Environmental Engineering Reference
In-Depth Information
Table 10.5.
Influence of factors in the likelihood of cracking or hydraulic fracturing - features giving
low stress conditions (Foster and Fell, 2000).
Influence on likelihood of cracking or hydraulic fracture
Factor
More likely
Neutral
Less likely
Overall abutment
Deep and narrow valley.
Reasonably uniform
Uniform abutment
profile
Abrupt changes in abutment
slopes and moderate
profile, or large scale
profile, continuous across
steepness, e.g. 0.25 H:1 V
slope modification.
core. Near vertical
to 0.5 H:1 V
Flat abutment
abutment slopes
slopes (
0.5 H:1 V)
Small scale
Steps, benches, depressions in
Irregularities present,
Careful slope
irregularities in
rock foundation, particularly
but not continuous
modification or
abutment profile
if continuous across width of
across width of the core
smooth profile
core (examples: haul road,
grouting platforms during
construction, river channel)
Differential
Deep soil foundation adjacent
Soil foundation, gradual
Low compressibility
foundation
to rock abutments. Variable
variation in depth
soil foundation. No
settlement
depth of foundation soils
soil in foundation
Variation in compressibility
of foundation soils
Core
Narrow core, H/W
2,
Average core width,
Wide core H/W
1
characteristics
particularly core with
2
H/W
1
vertical sides
Core material less stiff than
Core and shell materials
Core material stiffer
shell material
equivalent stiffness
than shell material
Central core
Upstream sloping core
Closure section
River diversion through
No closure section
(during
closure section in dam, or
(river diversion
construction)
new fill placed a long time
through outlet
after original construction
conduit or tunnel)
to suffusion depends on the particle size distribution. This can be assessed based on the gen-
eral shape of the grading curve or using the techniques of Sherard (1979), Kenney and Lau
(1985) or Burenkova (1993) to analyse the grading curve. Recent research still under way at
UNSW indicates that the Kenney and Lau (1985) and Sherard (1979) methods may be con-
servative for soils with a large proportion of silty fines.
We are of the opinion that suffusion cannot occur in cohesive soils. Except possibly in low
clay size content (
10% passing 0.075 mm) and low plasticity (plasticity index
7%) soils.
10.7.1.2 Continuation of erosion
Whether erosion will continue is dependent on the zoning of the dam, in particular,
whether there are filters or transition zones which will eventually cause the erosion which
has initiated to cease.
It is recommended that the assessment of the likely filter performance be considered
bythe compatibility of the core and filter (or downstream zone) materials in terms of the
filter test erosion boundaries as described in Foster (1999) and Foster and Fell (1999a and
b, 2000) and in Chapter 9.
These show that modern filter design criteria e.g. Sherard and Dunnigan (1989) are
based essentially on no erosion of the dam core and that coarser filters may eventually seal
with some erosion, which may only give limited leakage rates.
 
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