Environmental Engineering Reference
In-Depth Information
Figure 17.13.
Slope modification in the cutoff foundation for interbedded sandstone and siltstone,
steeply dipping bedding.
Figure 17.14.
Bennett Dam, typical core abutment excavation requirements (Pratt et al., 1972, repro-
duced with permission of ASCE).
Pratt et al. (1972) describe slope modification for Mica and Bennett Dams in Canada. The
work carried out is shown in Figure 17.14. Walker & Bock (1972) give details of slope
correction work at Blue Mesa Dam (
Figure 17.15
)
. In this case some of the slope correc-
tion work was required to remove loose unstable rock from the abutments.
Since these projects were constructed it has been recognized that earthfill core for dams
may crack even in ideal conditions and that the best line of defence is to provide good fil-
ters (see Chapter 9). Hence the desirability of such major slope correction works is less
clear. The authors' assessment is that provided the overall slope is less than 0.25 H:1 V
(preferably 0.5 H:1 V) and good filters are provided, one should not be too concerned
about the large scale slope modification carried out in the examples above.
A more conservative approach to large scale modification might apply for dams in
severe earthquake areas, where differential movements and cracking may be more likely, and
for very large dams.
