Environmental Engineering Reference
In-Depth Information
Table 15.14.
(Continued).
Methods for assisting in the estimation
Initiator
Factors to consider
of likelihood of concentrated leak
Crest wall joint
• Visual inspection/displacement on joint
opens
• Design detail
Piping under plinth
• Part or all of plinth foundation
UNSW method for piping in
erodible e.g. soils, completely
foundation (Fell et al., 2000)
weathered rock, clay infill joints
• Hydraulic gradient
•Grouting - curtain
•Grouting - consolidation
(B)
Additional factors applicable to flood loading
All initiators
• AEP of flood levels
Hydrological analysis
• Historic high flood level
Likelihoods much less for flood levels
below historic high than above
• Increased face slab deformations,
Calculate from dam geometry,
joint openings, under flood loading
properties, existing deformations
and openings allowing for added
water load
(C)
Additional factors applicable to seismic loading
All initiators
• Earthquake magnitude, PGA, vs AEP
Swaisgood (1998) method or other
•Additional settlement induced
by earthquake
• Normal operating load case
Judgement/other analyses
assessment of P
initiation
•Crest wall geometry
geometry
re spillway wall
•Are there liquefiable (not necessary
Conventional methods based on
flow liquefaction) zones in the
Standard Penetration Test or Cone
foundation. What is the AEP of
Penetration Test, earthquake
magnitude,
liquefaction, and will freeboard
AEP of PGA. Check post liquefaction
be lost if liquefaction occurs
factor of safety/deformations
factors would apply to first filling, but in that case the overall historic performance could
be used to assist in quantifying the likelihood.
Also detailed are suggestions on the likelihood of initiation of a concentrated leak. The
term “compared to population” suggests the measurable value, e.g. slab displacement,
can be compared to the data in Section 15.6, and for example, if the measured value is
large compared to the population, a higher likelihood might be assigned. It will be appar-
ent that the estimate will be highly subjective and difficult to quantify. Some points should
be kept in mind:
- It is very unlikely a concentrated leak will form under normal operating conditions
(water levels within annual levels), unless for example a perimetric joint is right at the
limit of its displacement;
- It is more likely that a leak would form under reservoir water levels higher than the
historic high (because the loads will be greater than the dam has experienced
before/or under large seismic loads (because of the added settlements induced by the
earthquake).
