Hydraulic Structures: Fourth Edition

THE ROLLER-COMPACTED CONCRETE GRAVITY DAM 177

3.7.3 Developments in roller-compacted concrete dam construction

The RCC dam has developed rapidly since construction of the earliest
examples in the early 1980s, and in excess of 200 large dams had been
completed in RCC by 2000. The majority of RCC dams have been gravity
structures, but the RCC technique has been extended to a number of arch-
gravity and thick arch dams. As confidence has grown RCC has been used
for progressively larger dams, and has been employed for the major part
of the 7.6 106 m^3 volume of the 217 m high Longtan gravity dam in China.
In a number of recent instances the RCC gravity dam option has been
selected in preference to initial proposals for the construction of a rockfill
embankment.
The early RCC dams were noted for problems associated with relat-
ively high seepage and leakage through the more permeable RCC, and for a
degree of uncontrolled cracking (Hollingworth and Geringer, 1992). A relat-
ively low interlayer bond strength also prompted some concern, particularly
in the context of seismic loading. The philosophy of RCC dam design has in
consequence evolved, with emphasis being placed on optimizing design and
detailing to construction in RCC rather than using RCC to construct a con-
ventional gravity dam. This trend has led to the common provision of an
‘impermeable’ upstream element or barrier, e.g. by a slip-formed facing (Fig.
3.22 and also New Victoria dam, Australia (Ward and Mann, 1992)).
An alternative is the use of a PVC or similar synthetic membrane
placed against or just downstream of a high-quality concrete upstream
face. In the case of the 68 m high Concepcíon gravity dam, Honduras, a
3.2 mm PVC geomembrane backed by a supporting geotextile drainage
layer was applied to the upstream face of the RCC (Giovagnoli, Schrader
and Ercoli, 1992). Recent practice has also moved towards control of

Table 3.11 Characteristics of RCCs for dams

Characteristics RCC type Conventional

Lean RCC RCD High-

lean hearting

(RDLC) paste RCC

concrete

Cement (C)PFA (F) (kg m^3 ) 100–125 120–130  150 150–230
F/(CF) (%) 000–30 020–35 070–80 020–35
Water:(CF) ratio 1.0–1.1 0.8–0.9 0.5–0.6 0.5–0.7
90-day compressive strength,
c(MN m^2 ) 008–12 012–16 020–40 018–40

Unit weight, (^) c(kN m^3 ) ←⎯⎯⎯ 023–25 ⎯⎯⎯→ 022–25
Layer thickness (m) 0.3 (lifts) 000.3 (lifts)
0.7–1.0 1.5–2.5
Contraction joints Sawn Sawn Sawn or Formed
formed