Design Model for Roughness and Serviceability of Pavements on Expansive Soils

Abstract

A model was developed to predict pavement roughness caused by both expansive soils and traffic in terms of the serviceability index (SI) and the International Roughness Index (IRI). The model correlates the roughness analysis to the vertical movement estimated from the Texas A&M University suction-based method. The total vertical movement (including both swelling and shrinking) at the edge of pavement sections, the geometry of the pavement, site conditions, traffic, and the level of reliability were used as model parameters. Total movements calculated at the edge of pavement sections were based on a relationship between moisture content and suction, exponential suction envelopes, volume change coefficients, pavement treatments, and roadside conditions. Pavement treatments included vertical and horizontal barriers, inert soil, and lime-stabilized or cement-stabilized layers. The movements in wheelpaths at a distance from the edge of pavement were estimated on the basis of both field observations and the computed results of a transient finite element analysis. Transverse distribution of vertical movements on a pavement cross section was estimated. A relationship between IRI and SI was developed on the basis of surface profile measurements in several pavement study sections. 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.