Environmental Engineering Reference
In-Depth Information
Figure 9.7.
USSCS “no erosion” filter test apparatus (schematic, no scale) (Sherard and Dunnigan,
1985, reproduced with permission of ASCE).
Sherard et al. (1984a and b) also used a test set up with the base soil as a slurry and slot
tests.
The test shown in Figure 9.7 is intended to model the situation where a concentrated
leak has formed through the dam core, so that high hydraulic heads and gradients can
occur at the interface between the base soil and the filter ( Figure 9.8 ) .
The tests carried out by Sherard et al. (1984a and b) were directed towards finding the
filter particle size distribution which would give no-erosion (or at least very minor ero-
sion) conditions.
Figure 9.9 shows the type of equipment used by Bakker et al. (1990) to test for parallel
flow conditions.
9.2
DESIGN OF CRITICAL AND NON-CRITICAL FILTERS
9.2.1
Review of available methods for designing filters with flow normal to the filter
ICOLD (1994) describes the evolution of filter design practice. These have basically evolved
from the concepts of Terzaghi (1926) who proposed that D 15F /D 85B
4 to control erosion
and D 15F /D 15B
4 to ensure the filter was sufficiently permeable.
 
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