Vertical movements calculated by the new design method for each of the six case study cross sections, in three different climatic zones in Texas, were compared with the swelling movement predicted by the PVR method that has been used by Texas Department of Transportation (TxDOT) in the past. The vertical movements included both swelling and shrinking. In reviewing the assumptions that underlie the PVR method, it is seen that two of assumptions are not realistic becasue they are not based on sound analytical principal and three of assumptions cannot be supported by subsequent findings on actual Texas pavements and on the soils of the United States. Pavement treatments were selected to provide an acceptable predicted performance at high levels of reliability, and the vertical movements were calculated both at the edges of the pavements and beneath the outer wheel paths. The case studies were based upon a variety of traffic levels, site conditions, and sample testing. The pavement treatments include lime- and cement-stabilized layers, removal and replacement with inert layers, and vertical and horizontal moisture barriers. The results of the case studies show that the PVR overpredicts the swelling movement that can be expected using the new method, and does not predict shrinkage movement, which is important because it is an indicator of future longitudinal shrinkage cracking along the edge of the pavement.
Abstract