Environmental Engineering Reference
In-Depth Information
Figure 2.29.
Original site for Talbingo Dam, cross section looking downstream.
and diamond drilling, which showed the slide mass to consist of extremely weathered
basalt containing a small percentage of irregularly distributed blocks of less weathered
basalt from gravel size up to several metres across.
An alternative site free of landslide evidence was adopted. At this site, more than 100 m
upstream, the 161 m high Talbingo Dam (rockfill) was built, using 2.3 million m
3
of the
basaltic landslide deposit for its impervious core. During operation of the borrow pit,
some renewed sliding movements occurred within the deposit.
2.10.3.2
Tooma Dam
Tooma Dam is a 68 m high earth and rockfill structure, constructed during 1958-1961 in
the Snowy Mountains of New South Wales.
The dam is located in a steep-sided valley which has been entrenched about 80 m below
an older, broad valley. Prior to construction, outcrops of granitic rocks were present along
both banks of the river and extended locally to 10 m to 40 m above river level. The largest
outcrop area formed a cliff about 30 m high on the right bank beneath the upstream
shoulder of the proposed dam (
Figure 2.30
and
Figure 2.31
).
This outcrop and a lower outcrop area directly opposite on the left bank, were termi-
nated on their upstream sides by soil-filled gullies. The rock outcrops above river level
showed near-vertical joints roughly parallel and normal to river direction.
During the planning stages subsurface exploration of the site included trenches up to
1.5 m deep cut by hand methods, and 17 diamond boreholes with water pressure testing.
