Environmental Engineering Reference
In-Depth Information
EARTH CORE
k H
R.L. 76.5
0.00001
W.L. 74.5
k V
0.000001
EARTH/ROCKFILL
k H
POOR QUALITY ROCKFILL
k H
1
100
k V
0.1
k V
10
HORIZONTAL DRAIN
k H
k V
10,000
R.L. 26.0
26
7 72
DIAPHRAGM
WALL
68
28
SAND &
GRAVEL
k H 75
k V 15
66
64
30
BOULDERS &
GRAVEL
k H
62
k V
1000
60
58
56
54
52
50
48
46
44
42
40
38
36
34
32
NOTE: ALL PERMEABILITIES 10 4 m/sec.
Figure 11.14.
Seepage equipotentials Lungga Dam, uniform foundation (Coffey and Partners, 1981b).
R.L. 76.5
EARTH CORE
k H
W.L. 74.5
0.00001
k V
0.000001
POOR QUALITY ROCKFILL
k H
100
EARTH/ROCKFILL
k H 1
k V 0.1
k V
10
HORIZONTAL DRAIN
k H
k V
10000
COMPACTED FOUNDATION
SANDY GRAVEL k H
k V
1
R.L. 26.0
28
30
32
72
DIAPHRAGM
WALL
70
68
SAND &
GRAVEL
k H
66
75
k V
15
54
34
BOULDERS &
GRAVEL
k H
k V
1000
62
60
58
56
54
52
50
48
46
44
42
40
38
36
(a)
NOTE: ALL PERMEABILITIES
10 4 m/sec.
EARTH CORE
k H
R.L. 76.5
0.00001
W.L. 74.5
k V
0.000001
EARTH/ROCKFILL
k H
POOR QUALITY ROCKFILL
k H
1
100
k V
0.1
k V
10
HORIZONTAL DRAIN
k H k V 10000
R.L. 26.0
26
7 72
DENSIFIED SAND
& GRAVEL
k H
DIAPHRAGM
WALL
5 58
k V
5
28
54
52
30
SAND & GRAVEL
k H
75
k V
15
BOULDERS &
GRAVEL
k H k V 1000
32
60
58
56
54
52
50
48
46
44
42
40
38
36
34
(b)
NOTE: ALL PERMEABILITIES 10 4 m/sec.
Figure 11.15.
Seepage equipotentials Lungga Dam foundation affected by (a) upper compacted zone;
(b) densification by vibroflotation (Coffey and Partners, 1981b).
The upper foundation layer has a lower permeability than the lower layer and the
confining effect led to pore pressures in the lower layer being above ground surface
at the downstream toe of the embankment. To remedy this situation pressure relief
wells were constructed which fully penetrated the lower (sand) layer. The original
wells shown in Figure 11.13 were only partially penetrating and therefore not very
effective in relieving pressures.
Figures 11.14 and 11.15 show the effect of foundation permeability on the seepage
flownets for Lungga Dam, Solomon Islands, which was to be constructed on perme-
able alluvial soils.
The analysis for Lungga Dam includes the use of a diaphragm wall which pene-
trates part way through the highly permeable foundation sands and gravels. Being par-
tially penetrating it reduces seepage only by a small amount (less than 5%) compared
 
 
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