Environmental Engineering Reference
In-Depth Information
Figure 2.30.
Tooma Dam, plan showing observed features and movements which occurred during
construction.
It was concluded from the results that the site would show wide variations in weathered
profile, but no special problems were envisaged.
During stripping of the foundation, the variations in weathered profile were confirmed
(
Figure 2.31
). However the exposed rock was much more mechanically loosened than
predicted. In the valley sides, the floor of the cutoff trench showed near-vertical joints par-
allel to the river which were open as much as 30 mm, apparently due to downslope block
movements (in the past) along prominent joints dipping towards the river at 10-30°.
Clay-infilled joints and weathered seams next to joints were abundant.
The last specified stripping was removal of 2 m to 3 m depth of boulders and gravel
from the river channel. During this operation, many cracks open from 10 mm up to
500 mm appeared in and above the cliffs on the right bank (Figure 2.30 and Figure 2.31).
The cracks were mapped to the upstream side of the cutoff trench where they became ill-
defined in a steeply dipping zone of open jointed, clearly disturbed and weathered rock
striking obliquely to the river (Figure 2.30). Lesser cracks and scarps appeared in
extremely weathered granite on the left bank.
