Use of CIRCLY (Austroads mechanistic design software) for overlay designs in Sri Lanka

Abstract

Road pavement design has been carried out complying with empirical methods which are not based on stress strain relationships. But the mechanistic methods which are based on stress strain relationships is the method that is complying with engineering fundamentals. CIRCLY is a pavement design software based on mechanistic approach and calculate damage factors after the design period for a given traffic load distribution. The Austroads flexible pavement design method uses CIRCLY to calculate load-induced strains and deflections in model pavements. CIRCLY is an integral component of the AUSTROADS Australian Pavement Design Guide. Considering about the data required to carry out the design of road pavement it was recognized that Flexural Modulus, Poisson’s Ratio, Volume of Binder in Asphalt Mix (VB %), Shift factor between laboratory and in-service fatigue lives (SF) ,Performance Exponent(b), as material properties while traffic load Distribution (TLD) data and Reliability (R) required to calculate loading conditions. Shift factor (SF), performance exponent (b) and reliability(R) are the factors that have been recognized as factors varied upon the environmental factors in many researches. However, Reliability is considered as a kind of safety factor in AUSTROADS and lower the reliability, thinner the Pavement layers and lower the capacity pavement structure. This may lead to lower the durability. In AUSTROADS Performance exponent has been taken by performing series of tests for different materials and Conditions. Under this conditions, main consideration paid for finding Suitable Shift factor for Sri Lankan conditions. Conditions of Empirically designed roads are taken in to consideration in finding the variation of pavement capacity while varying the Shift factor, reliability and Damage Exponent. Suitable shift factor value has been derived in the research while observing the behavior of Reliability and damage Exponent.