Expert System Design Guide for Lower Classification Roads over High PI Clays

This research was focused on low-volume roads over expansive clayey soils in Texas. In spite of the redundant pavement designs recommended and widely used in Texas for roads in high PI clay areas, these pavements often fail prematurely. This failure occurs primarily because of the highly variable properties of the clayey subgrade throughout the year due to moisture fluctuations. The problematic nature of high PI clays, despite the fact that volumetric changes such as heaving are sometime considered in the design, is of concern since they contribute to roughness and longitudinal shrinkage cracking of the road, and as such the loss of the functional serviceability of the roads. Therefore, it is imperative to improve the design and laboratory procedures to address expansive subsoil conditions and then design pavements accordingly to extend the life expectancy of these roads. The intent of this research project was to cultivate the vital features of strategies for improving low-volume flexible pavement design and thus improving the overall low-volume road performance. These include: 1)Identify the shortcomings of current design and construction practices associated with the less than desirable performance of pavements in low-volume roads constructed on high PI clays; 2)Identify the most significant soil parameters directly related to the performance of these types of roads; 3)Propose practical laboratory test methods and analyzing models to address the problem of premature failure of low-volume roads on high PI expansive subgrade; 4)Qualify and quantify current remediation procedures, climatic effects and road condition assessment (both successful and unsuccessful) used to mitigate the shrink-swell problems; 5)Develop a user-friendly expert system design tool to guide the designers through the process for more realistic designs and rehabilitations. The focus of this research is on how to improve design procedures of low-volume roads over expansive clayey subgrades. A computer guide to assist pavement engineers to design lower classification roads over high PI clays using the expert system approach has been developed. The guide combines numerical and engineering analyses with heuristic information about the site to recommend best design and construction practices. Numerical analysis is performed to predict longitudinal cracking distress, which reported by a district survey throughout Texas to be one of the most prevailing distresses. Other common distresses are studied. Traditional and new remediation methods are proposed to address the problem of pre-mature failure of low-volume roads on high-PI clays. Finally cost and benefit analysis are added to the design guide framework to compare cost-effectiveness of recommended strategies and to accomplish the objectives of this project