A model was developed to predict pavement roughness due to both expansive soils and traffic in terms of serviceability index (SI) and international roughness index (IRI) by correlating the roughness analysis to the vertical movement estimated from a vertical movement model. The total vertical movement, including both swelling and shrinkage, at the edge of pavement sections, the geometry of the pavement, and site conditions were used as model parameters. Total movements calculated at the edge were based on exponential suction envelopes, volume change coefficients, pavement treatments and roadside conditions. Pavement treatments include vertical and horizontal barriers, inert soil and lime- or cement-stabilized layers. The movements in wheel paths ata distance from the edge of pavement are estimated based upon both field observations and the computed results of a transient finite element analysis. A relationship between IRI and SI was developed. The design equations that were developed for both flexible and rigid pavements include the effects of traffic and expansive soil and permit the selection of the desired level of reliability.
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