Prediction of Expansive Clay Roughness in Pavements with Vertical Moisture Barriers (187-28F)

This report summaries the results and conclusions of a multi-year study of the monitoring of moisture barriers in expansive soils. During the study, the surface profile measurements in ten different sites with moisture barriers were obtained using the 690D Surface Dynamics Profilometer operated by the Texas Department of Transportation. These measurements were then analyzed in terms of Serviceability Index and International Roughness Index using the computer program VERTAC. These data were fitted to appropriate models for the growth of roughness with time, and regression constants were obtained.|The development of pavement roughness due to expansive clay activity is caused by the differential movement of subgrade soil. The vertical movement at the edge of the pavement due to shrinking and swelling is higher than that of the interior of the pavement. A model was developed to predict the vertical movement in any given wheel path of a pavement as it is affected by a vertical moisture barrier at the edge of the pavement. Using this model, the vertical movement in the all wheel paths of the ten sites studies was estimated.|Another model was developed to predict the pavement roughness in terms of Serviceability Index and International Roughness Index by correlating regression constants obtained from the roughness analysis to the vertical movement estimated from the vertical movement model. The model developed calculates the roughness development due to traffic using the AASHTO model.|The vertical movement model and the roughness model developed were then assembled in the computer program PRES, which is written in FORTRAN language. The input data required for the program include the basic soil properties, climatic data, depth of a vertical moisture barrier, pavement geometry and structural properties, lateral drainage and longitudinal slope conditions, and traffic. The output will be the predicted roughness with time in any given wheel path. The program may be used to determine the depth of a moisture barrier that will meet the designers target level of pavement roughness after a selected number of years of service. Example problems demonstrate the capabilities of the program.