Environmental Engineering Reference
In-Depth Information
Table 14.6.
Minimum required frequency of construction testing Zone 2A and 2B filters.
Shear
Dam
Country
Filter volume
Particle size
Relative density
Permeability
strength
9,500,000 yd
3
4,000 yd
3
150,000 yd
3
Oroville
USA
Each 24 hrs
-
36,000 yd
3
1,400 yd
3
1,400 yd
3
Culmback
USA
2 tests
2 tests
1,670,000 m
3
6,000 m
3
Beas
India
-
Occasionally
-
1,300,000 m
3
4,000 m
3
4,000 m
3
QA-8, La Grande
Canadia
-
-
22,000 yd
3
1,500 yd
3
1,500 yd
3
Brandy Ranch
USA
-
-
444,000 yd
3
4,000 yd
3
5,000 yd
3
Bloomington
USA
-
-
1,000 m
3
or
2,000 m
3
or each
Winneke
Australia
Filter blanket
N/A
N/A
each layer
alternate layer
297,000 m
3(1)
1,000 m
3
to
Ranger Mine
Australia
Method
Some
2,000 m
3
specification
Tailings Dam
Note:
(1)
Filter transition, combines function of Zones 2A & 2B.
technical consultants and these can outweigh the real technical issues. His comments are
still relevant today and are recommended reading for all who are involved in dam engi-
neering. Milligan (2003) also covers some of these issues.
14.5
TESTING OF ROCKFILL
14.5.1
Particle size, density and permeability
The testing of rockfill to determine the particle size compacted density and permeability
is complicated by the large size of the rock particles.
Bertram (1972) describes field density tests in rockfill with a maximum size of
0.45 m, using a 1.8 m diameter density ring to define the density-in-place hole. The
hole was dug to the full depth of the layer. ICOLD (1986b) give details of testing
for Oroville Dam, where a 1.8 m diameter ring was used for rockfill up to 0.6 m
size. Hence, a ring size 3 to 4 times the maximum particle size has been used to get
representative samples. For equivalent samples of rock up to 1 metre maximum size,
a ring and hole 3 metres diameter would be needed, giving about 15 tonnes of rockfill
to be excavated for a 1 metre thick layer. This highlights the magnitude of the problem,
and is the reason why it is impracticable to carry out density and particle size distribution
tests in rockfill for smaller dams. Penman (1983) and Forssblad (1981) describe a
compaction meter, which uses an accelerograph to monitor the response of a vibratory
roller and assists in determining when the required degree of compaction has been
achieved.
Test gradings on rip-rap are even more difficult to do. Spreading of a sample of rip-rap
over the ground and individual measurement of rock particles within a defined strip has
been used. On Prospect Dam remedial words (Sydney, 1996), one supplier went so far as
weighing the individual particles.
Permeability of rockfill can be determined by ring infiltration tests
in situ
. If the rock-
fill is permeable the quantities of water involved would be huge and the results of doubt-
ful value. For low permeability rockfill, tests through say 1.0 m to 1.8 m diameter rings,
depending on particle size, could be carried out. In most cases a subjective assessment, by
observing whether water will pond on the surface or in a hole dug through a layer, will be
adequate to ascertain if the fill is “free draining” or not. Bertram (1972) and ICOLD
(1986b) give references for field testing of rockfill.
