ”, i.e. the
foundation under the earthfill core of an earth and rockfill dam prepared to cutoff stan-
dard, or the plinth of a concrete face rockfill dam.
Figure 17.1 shows the terms used in this chapter.
The objectives are:

- General foundation : To remove low strength and compressible material to provide a
foundation of adequate strength and compressibility to support the embankment. In
most cases, but not always, the general foundation will be of higher strength than the
embankment and will not dictate the embankment stability. In most cases permeability
will not be a critical factor. Liquefiable materials may need to be removed or treated.
- Cutoff foundation : To remove highly permeable and erodible material below the gen-
eral foundation level to provide a low permeability non erodible foundation (consistent
with the design of filters and drains on the foundation). In many cases, e.g. in soil foun-
dations or rock foundations which are permeable to great depth, a low permeability
non-erodible cutoff foundation cannot be economically achieved by excavation alone
and other design measures are required. These are discussed in Chapter 10.

17.1.2 Concrete dams

The degree of foundation preparation for a concrete dam depends on the:

-Type of dam (gravity, arch, buttress);
- Height of the dam and the consequences of failure;
-Topography of the dam site;