Comparative design case studies of pavement performance on expansive soils
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Vertical movements calculated with the new design method for six case study cross sections in three different climatic zones in Texas were compared with the swelling movement predicted by the potential vertical rise (PVR) method, which has been used by the Texas Department of Transportation. Vertical movements included both swelling and shrinking. A review of assumptions that underlie the PVR method shows that two assumptions are unrealistic because they are not based on sound analytical principle and the three others cannot be supported by subsequent findings on actual Texas pavements or on soils of the United States. Pavement treatments were selected to provide acceptable predicted performance at high levels of reliability, and the vertical movements were calculated both at the edges of pavements and beneath the outer wheel-paths. The case studies were based on a variety of traffic levels, site conditions, and sample testing. The pavement treatments Included limestabilized and cement-stabilized layers, removal and replacement with inert layers, and vertical and horizontal moisture barriers. The results of the case studies showed that the PVR method overpredicts the swelling movement that can be expected with the new method and does not predict shrinkage movement, which is important because that is an indicator of future longitudinal shrinkage cracking along the pavement edge.
