Comparison of Four Design Methods on Rehabilitation of Flexible Pavements: For Nakuru - Nyahururu Road in Kenya

Abstract

This paper looks at the need of finding structurally sustainable and economical design methods among the usual Kenyan Road Design Manual Part- III & IV (1987), Tanzanian Design Manual (1999), AASHTO 1993 and South African mechanistic-empirical Pavement Analysis Design Software (mePADS).The paper is based on the design of rehabilitation of flexible pavement on Nakuru – Nyahururu road in Kenya.

Due to under design; roads are dilapidating before their design period is reached. The result is the need of the reconstruction or excessive maintenance which is going to make road construction industry uneconomical. 

Comparison of pavement structures obtained by use of Tanzanian Design Manual 1999, AASHTO 1993 and mechanistic-empirical Pavement Analysis Design Software of South Africa (mePADS) was made.  The most economical pavement structure was designed. The research looked in to the sustainability of the pavement structure and for how long? If the project doesn't reach the design period, further design is needed in order to match with the design period for comparison with other design methods.

On the aspect of structurally sustainable pavement, pavement designed by use of Tanzanian design manual (1999) is safe when analyzed through the mechanistic-empirical Pavement Analysis Software (mePADS) whereas the pavement designed by use of the Kenyan design manual fails to reach half way the design period.  AASHTO 1993 pavement reaches its service life one or two years before the design period.