Volumetric change is a property exhibited by expansive soils. Moisture in expansive soils determines the amount of swell or shrinkage in the expansive soil and is dependent on many factors. Some of these are, the climatic environment, the vegetation on the soil, the drainage of the site, the amount and type of clay within the expansive soil, the thickness of the layer of expansive soil and its active zone, and the depth of the water table. As the expansive soil loses moisture, shrinkage occurs and the soil matric generates large negative pore pressure or suction pressure. As a relatively dry expansive soil gains moisture, the suction pressures within is relived and the soil expands. This dissertation examines the cumulative effects of controlling moisture movement within the subgrade of a pavement by using vertical moisture barriers and how loss of performance on highway pavements built on expansive soils can be managed.; Using the moisture balance process of the Thornthwaite Moisture Index the probable maximum, minimum and mean annual moisture depths in an expansive soil subgrade are obtained. The Suction Compression Index (SCI) and the unsaturated hydraulic conductivity and diffusivity are used to characterize the subgrade soil. The SCI of the expansive soil is obtained as a function of the activity of the soil (PI/%fine clay) and the cation exchange activity (CEC/%fine clay). The diffusivity is determined as a function of the slope of the suction water content curve and of the SCI. The hydraulic conductivity depends on the diffusivity and the slope of the suction water content curve as well. A finite element flow and deformation program (FLODEF) is used to compute the transient unsaturated moisture flow and deformation in the expansive soil.; Profilometer data collected on pavements built on expansive soils at ten locations in Texas are used to develop regression constants to be used in the International Roughness Index (IRI) and the Serviceability Index (SI) models. These models are used to predict roughness performance on pavement wheelpaths over time. As climatic conditions change from wet to dry, the pavement is subjected to swell and shrinkage. Over time, the pavement cross-section assumes an exponential shape, with maximum heave at the edge, reducing exponentially towards the centerline. This dissertation develops a model to predict heave at any point along the cross-section of the pavement. A relationship is then developed between this model and the regression constants that can be used in the prediction of roughness performance on pavement wheelpaths.
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