Use of computers on public works
PART II
IT IS probably in the sphere of water supply that the Hong Kong community will shortly reap the most direct bene- fits from the use of computers.
In trying to solve the immense problems of utilising the colony's mea- gre natural water resources to the best advantage, the engineer is faced with a number of variables such as rainfall, seasonal demands and storage. It is with this type of problem that the computer comes into its own since it is able to examine many permutations of the variables and to simulate an infinite number of possible situations that could arise.
In this way the computer is able to assist with the prediction of yields from existing and proposed water schemes, and to produce rules for the regulation of supply and the operation of reservoirs. Computers have also been used during the design of various com- ponents of the major water schemes in Hong Kong.
Hydrological data
Of considerable value to engineers designing new water schemes and plan- ning the operation of existing facilities
is the mass of data that the Water Authority collects from some 23 reser- voir and stream gauging stations. This data is processed on the Government ICL 1902 computer to obtain mean daily, monthly and annual flows for all stations. In addition monthly and annual flow-duration and volume re- jection curves are computed. Much of this information, together with a sum- mary of all rainfall data, is published each year by the Water Authority in 'Hong Kong Rainfall and Run-off.'
In addition to this routine annual processing of data, special studies are made from time to time utilising the computer. At the present time a study is being carried out on the time-dis- tribution of flood flows on the Sai Kung peninsula. This study will pro- vide data for tunnel design for future water schemes.
Dam stability analyses
The stability of several recently completed composite earth and rock- fill dams, including the Plover Cove main marine dam, was computed by the consultants using an effective stress analysis. Three basic conditions were
by A.T. Armstrong-Wright
Chief Engineer,
Road & Drainage Division, Public Works Department, Hong Kong.
-
investigated stability during con- struction, on completion and during working draw-down.
In determining the stability of com- posite earth and rockfill dams or other types of earth embankments, a poten- tial circular failure surface is assumed. The weight of soil and rock above the slip surface is the force which causes slipping and this is resisted by the shear strength of the soil and rock and, if present, the weight of external water acting on the face of the slope. The influence of water, including excess pressures in pore water, on the shear strength of the soil can be taken into account and the effect on stability of the sudden drop in level of the external water, can also be investigated.
A program for the English Electric DEUCE computer has been prepared which rapidly carries out the operations involved in a computation of each potential slip surface. Information is supplied to the computer by means of punch cards and the print-out gives the results of each computation with geo- metric location of circle, overturning moments, restoring moment and factor of safety.
Plover Cove reservoir – designed and operated with computer aid
Far East BUILDER, August 1969
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