Environmental Engineering Reference
In-Depth Information
Figure 17.8.
Left abutment of Blowering Dam after treatment of large fault zone and weathered seam
(Courtesy of Snowy Hydro).
17.3.3
Cutoff in soil
- Remove soil with open fissures, open joints, roots, root-holes, permeable layers (e.g.
sand and gravel) and other permeable structure (e.g. leached zones in lateritic soils);
- Remove dispersive soils if possible;
- Carry out slope modification as described in Section 17.6;
- If the soil on the sides of the cutoff trench displays permeable layers or features which
would allow erosion of the earthfill into them, it should be trimmed and cleaned and
covered with a filter layer or layers which are designed to control such erosion. Details
of such treatment are shown in Figure 10.8 In extreme cases it may be necessary to also
cover the slope with pneumatically applied mortar;
- Remove loose and dry soil and other debris with light equipment, possibly with the aid of
an air jet. The base of the cutoff should be watered to within 2% dry and 1% wet of opti-
mum water content and rolled before placing the first layer of fill, to compact any soil
loosened by the construction work. If necessary it should be disked or tyned with a grader
to facilitate the moisture conditioning.
17.4
WIDTH AND BATTER SLOPES FOR CUTOFF IN EMBANKMENT DAMS
The width of cutoff trench adopted depends on:
- the rock or soil quality at cutoff foundation level;
- the size and consequences of failure of the dam;
-the type of embankment.
