LIMIT OF CORE
SANO DRAINS
❘ FIRST MOUND OF CORE MATERIAL PLACED BY
GRAB ON THE DREDGED FOUNDATION.
3. DRIFTED MATERIAL FROM DUMPING OPERATIONS REMOVED FROM THE TOP OF THE MOUND BY DREDGING
2. DECOMPOSED ROCK FILLING DUMPED FROM BARGES
INTO THE SHOULDER FOLLOWED BY SAND FILLING
IN THE DAM
4. SECOND MOUND OF CORE MATERIAL PLACED
BY GRAB. THE OPERATIONS ARE THEN REPEATED IN SEQUENCE AS THE CORE IS RAISED.
Fig. 1.6: Sequence of operations to form the core
tion was being exposed, the super- visory staff made careful note of the materials excavated by the dredger and took samples of the materials re- covered for subsequent laboratory examination. Thus a check was kept on the nature of the soils exposed at foundation level and a final assess- ment of the suitability of the designed dredging levels could be made. Where it was suspected that unsuitable ma- terial remained in the foundation after the designed dredging levels had been reached, detailed examinations were made by percussion borings and, if necessary.
additional dredging was carried out.
The policy adopted in filling opera- tions was that the quality of all barge-
20
EXCESS PIEZOMETRIC HEAD OF SEAWATER
M FEET
5
O
CORE
loads of fill arriving at the main dam should have been checked at the load- ing point to ensure that it complied with the specified requirements. Ma- terial in a barge was also classified to indicate for which zones of the dam it was suitable. Thus, when a barge- load of fill arrived at the dam, it could be routed to a suitable location with- out delay.
At the borrow areas the engineer's site staff worked closely with the con- tractor's staff, checking and agreeing the day-to-day programme of excava- tion so that material of suitable quality could be delivered to the dam at the right time. As a final check the stone and fines content of each bargeload of decomposed rock filling was assessed
LOCATION OF PIEZOMETERS
LEVEL OF FILL
JANUARY 1966
FEBRUARY 1960
MARCH
1966
Fig. 1.7: Dissipation of pore pressures
62
40
DEPTH OF FILL ABOVE PIEZOMETERS
FEET
20
as suitable for use in the "shoulders”, "blanket" or "core" before despatch to the dam. Similar supervisory acti- vities were carried out at the sand dredging areas and the quarries,
At the main dam the location at which each bargeload was dumped was recorded by sextant and plotted. It was thus immediately apparent when material was deposited outside the designated limits. This aspect of the supervisory work was of parti- cular importance in ensuring that dumped material was excluded from the core. The areas within which bargeloads of fill were placed were also recorded. At all stages of the filling operations surveys were carried out to check on the profiles to which material had been deposited or trim- med. Areas where the workmanship was in doubt were investigated and. where necessary, remedial works were ordered.
Special Investigations
Various problems have arisen dur- ing construction for which there has been no precedent, and special inves tigations have been undertaken to examine and solve such problems. On each occasion a fully detailed re- port has been written. To date these
than reports number more
thirty. Some of the more important of these special investigations are outlined be- low.
An extensive investigation has been undertaken to estimate the perme- ability of the core of the main dam. A large number of 4 in. dia. undis- turbed samples have been taken from the core, and grain-size analyses and laboratory permeability tests perform- ed.
As a result an approximate cor- relation was established between grain- size and permeability. Permeability of a cross-section was estimated by taking a series of undisturbed sam- ples, measuring grain-size, estimating individual permeabilities, computing the overall permeability of the section, and checking by means of conven- tional field permeability tests in bore- holes sunk in the core.
A special probe has also been de- vised for measuring permeability directly. This investigation has also given a large amount of information on the degree of segregation of the fill after placing and enabled the best method of placing to be determined for each items of placing plant. The design requirement is that the overall permeability of the core should not exceed 1 x 10-4 cm. sec. The in- vestigations indicate that this require- ment will be met.
A series of investigations have been made to determine the best way of removing both residual dredging de- bris and decomposed rock fines. Special sampling tools have been de- veloped and the properties of the materials examined in the site soils laboratory.
Barge loads of decomposed rock
Far East Architect & Builder November, 1967