A multilayered, mathematical model for analyzing the ultimate bearing capacity of soil subgrades and asphalt pavements is presented. Theoretical considerations and mathematical derivations of limit equilibrium equations, based on plasticity principles, for analyzing the ultimate bearing capacity of soil subgrades and partially completed asphalt pavements, and the extension of these equations to the analyses of asphalt pavements composed of multiple layers, are presented. The model is unique since shear strength parameters, Φ and c, (the angle of internal friction and cohesion, respectively) are used to describe each layer of material of the pavement structure and a factor of safety against failure is calculated. Problems involving total stress and effective stress analyses may be solved using the new model. Theoretical derivations of the shear surface selected for the model analyses is presented. The theoretical failure mass consists of three failure zones -- active and passive wedges connected by a central wedge whose shear surface is a logarithmic spiral curve. Creditibility of the model is established by solving three classes of pavement bearing capacity problems. Bearing capacity factors, Nc, Nq, and Ny, are computed from the new theoretical model and compared to the classical bearing capacity factors (Prandtl). Solutions obtained from a two-layered, semiempirical formula described by Vesic are compared to solutions obtained from the new mathematical model. Finally, factors of safety of asphalt pavements that failed during construction are analyzed. Factors of safety obtained from the model are compared to the failure factor of safety. These different analyses and comparisons show that the new model yields very reasonable solutions. Additionally, factors of safety of some 237 pavement sections of Loops 3, 4, 5, and 6 of the AASHO Road Test (1962) are computed and correlated to weighted. 18-kip. ESAL applications (P = 2.0). Analyses of the AASHO (flexille pavement) Road Test Equation (1962) and the 1981 Kentucky asphalt pavement curves using the new model show that there are situations where these design methods may yield pavement designs that may fail. Analyses of soil subgrades under typical construction traffic loadings using the model show that subgrade CBR-values should be in the range of about 6 to 8.5 to avoid bearing capacity failures during construction of subgrades and pavements. Several deficiencies of current design methods are identified and recommendations are made to correct these design and construction deficiencies.

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The contents of this report reflect the views of the author, who is responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the University of Kentucky, the Kentucky Transportation Cabinet, nor the Federal Highway Administration. This report does not constitute a standard, specification, or regulation.