Modern practice is to specify a graded rockfill, heavily compacted in
relatively thin layers by heavy plant. The construction method is
therefore essentially similar to that for the earthfill embankment.
The terms ‘zoned rockfill dam’ or ‘earthfill–rockfill dam’ are used to
describe rockfill embankments incorporating relatively wide impervious
zones of compacted earthfill. Rockfill embankments employing a thin
upstream membrane of asphaltic concrete, reinforced concrete or other
manufactured material are referred to as ‘decked rockfill dams’.
Representative sections for rockfill embankments of different types
are illustrated in Fig. 1.3. Comparison should be made between the
representative profile geometries indicated on the sections of Figs 1.2 and
1.3. The saving in fill quantity arising from the use of rockfill for a dam of
given height is very considerable. It arises from the frictional nature of
rockfill, which gives relatively high shear strength, and from high perme-
ability, resulting in the virtual elimination of porewater pressure problems
and permitting steeper slopes. Further savings arise from the reduced
foundation footprint and the reduction in length of outlet works etc.
14 ELEMENTS OF DAM ENGINEERING
(e) Wide rolled clay core: zoned with
transitions and drains: note base drain
m 2.5 – 3.5
(f) Earthfill/rockfill with central rolled
clay core: zoned with transitions and
drains
m 1.6 – 2.0
zone 2
transition/
drain
zone 3 zone 1 zone 2
zone 2a
zone 4 transition/drain
zone 3
zone 2
(c) Slender central clay core:
19th-century ‘Pennines’ type –
obsolete post 1950
m 2.5 – 3.5
(d) Central concrete core:
smaller dams – obsolescent
m 2.5 – 3.5
(a) Homogenous with toedrain:
small secondary dams
m 2.0 – 2.5
(b) Modern homogeneous with internal
chimney drain
m 2.5 – 3.5
Fig. 1.2 Principal variants of earthfill and earthfill–rockfill embankment
dams (values of mare indicative only)
