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Submitted on: 03 September 1998.
Revised on: 16 November 1998.
Accepted on: 01 December 1998.
___________________Engineer-Journal of the Institution of Engineers Sri Lanka
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Submitted on: 29 April 2000.
Revised on: 21 June 2000.
Accepted on: 07 July 2000.
___________________Engineer-Journal of the Institution of Engineers Sri Lanka
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Submitted on: 20 March 2000.
Revised on: 13 July 2000.
Accepted on: 31 August 2000.
___________________Engineer-Journal of the Institution of Engineers Sri Lanka
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