2.9 Rockfill embankments and rockfill
2.9.1 Rockfill embankments
Rockfill embankments may either have an internal watertight element or an
upstream deck, as illustrated on Fig. 1.3(a) to (d). In the case of the former,
the element is generally central and may be of earthfill or, in the absence of
suitable soils, of asphaltic concrete. The latter type of slender bituminous
element is increasingly common in Europe. The alternative upstream face
membrane or deck can be constructed of reinforced concrete or of asphaltic
concrete; in either event the deck is relatively thin. The concrete decked rock-
fill dam, commonly referred to as the CFRD type, has been widely used for
very large dams in South America and Australia. Deck thickness generally
increases with depth below crest level, and is typically of the order of
(0.30.005H) m for high dams. The concrete deck must, however, be sub-
divided into rectangular strips running normal to the dam axis, or into rectan-
gular panels, to accommodate deformation of the rockfill. This requires an
expensive and sometimes troublesome joint detail incorporating a waterstop.
An asphaltic concrete deck, which is generally somewhat thinner, has the
advantage of a degree of flexibility, and no joint system is therefore necessary.
A central asphaltic or bituminous core is typically of the order of
1.0–1.5 m maximum width, with a narrow transition zone on either side. A
rockfill embankment with a central asphaltic core is shown in Fig. 2.17 and
described in Gallacher (1988). The central membrane and the upstream
deck each have advantages, e.g. a dam with an upstream deck will have
greater resistance to horizontal sliding and is more easily repaired. The
central membrane, on the other hand, is less vulnerable to deterioration
and accidental or deliberate damage.
Rockfill embankments, if protected and/or reinforced, have the capa-
bility to accept throughflow or overflow of flood water without serious
damage. Suitable protective measures are discussed in Maranha das Neves
and ICOLD (1993c).
2.9.2 Rockfill
Compacted rockfills have displaced the dumped or sluiced rockfills for-
merly employed for embankment dam construction. The concept of
well-graded and intensively compacted rockfill has developed from
appreciation of the importance of grading and the introduction of heavy
compaction plant. Compacted density is the principal factor governing
rockfill shear strength and settlement.
Representative characteristics for graded compacted rockfill were
100 EMBANKMENT DAM ENGINEERING
