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JAFFÉ ON HONG KONG WATERWORKS,
amounted to 11,461 cubic yards, of which 5,704 cubic yards was rock.
The excavation for the foundations of the dam on either side Rock was of the stream-bed did not present much difficulty. generally found at very nearly the estimated depths, except for a length of 200 feet adjoining the stream-bed at the northern end of the dam. For this length the foundation had to be carried down to a maximum depth of 70 feet below the original surface of the ground, The excavations and this proved rather a troublesome matter. in the hillsides were in earth of a clayey nature, which increased in density with the depth below ground surface until soft laminated rock was reached. Sound rock was generally found after a few feet of soft rock had been removed. Practically no timbering was required for the foundation trench except for the length which had to be carried down 70 feet below ground-surface. The excavation for the foundation trench of the dam on either side of the stream- bed amounted to 58,928 cubic yards, of which 14,077 cubic yards was rock.
HEARTING OF THE DAM (Figs. 5 and 6, Plate 1).
The hearting of the dam is entirely of cement concrete, which, with the exception of a backing to the masonry of the up-stream face, has granite displacers embedded in it ranging in size from 2 to 10 cubic feet. Care was taken to see that all such stones were bedded on a fresh layer of concrete at least 6 inches in thickness, and that not less than 6 inches separated adjacent stones. Larger stones than 10 cubic feet could not be used, because no crane power was available. Stones of these weights are carried by the Chinese slung from bamboos supported on the shoulders In order to ensure the of two or more coolies as required, proper bedding of the stones in the plastic concrete, they were several times in succession levered up at one end a few inches and allowed to fall back. This system was found to be effective in getting rid of imprisoned air and much better than striking the stones with a heavy mall. The proportions of the concrete ranged from 1 of cement to 6 of sand and stone, at the base of the dam, to 1 of cement to 8 of sand and stone at top water-level. The proportions of sand to broken stone were: for the 6-to-1 mixture, 2 sand to 4 stone (1 inch); for the 7-to-1 mixture, 2 sand to 4 stone (1 inch); and for the 8-to-1 mixture, 3 sand to 5 stone (3 parts 2 inches and 2 parts 1 inch). The concrete backing adjoining the masonry of the water face of the dam is 4 to 1, and,
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Papers.] LOW-LEVEL RESERVOIRS AND WORKS FOR PUMPING. 13
as already mentioned, has no displacer stones embedded in it. The proportions of the mixture were 1 cement, 1 sand and 3 stone, all of which passed through a 11⁄2-inch diameter, and half through a 1-inch diameter ring. The thickness of the backing, including the face masonry, ranges from 11 feet at stream-bed level to 5 feet at top water-level. The stone used for the concrete throughout the work is granite and was all hand-broken, and the concrete was all hand-mixed. The total quantity of cement concrete in the dam is 128,668 cubic yards, of which 28,805 cubic yards is 4-to-1; 31,209 cubic yards 6-to-1; 39,900 cubic yards 7-to-1; and 28,754 cubic yards 8-to-1. Concreting was begun in January, 1914, but, owing to the short length of dam trench then finished, only 6,999 cubic yards were deposited during that year. In 1915, when the foundations of the dam across the stream-bed were ready for concrete, 48,690 cubic yards was deposited, and in 1916, when the entire length of the dam was available for concreting, 65,039 cubic yards. The remaining 7,940 cubic yards was deposited in the early months of 1917. Between top water-level and road-level, the hearting of the dam is of lime concrete surrounding a core of hand-packed rubble, the interstices being filled with earth. The quantity of lime concrete used for this purpose only amounted to 3,338 cubic yards and the rubble core to 655 cubic yards.
The whole of the cement used in the work was of local manu- facture and was supplied by the Green Island Cement Company of Hong Kong. It was required to conform to the specification of the British Standards Committee dated August, 1910.
MASONRY.
The dam is faced with masonry throughout, and in order to suit Chinese methods of handling without crane power, 12-inch coursing was generally used. Each course of ashlar was composed of alternate headers and stretchers set so as to break bond not less than 9 inches, the stretchers being not more than 6 feet or less than 3 feet in length, with a minimum breadth of bed of 12 inches, while the headers were not less than 2 feet in length nor less than 1 foot in width of face. All masonry was set in 2-to-1 cement mortar. Over the entire water face of the dam, the joints of the facework were raked out to a depth of 2 inches for the reception of 1-to-1 mortar, which was mixed very dry and thoroughly caulked into the joints with steel caulking-tools. The facing of the overflow-crest and toe of the dam is composed of larger stones
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