Environmental Engineering Reference
In-Depth Information
obviously contributed to the sliding, an extremely low shear strength was indicated for
the seam.
After removal of some rockfill which had already been placed, a 40 m by 70 m area of
the rockfill foundation was excavated down to below the seam level (
Figure 2.35
and
Figure 2.36). The slide was then stabilised by a spur of rockfill which later formed a project-
ing part of the dam shoulder. Other modifications to the dam included a local widening of
the downstream filter zones and placement of a filter blanket over an area of slide mate-
rial left in place beneath the rockfill (Figure 2.35 and Figure 2.36).
Monitoring during filling showed local downslope movements of up to 90 mm in and
upstream from the spillway approach area. Lilly (1986) explains that these were to be
expected, as cracks up to 150 mm previously noted in these areas would be closing up. No
significant unusual movements of the dam embankment were recorded.
Although a satisfactory dam was the end result, the landsliding and discovery of dis-
turbed materials extending into the rockfill and filter foundations caused serious ques-
tions to be raised, and delays to construction. With hindsight, more thorough
investigation and delineation of the slide during the planning stages might have resulted
in the dam being located well away from the affected area.
2.10.3.4
Sugarloaf Dam
Sugarloaf Dam is an 85 m high, 1000 m long concrete faced rockfill structure, constructed
near Melbourne, Australia during 1976-1979. It impounds an offstream storage of
95,000 megalitres.
The site geology and its influence on the design and construction of the dam are dis-
cussed in Stapledon and Casinader (1977), Casinader and Stapledon (1979) and
Casinader (1982).
The site is in a region of broadly folded siltstones and sandstones of Devonian age
which are distinctly weathered to depths of more than 30 m below ridges and plateaus.
Figure 2.36.
Wungong Dam, sections showing remedial works (based on Lilly, 1986).
