Examining k-E relationship of pavement subgrade based on load-deflection consideration

Abstract

Most rigid-pavement design methods in use today adopt the Westergaard's approach that characterizes pavement foundation by k, the modulus of subgrade reaction. k is measured by a standard plate loading test conducted in the field. However, since this test is elaborate, expensive, and time consuming, the k value of a subgrade soil is usually estimated from other soil properties. In this regard, the relationship between k and the modulus of elasticity E of the soil is of special interest. This is because E is a fundamental engineering property and that there exists various test methods for determining E either in the field or in the laboratory. This paper proposes a procedure to estimate k from E by establishing an equivalency between two theoretical pavement models, a model of pavement slab supported by an elastic solid foundation (termed the E model) and a model of pavement slab supported by a dense liquid foundation (termed the k model). Instead of matching the k and E models directly as is done in currently available k-E relationship models, this study proposes to define an equivalent k model and an equivalent E model, separately, with respect to actual rigid pavements. The equivalency is established using back-calculation analysis based on load-deflection considerations. Using the deflection test data of the long-term pavement performance database, it is found that there exists a relationship between the radii of relative stiffness of the two theoretical systems, and this relationship can be used to estimate k from a given E value. © 2009 ASCE.