Development of a mechanistic overlay design procedure for flexible pavements

Graduation date: 1990This dissertation describes the development of a mechanistic\ud overlay design procedure. The mechanistic analysis represents a new\ud trend in both new pavement and overlay design. The greatest advantage\ud of the mechanistic pavement analysis is that it considers the\ud fundamental characteristics of materials to be used, is capable of\ud considering changes in loading and tire pressure, and characterizes\ud the response of the pavement to traffic loads in terms of strains\ud and/or stresses. This type of analysis allows practicing engineers to\ud more realistically address pavement structure, materials, and other\ud influential variables such as environmental impacts so that the\ud behavior of the pavement may be better understood.\ud One of the critical steps in using the mechanistic type pavement\ud analysis is the determination of pavement layer properties (e.g,\ud resilient modulus). In this study, methods commonly used for\ud determining resilient modulus have been reviewed. Three existing\ud mechanistic overlay design procedures were also reviewed. Based on\ud the review, improved procedures for determining pavement layer moduli\ud and overlay design seem to be necessary.\ud Significant contributions of this study are the development and\ud computerization of an improved backcalculation procedure (BOUSDEF)\ud for determining pavement layer moduli and an improved mechanistic\ud overlay design procedure (MECHOD).\ud Initial evaluations on both procedures were performed. For\ud BOUSDEF, three approaches were used: 1) comparing with hypothesized\ud theoretical moduli, 2) comparing with other developed backcalculation\ud programs, and 3) comparing with laboratory tested modulus values. The\ud evaluation showed BOUSDEF provided favorable comparisons. Therefore,\ud the program can be effectively used as a tool to make initial\ud evaluation of deflection testing data for determining pavement layer\ud moduli. For MECHOD, actual pavement data from the states of Oregon\ud and Alaska were used. All pavements evaluated are conventional\ud structures consisting of an asphalt concrete surface, an aggregate\ud base and/or a subbase, over subgrade. The evaluation showed that the\ud improved method provided very similar results to those of standard\ud procedures (ODOT, AASHTO, and The Asphalt Institute).\ud The BOUSDEF and MECHOD programs can be implemented together as a\ud pavement evaluation and overlay design system. That is; 1) use\ud BOUSDEF to backcalculate pavement layer moduli, and 2) use MECHOD to\ud perform overlay design