P.W.E. Hongkong.
Q 74
A Contract for the construction of the Dam and Contingent Works was let to Messrs. Sang Lee & Co. on October 22nd 1912, five years being allowed for completion. Another Contract for the supply and erection in working order at the pumping station of two sets of pumping machinery was entered into by the Crown Agents with Messrs. James Simpson & Co., Ltd. on the 9th January 1914. Further Contracts were let to Messrs. Sang Lee & Co. from time to time for the construction of the foundations for the pumping machinery, the extension of the pumping station buildings, the provision of a reinforced concrete landing stage for the station, the laying of the suction and rising mains and sundry other minor works.
The following is a brief description of the works enumerated above:
The dam is constructed across the Taitam stream where it discharges on to the tidal flat at the head of Taitam Bay and is therefore at sea-level. Its extreme length is 1,255 feet and its extreme height from the deepest part of the foundations to the roadway which surmounts it is 170 feet or, to the crest of the overflow, 161 feet. Its maximum thickness at the base is 115 feet and the maximum depth of water impounded by it is 117 feet. A special feature of the work is that the foundations in the stream-bed had, for a length of 238 feet, to be excavated below sea-level, the general level of the sound rock at the deepest part of the foundations being 30 feet below the stream-bed or 27 feet below low-water ordinary spring tides. A tongue, varying from 10 to 20 feet in width, was cut into the rock to ensure greater watertightness and was carried down to a maximum depth of 41 feet below low-water ordinary spring tides. The dam is of cement concrete, faced on the inner side with granite ashlar and on the outer with granite rubble set and pointed in cement mortar. Except in the case of the backing of the inner facing, for which fine cement concrete (4 to 1) varying from 10'0" thick at the base to 3'8" thick at the top, was used, the whole of the cement concrete has granite displacers embedded in it.
The quantities of excavation for the dam and of cement concrete and granite masonry used in its construction were as follows:
Soft excavation, 62,980 cub. yds. Rock " 23,838 " Cement concrete hearting (6 to 1). 31,209 cub. yds. (7 to 1), 89,900 cub. yds. (8 to 1), 28,754 cub. yds. backing of inner facing (4 to 1), 28,805 cub. yds. Lime concrete filling from top-water level to road level, Hand-packed rubble filling from top-water level to road level, 3,338 cub. yds.655