Environmental Engineering Reference
In-Depth Information
Figure 10.11.
Effect of partial cutoff on position of line of seepage: (a) flownets,
z
/
D
0. (b) flownet,
z
/
D
0.6. (c) position of line of seepage to various values of
z
/
D
(Cedergren, 1972).
10.4.2
Cutoff trench
When the depth of permeable soil is relatively small, an effective way of providing a cut-
off is to excavate a trench through the permeable layer and backfill with Zone 1 earthfill
as shown in
Figure 10.8
. If there are continuous relatively low permeability layers within
the soil the cutoff trench may be stopped at such a layer rather than penetrating to rock.
The practicality and economics of constructing the cutoff this way depend on:
- Whether dewatering is necessary to construct the cutoff;
- The availability of equipment to construct cutoffs by other methods, e.g. slurry trench;
- The stability of the sides of the trench during construction (which is dependent on soil
type, consistency and effectiveness of dewatering).
