Geoscience Reference
In-Depth Information
14.14 Design elements of a dam walls
Some design elements of dam walls are summarised below.
Dam design and construction for medium to high walls needs detailed considera-
tions of all elements. These are covered in Fells et al. (2005).
Dam walls experience an unsymmetrical loading, yet many (small to medium)
dam walls are constructed as symmetrical. These cross-sections are relevant only
for ease of construction, and with an abundant supply of the required material.
Diaphragm walls are the most material efficient design, where sources of clayey
material are limited.
Table 14.14 Design elements of dam walls.
Design element
Consideration
Some dimensions for H
10 m
Comments
<
Type
Homogeneous
Applicable for
6 m
Type cross-section
<
Zoned
Minimum core width
H
depends on the
=
Diaphragm
Thickness
1.5 m for H
10 m
availability of material.
=
<
Seepage cut offs
Horizontal
0.5 m minimum thick extending
Blanket not effective on
Upstream
for
5H
highly permeable sands or
>
Blanket
Minimum 3 m width
gravels. See section 15.
Cut-off at base
Crest widths
Maintenance
Not less than 3 m
Capping layers at top.
Free board
Overtopping
1 m for small dams (0.5 m for
This is a critical design
flood flows
0.5 m wave action)
element for dam walls.
Most dams fail by
overtopping.
+
Settlement
Height
Allow 5% H for well-
Allow for this in free
dependent
constructed dam wall
board.
Slope protection
Rip rap
300 mm minimum thickness
Angular stones.
Outlet pipes
Cut-off collars
Placed every 3 m, typically 1.2 m
Compaction issues.
square for 150 mm diameter pipe
In a staged raising the capping layers still required in the years between each stage.
However it must be removed prior to each lift.
14.15 Stable slopes of levees and canals
The stability of a slope needs consideration of factors, other than limit equilibrium
type analysis. Some other factors are listed in the table below.
Table 14.15 Typical stable slopes for levees and canals.
Criteria
Slope
Comments
Ease of construction
1V: 2H
For stability of riprap layers
Maintenance
1V: 3H
Conveniently traversed with mowing equipment and
walked on during construction
Seepage
1V: 5H
To prevent damage from seepage with a uniform sandy material
Seepage
1V: 6H
To prevent damage from seepage with a uniform clayey material
 
 
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