Subgrade moisture variations interim report IX Effectiveness of existing highway designs

The purpose of this study was to determine which existing Oklahoma highway designs give acceptable performance and why/how they resist the effects of subgrade moisture variations. After a review of pertinent factors to be considered in evaluating both pavement performance and subgrade moisture conditions, a study of designs existing at 50 field research sites was made to determine which designs were performing well and the relations between particular design performance and observed subgrade moisture conditions. Results of the study indicate that the type of wearing surf ace had little effect on either pavement performance or subgrade moisture conditions, with underlying components being responsible for both. In general, the best performance was obtained from designs incorporating improved shoulders, flexible, impervious, or semi-pervious base materials continuous under pavement and shoulder, subbases, and adequate drainage.Interim Report IXN