BS sieve with an average of 10% pass- ing 3/16 in.
It was noted that very little move- ment of fines took place when rockfill was sluiced with twice its volume of water. On cutting trenches through the test embankment it was noted that there was a marked tendency for the fines to collect near the top of each lift. This was considered due partly to the method of tipping and dozing and partly to the fines near the surface rising when vibrated.
The plates set in the top of the foundation had settled an average of 3⁄41⁄4 in. No correction of the results has been made for this settlement nor for any further compaction of the first layer that could have occurred while compacting the second layer. The compaction of the second layer may not have contributed substantially to settlement of the plates.
Table 3 is produced from Table 1 to show percentage compaction of the original layer thickness achieved by each two passes of the roller over 6 ft. thick layers of Grades A and B rockfill compacted after sluicing.
Graphs 2, 3 and 4 generally in- dicate that either 3 ft. or 6 ft. layers should be adopted. However, 3 ft. layers may not be suitable as the rock fill size would have to be kept below 2 ft., which would increase the cost of blasting. Free draining rockfill is a pre- requisite of the design and some con- gregation of the fines takes place at the surface of each layer which in- hibits free drainage.
Therefore, it is desirable to have the least number of layers possible. The maximum life height is specified as 6 ft. and the test results do not jus- tify that it should be changed. In order to minimise the tendency for fines to collect at the surface, rockfill should
TABLE 2
Comparison Of % Compaction Of Rockfill Compacted Dry and After Sluicing.
Grade A Rockfill
Layer Depth
No. Of Observations
No. Of Roller Passes
Dry
Sluiced
4
6
8
10
12
14
2.5' to 3.5'
9
4
1.8
1.5
0.5
0.8
3.5' to 4.5'
10
(-0.8)
(-2.3) (-2.8)
(-3.1)
4.5' to 5.5'
4
5
2.6
(-0.1)
(-0.3) (-0.2)
5.5" to 6.5'
12
4.1
4.1
4.7
4.2
Grade B Rockfill
2.5' to 3.5' 3.5' to 4.5' 4.5' to 5.5' 5.5' to 6.5'
00
4
6
8
10
12
14
6
2.0
1.4
0.5
1.6
2.0
2.3
7
1.0
2.1
2.1
2.7
2.4
3.7
4
10
4.3
4.5
4.1
6.6
4.6 5.3
4.3
4.3
3.8
4.3
4.0 4.3
a69a
TABLE 3
3333
CANK
Comparison Of % Additional Compaction With Additional Roller Passes For 6'
Grade A (Compacted After Sluicing)
Grade B (
Layer.
No. Of Roller Passes
2
4
6
7.8 1.2
8
1.6 0.7 0.9
10
12
14 16 18
9.3
2.4
1.4
0.1 0.8 0.4 0.6 0.5 0.9
be tipped directly over the advancing of roller passes. It would appear from edge of the layer.
Table 2 indicates that sluicing will result in an additional 4% or more of compaction for Grade A and B rockfill compacted in a 6 ft. layer. Therefore, sluicing was considered necessary. However, it was decided that the volume of sluicing water could be reduced to half the volume of rockfill because it was only important to en- sure that the rockfill was thoroughly wet, and therefore softened, imme- diately before it was compacted.
The compaction of sluiced 6 ft. layers was compared with the number
SAW 185
ABG
CAT
Table 3 that six passes is a reasonable time to stop rolling for Grades A and B rockfill compacted after sluicing although a fairly significant rate of compaction was achieved after 8 passes and up to 18 passes.
The tests also confirmed that Grade B rockfill compacts more than Grade A rockfill.
Conclusions
The trial embankments demon- strated that the specified maximum layer thickness (6 ft.), minimum number of roller passes (6) and the requirement for sluicing were justified. However, the minimum volume of sluicing water could be reduced to half the volume of rockfill.
During construction of the trial embankments various tipping, sluicing, compaction, sampling and testing tech- niques were experimented with until satisfactory construction methods were arrived at which were applied to Pedu Dam.
Main contractors for the Pedu Dam were: Kajima Construction Co./Taisei Construction Co., Tokyo. The consult- ing engineers for the Muda Irrigation Project were Sir William Halcrow & Partners.
SAW 185 vibrating roller
Far East BUILDER, July 1971 Page 45
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