Environmental Engineering Reference
In-Depth Information
Horizontal
movement
Crest settlement
Face
settlement
Face
settlement
Reservoir filling
End of construction
Legend
Design section
Section at end of construction
Section after reservoir filling
Note: Deformation is exaggerated
Figure 15.33.
Diagrammatic deformation of the CFRD (adapted from Mori, 1999).
- The spillway chute slab should be built from the bottom up, with continuous reinforc-
ing in both directions, and extend into the side wall footings;
- For high dams, air grooves should be provided in the chute slab. These would also act
as contraction joints. Contraction joints would be needed in the spillway walls.
The Hydro-Electric Commission has constructed such a spillway on the 80 m high
Crotty Dam. The 12 m wide crest and chute have a discharge capacity of 210 m
3
/sec. The
chute has four “hinges” in it to accommodate settlement, aeration steps to prevent cavita-
tion and a flip bucket dissipator.
Carter et al. (2000) report that the Crotty Dam spillway has operated a few times since
1991 and has performed very adequately.
Namikas and Kulesza (1987) presented details of an emergency fuse plug spillway on a
32 m high CFRD. It is designed to operate for floods in excess of 1:1000 year return period.
15.6
OBSERVED SETTLEMENTS, AND DISPLACEMENTS OF THE
FACE SLAB, AND JOINTS
15.6.1
General behaviour
The upstream face of the dam is displaced during construction, on first filling, and during
operation (Figure15.33).
In most cases the face slab is constructed after the fill is all placed, so is not subject to the
movements shown to the end of construction.
During first filling, the water load acting on the face slab causes displacement of the
face slab normal to the plane of the slab, leading to tension around the perimeter, and
compression over the central part of the face, but also causes shear and tensile movements
at the perimetric joint. These movements continue with time. They may be sufficient to
open joints or cause cracking leading to leakage (
Figures 15.34
and
15.35
)
.
The following data and that in Section 15.7, have been collected to give readers an idea
of the range of settlements, displacements and leakage which has been observed, so they
can know what to expect, or can gauge the performance of their dam in comparison with
others. The data has been prepared with the assistance of Hunter (2003), Ang (2001) and
published data. More details on some aspects are available in Hunter (2003), Hunter and
Fell (2002, 2003c).
