Environmental Engineering Reference
In-Depth Information
topographic and foundation conditions at the site and to use available construction materi-
als, so there really are no “typical” or “standard” designs. To highlight this, examples are
given of the various types of dams. Many of these are drawn from Australian practice as
detailed in the ANCOLD (Australian National Committee on Large Dams) Bulletins and
from the authors' own experience. Figures 1.1 and 1.2 show typical cross sections for the
most common types of embankment dams. Table 1.1 describes the zoning numbering sys-
tem used in Figures 1.2 and 1.3 (and throughout this topic) and the function of the zones.
Table 1.2 describes terms used relating to foundation treatment.
Table 8.8 describes typical construction materials used for the different zones in
embankment dams. It is emphasised that good dam engineering involves use of the mate-
rials available at the site rather than to look for materials with a preconceived ideas about
the material properties needed. However this rule is not followed in the search for Zones
Table 8.8.
Embankment dam typical construction materials.
Zone
Description
Construction material
1
Earthfill
Clay, sandy clay, clayey sand, silty sand, possibly with some gravel. Usually
greater than 15% passing 0.075 mm, preferably more. Note that weathered
siltstone, shale and sandstone can sometimes be compacted in thin layers
to give sufficiently fine material
2A
Fine filter
Sand or gravelly sand, with less than 5% (preferably less than 2%)
fines passing 0.075 mm. Fines should be non plastic. Manufactured by
crushing, washing, screening and recombining sand-gravel deposits
and/or quarried rock
2B
Coarse filter
Gravelly sand or sandy gravel, manufactured as for Zone 2A. Zones 2A and
2B are required to be dense, hard durable aggregates with similar
requirements to that specified for concrete aggregates. They are designed
to strict particle size grading limits to act as filters
2C
Upstream filter
Sand gravel/gravelly sand, well graded e.g. 100% passing 75 mm, not
and filter under
greater than 8% passing 0.075 mm fines non plastic. Usually obtained
rip rap
as crusher run or gravel pit run with a minimum of washing, screening and
regarding. Relaxed durability and filter design requirements compared
to Zones 2A and 2B
2D
Fine cushion
Silty sandy gravel well graded, preferably with 2-12% passing 0.075 mm
layer
to reduce permeability. Obtained by crushing and screening rock or
naturally occurring gravels or as crusher run. Larger particles up to
200 mm are allowed by some authorities, but segregation and internal
instability is likely to result
2E
Coarse cushion
Fine rockfill placed in 500 mm layers to result in a well graded
layer
sand/gravel/cobbles mix which satisfies filter grading requirements
compared to Zone 2D
3A
Rockfill
Quarry run rockfill, possibly with oversize removed in quarry or on dam.
Preferably dense, strong, free draining after compaction, but lesser
properties are often accepted. Compacted in 0.5-1 m layers with
maximum particle size equal to compacted layer thickness
3B
Coarse rockfill
Quarry run rockfill. Preferably dense, strong, free draining after compaction,
but lesser properties are often accepted. Compacted in 1.5-2.0 m layers
with maximum particle size equal to compacted layer thickness
4
Rip rap
Selected dense durable rockfill sized to prevent erosion by wave action.
In earth and rockfill dams often constructed by sorting larger rocks from
adjacent 3A and 3B Zones. In earthfill dams either selected rockfill or a
wider zone of quarry run rockfill may be used
