Environmental Engineering Reference
In-Depth Information
Crack or hydraulic
fracture through core
“AND” gate
Brittleness of
core materials
Low stress
condition in core
Reservoir
operation
“OR” gate
Compaction
density
Compaction
water content
Soil
type
Abutment
profile
Irregularities
in foundation
Foundation
differential
settlement
Arching of
core between
shells
Closure
section
Figure 10.40. Fault tree diagram for the formation of a crack or hydraulic fracture through the core
(Foster, 1999).
Table 10.4. Influence of factors on likelihood of cracking or wetting induced collapse-susceptibility of
core materials (Foster and Fell, 2000).
Influence on likelihood of cracking or collapse
Factor
More likely
Neutral
Less likely
Compaction density
Poorly compacted,
95%
95-98% standard
Well compacted,
98%
ratio
(1)
standard compaction
compaction density
standard compaction
density ratio
(2)
ratio
density ratio
Compaction water
Dry of standard optimum
Approx OWC-1% to
Optimum or wet of
content
water content (approx.
OWC-2%
standard optimum water
OWC-3%)
content
Soil types
(3)
Low plasticity clay fines
Medium plasticity clay
High plasticity clay
fines
fines
Cohesionless silty fines
Notes:
(1)
For cracking, compaction density ratio is not a major factor. It is more important for wetting
induced collapse.
(2)
93% Standard compaction, dry of OWC, much more likely.
(3)
Soil type is not as important as compaction density and water content.
of likelihood of hydraulic fracture or crack through the core can be represented in a fault
tree structure, as illustrated in Figure 10.40.
Cracking or hydraulic fracturing of the core is more likely if the soil is brittle and there
is a low stress condition present. Therefore the “AND” gate is used to link these two
issues in the fault tree. The factors contributing to the presence of a low stress condition
in the core are linked using an “OR” gate as only one of these factors needs to be present.
Tables 10.4 to
10.8
and
Figures 10.41
to
10.45
summarize the factors which influence
the likelihood of a concentrated leak. These are based on the literature, including Lambe
(1958), Leonards and Narain (1963), Sherard et al. (1963), Sherard et al. (1972a and b),
Sherard (1973, 1985), Truscott (1977), Jaworski et al. (1981), Gillon and Newton
(1988), Lo and Kanairu (1990), Lawton et al. (1992), Charles (1997), Høeg et al. (1998)
and a review of case studies Foster (1999), Foster and Fell (1999b), Foster et al. (1998).
Table 10.9
summarises the factors influencing the likelihood of suffusion occurring in
the core if the core or the foundation is cohesionless material. The susceptibility of soils
