CIVIL ENGINEERING & PUBLIC WORKS
could easily be distinguished in the field by the colour and feel of the soils. The core material is slightly reddish in colour and soft, whereas the shoulder material is brittle and friable.
brownish,
& S. SIEVE NO
200
100 52
25
14
7
346
100
00
70
of
60
JUMITS OF GORE MATERIAL
The experience proved to be significance in that it enabled the
contractor to proceed
almost
im-
ap
ma-
mediately with placing on the propriate zone of the dam the terial which was obtained from a new borrow area, without having to wait for the results of classification tests in the laboratory.
Rockfill comprised sound granite obtained from the quarries about 1⁄2 mile upstream of the dam, and to a lesser extent from tunnel spoil as available from time to time. Because of the large quantity of rock requir- ed for the two rock zones, and for the production of filter materials as well as concrete aggregates, the con- tractor had to supplement his supply of rock and filter material from out- side sources when the demand heavy.
was
Construction of Embankment
materials
The core and shoulder were hauled from the borrow areas by tipper lorries, over distances be- tween 1/3 to 2 miles. The shoulder material was placed and rolled at its natural moisture content, which was very close to optimum as specified.
The core material, on the other hand, was placed and compacted at a moisture content 2 to 3 per cent above optimum in order to achieve flexibility. This was effected on the dam by spraying the core fill with water after spreading it with bull- dozers. Compaction of both types of fill in 9 in. layers was by means of rubber tyred rollers.
At the early stage of construction, the contractor had a self-propelled tyre roller, ballasted to 22 tons, and a smaller, towed tyre roller of 20 tons. However, the former was not very effective for use on the dam because it had insufficient tractive power to work on the soft core fill, and its mechanical breakdowns caused fre- quent delays.
A much heavier tyre roller was acquired later on hire from the P.W.D. It was ballasted up to 40 tons and was towed by a D8 bull- dozer. It was found that 4 to 6 passes on a 9 in. layer by this roller were sufficient to achieve a compac- tion factor of 95 per cent or more of the Proctor dry density of each type of earthfill.
To ensure proper compaction of fill materials around the projecting concrete cut-off wall, and in areas inaccessible to the rollers, mechanical rammers and vibrating plates were used.
embankment
Construction of the was carried out both by day and night, working two 11 hours shifts daily. The quality of the compacted earthfil! was controlled by three
30
20+++
تناه
,002
CLAY
SILT
.06
SAND
DER MATERIAL
2
60MM
GRAVEL
Fig. 4. Particle size curve of core and shoulder materials
PLASTICITY INDEX (%)
60
SO
30
201
10
10
x CORE MATERIAL
SHOULDER MATERIAL
20
30
ALINE
+
40
50
60
70
80
90
100
Fig. 5. Plasticity chart. Liquid limit (%)
laboratory assistants. Field density and moisture content tests were con- ducted on each compacted layer by the site assistants and Proctor density and classification tests were carried out in the laboratory.
At the end of construction, an average of one field density test had been carried out for every 121 cu. yd. of core material and one for every 211 cu. yd. of shoulder material. One set of classification and Proctor den- sity tests was conducted for about every 563 cu. yd. of core material and for about every 2,530 cu. yd. of shoulder material. In addition, un- disturbed samples were obtained of the compacted fill for triaxial com- pression tests with a view to compar- ing the actual strength of the com- pacted embankment with the design strength.
Results of triaxial drained shear tests, grouped together for each type of material, are shown in Fig. 6. It can be seen that the effective shear parameters range between cd of 7 lb. per sq. in., Pɑ of 341⁄2°, and cd of 3 lb. per sq. in., a of 31° for core material; and between cd of 9 lb. per sq. in., þa of 371⁄2o, and cd of 1 lb. per sq. in., pa of 331⁄2° for shoulder material. The speci- mens were 4 in. diameter, 8 in. long, and were saturated by back pressures.
Statistical analyses of field and laboratory tests were carried out at
Far East Architect & Builder December, 1965
the end of each month for each type of earthfill to determine the average compaction factor and placement moisture content. The average results at the end of construction are shown in Table 2.
Table 2
Average Compaction Factor and Placement Moisture Content.
Type of Fill
(a) Field Dry Density (lb.
per cu. ft.)
(b) Proctor Dry Density
(lb. per cu. ft.)
F
Core Shoulder
102.3 104.0
107.2
108.0
Compaction Factor
а
X 100 ( %}
95.2
96.3
(c) Placement Moisture
Content ( %)
21.2
17.5
18.5
17.8
(d) Optimum Moisture Content { %)
Deviation from Opti-
mum
C d ( %)
2.7 -0.3
The filter layers as well as the horizontal drainage blankets were compacted by means of a 4-ton vibrating steel-wheel roller, supple- mented by hand-operated vibrating plates. Initially, the rockfill was compacted by a 10 ton vibrating rub-
75