Environmental Engineering Reference
In-Depth Information
Table 10.3.
Effect of design and construction details on the likelihood of internal erosion and piping in
the embankment (Foster and Fell, 2000).
Relative importance
Factor
Initiation
Continuation
Progression
Breach
Geometry
General zoning
L
-
M
H
Core width
M/H
-
L
L
Core width/height
L/M
-
M
L
Crest width
-
-
-
L/M
Freeboard
-
-
-
M/H
Downstream zone properties
-
-
M/H
H
Filter/code
-
H
H
M
Compatibility dam core
Classification
M
-
H
L
Erodibility/dispersivity
L
-
H
L
Compaction density ratio
M
-
M
L
Compaction water content
H
-
H
L
Permeability
M
-
M
L
Degree of saturation
M
-
H
L
Foundation
Large scale irregularities
H
-
L
-
Small scale irregularities
M
-
L
-
Compressible soils
M
-
L
L
Conduits
If present
H
-
H
L
Type/joint details
L
-
L
-
Settlement
L
-
L
-
Trench details
H
-
H
L
Walls abutting core
If present
H
-
H
L
Slope
M
-
L
-
Collars/finish
L
-
L
-
Storage volume
-
-
-
M
Closure section
M
-
M
L
Notes: (1) Relative importance weightings are judgemental and will vary from dam to dam.
(2) -
not applicable, L
low, M
medium, H
high.
10.7.1
Piping through the embankment
Table 10.3 summarizes the effect of design and construction details on the likelihood of
internal erosion and piping in the embankment. It is based on a detailed review of the lit-
erature (which generally only considers one aspect e.g. erodibility) and a review of case
studies of dams which have failed or experienced piping accidents.
The relative importance weightings are judgemental and the table is only meant to high-
light how the different factors influence the different stages of the development of piping,
from initiation through to breach.
The following sections summarize the factors affecting the internal erosion and piping
process. They are taken from Foster and Fell (2000).
10.7.1.1
Formation of a concentrated leak
A concentrated leak may form by transverse cracking, wetting induced collapse, hydraulic
fracture, a high permeability zone or association with a conduit or wall. The assessment
