100
200
100.
COPD..
300
296
ROCKFILE
FILTER
QUI
RIPRAP SURFACE
SCALE
700 ET
0014
281
かじゅ
cio Eu
9011
OD12
US
99
SHOULDER
SHOULDER
OUT
eve
°C?
0010
004
OUS OU2
a.
CORE
007
оро
096
OCA
003
• DI
004
+ D2
GROUTHOLES
CUT-OFF
DF6
DF7
DRAINAGE BLANKET
FILTER,
DFB
IIS TWL (SUPPLY BASIN
ROCKFILL
DAM
Fig. 2. Cross section
In the original design, horizontal drainage blankets of 18 in. thick at vertical intervals of 20 ft. were re- quired in both the upstream and downstream shoulders. The purpose of these drainage blankets was to accelerate the dissipation of pore water pressures during construction in both shoulders, and during rapid draw-down in the upstream shoulder. However, as the constructional pore water pressures in the shoulders prov- ed to be negligible, only two such blankets were put in each shoulder.
The 6 ft. thick mass concrete cut- off wall which was constructed into fresh to slightly weathered granite along the centre line of the embank- ment extends well into the left and right abutments, in places about 120 ft. deep (Fig. 3).
Three lines of AX-size groutholes, one along and one 10 ft. each side of the centre line, were put down under the core to seal up any cavities or fissures in the bedrock by injecting cement grout. The depths of the groutholes varied, being governed by the permeability of the rock encoun- tered.
The criterion was that the treated rock should have a coefficient of per- meability of not more than 1 Lugeon
ALL LEVELS ARE IN FEET ABOVE PD
PIEZOMETERS ARE SHOWN THUS O
Unit* obtained by water pressure testing in the drillhole.
The maximum height of the dam is 186 ft. and the crest length is about 750 ft. Its maximum width at the base is about 1,100 ft. The width of the core varies from 100 ft. at the base to 20 ft. at the top.
The quantities of materials for the dam are shown in Table 1 below:—
Table 1
Quantities of Materials
Material
Core fill
Quantity (cu. yd.)
158,200
Shoulder fill
983,700
Rock fill
317,700
Filter
Total
158,000
1,617,600
Embanking Materials
The main embanking material for the rolled earthfill was completely decomposed granite. This occurs in
* Water loss of 1 litre per minute per metre length of drillhole, under a pres- sure of 10 kg. per sq. cm.
abundance in the neighbouring hills. The weathering profile of granite has been described by Ruxton and Berry, 1957 (1).
A zone of about 4 to 10 ft. of more clayey structureless residual soil exists below the top soil, and this material was selected as core fill. Below this zone, where the weather- ing is less intense, the residual soil is coarser, and the granitic structure is still apparent. This material was selected as shoulder fill. The upper and lower limits of particle-size curves for each type of material are shown in Fig. 4.
Although the specification stipulat- ed that the core material should con- tain not less than 25 per cent by weight particles passing a No. 200 B.S. sieve, it was found that this alone was not adequate to identify the core material, because the grading limits of core and shoulder materials over- lap, as shown in Fig. 4. The cri- terion of a plasticity index of 20 per cent was used to supplement the identification of the two types of materials, as suggested by Lamb. 1962 (2). This was found to be quite reliable, as will be seen in Fig. 5.
It was also found that with some experience, the two types of materials
400
LEVEL IN FT.
CH 800
AX-SIZE GROUT HOLES
SPILLWAY TUNNEL
CONCRETE
CUT-OFF WALL
— - CH 1200
Fig. 3. Longitudinal section along centre line (looking downstream)
74
CM 1300
CH 1400
OOST HO、
DAM CREST 306
-TW.L.296
ORIGINAL GROUND LINE,
CH 1600
CH 1700
TOP OF CONCRETE CUT-OFF WALL
AX-SIZE GROUT HOLES
SCALE
མ་་
OOK HƏ
Far East Architect & Builder
December, 1965